# Patent

## Title
Controlling a power converter

## Abstract

A load is powered by a power source and a capacitive element in series such that the voltage provided to the load is the sum of the voltages of the power source and the capacitive element. A power converter imposing a limit on a flow of current through at least a portion of the power converter is coupled to the power source and the capacitive element, and selectively causes the capacitive element to either be charged or to discharge depending on the amount of current drawn by the load. As the capacitor discharges, the power source is permitted to supply a relatively higher amount of current to the load.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of prior U.S. patent application Ser. No. 10/872,040, filed on Jun. 18, 2004, now U.S. Pat. No. 7,245,185 the contents of which are incorporated by reference.


BACKGROUND
This description relates to controlling a power converter.
Power converters are used to supply power to a load. Some power converters are DC-DC converters supplying direct current (DC) power from a DC source such as a battery. Other power converters are AC-DC converters supplying DC power from an alternating current (AC) source such as a wall outlet. In some cases a capacitor in parallel with the power converter (e.g., a “super capacitor”) is used as a back-up source.
SUMMARY
In one aspect, the invention features an apparatus that includes a load; a power source; a capacitive element coupled in series with the power source to enable the power source and the capacitive element to provide the load with a supply voltage that is a sum of the voltages of the power source and the capacitive element; and a power converter coupled to the capacitive element and the power source, wherein the power converter imposes a limit on a current flowing through the power converter, thereby causing the power converter to charge the capacitive element while the load draws a relatively smaller amount of current and causing the power converter to enable the capacitive element to discharge to enable the load to draw a relatively higher amount of current through both the power converter and the capacitive element as the capacitive element discharges.
Implementations of the invention may include one or more of the following features. The load could be an amplifier, an electromechanical actuator, or other type of device drawing current. The power source could be a battery, power supply or other type of power source. The capacitive element could be a supercapacitor (otherwise known as an ultracapacitor), and/or could include more than one device capable of storing electrical energy coupled in series and/or in parallel. The power converter could be a back converter and/or a converter able to allow the capacitive element to return stored power to the power source.
In one aspect, the invention features an electronic device that includes an amplifier to amplify an audio signal and drive an acoustic driver; a power source; a capacitive element coupled in series with the power source to enable the power source and the capacitive element to provide the amplifier with a supply voltage that is a sum of the voltages of the power source and the capacitive element; and a power converter coupled to the capacitive element and the power source, wherein the power converter imposes a limit on current flowing through the power converter, thereby causing the power converter to charge the capacitive element while the amplifier draws a relatively smaller amount of current and causing the power converter to enable the capacitive element to discharge to enable the amplifier to draw a relatively higher amount of current through both the power converter and the capacitive element as the capacitive element discharges.
Implementations of the invention may include one or more of the following features. The amplifier could receive an input through a compressor and/or the amplifier could incorporate a gain control by which the input could be altered to selectively reduce the amount of current drawn by the amplifier. The power source could be a battery, power supply or other type of power source. The capacitive element could be a supercapacitor (otherwise known as an ultracapacitor), and/or could include more than one device capable of storing electrical energy coupled in series and/or in parallel. The power converter could be a buck converter and/or a converter able to allow the capacitive element to return stored power to the power source.
In one aspect, the invention features a method that includes coupling a power source and a capacitive element in series to provide a load with power having a voltage that is the sum of the voltages of the power source and the capacitive element; causing the capacitive element to be charged as the load draws a relatively smaller amount of current; and enabling the power source to provide a relatively higher amount of current through the capacitive element by causing the capacitive element to discharge as the load draws a relatively higher current.
Implementation s of the invention may include one or more of the following features. Implementations could include imposing a limit on the amount of current flowing through at least a portion of power converter. Implementations in which the load is an amplifier could include triggering a compressor and/or a gain control of the load to alter an input to the load to reduce the amount of current drawn by the load.
Other features and advantages of the invention will become apparent from the following description, and from the claims.



DESCRIPTION OF DRAWINGS
FIG. 1 is a circuit diagram of a power converter in parallel with a capacitive element coupled to a load.
FIG. 2A is a circuit diagram of an DC-DC power converter in parallel with a capacitive element coupled to an audio amplifier.
FIG. 2B is a circuit diagram of an AC-DC power converter in parallel with a capacitive element coupled to an audio amplifier.
FIG. 3A is a circuit diagram of a voltage source driving a load.
FIG. 3B is a current-voltage characteristic for the circuit of FIG. 3A.
FIGS. 4A and 4C are equivalent circuit diagrams of a current source driving a load.
FIG. 4B is current-voltage characteristic for the circuit of FIGS. 4A and 4C.
FIGS. 5A and 6A are circuit diagrams of a power converter in parallel with a capacitor coupled to a load.
FIGS. 5B and 6B are current-voltage characteristics for the circuits of FIGS. 5A and 6A, respectively.
FIGS. 5C and 5D are time plots for circuit variables of the circuit of FIG. 5A.
FIG. 6C is a time plot for a circuit variable of the circuit of FIG. 6A.
FIGS. 6D-6F are plots of power consumption dynamics for different types of music.
FIGS. 7A-7D are circuit diagrams showing different sensing techniques.
FIG. 8 is a circuit diagram for an implementation of the sensing technique of FIG. 7A.
FIG. 9 is a plot of a converter switch operation as a function of time.
FIGS. 10A and 10B are exemplary current-voltage characteristics.
FIGS. 10C and 10D are examples including an audio amplifier with gain that depends on the power converter behavior.
FIG. 11 is a plot of reduction in peak power demand versus effective time constant for different types of music.
FIGS. 12-14 are circuit diagrams for implementations of a power converter in parallel with a capacitive element coupled to an audio amplifier.
FIGS. 15A-15D are circuit diagrams of a power source, power converter and capacitive element coupled to a load.
FIGS. 16A-16B are time plots of electrical current and voltage provided to the load of FIG. 15A.
FIG. 17 is a circuit diagram of a power source, power converter and capacitive element coupled to an amplifier and an acoustic driver.
FIG. 18 is a circuit diagram of a power source, power converter, capacitive element and compressor coupled to an amplifier and an acoustic driver.
FIG. 19 is a time plot of electrical current and voltage provided to the amplifier of FIG. 18.
FIG. 20 is a circuit diagram of a power source, power converter and capacitive element coupled to an amplifier having a gain control and an acoustic driver.
FIG. 21 is a circuit diagram of a power source, power converter and capacitive element coupled to an electromechanical actuator through a power switching device.
FIG. 22 is a time plot of electrical current and voltage provided to the mechanical actuator of FIG. 21.



DESCRIPTION
FIG. 1 shows a circuit that includes a power converter 100 in parallel with a capacitive element 102 (e.g., circuitry having an impedance with negative reactance). The power converter 100 and capacitive element 102 are coupled to a load 104 that demands an amount of power PL based on the input resistance RL of the load 104. For a load 104 having a variable demand for power (a “variable load”), the input resistance RL(t) varies as a function of time t. For a power converter 100 that supplies a constant voltage VS, the power PL(t) supplied to the load 104 is determined by PL(t)=VN2/RL(t). In steady-state conditions (e.g., RL(t) is slowly varying with respect to the effective time constant associated with the capacitive element 102), the load 104 draws a current IL(t) from the power converter 100 that is approximately IL(t)=VS/RL(t).
Some variable loads (e.g., an audio power amplifier or a motor) have a peak power demand that is many times higher than the average power demand. In such cases, a power converter 100 with a controlled current-voltage characteristic, as described in more detail below, is able to supply the average power demanded by the load, while causing a brief demand for a high peak power to be supplied from energy stored in the capacitive element 102. By causing at least some of the peak power to be supplied from the capacitive element 102, the power converter 100 can maintain a relatively low amount of power drawn from a power source such as a battery or AC mains.
As shown in FIGS. 2A and 2B, a DC-DC power converter 200A in parallel with a capacitive element 202A can be used to supply power to an audio amplifier 204 from a battery 206 (FIG. 2A), and an AC-DC power converter 200B in parallel with a capacitive element 202B can be used to supply power to the audio amplifier 204 from an AC mains 208 (FIG. 2B). The varying nature of the power demand from the audio amplifier 204 is determined, for example, by a music signal 210 that is amplified to drive a speaker 212. A power converter and capacitive element can be used to supply power to other types of devices or combinations of devices where power demand may vary (e.g., a charging cradle for a cell phone, where the cradle also acts as a powered loudspeaker and many other examples).
The capacitive element 202A can be implemented using a “super capacitor” or “ultra capacitor” (e.g., using aerogel technology) to obtain a capacitance in the range of approximately 1-30 Farads (F) and a maximum voltage of approximately 2.5 V. In another implementation, the capacitive element 202B includes two 10 F/2.5 V capacitors in series, each capacitor having a 5.1 kΩ shunt resistor (e.g., to provide even steady-state charge storage among the capacitors). The resulting capacitance of the capacitive element 202B is 5 F, and the maximum voltage of the capacitive element 202B is 5 V. In other implementations the capacitive element can include three or more capacitors connected in series. Any of a variety of implementations of a capacitive element including 202A, 202B or others may be used in any of a variety of power converter configurations including a DC-DC power converter, an AC-DC power converter or others.
FIG. 3A shows a circuit with a voltage source 300 and a load resistor 310. The voltage source 300 (e.g., a Li-Ion or NiMHd battery) is modeled by an ideal voltage source 302 (of constant voltage V0) is series with a resistor 304 representing the output resistance of the voltage source 300. The current-voltage characteristic 306 for this voltage source 300 is shown in FIG. 3B, along with the “load line” for the load 310 (i.e., the current-voltage characteristic of the load resistor 310). The small output resistance RV represented by the resistor 304 causes a sag 308 in the output voltage VV of the voltage source 300 as a function of output current IV. The size of the sag 308 increases as the load resistance RL (i.e., the slope of the load line) decreases.
FIG. 4A shows a circuit with a current source 400 and a load resistor 310. The current source 400 is modeled by an ideal current source 402 (of constant current I0) in parallel with a resistor 404 representing the output resistance of the current source 400. The current voltage characteristic 406 for this current source 400 is shown in FIG. 4B, along with the load line for the load resistor 310. In this case, the larger output resistance RI represented by the resistor 404 causes a sag 408 in the output current II of the current source 400 as a function of output voltage VI. The size of the sag 408 increases as the load resistance RL increases . This current source 400 can equivalently be modeled by an ideal voltage source 412 in series with the resistor 404, where the voltage VEQ of the equivalent ideal voltage source 412 is VEQ=I0RI (FIG. 4C).
FIG. 5A shows an example of a power converter 500 in parallel with a capacitor 502. The power converter and the capacitor cooperatively supply power to a variable load 504. In this example, the power converter 500 has a current-voltage characteristic 506 as shown in FIG. 5B. The power converter 500 has the characteristics of the voltage source 300 (e.g., has a low effective output resistance RV) for output current RS values from 0 to IA and ha the characteristics of the current source 400 (e.g., has a high effective output resistance RI) for output current IS above IA, limiting the current that can be supplied from the power converter 500. In one example, the variable load 504 temporarily demands more power by dropping an input resistance RL(t) from a value of R0 (corresponding to a “nominal” load line 510) to a value of R0/3 (corresponding to a “peak” load line 512) for a time period T=tA -tB, after which the resistance returns to the value R0, as shown in the plot of FIG. 5C.
The nominal load line 510 intersects the current-voltage characteristic 506 at a current I1 and a voltage V1. The peak load line 512 intersects the current-voltage characteristic 506 at a current I2 that is larger than I1, and a voltage V2 that is slightly lower than V1. These intersections of the load lines with the current-voltage characteristic 506 give the asymptotic “DC solutions” for current and voltage after transients due to the capacitor 502 decay. The capacitor 502 provides continuity in the change of the capacitor voltage (equal to VS(t)) over time. FIG. 5D shows the voltage VS(t) across the power converter 500, the capacitor 502, and the variable load 504 as a function of time. After the load resistance drops at time tA, the voltage VX(t) drops exponentially from tA and tB according to:

VS(t)=V2+(V1−V2)exp(−(t−tA)/τA),

where τA is the effective time constant associated with the capacitor 502 (with capacitance C), which in this example, is





  
    τ
    A
  
  =
  
    
      
        [
        
          
            1
            
              CR
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              0
            
          
        
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        -
        1
      
    
    ≈
    
      CR
      V
    
  




since the output resistance RV of the power converter 500 is much smaller than the input resistance R0/3 of the variable load 504. After time tB, the voltage VS(t) rises exponentially back to V1 with the same time constant τA. The values of other circuit variables between times tA and tB, such as the capacitor current IC(t) and the load current I1(t), are determined from VS(t) as:





  
    
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and





  
    
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In this example, the power supplied by the capacitor 502




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          C
        
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          (
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is limited since the capacitor does not discharge deeply when the variable load 504 demands more power. The change in voltage VS(t) only lasts for a small fraction of the time interval T, causing





  
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        V
        S
      
      ⁡
      
        (
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and thus the power IC(t)VS(t) supplied by the capacitor 502 to be limited. To cause the capacitor to discharge deeply (e.g., by more than about 20% and in some examples by more than about 50%) to supply more power to the variable load 504, the current limit can be lowered to correspond to the expected peak demand of the variable load 504 so that the power converter 500 provides a dual-mode capability, as described in the next example (FIGS. 6A-6D).

FIG. 6A shows an example of a power converter 500′ in parallel with a capacitor 502 cooperatively supplying power to a variable load 504. In this example, the power converter 500′ has a current-voltage characteristic 606 as shown in FIG. 6B. The power converter 500′ has the characteristics of the voltage source 300 (e.g., has a low effective output resistance) for output current IS values from 0 to IB and has the characteristics of the current source 400 (e.g., has a high effective output resistance) for output current IS above IB. Again, in one example, the variable load 504 temporarily demands more power by dropping an input resistance RL(t) from a value of R0 (corresponding to a “nominal” load line 610) to a value of R0/3 (corresponding to load line 612) over a time period T, after which the resistance returns to the value R0, as shown in the plot of FIG. 5C.
The nominal load line 610 intersects the current-voltage characteristic 606 at a current I1 and a voltage V1, as in the previous example (FIG. 5B). However, in this example (FIG. 6B), the peak load line 612 intersects the current-voltage characteristic 606 at a current I3 that is larger than I1 but less than I2 and a voltage V3 that is substantially lower than V1 and V2. These intersections of the load lines with the current-voltage characteristic 606 also give the asymptotic DC solutions for current and voltage. FIG. 6C shows the voltage VX(t) across the power converter 500′, the capacitor 502, and the variable load 504 as a function of time. After the load resistance drops at time t3, the voltage VS(t) drops exponentially from tA and tC according to:

VS(t)=V2+(V1−V2)exp(−(t−tA/τA).

In this example, at tC the power converter 500′ shifts from a “voltage source” (e.g., a low output resistance) mode to a “current source” (e.g., a high output resistance) mode. Accordingly, the voltage VS(t) drops exponentially from tC and tS according to:

VS(t)=V3+(VS(tC)−V3)exp(−(t−tC/τB).

where τB is the effective time constant associated with the capacitor 502 when the power converter 500 is in the current source mode





  
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    ≈
    
      
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since the output resistance R1 of the power converter 500′ in the current source mode is much larger than the input resistance R0/3 of the variable load 504. Since V3 is substantially lower than V1, the capacitor 502 is able to discharge deeply (e.g., by about 50% in this example). After time tB, the voltage VS(t) rises exponentially back to the voltage VS(tC) at which the power converter 500′ switches modes with the time constant





  
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At a time tD, the power converter 500′ switches back to the voltage source mode. As in the previous example, the values of other circuit variables between times tA and tB, such as the capacitor current IC(t) and the load current IL(t), are determined from VS(t) as:





  
    
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In this example, the power supplied by the capacitor




  502
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is larger since the capacitor does discharge deeply when the variable load 504 demands more power. The change in voltage VS(t) lasts over the entire time interval T, causing





  
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and thus the power IU(t)VS(t) supplied by the capacitor 502 to be large enough to supply most of the additional power in a brief demand for more power by a variable load.

While the demand for more power in these examples is modeled as an instantaneous reduction of input resistance RL(t) for a time period T, a variable load such as an audio power amplifier may exhibit a continuous change in input resistance RL(t) with a more complex time dependency having changes that follow time scales present in a music signal (e.g., on the order of milliseconds or as high as tens of seconds) that represent a brief demand for a high peak power. Examples of power consumption dynamics for different types of music are shown in FIGS. 6D-6F. The plots shown in FIGS. 6D-6F are based on a simulated typical audio system, incorporating power converter control as described herein, playing exemplary music passages of different music types.
FIG. 6D shows plots 620-627 of residual power drawn from a power source to play an exemplary passage of uncompressed popular music (after the power converter causes some of the power to be supplied from a capacitive element) as a function of time for different values of the effective time constant τ of the capacitive element during a peak power demand (e.g., τ=RLpC where C is the effective capacitance of the capacitive element 102 and RLp is the resistance of the amplifier at peak power demand). In each plot, the vertical axis gives instantaneous residual power drawn from the power source in Watts, and the horizontal axis gives time in seconds. Each of the plots 620-627 corresponds to a different time constant labeled as “RC.” The peak residual power for each plot is shown as a dotted line. In this example, peak residual power is progressively reduced from about 40 W (plot 621) to about 7 W (plot 627) when RC is increased from 0.01 seconds (plot 621) to 10 seconds (plot 627). For comparison, plot 620 shows the power without a capacitive element (or RC=0).
FIG. 6E shows similar plots 630-637 for an exemplary passage of compressed popular music. In this example, peak residual power is reduced from about 70 W (plot 631) to about 20 W (plot 647) when RC is increased from 0.01 seconds (plot 641) to 10 seconds (plot 647).
FIG. 6F shows similar plots 640-647 for an exemplary passage of classical music. In this example, peak residual power is reduced from about 67 W (plot 641) to about 20 W (plot 647) when RC is increased from 0.01 seconds (plot 641) to 10 seconds (plot 647).
These plots in FIGS. 6D-6F demonstrate the difference in power dynamics of various types of music: the uncompressed popular music passage has a lot of strong spikes of a relatively short duration (e.g., about 1-100 ms), the compressed popular music passage has on average about a 12 dB lower peak-to-average (PTA) power ratio (or “crest factor”), while the classical music passage exhibits periods of very loud passages which may last, for example, for many seconds or tens of seconds.
As shown in FIGS. 7A-7C, the DC-DC power converter 200A (FIG. 2A) can use any of a variety of parameters to implement the dual-mode capabilities described above. For example, the circuit in FIG. 7A includes a resistor 702 for sensing the output current of a switching power supply 704. The voltage across the resistor 702 is fed back to the switching power supply 704 and used to control the output voltage according to a desired current-voltage characteristic. In another example, the circuit in FIG. 7B includes a resistor 706 for sensing the input current of the switching power supply 704 for achieving a desired current-voltage characteristic. In another example, the circuit in FIG. 7C includes circuitry 708 for sensing the input power of the switching power supply 704. The circuitry 708 generates a voltage 710 that is the product of the input voltage and a voltage proportional to the input current, and is therefore proportional to the input power. When the input power is below a threshold power level the power supply 704 operates according to a current-voltage characteristic of a first mode, and when the input power is above the threshold power level the power supply 704 operates according to a current-voltage characteristic of a second mode. Other parameters can be used to control the current-voltage characteristic of the switching power supply 704. The power supply 704 includes a control module 705 to switch modes based on the sensed parameter. One possible implementation of such a control module is described in more detail below (e.g., control module 814 in FIG. 8).
In order to achieve high system efficiency, there should be negligible loss in the power converter 200A. The switching power supply 704 can use any of a variety of low-loss conversion techniques (e.g., a boost converter, a buck converter, a flyback converter, or a single-ended primary inductance converter).
Similarly, the AC-DC power converter 200B (FIG. 2B) can use any of a variety of parameters to implement the dual-mode capabilities described above. The AC-DC power converter 200B can use techniques similar to those described above. Alternatively, as shown in FIG. 7D, an AC-DC converter 712 includes circuitry 714 for sensing the temperature of the AC transformer core 716. The AC-DC converter 712 switches between different current-voltage characteristics (i.e., different modes) based on comparing the sensed temperature to a threshold temperature. In some implementations temperature may optionally be used in conjunction with other control parameters (e.g., output current, input power, input current, etc.). In some implementations temperature modifies the current-voltage characteristic (e.g., by making IB a function of temperature). Other parameters can be used to control the current-voltage characteristic of the switching converter 712. The converter 712 also includes a control module 705 to switch modes based on the sensed parameter.
In some implementations, the trigger condition that causes the control module 705 to switch modes is programmable (e.g., by programming the trigger condition into a microprocessor). For example, the converter 712 senses various circuit parameters (e.g., input power, output current, temperature, etc.) and the circuit parameter that is used by the control module 705 to switch modes is programmable. Alternatively, the value of a circuit parameter that triggers a change in modes can be programmable.
FIG. 8 shows a Boost type power converter circuit 800 implementing the sensing technique of FIG. 7A. The input of the circuit 800 is connected to a battery 802 with voltage VB and the output of the circuit 800 is coupled to a capacitor 804 is parallel with a variable load 806. The circuit 800 includes an inductor 808, a diode 810, and a switch 812 that is controlled by a control module 814 based on the output current Iout(t) in a sensing resistor 816. The circuit 800 also includes a capacitor 818 with a relatively small capacitance to filter out much of the switching frequency, and reduce ripple on the output voltage. In some implementations, the control module 814 includes a microprocessor for controlling the switch operation as a function of sensed output current. The resistance RS of the sensing resistor 816 is small compared to the load resistance RL(t).
Since the circuit 800 is a Boost type, the output voltage Vout(t) is higher than the constant input voltage VB. The output voltage is determined by the duty cycle D of the opening and closing of the switch 812. As shown in FIG. 9, the switch 812 is closed for a time Ton and open for a time Toff, so the duty cycle is D=Ton/(Ton+Toff). The output voltage Vout(t) in steady-state conditions (and neglecting losses in the inductor 808 and the diode 810) is:

Vout(t)=VB/(1−D).  (1)

When the control module 814 senses an output current Iout(t) less than a threshold current Ith, the control module 814 sets the circuit 800 to a voltage source mode. In the voltage source mode, the target output voltage is approximately constant Vout(t)−V0. To generate this voltage, the control module 814 sets the duty cycle D to:

D=D0=1−VB/V0.  (2)

When the control module 814 senses an output current Iout(t) greater than the threshold current Ith, the control module 814 sets the circuit 800 to a current source mode. In the current source mode the, the target output voltage varies with output current according to a target current-voltage characteristic:

Vout(t)=V0−(Iout(t)−Ith)Rout,   (3)

where Rout is a simulated output resistance parameter for the circuit 800 that is controlled by the control module 814. To implement a high output impedance source, the control module 814 selects a large value of Rout (e.g., Rout>>RL(t)). The value of Rout may be constant, or alternatively, the value of Rout may vary with sensed output current Iout(t). Equations (1)-(3) yield the following value of duty cycle D that the control module 814 uses to control the switch 812 in response to the sensed output current Iout(t) in the current source mode:





  
    
      
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        =
        
          
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        )
      
    
  




A control module using other control parameters can be implemented in a similar way. For example, the duty cycle of a Boost type or other type of switching power converter can be a function of input power when the input power crosses a threshold value.
FIGS. 10A and 10B show exemplary current-voltage characteristics for a power converter that can be used to cause a capacitive element to discharge deeply to supply more power to a variable load. In FIG. 10A, the characteristic 1002 has a first mode 1004 characterized by a shallow slope of the voltage versus current plot, and a second mode 1006 in which the current IS is limited to a maximum current Ith for voltages VS below a transition voltage VT. For example, in the implementation of FIG. 8, the first mode 1004 may be achieved by setting Rout in Equation (4) to small value for IS values less than Ith and the second mode 1006 may be achieved by setting Rout in Equation (4) to a large value for IS values equal to or greater than Ith.
In FIG. 10B, the characteristic 1008 has a first mode 1010 characterized by a shallow slope of the voltage versus current plot, and a second mode 1012 characterized by a steep slope of the voltage versus current plot. Between the first and second modes, the characteristic 1008 has a “transition zone” 1014 that has a “knee” 1016 in the voltage versus current plot. For example, in the implementation of FIG. 8, the first mode 1010 may be achieved by setting Rout in Equation (4) to a small value for IS values less than Ith. The transition zone 1014 and second mode 1012 may be achieved by setting Rout in Equation (4) to an increasing value as a function of IS for IS values equal to or greater than Ith. In one implementation, the value of D in Equation (4) can be controlled using a programmable device (e.g., a microprocessor). In this implementation, the value of Rout in Equation (4) can be controlled ( as a function of IS) in software, for example, using a look-up table or a polynomial curve fit.
Other features of a current-voltage characteristic can be controlled in various implementations. For example, the transition between modes and the slope of the voltage versus current plot can be selected to ensure a minimum operating voltage (e.g., for an audio amplifier) is maintained for a given peak demand (e.g., minimum load resistance). The transition between modes can optionally be tunable.
For a power converter that supplies power to an audio amplifier (e.g., power converter 200A or 200B), features of the audio amplifier can be dependent on the power converter behavior. For example, when the voltage supplied by the power converter drops (e.g., after switching to the current supply mode) the gain of the audio amplifier can be reduced to avoid distortion in the music signal 210 at the amplifier or speaker (e.g., due to signal clipping). In one implementation, shown in FIG. 10C, an audio amplifier 1100 includes a compressor 1102 with a threshold that scales with the voltage supplied y the power converter 100 and capacitive element 102. This variable-threshold compressor 1102 reduces distortion of music played over a speaker 1106. In another implementation, shown in FIG. 10D, an audio amplifier 1108 includes a variable gain circuit 1110 that reduces the gain as the voltage VS(t) supplied by the power converter 100 and capacitive element 102 reduces, according to a predetermined function. These or other techniques (e.g., a system with any kind of wide-band or multi-band amplitude compressor) can be used to reduce the likelihood of signal clipping at any power converter voltage above a given minimum operating voltage. A compressor could operate based on the voltage supplied by the power converter and capacitor, or on other parameters such as power transformer temperature, loudspeaker temperature, loudspeaker displacement, or any other parameter indicative of an amplified signal level.
By causing some of an increased demand for power to be supplied from a capacitive element, the residual peak power demanded from a source is reduced. The amount of reduction in residual peak power demand depends on the effective time constant τ and on the type of music that is being amplified. One characteristic of the music that affects the reduction in residual peak power demand is the PTA power ratio. Music with a high PTA power ratio (e.g., uncompressed popular music) is more affected by the integrating effect of a large time constant than music with a low PTA power ratio (e.g., broadcast AM music).
FIG. 11 shows semi-log plots of the reduction R in peak power demand due to the capacitive element (in dB) versus the effective time constant τ (in seconds) for three different types of music: uncompressed popular music (plot 1102), compressed popular music (plot 1104), and classical music (plot 1106). The reduction in peak power demand R is quantified as the ratio between peak power for a power converter having a time constant of zero to peak power for a power converter having the given effective time constant τ, R=Ppeak(τ=0)/Ppeak(τ). These empirically derived plots demonstrate that the uncompressed popular music used in this example, due to its high PTA power ratio and relatively short duration of the amplitude spikes is the most affected by effective time constant τ of the power converter. For example, for τ ̃5.5 seconds (FIG. 11, plot 1102), the reduction of the residual peak power demand is 10 dB (or 10 times).
On another end—compressed popular music (e.g., FM or AM broadcast type) has a much lower PTA power ratio (in order to sound louder on average), so the effects of the effective time constant τ are less pronounced. For example, for the same time constant τ ̃5.5 seconds (FIG. 11, plot 1104) the reduction of the residual peak power demand is 8.7 dB (or 7.5 times).
Classical music typically has PTA power ratio in between that of compressed and uncompressed popular music, but much longer duration of the amplitude spikes. Therefore, the classical music used in this example is affected by the effective time constant of the power supply the least. For example, for the same time constant τ ̃5.5 sec (FIG. 11, plot 1106) the reduction of the residual peak power demand is only 6 dB (or 4 times).
Another way to look at FIG. 11 is that a system having a power source with limited power capabilities is able to play louder by using a capacitive element to provide some of the peak power demand. From the example above for uncompressed popular music with τ ̃5.5 seconds, the available peak power for playing the music will be 10 dB higher from a system that causes peak power to be supplied from a capacitive element than from a system that does not.
In one implementation shown in FIG. 12, a power supply 1202 (a Hewlett Packard model 6253A DC power supply) powered from an AC mains is connected in parallel with a capacitive element 1204 consisting of six 33 F/2.5 V aerogel super capacitors in series, each capacitor having a 5.1 kΩ shunt resistor, providing a total capacitance of 5.5 F and a maximum voltage of 15 V. The power supply 1202 and capacitive element 1204 power a switching audio amplifier 1206 (a Bose 100 W switching audio amplifier, Bose Corporation) driving a speaker 1208. A music signal 1210 is input into amplifier 1206. When the power supply 1202 had an output current limit set to approximately 3.2 A and a nominal output voltage (i.e., with no load) set to 15 V (for a maximum output power of 48 W), the power supply 1202 and capacitive element 1204 together provided a peak power of 98.7 W to the amplifier 1206 with the output voltage staying above 9 V for all music tested.
In another implementation shown in FIG. 13, a power supply 1302 (a DC-DC boost converter based on a Linear Technology model LTC1624 switching regulator controller) powered from six 1.2 V batteries (providing 7.2 V total input voltage) is connected in parallel with a capacitive element 1304 consisting of six 10 F/2.5 V aerogel super capacitors in series, each capacitor having a 5.1 kΩ shunt resistor, providing a total capacitance of 1.67 F and a maximum voltage of 15 V. The power supply 1302 and capacitive element 1304 power a pair of audio amplifiers 1306A and 1306B each driving a speaker 1308A and 1308B, respectively. Music signals 1310A and 1310B input into amplifiers 1306A and 1306B, respectively. When the power supply 1302 had an output current limit set to approximately 0.6 A and a nominal output voltage set to 14 V (for a maximum output power of 8.5 W), the power supply 1302 and capacitive element 1304 together provided a peak power of 25.2 W to the amplifiers 1306A and 1306B with the output voltage staying above 9.5 V for all music tested.
In another implementation shown in FIG. 14, a power supply 1402 (a DC-DC buck converter based on a Linear Technology model LTC1624 switching regulator controller) powered from an AC mains via an AC-DC converter 1403 (an Apple Computer 12 V/1 A wall pack) is connected in parallel with a capacitive element 1404 consisting of five 4 F/2.5 V aerogel super capacitors in series, each capacitor having a 20 kΩ shunt resistor, providing a total capacitance of 0.8 F and a maximum voltage of 12.5 V. The power supply 1402 and capacitive element 1404 power a pair of audio amplifiers 1406A and 1406B each driving a speaker 1408A and 1408B, respectively. Music signals 1410A and 1410B input into amplifiers 1406A and 1406B, respectively. When the power supply 1402 had an input current limit set to approximately 0.8 A and a nominal output voltage set to 12 V (for a maximum input power of 9.6 W), the power supply 1402 and capacitive element 1404 together provided a peak power of 25 W to the amplifiers 1406A and 1406B with the output voltage staying above the minimum operating voltage for all music tested.
FIGS. 15a-15d depict circuits 2100-2400, respectively, in which a power source is in series with a capacitor to supply power to a load with a voltage that is the sum of the voltages output by the power source and the capacitor. In each of the circuits 2100-2400, a power converter selectively either charges the capacitor or cooperates with the capacitor to limit the current drawn from the power source, depending on how much current the load attempts to draw from the combination of the power source and the capacitor. In each of the circuits 2100-2400, the power source may be a battery, a power source providing DC output from an AC main, a power feed provided form an external device (e.g., cabling conveying power in additional to digital serial communications from an electronic device such as a computer), or any of a variety of other types of power source. Also, the capacitor may be any of a variety of types of capacitive element, including a super capacitor or ultra capacitor. Further, although the power converter is preferably a buck converter, those skilled in the art will readily understand that other types of power converter may be used. Although circuit 210 will now be described in detail, the operation of each of these circuits 2100-2400 is substantially similar. However, in some embodiments, the manner in which the anodes, cathodes and terminals of the power source, capacitor and power converter are coupled in the circuit 2100 may be preferred due to its efficiency in comparison to the configurations depicted in the circuits 2200-2400.
In the circuit 2100 depicted in FIG. 15, a load 2170 is supplied with power having a voltage that is the sum of the voltages output by the power source 2110 and the capacitor 2135, which are coupled in series. The load 2170 is coupled to the anode of the power source 2110 and the cathode of the capacitor 2135, and the cathode of the power source 2110 is coupled to the anode of the capacitor 2135. Further, the input terminal of the power converter 2130 is coupled to the anode of the power source 2110, the output terminal of the power converter 2130 is coupled to both the cathode of the power source 2110 and the anode of the capacitor 2135, and the common terminal of the power converter 2130 is coupled to the cathode of the capacitor 2135.
There are two current flows provided by the power source 2110 that flow out through the output terminal of the power converter 2130. A first current flows from the anode of the power source 2110, through the load 2170, through the common and output terminals of the power converter 2130, and back to the cathode of the power source 2110. A second current flows from the anode of the power source 2110, through the input and output terminals of the power converter 2130, and back to the cathode of the power source 2110. The power converter 2130 imposes a limit on the amount of current that it permits to flow out through the output terminal, and the sum of these two current flows out through the output terminal is not permitted by the power converter 2130 to exceed this limit. It is this limit imposed on the sum of these two current flows that determines whether the capacitor 2135 is charged or discharged, depending on the amount of current drawn by the load 2170, as will now be explained.
At times when the load 2170 draws a relatively small amount of current, such that the limit of current flowing out through the output terminal of the power converter 2130 is not exceeded, both of the first and second current flows are able to take place without limits being imposed on them by the power converter 2130. The power converter 2130 is able to function as a voltage source with a portion of the current flowing out through the output terminal being able to charge the capacitor 2135. As a result, the load 2170 is supplied with power having a voltage equal to the sum of the full output voltage of the power source 2110 and the full capacity voltage of the capacitor 2135.
However, at times when the load 2170 attempts to draw a relatively large amount of current, such that the limit of current flowing out through the output terminal of the power converter 2130 would be exceeded if this amount of current were permitted through the power converter, the second current flow is reduced as a greater proportion of the current flow out through the output terminal is taken by the first current flow. The power converter 2130 then functions as a current source, and the capacitor 2135 discharges. The discharging of the capacitor 2130 allows a portion of the higher current draw of the load 2170 to circumvent the limit on current flowing out through the output terminal of the power converter 2130 allows the power source 2110 to support the higher current draw of the load 2170. As a result, voltage of the power source 2110 is able to be initially maintained at the full output voltage of the power source 2110. However, the power source 2110 is permitted to support this higher current draw of the load 2170 for only the amount of time that the capacitor 2135 requires to fully discharge, and after that, the amount of current that the power source 2110 is permitted to provide is limited by the limit imposed by the power converter 2130 through its output terminal.
In other words, at times when the load 2170 attempts to draw a relatively large amount of current, the capacitor 2135 and the power converter 2130 cooperate to initially allow the power source 2110 to support that higher amount of current for only the brief period of time required for the capacitor 2135 to discharge. After that, the discharged state of the capacitor 2135 and the limit on current flowing out through the output terminal of the power converter 2130 cooperate to limit the amount of current that the power source 2110 is allowed to provide. This accommodates the ability of a number of types of power sources to support a relatively large draw of current for only a brief period without damage. However, after that brief period, many of those power sources may be damaged due to overheating or other factors if they are allowed to continue supporting such a relatively large draw of current. Indeed, the storage capacity of the capacitor 2135 may be deliberately selected to control both the amount of time during which the power source 2110 is permitted to supply all of the relatively large amount of current (an amount of time that ends when the capacitor 2135 is discharged), and/or the limit on current following out through the output terminal of the power converter 2130 may be deliberately selected to control the amount of current that the power source 2110 is permitted to supply after the capacitor 2135 is discharged.
Although a single capacitor 2135 is depicted, it will be readily apparent to those skilled in the art that multiple capacitors may be grouped together in some embodiments in series and/or in parallel to increase voltage and/or storage capacity. Further, in some embodiments, including embodiments in which the power source 2110 is a battery or other type of power storage device, the power converter 2130 may be designed and/or selected to enable the capacitor 2135 to discharge stored power back to the power source 2110 (perhaps back through the output and input connections of the power converter 2130) when the circuit 2100 is to be turned off. This may be implemented as part of a sequence of steps for powering down the circuit 2100 in which the power converter 2130 is signaled to cease charging the capacitor 2135, and instead, to allow current from the capacitor 2135 to return to the power source 2110.
FIGS. 16a and 16b depict possible changes in the voltage (Vload) provided to the load 2170 in the circuit 2100 as a result of changes in the current (Iload) drawn by the load 2170 from drawing a relatively small amount of current to drawing a relatively large amount of current. Prior to time Ta in both FIGS. 16a and 16b, the load 2170 draws a relatively small Iload that does not cause the limit imposed by the power converter 2130 on the amount of current flowing out through its output terminal to be exceeded. As a result, the power converter 2130 is able to function as a voltage source, and Vload is the sum of the fall voltage output of the power source 2110 and the full capacity voltage of the capacitor 2135.
However, at time Ta, the load 2170 begins attempting to draw a relatively larger Iload. This relatively larger Iload causes the limit on the total current flowing out through the output terminal of the power converter 2130 to be reached, and would cause that limit to be exceeded if the power converter 2130 did not impose the limit. As a result, there is no longer current capacity through the output terminal to allow a current flow from the input terminal to be used to charge the capacitor 2135, and the capacitor 2135 starts to discharge. The discharging of the capacitor 2135 allows part of the relatively larger Iload to flow through the capacitor 2135, thereby circumventing the limit imposed by the power converter 2130 and allowing Iload to initially increase considerably at time Ta. However, starting at time Ta, the discharging of the capacitor 2135 causes both the voltage output by the capacitor 2135 and the current flowing thought the capacitor 2135 to fall exponentially towards zero, thereby forcing both Vload and Iload to drop starting at time Ta.
If, as shown in FIG. 16a, the load 2170 ceases at time Tb to attempt to draw the relatively larger Iload before the capacitor 2135 is fully discharged, then the amount of current flowing out through the output terminal of the power converter 2130 ceases to exceed the limit imposed by the power converter 2130. As a result, the capacitor 2135 is once again charged, and Vload returns to the level at which it was before time Ta.
Alternatively, if as shown in FIG. 16b, the load 2170 continues attempting to draw a relatively larger Iload past time Tc, at which the capacitor is fully discharged, then Iload is forced to be limited by the limit in current flow imposed by the power converter 2130. As a result, Vload is also forced to be limited to a level dictated by the limit on current flow imposed by the power converter 2130 as the power converter 2130 functions as a current source. Later at time Td, when the load 2170 ceases to attempt to draw a relatively larger Iload and returns to drawing the relatively small Iload, the amount of current flowing out through the output terminal of the power converter return to a level that does not exceed the limit and the capacitor 2135 again charges. As a result, Vload returns to the level at which it was before time Ta.
FIG. 17 depicts a circuit 3100 having an amplifier 3170 that is powered by a power source 3110 in series with a capacitor 3135 that is selectively charged by a power converter 3130. The amplifier 3170 is able to drive an acoustic driver 3175 when the acoustic driver 3175 is coupled to the circuit 3100. The coupling of anodes, cathodes and terminals among the power source 3110, the capacitor 3135 and the power converter 3130 in the circuit 3100 is substantially similar to that in the circuit 2100 of FIG. 15a. However, as those skilled in the art will readily recognize, the coupling of these anodes, cathodes and terminals may alternatively be made substantially similar to that in any of the circuits 2200-2400 of FIGS. 15b-15d, respectively. In a manner not unlike the load 2170 of the circuit 2100, the amplifier 3170 of the circuit 3100 is supplied with power having a voltage that is the sum of the voltages output by the power source 3110 and the capacitor 3135. Also not unlike the power converter 2130 of the circuit 2100, the power converter 3130 of the circuit 3100 selectively charges the capacitor 3135 depending on the amount of current drawn by the amplifier 3170.
As was the case with the circuits 2100-2400, the power source 3110 may be a battery, a power source providing DC output from an AC main, a power feed provided from an external device (e.g., cabling conveying power in additional to digital serial communications from an electronic device such as a computer), or any of a variety of other types of power source. Also, the capacitor 3135 may be any of a variety of types of capacitive element, including a super capacitor or ultra capacitor. Further, although the power converter 3130 is preferably a back converter, those skilled in the art will readily understand that other types of power converter may be used. The acoustic driver 3175 may represent one or more speakers in an entertainment system, one or more sound emitting elements of a pair of headphones, or any of a variety of other types of device capable of producing sound.
In a manner not unlike previously discussed embodiments of power being supplied to an amplifier, the amount of current drawn by the amplifier 3170 of the circuit 3100 at any given time is based primarily on the amount of power the amplifier 3170 requires to drive the acoustic driver 3175 to produce a given sound at a given volume. As previously discussed, many pieces of music have brief portions that cause the amplifier 3170 to briefly draw a relatively greater amount of current in order to drive the acoustic driver 3175 during those portions. Not unlike the circuit 2100, in the circuit 3100 there are two current flows provided by the power source 3110 that flow out through the output terminal of the power converter 3130. A first current flows from the power source 3110, through the amplifier 3170, through the common and output terminals of the power converter 3130, and back to the power source 3110. A second current flows from the power source 3110, through the input and output terminals of the power converter 3130, and back to the power source 3110. The power converter 3130 imposes a limit on the amount of current that it permits to flow out through the output terminal, and the sum of these two current flows out through the output terminal is not permitted by the power converter 3130 to exceed this limit.
At times when the amplifier 3170 draws a relatively small amount of current, such that the limit of current flowing out through the output terminal of the power converter 3130 is not exceeded, both of the first and second current flows are able to take place without limits being imposed on them by the power converter 3130. As a result, the capacitor 3135 is charged, and the amplifier 3170 is supplied with power having a voltage equal to the sum of the full output voltage of the power source 3110 and the full capacity voltage of the capacitor 3135. However, at times when a piece of music (or other signal representative of a sound) causes the amplifier 3170 to attempt to draw a relatively large amount of current, such that the limit of current flowing out through the output terminal of the power converter 3130 would be exceeded if this amount of current were permitted through the power converter, the second current flow is reduced as a greater proportion of the current flowing out through the output terminal is taken by the first current flow. As a result, the capacitor 3135 discharges, and while this discharging continues to take place, the power source 3110 is permitted to support the higher current draw of the amplifier 3170. Part of this higher current returns to the power source 3110 through the power converter 3130 and part through the capacitor 3135 such that the limit on current flow through the output terminal of the power converter is circumvented. As a result, voltage of the power source 3110 is able to be initially maintained at the full output voltage of the power source 3110. However, after the capacitor 3135 has fully discharged, current no longer flows through the capacitor 3135, and so the amount of current that the power source 3110 is permitted to provide is limited by the limit imposed by the power converter 3130 on the flow of current out through its output terminal.
The storage capacity of the capacitor 3135 may be selected to be large enough to ensure that the time required to discharge the capacitor is sufficiently long as to accommodate a desired percentage of brief passages requiring increased power as are known to exist within a known set of pieces of music. Additionally or alternatively, the storage capacity of the capacitor 3135 may be selected to be small enough to ensure that the time required to discharge the capacitor is sufficiently limited to prevent the power source 3110 from being permitted to support a relatively higher current draw for too long a period of time such that the power source 3110 is damaged. Also, the limit on current flowing out through the output terminal of the power converter 3130 may be selected to control the amount of current that the power source 3110 is permitted to supply after the capacitor 3135 is discharged to prevent damage to the power source 3110.
Although a single capacitor 3135 is depicted, it will be readily apparent to those skilled in the art that multiple capacitors may be grouped together in some embodiments in series and/or in parallel to increase voltage and/or storage capacity. Further, in some embodiments, including embodiments in which the power source 3110 is a battery or other type of power storage device, the power converter 3130 may be designed and/or selected to enable the capacitor 3135 to discharge stored power back to the power source 3110 (perhaps back through the output and input connections of the power converter 3130) when the circuit 3100 is to be turned off. This may be implemented as part of a sequence of steps for powering down the circuit 3100 in which the power converter 3130 is signaled to cease charging the capacitor 3135, and instead, to allow current from the capacitor 3135 to return to the power source 3110.
FIGS. 16a-16b, although discussed with regard to Vload provided to the load 2170 of the circuit 2100 in FIG. 15a, are also indicative of the changes that may occur in the voltage provided to the amplifier 3170 of the circuit 3100. Further, as was the case with the circuit 2100, whether the voltage provided to the amplifier 3170 follows the changes depicted in FIG. 16a or the changes depicted in FIG. 16b depends on whether the amplifier 3170 ceases drawing a relatively larger amount of current either before the capacitor 3135 is fully discharged (i.e., at time Tb, or after the capacitor 3135 is fully discharged (i.e., at time Td).
FIG. 18 depicts a circuit 3200 having an amplifier 3270 that is powered by a power source 3210 in series with a capacitor 3235 that is selectively charged by a power converter 3230. The amplifier 3270 is able to drive an acoustic driver 3275 with audio input received through a compressor 3250 when the acoustic driver 3275 is coupled to the circuit 3200. The coupling of anodes, cathodes and terminals among the power source 3210, the capacitor 3235 and the power converter 3230 in the circuit 3200 is substantially similar to that in the circuits 2100 and 3100 of FIGS. 15a and 17, respectively. However, as those skilled in the art will readily recognize, the coupling of these anodes, cathodes and terminals may alternatively be made substantially similar to that in any of the circuits 2200-2400 of FIGS. 15b-15d, respectively. In a manner not unlike the amplifier 3170 of the circuit 3100, the amplifier 3270 of the circuit 3200 is supplied with power having a voltage that is the sum of the voltages output by the power source 3210 and the capacitor 3235. Also not unlike the power converter 3130 of the circuit 3100, the power converter 3230 of the circuit 3200 selectively charges the capacitor 3235 depending on the amount of current the amplifier 3270 is caused to draw as a result of driving the acoustic driver 3275.
As was the case with previously discussed circuits, the power source 3210 may be any of a variety of other types of power source, and the power converter 3230 may be any of a variety of types of power converter. Further, the power converter 3230 may be capable of enabling energy stored in the capacitor 3235 to be returned to the power source 3210 upon the powering down of the circuit 3200. Also, the capacitor 3235 may be any of a variety of types of capacitive element, including more than one capacitive element, and the acoustic driver 3275 may be any of a variety of types of device capable of producing sound, including more than one of such devices.
The substantial difference between the circuit 3200 and the circuit 3100 of FIG. 17 is the addition of the compressor 3250 in the circuit 3200 that serves to selectively reduce the amplitude of at least some peak portions of the audio input presented to the amplifier 3270. As previously discussed, many pieces of music have brief portions that cause an amplifier to require relatively greater amounts of current. However, a small percentage of music may have relatively longer portions that cause such relatively greater amounts of current to be required, and these longer portions may be long enough to exceed the amount of time during which the power source 3210 is able to provide such relatively greater amounts of current without damage and/or long enough to exceed the amount of time during which the capacitor 3235 is able to allow the power source 3210 to support such relatively greater amounts of current. In other words, such longer portions may be long enough that the capacitor 3235 is substantially discharged before such longer portions end, thereby removing the path by which part of the relatively larger amount of current circumvents the limit imposed by the power converter 3230. Where a situation arises in which the amplifier 3270 requires more current, but that amount of current is not provided, undesirable events may occur in the signal driven by the amplifier 3270 to the acoustic driver 3275, such as the clipping of peaks in that output.
The compressor 3250 may be coupled to a sensor 3255 to sense the voltage provided to the amplifier 3270, may be coupled to a sensor 3257 to sense occurrences of undesirable events in the signal driven to the acoustic driver 3275 (e.g., clipping), and/or may receive an input from the power converter 3230 indicating occurrences of the current flowing out through the output terminal reaching the limit imposed by the power converter 3230. As will be explained in greater detail, as a relatively longer portion of music (or other sound) is encountered that continues beyond the time at which the capacitor 3235 is substantially discharged, the compressor 3250 is triggered to reduce the amplitude of at least some peak portions of the audio input provided to the amplifier 3270. As a result, the amplitude of at least some peak portions of the output driven by the amplifier 3270 to the acoustic driver 3275 is reduced to avoid clipping and/or other undesirable events.
Not unlike the circuits 2100 and 3100, in the circuit 3200 there are two current flows that are provided by the power source 3210 and that both flow out through the output terminal of the power converter 3230, and the power converter 3230 imposes a limit on the amount of current that it permits to flow out through the output terminal. At times when the amplifier 3270 draws a relatively small amount of current, such that the limit of current flowing out through the output terminal of the power converter 3230 is not exceeded, both current flows are able to take place without limits being imposed on them by the power converter 3230. As a result, the capacitor 3235 is charged, and the amplifier 3270 is supplied with power having a voltage equal to the sum of the full output voltage of the power source 3210 and the full capacity voltage of the capacitor 3235.
At times when a piece of music (or other signal representative of a sound) causes the amplifier 3270 to begin drawing a relatively large amount of current, such that the limit of current flowing out through the output terminal of the power converter 3230 would be exceeded if this amount of current were permitted through the power converter, the second current flow is reduced as a greater proportion of the current flowing out through the output terminal is taken by the first current flow. As a result, the capacitor 3235 discharges, and while this discharging continues to take place, the power source 3210 is permitted to support the higher current draw of the amplifier 3270. Part of this higher current returns to the power source 3210 through the power converter 3230 and part through the capacitor 3235 such that the limit on current flow through the output terminal of the power converter si circumvented. As a result, voltage of the power source 3210 is able to be initially maintained at the full output voltage of the power source 3210. However, after the capacitor 3235 has fully discharged, current no longer flows through the capacitor 3235, and so the amount of current that the power source 3210 is permitted to provide is limited by the limit imposed by the power converter 3230 on the flow of current out through its output terminal.
However, unlike the circuit 3100 of FIG. 17, of the period of time during which the amplifier 3270 draws relatively more current approaches or exceeds the time required for the capacitor 3235 to substantially discharge, then the compressor 3250 is triggered to alter the audio signal provided to the amplifier 3270 to reduce the amplitude of at least some peaks. In embodiments where the compressor 3250 is coupled to the sensor 3255 sensing the voltage provided to the amplifier 3270, the compressor 3250 may be triggered in response to the drop in the voltage provided to the amplifier 3270 as the capacitor 3235 is substantially discharged. In embodiments where the compressor 3250 is coupled to the sensor 3257 sensing undesired events in the signal driven to the acoustic driver 3275, the compressor 3250 may be triggered in response to the occurrence of one or more of such undesired events. In embodiments where the compressor 3270 receives an input from the power converter 3230 indicating occurrences of the limit on current flowing out through the output terminal being reached, the compressor 3250 may be triggered in response to that limit being reached. In other embodiments, the compressor 3250 may employ a timer that triggers the compressor 3250 if the audio input continues to exhibit a characteristic (e.g., ka threshold of amplitude being exceed by at least one peak) that causes the amplifier 3270 to require a relatively greater amount of current for a period of time longer than a present interval of time, and that interval may chosen to correspond to the amount of time required for the capacitor 3235 to substantially discharge. In each of these embodiments, the compressor 3250 may monitor one or more characteristics of the audio input and cease reducing the amplitude of at least some peaks in the signal provided to the amplifier 3270 in response to the audio input ceasing to have a characteristic causing the amplifier 3270 to require a relatively greater amount of current.
Not unlike the capacitor 3135 of the circuit 3100, the storage capacity of the capacitor 3235 may be selected to be large enough to ensure that the time required to discharge the capacitor is sufficiently long as to accommodate a desired percentage of brief passages requiring increased power as are known to exist within a known set of pieces of music. Additionally or alternatively, the storage capacity of the capacitor 3235 may be selected to be small enough to ensure that the time required to discharge the capacitor is sufficiently limited to prevent the power source 3210 from being permitted to support a relatively higher current draw for too long a period of time such that the power source 3210 is damaged. Also, the limit on current flowing out through the output terminal of the power converter 3230 may be selected to control the amount of current that the power source 3210 is permitted to supply after the capacitor 3235 is discharged to prevent damage to the power source 3210.
FIG. 19 depicts the possible changes in the voltage (Vamp) provided to the amplifier 3270 in the circuit 3200 as a result of changes in the current (lamp) drawn by the amplifier 3270, including attempt to draw a relatively large amount for a period of time sufficiently long as to trigger the compressor 3250. Prior to time Ta, the amplifier 3270 draws a relatively small lamp that does not cause the limit imposed by the power converter 3230 on the amount of current flowing out through its output terminal to be exceeded. As a result, the power converter 3230 is able to function as a voltage source, and Vamp is the sum of the full voltage output of the power source 3210 and the full capacity voltage of the capacitor 3235.
However, at time Ta, a portion of music (or other sound) received as an audio input causes the amplifier 3270 to attempt to draw a relatively larger lamp. This causes the limit on the total current flowing out through the output terminal of the power converter 3230 to be reached, and would cause that limit to be exceeded if the power converter 3230 did not impose this limit. As a result, there is no longer current capacity through the output terminal to allow a current flow from the input terminal to be used to charge the capacitor 3235, and the capacitor 3235 starts to discharge. The discharging of the capacitor 3235 allows part of the relatively larger lamp to flow through the capacitor 3235, thereby circumventing the limit imposed by the power converter 3230. However, starting at time Ta, the discharging of the capacitor 3235 causes the voltage output by the capacitor 3235 and the capacity for current flowing through the capacitor 3235 to fall exponentially towards zero, forcing both lamp and Vamp to drop.
As the amplifier 3270 continues drawing the relatively larger lamp, at time Tb, the compressor 3250 is triggered to begin altering the audio input to reduce the amplitude of at least some peaks in the audio input, and provides this version of the audio input to the amplifier 3270. This altered version of the audio input reduces the current requirements of the amplifier 3270, thereby allowing the amplifier 3270 to operate within the forcibly limited lamp and continue to provide an output to the acoustic driver 3275 while avoiding at least one or more undesirable events (e.g., clipping).
As previously discussed, the compressor 3250 may be triggered by one or more of a number of events, including an event corresponding or otherwise linked to the discharge of the capacitor 3235. As a result, time Tb may coincide or be otherwise coordinated with the time at which the capacitor 3235 is discharged to a preselected degree or at which the capacitor 3235 is fully discharged. From the time the capacitor 3235 is fully discharged such that there can no longer be current flowing through the capacitor 3235, lamp will be limited by the limit imposed on current flowing out through the output terminal of the power converter 3230. As a result, by the time the capacitor 3235 has fully discharged, Vamp has dropped to a level dictated by the limit on current flow imposed by the power converter 3230 as the power converter 3230 functions as a current source.
At time Tc, the audio input changes such that the one or more characteristics of the audio input that had caused the amplifier 3270 to attempt to draw a relatively greater lamp are no longer present, and the compressor 3250 ceases altering the audio input. Furthermore, with the amplifier 3270 no longer attempting to draw a relatively greater lamp, the amount of current flowing out through the output terminal of the power converter returns to a level that does not exceed the limit. As a result, the capacitor 3235 again charges, and Vamp returns to the level at which it was before time Ta.
FIG. 20 depicts a circuit 3300 having an amplifier 3370 that is powered by a power source 3310 in series with a capacitor 3335 that is selectively charged by a power converter 3330. The amplifier 3370 has a gain control 3372 and is able to drive an acoustic driver 3375 when the acoustic driver 3375 is coupled to the circuit 3300. The coupling of anodes, cathodes and terminals among the power source 3310, the capacitor 3335 and the power converter 3330 in the circuit 3300 is substantially similar to that in the circuits 2100, 3100 and 3200 of FIGS. 15a, 17 and 18, respectively. However, as those skilled in the art will readily recognize, the coupling of these anodes, cathodes and terminals may alternatively be made substantially similar to that in any of the circuits 2200-2400 of FIGS. 15b-15d, respectively. In a manner not unlike the amplifiers 3170 and 3270 of the circuits 3100 and 3200, the amplifier 3370 of the circuit 3300 is supplied with power having a voltage that is the sum of the voltages output by the power source 3310 and the capacitor 3335. Also not unlike the power converters 3130 and 3230 of the circuits 3100 and 3200, respectively, the power converter 3330 of the circuit 3300 selectively charges the capacitor 3335 depending on the amount of current the amplifier 3370 is caused to draw as a result of driving the acoustic driver 3375.
As was the case with previously discussed circuits, the power source 3310 may be any of a variety of other types of power source, and the power converter 3330 may be any of a variety of types of power converter. Further, the power converter 3330 may be capable of enabling energy stored in the capacitor 3335 to be returned to the power source 3310 upon the powering down of the circuit 3300. Also, the capacitor 3335 may be any of a variety of types of capacitive element, including more than one capacitive element, and the acoustic driver 3375 may be any of a variety of types of device capable of producing sound, including more than one of such devices.
The substantial difference between the circuit 3300 from the circuit 3200 is the substitution of the gain control 3372 for the compressor 3250. Whereas the compressor 3250 selectively reduces at least some peaks of the audio input presented to the amplifier 3270, the gain control 3372 selectively reduces the gain employed by the amplifier 3370 in amplifying the audio input. In support of triggering tog the gain control 3372, the amplifier 3370 may receive an input from the power converter 3330 indicating occurrences of the current flowing out through the output pin reaching the limit imposed on that current flow by the power converter 3330. As a relatively longer portion of music (or other sound) causes the amplifier 3370 to require a relatively larger amount of current for a period of time long enough to substantially discharge the capacitor 3335, the gain control 3372 is triggered to reduce the gain of amplifier 3370 in amplifying the audio input such that the amplitude of the output of the driven by the amplifier 2370 to the acoustic driver 2375 is reduced to avoid clipping and/or other undesirable events.
Not unlike the circuits 2100, 3100 and 3200, in the circuit 3300, at times when the amplifier 3370 draws a relatively small amount of current, such that the limit imposed by the power converter 3330 on current flowing out through the output terminal is not exceeded, no limit is placed on current flowing out through the output terminal. As a result, the capacitor 3335 is charged, and the amplifier 3370 is supplied with power having a voltage equal to the sum of the full output voltage of the power source 3310 and the full capacity voltage of the capacitor 3335. At times when a piece of music for other signal representative of a sound) causes the amplifier 3370 to begin drawing a relatively large amount of current, such that the limit of current flowing out through the output terminal of the power converter 3330 would be exceeded if this amount of current were permitted through the power converter, the imposed limit results in the capacitor 3335 discharging. While this discharging takes place, the power source 3310 is permitted to support the higher current draw of the amplifier 3370 and part of this higher current returns to the power source through the capacitor 3335 such that the limit imposed on current flowing out through the output terminal is circumvented. As a result, the full output voltage of the power source 3210 is able to be maintained until the capacitor 3335 has fully discharged, resulting in the amount of current that the power source 3310 is permitted to provide being limited by the limit imposed by the power converter 3230 on the flow of current out through its output terminal.
However, if the period of time during which the amplifier 3370 draws relatively more current begins to exceed the time during which the capacitor 3335 substantially discharges, then the gain control 3372 alters the gain applied by the amplifier 3370 to the audio input to reduce the amplitude of the resulting output driven to the acoustic driver 3375. In some embodiments, the gain control 3372 may monitor the voltage provided to the amplifier 3370, and reduce the gain in response to the drop in the voltage provided to the amplifier 3370 as the capacitor 3335 is substantially discharged. In some embodiments, the gain control 3372 may monitor the output driven to the acoustic driver 3375 for undesired events (including clipping), and reduce the gain in response to the occurrence of one or more of such undesired events. In embodiments where the amplifier 3370 receives an input from the power converter 3330 indicating occurrences of disconnection of the output connection of the power converter 3330, the gain control 3372 may reduce the gain in response to the occurrence of one or more instances of such disconnection. In other embodiments, the gain control 3372 may employ a timer triggering a reduction in the gain if the audio input continues to cause the amplifier 3370 to require relatively greater amounts of power for a period of time longer than a preset interval of time that may be chosen to correspond to the amount of time required for the capacitor 3335 to substantially discharge. In each of these embodiments, the gain control 3372 may monitor one or more characteristics of the audio input and cease reducing the gain if the audio input changes so as to no longer cause the amplifier 3370 to require such relatively greater amounts of power.
Not unlike the capacitors of previously discussed circuits, the storage capacity of the capacitor 3335 may be selected to be large enough to ensure that the time required to discharge the capacitor is sufficiently long as to accommodate a desired percentage of brief passages requiring increased power as are known to exist within a known set of pieces of music. Additionally or alternatively, the storage capacity of the capacitor 3335 may be selected to be small enough to ensure that the time required to discharge the capacitor is sufficiently limited to prevent the power source 3310 from being permitted to support a relatively higher current draw for too long a period of time such that the power source 3310 is damaged. Also, the limit on current flowing out through the output terminal of the power converter 3330 may be selected to control the amount of current that the power source 3310 is permitted to supply after the capacitor 3335 is discharged to prevent damage to the power source 3310.
The effect of the operation of the circuit 3300 on the voltage provided to the amplifier 3370 may, in some embodiments, be substantially the same as depicted in FIG. 19, with the substantial difference being that at time Tc, the gain with which the audio input is amplified by the amplifier 3370 is changed, rather than the amplitude of peaks in the audio input.
It should be noted that although speakers 212, 1106, 1208, 1308A, 1308B, 1408A and 1408B have all been depicted in their respective Figures as though they were single devices receiving a single channel of an audio signal from which to produce sound, as already alluded to in the later discussion of the acoustic drivers 3175, 3275 and 3375, those skilled in the art will readily recognize that each of these depicted components may represent a plurality of devices capable of producing sound. Indeed, each of these depicted components may represent a more complex device capable of producing sound, including speakers employing at least one crossover and/or a multitude of sound-producing elements. Furthermore, each of these depicted components may represent a sound-producing device in which further amplification and/or signal processing is employed. Also, in the various embodiments discussed herein in which a compressor, a gain control or other adjustable device capable of altering a signal providing audio to an amplifier or altering the amplification of such a signal, such compressor, gain control or other adjustable device may be provided with the ability to employ select and/or utilize preselected settings based on one or more characteristics of one or more known sound-producing devices. Such preselected settings may be utilized to provide the ability to automatically adjust the gain or output driving strength employed by an amplifier and/or the timing at which a compressor or a gain control may begin or cease acting on a signal representing an audio input in coordination with the use of a capacitor to boost the power provided to an amplifier.
In some embodiments, one of the circuits 2100, 2200 or 2300, or one of the circuits incorporating an amplifier that is depicted in one of the earlier Figures is disposed about the casing of an electronic device to produce sound from an audio signal (e.g., a docking station for a digital audio file player, a “boom box” audio device, a cell phone, a “satellite” speaker for a computer system, a pair of amplified headphones, an amplifying component of a home entertainment system, etc.). Such a casing may also incorporate one of the speakers 212, 1106, 1208, 1308A, 1408A, or 1408B, or one of the acoustic drivers 3175, 3275 or 3375, or may incorporate the ability for the electronic device to be coupled to one of these speakers or acoustic drivers.
FIG. 21 depicts a circuit 3600 having an electromechanical actuator 3670 that is powered by a power source 3610 in series with a capacitor 3635 that is selectively charged by a power converter 3630. A power switching device 3650 is interposed between the electromechanical actuator 3670 and the supply of power provided by the power source 3610 and the capacitor 3635 to control the provision of power and/or the polarity of power to the electromechanical actuator 3670 in response to a control input. The coupling of anodes, cathodes and terminals among the power source 3610, the capacitor 3635 and the power converter 3630 in the circuit 3600 is substantially similar to that in the circuits 2100, 3100, 3200 and 3300 of FIGS. 15a, 17, 18 and 20, respectively. However, as those skilled in the art will readily recognize, the coupling of these anodes, cathodes and terminals may alternatively be made substantially similar to that in any of the circuits 2200-2400 of FIGS. 15b-15d, respectively. In a manner not unlike the loads and amplifiers of previously discussed circuits, the electromechanically actuator 3670 of the circuit 3600 is supplied with power (through the power switching device 3650) having a voltage that is the sum of the voltages output by the power source 3610 and the capacitor 3635. Also, the power converter 3630 of the circuit 3600 selectively charges the capacitor 3635 depending on the amount of current drawn by the electromechanical actuator 3670.
As was the case with previously discussed circuits, the power source 3610 may be any of a variety of other types of power source, and the power converter 3630 may be any of a variety of types of power converter. Further, the power converter 3630 may be capable of enabling energy stored in the capacitor 3635 to be returned to the power source 3610 upon the powering down of the circuit 3600. Also, the capacitor 3635 may be any of a variety of types of capacitive element, including more than one capacitive element, and the acoustic driver 3675 may be any of a variety of types of device capable of producing sound, including more than one of such devices.
The electromechanical actuator 3760 may be any of a variety of types of electromechanical device, including a rotary motor, a stepper motor, a linear motor, a solenoid, a relay, a contactor, a magnet, etc. Like the amplifiers discussed at length herein, there are moments where the electromechanical actuator 3670 momentarily requires a relatively greater amount of power, although for the electromechanical actuator 3670, such moments are usually associated with being actuated, changes in speed of movement, or changes in direction of movement.
Not unlike the circuit 2100 of FIG. 15a, in the circuit 3600 there are two current flows provided by the power source 3610 that flow out through the output terminal of the power converter 3630. A first current flows from the power source 3610, through the combination of the power switching device 3650 and the electromechanical actuator 3670, through the common and output terminals of the power converter 3630, and back to the power source 3610. A second current flows from the power source 3610, through the input and output terminals of the power converter 3630, and back to the power source 3610. The power converter 3630 imposes a limit on the amount of current that it permits to flow out through the output terminal, and the sum of these two current flows out through the output terminal is not permitted by the power converter 3630 to exceed this limit.
At times when the electromechanical actuator 3670 draws a relatively small amount of current, such that the limit of current flowing out through the output terminal of the power converter 3630 is not exceeded, both of the first and second current flows are able to take place without limits being imposed on them by the power converter 3630. As a result, the capacitor 3635 is charged, and the electromechanical actuator 3670 is supplied with power having a voltage equal to the sum of the full output voltage of the power source 3610 and the full capacity voltage of the capacitor 3635. However, at times when an obstruction or other mechanical interference malfunction causes the electromechanical actuator 3670 to attempt to draw a relatively large amount of current, such that the limit of current flowing out through the output terminal of the power converter 3630 would be exceeded if this amount of current were permitted through the power converter, the second current flow is reduced as a greater proportion of the current flowing out through the output terminal is taken by the first current flow. As a result, the capacitor 3635 discharges, and while this discharging continues to take place, the power source 3610 is permitted to support the higher current draw of the electromechanical actuator 3670. Part of this higher current returns to the power source 3610 through the power converter 3630 and part through the capacitor 3635 such that the limit on current flow through the output terminal of the power converter is circumvented. As a result, voltage output by the power source 3610 is able to be initially maintained at the full output voltage of the power source 3610. However, after the capacitor 3635 has fully discharged, current no longer flows through the capacitor 3635, and so the amount of current that the power source 3610 is permitted to provide is limited by the limit imposed by the power converter 3630 on the flow of current out through its output terminal.
The storage capacity of the capacitor 3635 may be selected to be large enough to ensure that the time required to discharge the capacitor is sufficiently long as to accommodate the amount of time that the electromechanical actuator 3670 is expected to require a relatively greater amount of current during normal operation. Additionally or alternatively, the storage capacity of the capacitor 3635 may be selected to be small enough to ensure that the time required to discharge the capacitor is sufficiently limited to prevent the power source 3610 from being permitted to support a relatively higher current draw for too long a period of time such that the power source 3610 is damaged. Also, the limit on current flowing out through the output terminal of the power converter 3630 may be selected to control the amount of current that the power source 3610 is permitted to supply after the capacitor 3635 si discharged to prevent damage to the power source 3610.
In some embodiments, the power switching device 3650 may incorporate a power control 3652 capable of addressing instances in which the electromechanical actuator 3670 requires a relatively greater amount of current for an extended period of time longer than can be accommodated by the amount of time required to discharge the capacitor 3635 and/or the amount of time that the power source 3610 is able to supply a relatively greater amount of current without damage. The power control 3652 may respond to such an extended period of time for which a relatively greater amount of current is required by cutting off all power to the electromechanical actuator 3670, and after an interval of time, may attempt to reapply power to the electromechanical actuator. Such a cutting off response may be desirable to protect the power source 3610 and/or the electromechanical actuator 3670 from damage due to instances of the electromechanical actuator 3670 being physically prevented from performing its function (e.g., debris or some other object being in the path of movement of the electromechanical actuator 3670, etc.).
To determine when the electromechanical actuator 3670 requires a relatively greater amount of current, the power control 3652 may monitor the amount of current drawn by the electromechanical actuator 3670 through the power switching device 3650, or the power control 3652 may receive a signal from the power converter 3630 indicating when the amount of current flowing out through its output terminal has reached the imposed limit. To determine when the capacitor 3635 has been discharged such that the power source 3630 is no longer permitted to supply a relatively greater amount of current, the power control 3652 may maintain a timer preset to an amount of time chosen to be coordinated with the amount of time required to discharge the capacitor 3635, or the power control 3652 may monitor the voltage provided to the electromechanical actuator 3670 for the decay of the voltage provided by the discharge of the capacitor 3635.
The power control 3652 may be coupled to a thermal sensor (not shown) monitoring the temperature of the electromechanical actuator 3670 and/or the capacitor 3635, or may employ a timer to determine how long to wait after cutting off all power to the electromechanical actuator 3670 before attempting to reapply power to the electromechanical actuator. Where a timer is used, the timer may be preset to an interval long enough to ensure a substantial recharging of the capacitor 3635.
FIG. 22 depicts the possible changes in the voltage (Vact) provided to the electromechanical actuator 3670 in the circuit 3600 as a result of changes in the current (Iact) drawn by the electromechanical actuator 3670, including the electromechanical actuator 3670 momentarily attempting to draw a requiring relatively greater Iact. At time Ta, a control input to the power switching device 3650 causes the power switching device 3650 to alter the application of power to the electromechanical actuator 3670 such that the electromechanically actuator 3670 requires a relatively greater Iact. From time Ta to time Tb, the capacitor 3635 discharges, initially allowing the power source 3610 to supply the relatively greater Iact. However, as the capacitor 3635 discharges, both Iact and Vact diminish as the voltage output and capacity for current flow of the capacitor 3635 drop towards zero. At time Tb, the power control 3652 responds to an impetus corresponding to the discharge of the capacitor 3635 (such as the drop in the voltage output of the capacitor 3635, a timer preset to a time corresponding to the amount of time required for the capacitor 3635 to fully discharge, etc.) by operating the power switch 3650 to cut power to the electromechanical actuator 3670 such that both Iact and Vact drop to zero.
The cutting off of power to the electromechanical actuator 3670 allows the capacitor 3635 to recharge, and after the passage of a period of time from time Tb to time Tc (a period of time that may be determined by any of a number of factors as previously discussed), the power control 3652 may operate the power switch 3650 to again attempt to operate the electromechanical actuator 3670 in the manner originally intended at time Ta.
It should be noted that although Iact and Vact are depicted in FIG. 22 as being at non-zero levels prior to Ta, those skilled in the art will readily recognize that whether these levels preceding time Ta are non-zero or at zero depends on the nature of the electromechanical actuator 3670 and the function it performs. Where the electromechanical actuator 3670 was already in operation at time Ta, and the higher Iact and Vact at time Ta are the result of a change in direction and/or speed, then non-zero levels preceding time Ta would be expected. However, where the electromechanical actuator was not already in operation at time Ta, then zero levels preceding time Ta would be expected.
Other embodiments are within the scope of the following claims.

## Claims

1. An apparatus comprising:
a load;
a power source;
a capacitive element coupled in series with the power source to enable the power source and the capacitive element to provide the load with a supply voltage that is a sum of the voltages of the power source and the capacitive element, wherein the capacitive element remains coupled in series with the power source as the capacitive element is both charged and discharged; and
a power converter coupled to the capacitive element and the power source, wherein the power converter imposes a limit on current flowing through the power converter, thereby causing the power converter to charge the capacitive element while the load draws a relatively smaller amount of current and causing the power converter to enable the capacitive element to discharge to enable the load to draw a relatively higher amount of current through both the power converter and the capacitive element as the capacitive element discharges.

2. The apparatus of claim 1, wherein the load is an amplifier capable of driving at least one acoustic driver.

3. The apparatus of claim 2, wherein the at least one acoustic driver is a speaker.

4. The apparatus of claim 3, wherein the speaker is disposed on a casing of a portable electronic device.

5. The apparatus of claim 2, further comprising a compressor to receive and alter an input signal provided to the load.

6. The apparatus of claim 5, further comprising a sensor to monitor the supply voltage and to enable the compressor to reduce the amplitude of at least one peak of the input signal to the load in response to a reduction in the supply voltage.

7. The apparatus of claim 5, further comprising a sensor to monitor an output signal from the load to the at least one acoustic driver and to enable the compressor to reduce the amplitude of at least one peak of the input signal to the load in response to an occurrence of clipping in the output signal.

8. The apparatus of claim 2, wherein the load incorporates a gain control to reduce a gain employed by the load in amplifying an input signal received by the load in driving the at least one acoustic driver.

9. The apparatus of claim 1, wherein the load is an electromechanical actuator.

10. The apparatus of claim 9, wherein the electromechanical actuator is a linear motor.

11. The apparatus of claim 1, wherein the power source is a battery.

12. The apparatus of claim 1, wherein the power source is provided via a cable from an electronic device.

13. The apparatus of claim 12, wherein the cable carries digital serial communications.

14. The apparatus of claim 1, wherein the capacitive element comprises at least one supercapacitor.

15. The apparatus of claim 1, wherein the power converter is a buck converter.

16. The apparatus of claim 1, wherein the power converter is structured to enable the capacitor to discharge to return stored energy to the power source in response to the apparatus being turned off.

17. The apparatus of claim 1, wherein:
an anode of the power source is coupled to the load and to an input terminal of the power converter;
a cathode of the power source is coupled to an anode of the capacitive element and an output terminal of the power converter; and
a cathode of the capacitive element is coupled to the load and to a common terminal of the power converter.

18. An electronic device comprising:
an amplifier to amplify an audio signal and drive an acoustic driver;
a power source;
a capacitive element coupled in series with the power source to enable the power source and the capacitive element to provide the amplifier with a supply voltage that is a sum of the voltages of the power source and the capacitive element, wherein the capacitive element remains coupled in series with the power source as the capacitive element is both charged and discharged; and
a power converter coupled to the capacitive element and the power source, wherein the power converter imposes a limit on current flowing through the power converter, thereby causing the power converter to charge the capacitive element while the amplifier draws a relatively smaller amount of current and causing the power converter to enable the capacitive element to discharge to enable the amplifier to draw a relatively higher amount of current through both the power converter and the capacitive element as the capacitive element discharges.

19. The electronic device of claim 18, further comprising a casing, and wherein the acoustic driver is a speaker disposed on the casing.

20. The electronic device of claim 19, wherein the electronic device is a cellular telephone.

21. The electronic device of claim 18, further comprising a compressor to alter the audio signal before the audio signal is provided as an input to the amplifier.

22. The electronic device of claim 21, further comprising a sensor to monitor the supply voltage and to enable the compressor to reduce the amplitude of at least one peak of the audio signal in response to a reduction in the supply voltage.

23. The electronic device of claim 21, further comprising a sensor to monitor an output signal from the amplifier and to enable the compressor to reduce the amplitude of at least one peak of the audio signal in response to an occurrence of clipping in the output signal.

24. The electronic device of claim 18, wherein the amplifier incorporates a gain control to reduce a gain employed by the amplifier in amplifying an audio signal.

25. The electronic device of claim 18, wherein the power source is a battery.

26. The electronic device of claim 18, wherein the power source is provided via a cable conveying digital serial communications from another electronic device.

27. The electronic device of claim 18, wherein the capacitive element comprises at least one supercapacitor.

28. The electronic device of claim 18, wherein the power converter is a buck converter.

29. The electronic device of claim 18, wherein the power converter is structured to enable the capacitor to discharge to return stored energy to the power source in response to the apparatus being turned off.

30. A method comprising:
coupling a power source and a capacitive element in series to provide a load with power having a voltage that is the sum of the voltages of the power source and the capacitive element;
causing the capacitive element to be charged as the load draws a relatively smaller amount of current;
enabling the power source to provide a relatively higher amount of current through the capacitive element by causing the capacitive element to discharge as the load draws a relatively higher current; and
causing the capacitive element to remain coupled in series with the power source as the capacitive element is both charged and discharged.

31. The method of claim 30, further comprising:
coupling a power converter to the power source and the capacitive element; and
imposing a limit on a flow of current through at least one portion of the power converter, whereby the limit selectively causes the capacitive element to be charged and causes the capacitive element to discharge.

32. The method of claim 31, further comprising imposing the limit on the flow of current through the at least one portion of the power converter as a limit on an amount of current permitted to be provided by the power source to the load subsequent to the discharge of the capacitive element.

33. The method of claim 30, wherein the load is an amplifier, and further comprising operating a compressor to reduce an amplitude of at least one peak of a signal provided to the load that causes the load to require the increase in the amount of current drawn by the load.

34. The method of claim 33, further comprising triggering the compressor to reduce the amplitude of at least one peak of the signal provided to the load in response to a preselected amount of time elapsing since a start in the increase in the amount of current drawn by the load.

35. The method of claim 34, wherein the preselected amount of time is chosen to correspond to an amount of time required to substantially discharge the capacitive element.

36. The method of claim 33, further comprising triggering the compressor to reduce the amplitude of at least one peak of the signal provided to the load in response to detecting a reduction in the voltage provided to the load.

37. The method of claim 30, wherein the load is an amplifier, and the load further comprises a gain control to reduce a gain by which the load amplifies a signal provided to the load that causes the load to require the increase in the amount of current drawn by the load.

38. The method of claim 37, further comprising triggering the gain control to reduce the gain in response to a preselected amount of time elapsing since a start in the increase in the amount of current drawn by the load.

39. The method of claim 38, wherein the preselected amount of time is chosen to correspond to an amount of time required to substantially discharge the capacitive element.

40. The method of claim 37, further comprising triggering the gain control to reduce the gain in response to detecting a reduction in the voltage provided to the load.

41. The method of claim 30, wherein the load is an electromechanical actuator, the method further comprising cutting off power to the load at a time when the capacitive element is substantially discharged in response to the increase in the amount of current drawn by the load continuing to the time when the capacitive element is substantially discharged.

42. The method of claim 41, further comprising:
enabling the capacitive element to recharge; and
reapplying power to the load after a period of time has elapsed.

43. The method of claim 42, wherein the length of the period of time is chosen to correspond to an amount of time required to substantially recharge the capacitive element.

44. The method of claim 30, further comprising returning power stored in the capacitive element to the power source.

45. An apparatus comprising:
a load;
a power source;
a capacitive element coupled in series with the power source to enable the power source and the capacitive element to provide the load with a supply voltage that is a sum of the voltages of the power source and the capacitive element; and
a power converter coupled to the capacitive element and the power source, wherein the power converter imposes a limit on current flowing through the power converter, thereby causing the power converter to charge the capacitive element while the load draws a relatively smaller amount of current and causing the power converter to enable the capacitive element to discharge to enable the load to draw a relatively higher amount of current through both the power converter and the capacitive element as the capacitive element discharges, wherein:
an anode of the power source is coupled to the load and to an input terminal of the power converter;
a cathode of the power source is coupled to an anode of the capacitive element and an output terminal of the power converter; and
a cathode of the capacitive element is coupled to the load and to a common terminal of the power converter.