Abstract:
A dual-mode converter for converting power from an input voltage level to an output voltage level, the dual-mode converter including an inductor section having an input side and an output side, the input side receiving an input signal and the output side outputting at least one output signal based on a power value of the input signal, a feedback loop section which receives a feedback signal from one or more of the at least one output signals, the feedback loop section including a first transistor, a second transistor and a comparator unit which outputs a comparator output signal based on a comparison of the feedback signal to a comparator reference signal, wherein the respective states of the first and second transistors configure the feedback loop section to function as either a linear mode or a comparator mode, a current mode controller unit which receives the input signal, the feedback signal, and a current sense signal representing a sensed current flowing through the input side of the inductor section, the current mode controller unit outputting an output control signal based on the received input signal, the feedback signal, and the current sense signal, and a control gate that enables the current flow through the input side of the inductor section when either the output control signal or the comparator output signal is greater than a predetermined threshold.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to U.S. Provisional Patent Application No. 60/563,459, filed Apr. 20, 2004, entitled “LINCOMP CONVERTER,” which is incorporated by reference herein for all purposes. 

   STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable to this invention. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention is generally directed to a dual mode converter which converts power and which has a feedback loop that operates in a linear mode during continuous input loads and which operates in a comparative modes during a step input load. 
   2. Description of the Related Art 
   In the field of electric circuits, converters are used in many applications such as power conversion in which the voltage level from a power source is decreased to a desired voltage. In many applications using conventional converters, linearity errors can cause distortion, which limits the performance of the system that relies on the converter. For example, such distortion can decrease the operational bandwidth of the system which uses the converter. 
   In addition, many conventional converters use linear feedback which does not perform as well for step input loads as it does for continuous input loads. Such converters often result in overshoot or undershoot output voltage in response to a discontinuous step load. Many converters that are used to work with discontinuous step loads have slow transient response. Also, many conventional converters require feedback loop compensation because such converters are inherently unstable. The use of feedback loop compensation adds additional complexity and cost to the converter, and often requires adjustment of the compensation parameters when the converter is implemented into a specific application, thereby requiring additional setup time. 
   Converters are used in many applications in which the converter must work well with both continuous loads and non-continuous step loads. These applications, such as require converters that operate in a high performance mode for both continuous and discontinuous loads. 
   Accordingly, it is desirable invent a converter that can operate in a high performance mode for both continuous and discontinuous loads, that is inherently stable, and that uses fewer and less complex components, thereby reducing size and cost. 
   SUMMARY OF THE INVENTION 
   This present invention solves the foregoing problems by providing a dual mode converter that converts power and that uses a feedback loop that operates in a linear mode during continuous input loads and that operates in a comparative mode during a step input load, with inherent stability. 
   Specifically, according to one aspect of the invention, a dual-mode converter is provided for converting power from an input voltage level to an output voltage level. The dual-mode converter includes an inductor section having an input side and an output side, the input side receiving an input signal and the output side outputting at least one output signal based on a power value of the input signal, a feedback loop section which receives a feedback signal from one or more of the at least one output signals, the feedback loop section including a first transistor, a second transistor and a comparator unit which outputs a comparator output signal based on a comparison of the feedback signal to a comparator reference signal, wherein the respective states of the first and second transistors configure the feedback loop section to function in either a linear mode or a comparator mode, a current mode controller unit which receives the input signal, the feedback signal, and a current sense signal representing a sensed current flowing through the input side of the inductor section, the current mode controller unit outputting an output control signal based on the received input signal, the feedback signal, and the current sense signal, and a control gate that enables the current flow through the input side of the inductor section when either the output control signal or the comparator output signal is greater than a predetermined threshold. 
   Preferably, the input side of the inductor section includes a single primary inductor and the output side includes multiple secondary inductors, each of which outputs a corresponding output signal. Also, when the input signal has a continuous voltage value, the first transistor is in an on-state and the second transistor is in an off-state, the feedback loop section is configured to operate in a linear mode by connecting the feedback signal with the current sense signal that is input to the current controller unit, and by connecting the feedback signal to the comparator unit. Similarly, when the input signal represents a step load having a non-continuous voltage value, the first transistor is in an off-state and the second transistor is in an on-state, thereby configuring the feedback loop section to operate in a comparator mode by disconnecting the feedback signal from the current sense signal, and by disconnecting the feedback signal from the comparator unit so that the comparator unit does not output the comparator output signal. 
   In this manner, the present invention provides a converter having a feedback loop that operates with high performance in a linear mode during continuous input loads and that operates in a comparative mode during a step input load, with inherent stability. Accordingly, the converter of the present invention provides increased performance without the need for feedback loop compensation or other complex components. 
   The invention will be better understood upon reference to the following detailed description in connection with the accompanying drawings and appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a schematic for a converter according to one embodiment of the present invention. 
       FIG. 2  shows a schematic for the converter of  FIG. 1  in another configuration. 
       FIG. 3  is a chart depicting the performance of the converter shown in  FIG. 1  according to one embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a schematic of a converter according to one embodiment of the present invention. As seen in  FIG. 1 , converter  1  includes many common circuit components and is configured to provide a controlled dual-mode converter with a feedback loop that operates in a linear mode under continuous loads, and that operates in a comparative mode under non-continuous step loads. 
   Converter  1  receives input signal (load)  2  from a source such as a power supply. Input signal  2  is passed through resistor  3 , which is a known type of resistor and may be of a desired resistance to step down the voltage level of input signal  2  to a desired level. Next, input signal  2  is branched to signal  4  which is passed through resistor  5  and split to input signal  9 . Also on the path of signal  4  is capacitor  6  for filtering signal  4 . The other side of capacitor  6  is grounded. As with resistor  3 , resistor  5  and capacitor  6  are known types of components and may be of desired values in different embodiments, without departing from the scope of the invention. 
   Input signal  9  is joined with feedback signal  42  and passed to input pin  61  of current mode controller unit  60 . In this regard, feedback signal  42  and current mode controller unit  60  are discussed in more detail below. Returning to input signal  2 , it can be seen that input signal  2  continues past capacitor  8  toward inductor section  11 . Capacitor  6  is a known type of capacitor and my have a specific value to provide filtering as desired. Inductor section  11  is the core component of converter  1  for converting voltage from an input voltage level to an output level. As seen in  FIG. 1 , inductor section  11  has input side including inductor  12  and an output side with inductors  13 ,  14  and  15 . A core is in the middle of inductor section  11 , which may be one of many known types of cores, such as iron or air. Accordingly, inductor section  11  acts to convert the voltage level of input signal  2  to an output voltage of output signals  31 ,  32  and  33 . It should be appreciated that the example of inductor section  11  shown in  FIG. 1  is an isolating flyback transformer; however, the present invention also works with a simple inductor or with a multiple inductor configuration. As seen in  FIG. 1 , input signal will only cross inductor  12  of the input side of inductor section  11  when gate  71  is closed by gate drive  70  to provide a closed circuit to resistor  73 , which is grounded at the backside. The feedback and control of inductor section  11  incorporate unique features of the present invention and are discussed in more detail below. 
   Returning to  FIG. 1 , the output side of inductor section  11  picks up output signals  31 ,  32  and  33  from inductors  13 ,  14  and  15 . Output signal  31  passes through diode  16 , which restricts current flow to the output direction, and also passes by capacitor  20  and diode  25  before final output. Redundant supply input  35  is input to output signal  31  via diode  28  in order to provide hot redundancy in the event of a failure of converter  1  or input signal  2 . In a similar fashion, output signal  32  passes through diode  17 , which restricts current flow to the output direction, and also passes by capacitors  21  and  22 , followed by diode  26  before final output. Redundant supply input  36  is input to output signal  32  via diode  29  in order to provide hot redundancy in the event of a failure of converter  1  or input signal  2 . Output signal  33  passes through diode  18 , which restricts current flow to the output direction, and also passes by capacitor  23 , followed by diode  27  before final output. Redundant supply input  37  is input to output signal  33  via diode  30  in order to provide hot redundancy in the event of a failure of converter  1  or input signal  2 . In this manner, converter  1  is provides reliable performance for use in demanding applications that require high reliability, such as in military and other critical applications. Redundant supply inputs  35 ,  36  and  37  are obtained from a redundant supply (not shown) and allows feedback loop section to provide instant pickup of load in hot redundant system applications, thereby providing glitch-free output voltages. 
   The present invention is implemented by providing a dual-mode feedback from the output side of inductor section  11 , in conjunction with the use of current mode controller  60 , to control the operation of inductor section  11  for desired performance under continuous loads or step loads. Feedback loop section  40  is shown in  FIG. 1 , in which feedback signal  41  is drawn from output signal  33  prior to combination with redundant supply input  37 , in order to provide an inductor feedback signal to current mode controller unit  60 . In this regard, feedback signal  41  is split off to feedback signal  42  which is passed through diode  53  to control current flow direction and is then joined with input signal  9  and provided to input pin  61  of current mode controller unit  60 , as discussed above. 
   Returning to feedback loop section  40 , feedback signal  41  is passed through resistor  45  and then is split to provide source loads  51  and  52  to each of transistors  48  and  54 , respectively. Like the other components mentioned above, transistors  48  and  54  are known types of transistors. Feedback signal  42  is split to provide gate signal  43  which is reduced in voltage by resistors  46  and  47  and then provided to transistor  48 . When the voltage of gate signal  43  is at the requisite level in accordance with the properties of transistor  48 , transistor  48  is “opened” and source load  51  is passed to ground  50  at the drain side of transistor  48 , thereby providing a ground to feedback signal  41 . In the alternative, when the voltage of gate signal  43  is not at the requisite level in accordance with the properties of transistor  48 , transistor  48  is “closed” and source load  51  does not flow through transistor  48 . 
   Similarly, output pin  63  of current mode controller unit  60  provides a reference voltage as gate signal  55  to transistor  54 . When the voltage of gate signal  55  is at the requisite level in accordance with the properties of transistor  54 , transistor  54  is “opened” and source load  52  is passed to feedback signal  56  at the drain side of transistor  54 , thereby providing feedback signal  56  to current sense signal  68 . In the alternative, when the voltage of gate signal  55  is not at the requisite level in accordance with the properties of transistor  54 , transistor  54  is “closed” and source load  52  does not flow through transistor  54  to feedback signal  56 . 
   Also shown in feedback loop section  40  of  FIG. 1  is comparator unit  57 , which is disposed above current mode controller unit  60 . It should be appreciated that comparator unit  57  is not essential for operation of the present invention, but is included in the example shown in  FIG. 1  to act as an over-voltage protection circuit in case the main feedback loop, section  40 , fails. Comparator unit  57  receives feedback signal  56  when transistor  54  is open, and compares feedback signal  56  to reference voltage signal  58 , which in this case is ground, via zener diode  7 , acting as an over-voltage regulator. When feedback signal  56  is different than reference voltage signal  58 , comparator output signal  59  is output to gate drive  70 . In the alternative, when feedback signal  56  is the same as reference voltage signal  58 , comparator output signal  59  is not output to gate drive  70 . 
   Turning to gate drive  70 , it can be seen that current mode controller unit  60  outputs output control signal  67  to gate drive  70 . Accordingly, when comparator output signal  59  or output control signal  67  are greater than a predetermined value (typically zero) according to the characteristics of gate drive  70 , gate drive  70  operates to close gate  71 , thereby closing the circuit for the input side of inductor section  11  to result in the generation of output signals  31  to  33 . Current mode controller unit  60  is a typical, standardized type of current controller and, in the example shown in  FIG. 1 , is an SG 1845 standard controller, with known logic parameters. It should be appreciated that other types of controllers can be used equally well in the present invention, and that an equivalent control section can also be used which is comprised of discrete components to replicate the controller&#39;s functionality. As seen in  FIG. 1 , current mode controller unit  60  receives input signal  9  at input pin  61 , after input signal  9  has been joined feedback signal  42 . This signal acts as the sleep start for current mode controller unit  60 . The other connections of current mode controller unit  60  include input pin  62  which is grounded, output pin  63  which outputs gate signal  55  to transistor  54 , output pin  64  which is grounded, input pin  65  which inputs current sense signal  68 , and output pin  66  which outputs output control signal  67  to gate drive  70 . Current sense signal  68  detects whether current is flowing across the input side of inductor section  11 , such as when gate drive  70  closes gate  70 . Based on these inputs, and the standardized logic of current mode controller unit  60 , current mode controller unit  60  controls whether or not output control signal  67  operates gate drive  70  to close or open gate  71 , thereby controlling operation of inductor section  11 . 
   In this manner, feedback loop section  40 , which technically includes comparator unit  57 , is configurable to operate as a linear feedback loop when a continuous load is applied at input signal  2 , or to operate as a comparator feedback loop when a non-continuous step load is applied at input signal  2 . Transistors  48  and  54  operate to configure feedback loop section  40  by acting as a high-speed differential pair. As can be appreciated from viewing  FIG. 1 , when input signal  2  is a continuous voltage value, transistor  48  is in an open state and transistor  54  is in a closed state, thereby configuring feedback loop section  40  to operate in a linear feedback mode by disconnecting feedback signal  41  from feedback signal  56  so as to prevent feedback signal  41  from reaching current sense signal  68  and from reaching comparator unit  57 . In this mode, comparator unit  57  is disabled from outputting comparator output signal  59  to gate drive  70 . In the linear feedback mode, converter  1  operates with high performance and provides constant duty control, while giving a small signal response, and in one embodiment may operate at a bandwidth below 10 kHz. 
   In the alternative, when input signal  2  is a non-continuous step voltage load, transistor  48  is in a closed state and transistor  54  is in an open state, thereby configuring feedback loop section  40  to operate in a comparator feedback mode by connecting feedback signal  41  to feedback signal  56  which is joined to current sense signal  68 , and which is provided to comparator unit  57 , thereby enabling comparator unit  57  to output comparator output signal  59  to gate drive  70 . In the comparator feedback mode, converter  1  operates with high performance and instantly responds to the step load with negligible undershoot or overshoot of the output voltage at the output side of inductor section  11 . 
   According to the above, the converter provides dual-mode high-performance capability. In one embodiment, the operational frequency range of the converter is 50 kHz to 200 kHz, and the operating power range for the output signals is 1.1 to 8.9 Watts. Of course, it can be appreciated that other embodiments of the present invention can operate in a frequency range that is only limited by the state of the art, and in a power range of up to 1000 Watts or more. Also, the capacitors in the output side of inductor section, such as capacitors  20  to  23 , are made of tantalum and ceramic materials for providing output filtering under high temperature operation. 
     FIG. 2  shows an example of converter  1  when re-configured by the differential pair of transistors  48  and  54 . The components of converter  1  shown in  FIG. 2  are substantially similar as those shown in  FIG. 1  and are not described again here for the sake of brevity. The differential amp, comprised of transistors  48  and  54 , controls the configuration between the linear and the comparative modes. When converter  1  is in the linear mode, both transistors  48  and  54  are in a conducting state, and when converter  1  is in the comparative mode, either one of transistors  48  and  54 , but not both, is in a conducting state. In the linear mode, converter  1  generates continuous duty waveforms, and in the comparative mode, the duty cycle can instantaneously jump to zero or to maximum duty cycle in response to a step transient of the input load. Once the step transient has passed, converter  1  automatically reverts to the linear mode configuration, which is not represented by  FIG. 2 . In this manner, the quick mode changes of converter  1  between linear and comparative modes allows converter  1  to instantly respond to transients, when necessary. 
   As an example of the performance of converter  1 ,  FIG. 3  shows the performance according to one simulated embodiment. As seen in  FIG. 3 , signal  301  represents the input load applied to converter  1 , which shows a step transient. Signal  302  represents the output signal in response to the input load of signal  301 . As seen in  FIG. 3 , the magnitude of output signal  302  adjusts quickly to the step in input signal  301  without significant overshoot or undershoot of output voltage. During the continuous sections of input signal  301 , output signal  302  responds with constant duty control. Signal  303  represents the current load corresponding to the input load of signal  301 . Upon review of output signal  302 , it can be seen that the dual-mode converter of the present invention handles the step transient of the input load without significant overshoot or undershoot in the output signal. 
   In this manner, the present invention provides a converter that uses a dual-mode feedback loop that operates with high performance in a linear mode during continuous input loads and in a comparative mode during a step input load, with inherent stability. Accordingly, the converter of the present invention provides increased performance without the need for feedback loop compensation or other additional classical feedback components. The components of the converter are readily available and provides for a converter of high reliability and durability because the feedback components are discrete. The converter acts like a comparator when step loads are applied and instantly responds to the step demand with negligible undershoot or overshoot of output voltage. Similarly, the converter acts in a linear mode when a continuous load is applied and provides constant duty control. 
   The invention has been described with respect to particular illustrative embodiments. It is to be understood that the invention is not limited to the above-described embodiments and that various changes and modifications may be made by those of ordinary skill in the art without departing from the spirit and scope of the invention described herein. For example, the invention is not limited to using the specific types of components described above, such as the isolating flyback converter, and other components with other characteristics can be used in other embodiments of the present invention equally well.