Charge pump-based drive circuitry for bipolar junction transistor (BJT)-based power supply

A bipolar junction transistor (BJT) may be used to generate a supply voltage for operating a controller, such as a lighting controller for a LED-based light bulb. A base of the BJT may receive current generated from the supply voltage to control operation of the BJT. Although the base of the BJT would be at a lower voltage than the emitter, a base drive circuit may be coupled between the emitter and the base of the BJT to increase the voltage. As one example, the base drive circuit may be a charge pump. In another example, the BJT may function as its own charge pump. In yet another example, a positive and a negative base current of the BJT may be independently controlled to regulate an output supply voltage VDD from the BJT.

FIELD OF THE DISCLOSURE

The instant disclosure relates generally to methods, apparatus, or implementations concerning or relating to drive circuitry and auxiliary power generation for dimmer compatible lamps.

BACKGROUND

Alternative lighting devices to replace incandescent light bulbs differ from incandescent light bulbs in the manner that energy is converted to light. Incandescent light bulbs include a metal filament. When electricity is applied to the metal filament, the metal filament heats and glows, radiating light into the surrounding area. The metal filament of conventional incandescent light bulbs generally has no specific power requirements. That is, any voltage and any current may be applied to the metal filament, because the metal filament is a passive device. Although the voltage and current need to be sufficient to heat the metal filament to a glowing state, any other characteristics of the delivered energy to the metal filament do not affect operation of the incandescent light bulb. Thus, conventional line voltages in most residences and commercial buildings are sufficient for operation of the incandescent bulb.

However, alternative lighting devices, such as compact fluorescent light (CFL) bulbs and light emitting diode (LED)-based bulbs contain active elements that interact with the energy supply to the light bulb. These alternative devices are desirable for their reduced energy consumption, but the alternative devices have specific requirements for the energy delivered to the bulb. For example, compact fluorescent light (CFL) bulbs often have an electronic ballast designed to convert energy from a line voltage to a very high frequency for application to a gas contained in the CFL bulb, which excites the gas and causes the gas to glow. In another example, light emitting diode (LEDs)-based bulbs include a power stage designed to convert energy from a line voltage to a low voltage for application to a set of semiconductor devices, which excites electrons in the semiconductor devices and causes the semiconductor devices to glow. Thus, to operate either a CFL bulb or LED-based bulb, the line voltage must be converted to an appropriate input level for the lighting device of a CFL bulb or LED-based bulb. Conventionally, a power stage is placed between the lighting device and the line voltage to provide this conversion. Although a necessary component, this power stage increases the cost of the alternate lighting device relative to an incandescent bulb.

One conventional power stage configuration is the buck-boost power stage.FIG. 1is a circuit schematic showing a buck-boost power stage for a light-emitting diode (LED)-based bulb. An input node102receives an input voltage, such as line voltage, for a circuit100. The input voltage is applied across an inductor104under control of a switch110coupled to ground. When the switch110is activated, current flows from the input node102to the ground and charges the inductor104. A diode106is coupled between the inductor104and light emitting diodes (LEDs)108. When the switch110is deactivated, the inductor104discharges into the light emitting diodes (LEDs)108through the diode106. The energy transferred to the light emitting diodes (LEDs)108from the inductor104is converted to light by LEDs108.

The conventional power stage configuration ofFIG. 1provides limited control over the conversion of energy from a source line voltage to the lighting device. The only control available is through operation of the switch110by a controller. However, that controller would require a separate power supply or power stage circuit to receive a suitable voltage supply from the line voltage. Additionally, the switch110presents an additional expense to the light bulb containing the power stage. Because the switch110is coupled to the line voltage, which may be approximately 120-240 Volts RMS with large variations, the switch110must be a high voltage switch, which are large, difficult to incorporate into small bulbs, and expensive.

Shortcomings mentioned here are only representative and are included simply to highlight that a need exists for improved drive and auxiliary power generation circuitry, particularly for LED lighting devices. Embodiments described here address certain shortcomings but not necessarily each and every one described here or known in the art.

SUMMARY

A bipolar junction transistor (BJT) may be used as a switch for controlling a power stage or other component of a lighting device, such as a light-emitting diode (LED)-based light bulb. Bipolar junction transistors (BJTs) may be suitable for high voltage applications, such as for use in the power stage and coupled to a line voltage. Further, bipolar junction transistors (BJTs) are lower cost devices than conventional high voltage field effect transistors (HV FETs). Thus, implementations of LED-based light bulbs having bipolar junction transistor (BJT) switches may be lower cost than power stage implementations having field effect transistor (FET) switches.

However, the use of low-cost BJT devices with limited capabilities compared to higher-cost field effect transistors (FETs) may create difficulties in implementation of circuits, such as lighting device power stages, with BJTs. For example, BJTs are current-controlled rather than voltage-controlled devices. Thus, a base current may need to be supplied to a BJT in the power stage. The base current applied to the base of the BJT determines, in part, the current that flows through the collector and emitter of the BJT. Thus, a supply of current for the base of the BJT may be needed, and control over that base current supply may also be needed to implement a BJT in devices with power stages. In embodiments described below, a base current for the BJT may be generated from an emitter output of the BJT. In some embodiments, the base current for the BJT may be controlled through adjusting the timing of control signals.

In some embodiments, a BJT may be used to generate a power supply voltage for a controller in the LED-based light bulb. Although controllers for LED-based light bulbs are described as one possible load for a power supply voltage, other circuits and/or controllers may be operated from the power supply voltage generated by the BJT. Further, these BJT configurations may be used in devices other than LED-based light bulbs.

When the BJT is used to generate a power supply voltage for a controller, a feedback loop may be configured for the BJT such that the power supply voltage is supplied back to the BJT to drive operation of the BJT. For example, a BJT may be configured to provide a power supply voltage at an emitter of the BJT and a base drive circuit may be coupled between the emitter and a base of the BJT to provide a feedback path from the power supply voltage to the base of the BJT.

In certain embodiments, a device may be used in a dimmer compatibility circuit to reduce power dissipation in an integrated circuit (IC) of the dimmer compatibility circuit. For example, a BJT may be used to create a power supply for the IC using a control voltage. The BJT may be used to create the supply voltage while also driving the BJT from the supply voltage. Based on the gain of the BJT, the BJT draws current to create a larger amount of current.

In one method of operation, the base of the BJT may be first charged. Then, the base may be disconnected from the supply voltage, and the emitter may be connected to the control voltage, causing a collector current of the BJT to flow through the emitter and out to the control voltage. The period of time may be faster than the time needed for the BJT to change its mode. This may allow the BJT to be used as a charge pump to create a feedback loop where the BJT operates from the supply voltage and generates the supply voltage.

According to one embodiment, an apparatus that includes a bipolar junction transistor (BJT) may be configured to provide power to a controller. The transistor may include a collector coupled to a high voltage source, an emitter configured to drive current to generate a supply voltage at a supply voltage node; and a base. A base drive circuit may be coupled to the base and configured to receive the supply voltage and drive current to the base to generate a voltage at the base higher than the supply voltage. According to another embodiment, the base drive circuit may also include a charge pump.

The charge pump may include a capacitor coupled between the emitter and a ground and an inverter. The inverter may include a first input coupled to the emitter, a second input coupled to the ground, an output coupled to the base, and a control signal input coupled to receive an input select signal. The input select signal may include a square wave at a frequency selected to generate a desired average direct current (DC) voltage at the output of the inverter.

According to another embodiment, the base drive circuit may include a first switch coupled to the emitter and a ground and configured to receive a first control signal for coupling the emitter to the ground. The base drive circuit may further include a second switch coupled to the base and the supply voltage node and configured to receive a first control signal for coupling the base to the supply voltage node and a third switch coupled between the emitter and the supply voltage node and configured to receive a second control signal for coupling the emitter to the supply voltage node.

The controller may be configured to generate the first control signal and the second control signal such that during a first time period current is driven into the base from the supply voltage node and such that during a second time period current is driven from the collector through the emitter to the supply voltage node. The controller may further generate the first control signal and the second control signal with a switching rate between the first time period and the second time period that is greater than a turn-off time of the bipolar junction transistor (BJT).

According to another embodiment, the base drive circuit may further include a first switch coupled to the emitter and to a ground, and a resistor coupled to the base and to the supply voltage node. The controller may be configured to operate the first switch to disconnect the emitter and the ground to increase a voltage at the supply voltage node.

The apparatus may further include an inductor coupled between the collector and the high voltage source. The base drive circuit may further include a second switch coupled to the emitter and coupled to the supply voltage node, a third switch coupled to the base and to the ground; and a fourth switch coupled to the base and to the supply voltage node. The controller may be configured to operate the first switch, the second switch, the third switch, and the fourth switch to regulate the supply voltage.

According to another embodiment, the base drive circuit may further comprise a first switch coupled to the emitter of the bipolar junction transistor (BJT), wherein the first switch is configured to control a reverse recovery phase of the bipolar junction transistor (BJT) to direct current to the supply voltage node during a first time period and direct current to a load during a second time period.

According to another embodiment, the apparatus may further include a switch coupled to the base of the bipolar junction transistor (BJT) and a resistive digital-to-analog converter (DAC) coupled to the switch. The controller may be configured to adjust the resistive digital-to-analog converter (DAC) to control a duration of a reverse recovery time of the bipolar junction transistor (BJT).

According to another embodiment, the apparatus may further include a second bipolar junction transistor (BJT) comprising a second base; a second emitter coupled to the emitter of the bipolar junction transistor (BJT), a second collector coupled to the high voltage source, and a second base drive circuit coupled to the second base of the second bipolar junction transistor (BJT) and coupled to the supply voltage node. The bipolar junction transistor (BJT) may be configured to drive current to the power supply node during a start-up phase of the controller, and drive current to the power supply node after the start-up phase of the controller.

The controller may include a lighting controller configured to operate a plurality of light emitting diodes (LEDs), wherein the high voltage source is a line voltage source. The lighting controller and the bipolar junction transistor (BJT) may be integrated into an integrated circuit (IC). The apparatus may further include one or more charge switches coupled to a base of the bipolar junction transistor (BJT), the one or more charge switches configured to control current flow to the base; one or more disable switches coupled to the base, the switches configured to stop current flow to the base, and one or more delivery switches coupled to the emitter, the switches configured to deliver the control voltage to the controller.

According to another embodiment, a method may further include receiving, at a collector of a bipolar junction transistor (BJT), a high voltage from a high voltage source; driving, from an emitter of the bipolar junction transistor (BJT), current to a supply voltage node from the high voltage source to generate a supply voltage; and generating, in a base drive circuit, a base drive current for driving a base of the bipolar junction transistor (BJT) to a voltage higher than the supply voltage.

The method may further include charging a junction capacitance of the transistor by closing a transistor charge switch coupled to a base-emitter junction of the transistor at a first time; delivering current from the emitter to the charge voltage by opening the transistor charge and closing a delivery switch at a second time; repeating the charging and delivering at a frequency greater than a turn-off time of the transistor. The base drive circuit may include a charge pump.

The charge pump may include a capacitor coupled between the emitter and a ground, and an inverter. The inverter may include a first input coupled to the emitter, a second input coupled to the ground, an output coupled to the base, and a control signal input coupled to receive an input select signal. The input select signal may include a square wave at a frequency selected to generate a desired average direct current (DC) voltage at the output of the inverter.

The method may further include receiving, at a first switch of the base drive circuit coupled to the emitter and a ground, a first control signal for coupling the emitter to the ground; receiving, at a second switch of the base drive circuit coupled to the base and the supply voltage node, a first control signal for coupling the base to the supply voltage node; and receiving, at a third switch of the base drive circuit coupled between the emitter and the supply voltage node, a second control signal for coupling the emitter to the supply voltage node, and generating, by the controller, the first control signal and the second control signal such that during a first time period current is driven into the base from the supply voltage node and such that during a second time period current is driven from the collector through the emitter to the supply voltage node.

The method may further include generating, by the controller, the first control signal and the second control signal with a switching rate between the first time period and the second time period that is greater than a turn-off time of the bipolar junction transistor (BJT).

The method may further include operating, by the controller, a first switch coupled to the emitter and to a ground; and disconnecting the emitter and the ground to increase a voltage at the supply voltage node, wherein the base drive circuit comprises a resistor coupled to the base and to the supply voltage node. An inductor may be coupled between the collector and the high voltage source.

The method may further include operating, by the controller, the first switch, a second switch coupled to the emitter and coupled to the supply voltage node, a third switch coupled to the base and to the ground, and a fourth switch coupled to the base and to the supply voltage node; and regulating the supply voltage.

The method may further include controlling, by a base drive circuit comprising a first switch coupled to the emitter of the bipolar junction transistor (BJT), a reverse recovery phase of the bipolar junction transistor (BJT); directing current to the supply voltage node during a first time period; and directing current to a load during a second time period.

The method may further include adjusting, by the controller, a resistive digital-to-analog converter (DAC) coupled to a switch coupled to the base of the bipolar junction transistor (BJT); and controlling a duration of a reverse recovery time of the bipolar junction transistor (BJT).

The method may further include driving current, by the bipolar junction transistor (BJT), to the power supply node during a start-up phase of the controller, and driving current, by a second bipolar junction transistor (BJT), to the power supply node after the start-up phase of the controller. The second bipolar junction transistor (BJT) may include a second base; a second emitter coupled to the emitter of the bipolar junction transistor (BJT); a second collector coupled to the high voltage source; and a second base drive circuit coupled to the second base of the second bipolar junction transistor (BJT) and coupled to the supply voltage node.

The method may further include controlling current flow to a base of the bipolar junction transistor (BJT) by operating one or more charge switches coupled to the base; stopping current flow to the base by operating one or more disable switches coupled to the base; and delivering the control voltage to the controller by operating one or more delivery switches coupled to the emitter.

According to another embodiment, a system may include one or more light emitting diodes (LEDs); a line voltage input node configured to receive a high voltage; a controller coupled to the light emitting diodes (LEDs) and configured regulate energy transfer from the line voltage input node to the one or more light emitting diodes (LEDs). The system may further include a bipolar junction transistor (BJT) configured to provide power to the controller. The transistor may include a collector coupled to the line voltage input node, an emitter configured to drive current to generate a supply voltage at a supply voltage node, and a base. A base drive circuit may be coupled to the base and configured to receive the supply voltage and drive current to the base to generate a voltage at the base higher than the supply voltage.

The system may further include one or more charge switches coupled to a base of the bipolar junction transistor (BJT), the one or more charge switches configured to control current flow to the base. The system may further include one or more disable switches coupled to the base, the switches configured to stop current flow to the base. The system may further include one or more delivery switches coupled to the emitter, the switches configured to deliver the control voltage to the controller.

According to another embodiment, an apparatus may include an integrated circuit (IC) configured to couple to a bipolar junction transistor (BJT) through a single pin coupled to an emitter of the bipolar junction transistor (BJT). The integrated circuit (IC) may include a switch coupled to the emitter of the bipolar junction transistor (BJT), and a controller coupled to the switch and configured to control delivery of power to a load by operating the switch.

DETAILED DESCRIPTION

FIG. 2is a schematic diagram illustrating an auxiliary power supply generation circuit according to an embodiment of the disclosure. A circuit200includes a bipolar junction transistor (BJT)210with an input voltage node202coupled to a collector node of the BJT210. The input node202may receive a high voltage input VIN, such as a line voltage of approximately 100-240 Volts. The BJT210may be coupled at an emitter node through a switch206to a power supply output node204. The BJT210may provide an output voltage VDDat the node204suitable for operating low-voltage electronics, such as a controller or other integrated circuits (ICs). A base node of the BJT210may be coupled to a base drive circuit212. The base drive circuit212may be powered from the output voltage VDDat the emitter node of the BJT210through a feedback path216.

There may be a voltage drop VBEbetween the emitter node of the BJT210and the base node of the BJT210. For example, when the desired VDDvoltage is 5 Volts, the voltage drop VBEcauses the voltage at the base of the BJT210to be 5.6 Volts. Electric current will generally not flow from a lower voltage node to a higher voltage node. Thus, the base drive circuit212may increase the supply voltage VDDbefore application to the base node of the BJT210. For example, the base drive circuit212may increase the 5 Volt output to 6 Volts for application to the base node, which allows current to be driven to the base node of the BJT210from the output node204at the emitter of the BJT210. The BJT210may have an associated gain β that is a ratio of IC/IB. When the gain β is larger than one, an increase in base current IBresults in a larger increase in collector-emitter current ICE. Thus, driving an increased base current to the base node of the BJT210results in a net current gain.

Also coupled to the emitter node of the BJT210may be a switch206for controlling operation of the BJT210. For example, the switch206may be turned on to charge a capacitor214coupled to the output node204. When the switch206is turned off, the supply voltage VDDat the output node204may be held relatively constant by charge on the capacitor214. Toggling of the switch206may control operation of the BJT210creating an emitter-controlled BJT.

In one embodiment, the base drive circuit212may be a charge pump. A charge pump circuit receives an input voltage and generates a higher output voltage from the input voltage. The charge pump may be configured as the base drive circuit212coupled between the emitter node and the base node of the BJT210for generating a higher voltage at the base node from the supply voltage VDDat the emitter node.FIG. 3is a schematic diagram illustrating an auxiliary power supply generation device with a charge pump base drive circuit according to one embodiment of the disclosure. A circuit300may include the base drive circuit212coupled to the emitter node of the BJT210through the feedback path216. The base drive circuit212may include an inverter320coupled to a capacitor318, a resistor316, a diode314, and a diode312. The inverter320may be driven by a signal received at node302, which may be driven, for example, from an external signal generated by a controller receiving power from the output node204.

The inverter320receives power from supply voltage VDDthrough the feedback path216and switches the supply voltage VDDon and off of the capacitor318based on the input signal302. The input signal302may be, for example, a square wave signal with a frequency higher than the switching frequency of the BJT210. In one embodiment the frequency of signal302may be approximately 1-20 Megahertz. The inverter320charges the capacitor318, which discharges into the base node of the BJT210through the diode312and the resistor316. When the frequency of the signal302is higher than the switching frequency of the BJT210, the BJT210operates based on the average direct current (DC) voltage of the output of the capacitor318. Further, the current to the base node of the BJT210may be adjusted by varying the frequency of the signal302. For example, a controller powered from the supply voltage VDDmay vary the frequency of signal302to adjust operation of the BJT210and vary the supply voltage VDDat output node204. For example, if the output of the BJT210is insufficient to maintain a minimum supply voltage VDDfor proper operation of a controller (not shown), the controller may increase a frequency of the signal302.

A resistor330, which may be used to start the circuit200, may be coupled between the BJT210and the input node202. The resistor330may also be used to sense voltage at the input node202. The diode312may also be used to startup the base drive circuit212. Alternate configurations of the circuit200may replace diodes312and314with other semiconductor devices, such as low-voltage field effect transistor (FET) switches.

In some embodiments, the capacitor318may be incorporated into an integrated circuit (IC) with other components. When integrated, the capacitor318may be implemented with a metal-oxide-semiconductor (MOS) FET transistor and switched at a high frequency (e.g., 20 MHz) to allow use of a physically small capacitor. In some embodiments, the charge pump circuit212may be used in a TRIAC compatibility circuit to provide either a glue current or a TRIAC attach current.

In a TRIAC-based dimmer during a period (referred to as “TOFF”) of a phase-cut input voltage half line cycle from the time the half line cycle reaches a zero crossing until reaching a leading edge of a phase-cut input voltage, the dimmer does not conduct and, thus, phase cuts the supply voltage prior to conducting. During the non-conduction period TOFF, to properly recharge timing circuitry of the dimmer, the dimmer current has a glue value and is sometimes referred to in this non-conduction phase as a glue current. The glue value varies by dimmer, for example, from 10 mA to 300 mA. When the output voltage of the dimmer (referred to as phase-cut voltage VO,DIM) reaches a firing voltage VFlevel, the dimmer fires (i.e. begins conducting) and conducts a dimmer current having a firing value and is sometimes referred to at this event as a firing current. A typical firing value is 5 mA-50 mA. In at least one embodiment, the firing value equals an attach current value and is, for example, 50 mA. An attach state begins at the leading edge LE(n) and occurs during an initial charge transfer period from the leading edge LE(n).

In another embodiment of an auxiliary power supply generation circuit, the BJT210may be configured to operate as a charge pump using an intrinsic capacitance of the BJT210.FIG. 4Ais a schematic diagram illustrating an auxiliary power supply generation device with a transistor configured to operate as a charge pump according to one embodiment of the disclosure. The base drive circuit212coupled between the base node and emitter node of the BJT210may include a current source420and a switch412. The switch412may toggle to couple or decouple the base node of the BJT210from the current source420powered by the supply voltage VDDreceived through the feedback loop216from output node204. The feedback loop216couples the emitter node output of the BJT210to the base node input of the BJT210.

Switches416and418may be coupled at the emitter node of the BJT210, similar to emitter switch206ofFIG. 2. The switch416may toggle to couple the emitter node to ground, and the switch418may toggle to couple the emitter node to output node204. When the switch412is on, the switch416is on, and the switch418is off, current is driven from the current source420to the base node of the BJT210to charge the base of the BJT210. When the switch412is off, the switch416is off, and the switch418is on, current is passed from the input voltage202at the collector node to the emitter node of the BJT210to generate power supply voltage VDD. A cycle may be created including, during a first time period, charging the base node of the BJT210from the power supply voltage VDDto operate the BJT210and, during a second time period, charging the capacitor214to generate the supply voltage VDD, while the base charge discharges.

The operation of the circuit400is shown in graphs inFIG. 4B.FIG. 4Bis are graphs illustrating operation of an auxiliary power supply generation device, such as that ofFIG. 4A, according to one embodiment of the disclosure. A VPLS,1signal452may be applied to the switch412and the switch416through input node402, and a VPLS,2signal454may be applied to the switch418through input node404. At time462, the VPLS,1signal452switches to high to turn on switches412and416and the VPLS,2signal454switches to low to turn off switch418. After a first duration T1, the VPLS,1signal452switches to low and the VPLS,2signal454switches to high. After a second duration T2, the signals452and454may continue to cycle through the time periods T1 and T2. During the first duration T1, the base of the BJT210is charged from the current source420, and during the second duration T2, the capacitor214is charged to generate supply voltage VDD. The duration of time for T1 and T2 may be varied by a controller to adjust a level of the supply voltage VDD. In one embodiment, the signals452and454may be received as a single signal. The single signal may be split and one branch passed through as the VPLS,1signal and a second branch passed to an inverter for generating VPLS,2signal. Thus, the circuit400may be controlled through a single signaling pin connection from a controller.

The circuit400utilizes an intrinsic capacitance at the base node of the BJT210and operates the intrinsic capacitance as a charge pump for operating the BJT210. In this configuration, the BJT210provides double-duty as a charge pump and a generator of the supply voltage VDD. The switching frequency from T1 to T2 and back to T1 by signals VPLS,1and VPLS,2may be at a frequency faster than the response period of the BJT210. Thus, the BJT210may remain switched on during the T1 and T2 time periods. Further, with sufficiently high switching frequency, a collector current from the BJT210may be relatively constant and more charge may be delivered to supply voltage VDDduring time period T2 than was consumed in a base current during time period T1. A net current generation may be obtained when time period T1 is less than time period T2.

In one configuration of the circuit400, a switch414may couple the base node of the BJT210to a ground. The switch414may disable operation of the circuit400by coupling the base of the BJT210to turn off the BJT210. The switch414may be controlled by a disable signal received at input node406. This functionality may be useful when using the circuit400for glue and release functions in LED lighting dimming applications. Additional details regarding functions in LED lighting dimming applications are described in U.S. Pat. No. 8,610,364 to John L. Melanson and entitled “Coordinated dimmer compatibility functions” and in U.S. Patent Application Publication No. 2012/0049752 to Eric J. King and John L. Melanson and entitled “Multi-mode Dimmer Interfacing Including Attach State Control,” which are hereby incorporated by reference in their entirety.

In some embodiments, switches412,414,416, and/or418may be integrated into a controller IC powered from the generated supply voltage VDD. The switches412,414,416, and/or418may be FETs, BJTs, or diodes. In some embodiments, the rate, duty cycle of operation, and the forward base current may all be chosen to operate at a desired collector current and auxiliary current flowing from the output node204. As with the circuit300ofFIG. 3, a resistor330may be coupled between the base node of the BJT210and the input node202to provide start-up of the base drive circuit212.

An auxiliary power supply generation circuit may be configured to share an input voltage with a load other than the controller operating from supply voltage VDD. In the case of a LED-based light bulb, the other load may be light emitting diodes (LEDs). Further, efficiency of power conversion from the line voltage to the supply voltage VDDmay be improved by use of an inductor with the BJT210. The embodiments described above with reference toFIG. 3AandFIG. 4Acouple the line voltage at input node202directly to the BJT210. As a result, the entire voltage of the line voltage is dissipated through the circuits300and400ofFIG. 3AandFIG. 4A. Such power dissipation may be desirous in circuits, such as dimmer compatibility circuits, startup circuits, glue circuits, and leading edge attach circuits. However, the power dissipation may be reduced through use of an inductor coupled between the collector node of the BJT210and the line voltage at input node202.

FIG. 5Ais a circuit illustrating an auxiliary power supply generation circuit with an inductor coupling at the BJT according to one embodiment of the disclosure. A circuit500may include the BJT210coupled to the input node202through an inductor520. A base drive circuit212may be coupled to the base node of the BJT210and drive the base from a supply voltage VDDreceived through the feedback loop216. The emitter node of the BJT210is coupled to capacitor214at the output node204to generate the supply voltage VDD. The inductor520may allow the circuit500to provide multiple functions including generating the supply voltage VDDwith the BJT210and providing an output voltage, VOUT, to operate a load, such as light emitting diodes (LEDs) for generating light from a light bulb.

To generate the output voltage, VOUT, a winding of the inductor520may be coupled to a diode522and capacitor524. Output node502coupled to the capacitor524may be coupled to a lighting load for operation from the input voltage202.

To generate the supply voltage, VDD, a winding of the inductor520may couple input voltage VINto the collector node of the BJT210. The BJT210passes current from the input node202through the collector node and the emitter node of BJT210to the capacitor214through diode534. The base drive circuit212for maintaining operation of the BJT210may include a first current path including the resistor512and the diode514and a second current path including the resistor516. Each of the current paths may begin at input node204of supply voltage VDDand end at the base node of the BJT210. Selection of which current path is active may be controlled based in part through a switch532at the emitter node of the BJT210.

The operation of the BJT210may be controlled through the switch532coupled between the emitter node of the BJT210and ground. The switch532operates similarly to the switch206ofFIG. 2. The switch532may be toggled based on a VPLSsignal received at input node504. Operation of the circuit500is illustrated through the graphs ofFIG. 5B.FIG. 5Bare graphs illustrating operation of the circuit ofFIG. 5Athrough a control signal according to one embodiment of the disclosure.

At time562, a VPLScontrol signal552is high and the switch532is closed. The VPLSsignal552remains high for duration T1 during which the BJT210is on, and current passes through the collector node and the emitter node of the BJT210from the input node202to ground. During time period T1, the collector current ICincreases linearly as shown in line556.

While the switch532is closed, current in the base drive circuit212flows through the second current path of resistor516to charge the base of the BJT210. A positive base current IBis shown in line554.

At time564, the VPLScontrol signal552switches to low and the switch532opens. After the switch532opens, the BJT210may continue to conduct for a short duration, such as several microseconds, during which base charge discharges from the BJT210through the first current path of the base drive circuit212including the resistor512and the diode514. For the duration T2, during which the BJT210continues to conduct, the collector current ICis passed through the diode534to the capacitor214to generate the supply voltage VDD. This current is shown as Iauxin line558as the current through the diode534.

Through the process of time periods T1 and T2, the circuit500may be a net generator of power for the supply voltage VDDwhile the inductor520provides power to a load at VOUT, such as LEDs in a light bulb. The BJT210may generate the supply voltage VDDby consuming a limited amount of power from the input node202through the inductor520. The circuit500may be efficient and provide, for example, nearly one-to-one ratio in power consumed by the circuit500and power generated by the circuit500. In one embodiment, the circuit500may be configured to generate a 5 Volts, 10 mA (50 mW) output and consume approximately 50 mW from the input node202.

Additional control of a circuit with the BJT210and the inductor520may be gained through implementation of additional switches.FIG. 6Ais a circuit illustrating an auxiliary power supply generation circuit with an inductor coupling at the BJT according to another embodiment of the disclosure. A circuit600may include a BJT210coupled to the input node202through the inductor520. The emitter node of the BJT210may be coupled to ground through a switch618controlled by a VPLS,4signal received at input node608. The emitter node of the BJT210may be also coupled to the output node204for supply voltage VDDthrough switch616controlled by VPLS,3signal received at input node606. The base drive circuit212may include a first switch612coupling the base node of the BJT210to a first current source622powered by the supply voltage VDDthrough the feedback loop216. The base drive circuit212may also include a second switch614coupling the base node of the BJT210to a second current source624coupled to ground. The current source624may be, for example, set as a ratio of a peak current IC,peakat the collector node of the BJT210. In one embodiment, the current source624may be set as 40% of the peak current IC,peak.

The switches612,614,616, and/or618may allow timing of the reverse base current to be controlled and the level of forward base current and the level of the reverse base current to be controlled. This may allow for a controller generating the VPLS,1-VPLS,4signals to regulate the supply voltage VDD. In one embodiment, the controller may regulate the supply voltage VDDto minimize lost charge and efficiency by generating only a supply current needed for the controller and/or other loads powered from node204.

One mode of operation of the circuit600is shown inFIG. 6B.FIG. 6Billustrates currents within circuit600ofFIG. 6Aat various states of the control signals illustrated inFIG. 6Aaccording to one embodiment of the disclosure. At time672, a VPLS,1signal652and a VPLS,4signal654may be high to close the switches612and618. The signals652and654may remain high for a first time duration, T1. During T1, current flows through the collector node to the emitter node of the BJT210and to the ground through the switch618and the collector current IC650linearly increases. Further during time period T1, current flows to the base node of the BJT210to operate the BJT210from the supply voltage VDD.

At time674, the signals652and654are switched low to open the switches612and618. The VPLS,3signal656is switched to high to close the switch616and current flows through the BJT210from the input node202through the collector node and the emitter node of BJT210to the output node204to charge the capacitor214. The current from the emitter node of the BJT210to the output node204is shown as auxiliary current iauxin line660and generates supply voltage VDD. During a second time period T2, when the signal656is high, auxiliary current iauxlinearly increases by following the current ramp rate of the collector current ICof line650from time period T1. During T2, the BJT210is acting as a storage element for charge on its base node and this stored charge maintains operation of the BJT210.

At time676, the signal656switches to a low signal to open the switch616, which terminates output of the auxiliary current iauxand terminates charging of the capacitor214. The VPLS,2signal658is switched to a high signal for duration T3 to close the switch614to drive a negative base current from the BJT210. The conditions for time672may then be returned to after duration T3. The cycle of T1, T2, and T3 may be repeated to operate the circuit600and generate supply voltage VDD.

The VPLS,1-VPLS,4signals may be generated by a controller operating from the supply voltage VDD. The controller may adjust the timings T1, T2, and T3 by manipulating the VPLS,1-VPLS,4signals to obtain a desired supply voltage VDD. In particular, the time period T2 may be increased in duration to provide a higher supply voltage VDDor decreased in duration to provide a lower supply voltage VDD. In one embodiment, a controller IC powered from the supply voltage VDDmay operate at between 4-6 Volts. Thus, the time period T2 may be increased when VDDnears 4V, and the time period T2 may be decreased when VDDnears 6V.

Bipolar junction transistors (BJTs) configured as described above may be used in a dimmer interface circuit for a LED light bulb. BJTs are a lower cost component than many other semiconductor devices and thus may result in a lower cost LED light bulb. Further, in certain configurations, the BJT may be shared for both switch mode supply and for glue operation in a LED light bulb. Although light bulb applications are described below, the BJT configurations described above may be used in any circuit for generating a supply voltage VDD.

FIG. 7is a circuit illustrating a dimmer interface circuit for a LED-based light bulb using bipolar junction transistors according to one embodiment of the disclosure. Circuit700may include an input node702for receiving a high voltage, such as a line voltage, relative to the operation of controller devices. The circuit700may generate supply voltage VDDat node704through a BJT712with a base drive circuit722. The BJT712and base drive circuit722may be any of the configurations described above with reference toFIGS. 2-6. The supply voltage VDDmay be used to operate the base drive circuits722and724. Thus, a feedback loop216may allow operation of the BJTs712and714from a supply voltage generated with the BJTs712and714. The base drive circuit724may drive a BJT714to control current through LEDs710. The supply voltage VDDmay also be used to power a control IC732, which may control operation of components of the circuit700, such as by generating control signals for switches of the circuit700.

The circuit700may be configured to run in two modes of operation. In a first mode, the emitter node of BJT714may be connected to supply voltage VDDand the base node of the BJT714may be driven by base drive circuit724. The base node of the BJT714may also be driven by base drive circuit722that drives the BJT712, such as when components are shared between the charge pumps722and724. In a second mode of operation, the emitter node of BJT714may be coupled to ground, and the base node of the BJT714may be driven by supply voltage VDD. In this mode, a high current capacitor may be used. In both modes, the current in the BJT714may be measured by the current into a pin (not shown).

A Zener diode734may be coupled between the collector node of BJT714and ground. In one embodiment, the Zener diode734may have an 80 V threshold, and BJT714may have a 100 V breakdown threshold. The configuration of BJT714with the Zener diode734may provide a higher current gain at the BJT714, on the order of 50-100 Amps/Amps. Switching output circuitry built around a BJT716, such as BJTs712and714and circuitry coupled around the BJTs712and714, may allow for low power supply current drain. Depending on the choice of drive current, much of the base charge may be recovered.

The circuit700may operate to provide a glue phase in a LED-based light bulb. When the BJT712is off, a current through resistor742may be measured to determine an input voltage (VIN). When input voltage VINis sensed to rise above a threshold level, the BJT712may be activated by the charge pump722. This charge pump activation may drop the input voltage VINand return charge to the supply voltage VDD. The charge provided by charge pump722may be modulated, providing regulation of the input voltage V. The charge can alternatively be controlled in a hysteretic mode. One charge threshold may be on the order of 10 V to assist in avoiding a significant increase in the power dissipation of the BJT712. When not in use, the glue circuitry (e.g., circuitry associated with BJT712including the BJT712) may be disabled by closing disable switch744.

The circuit700may also operate to provide a full line-energy harvesting mode in a LED-based light bulb. Charge pump724associated with BJT714may be activated when a line voltage is below 20 V and when supply voltage VDDis determined to be insufficient, such as too low to operate control IC732. Activation of the charge pump724may then allow sufficient energy for IC controller operation. Charge pump724may also be enabled when a trailing edge (TE) is sensed or calculated.

The circuit700may also operate in an attach phase of an LED-based light bulb. Circuitry associated with the BJT714, including the base drive circuit724, may be enabled to draw current from a dimmer only when the input voltage at a lamp is greater in magnitude than the input voltage (VIN) to the dimmer. Wasted power may thus be minimized. For a high attach current, the emitter of the BJT714may be pulled to ground, and the base of the BJT714may be driven by supply voltage VDD. The drive may be from a current source to ground to tightly control the current. Alternatively, the base current may be controlled if the BJT714has limited current gain. Additional current may be drawn by the BJT712, which may be used to provide attach current directly to the base drive of the BJT714.

After an attach phase, it may be desirable to charge capacitor746to a higher voltage. This charging may be accomplished by emitter to ground switching of the BJT714or emitter to supply voltage VDDswitching of the BJT714with charge pump722or724. The mode may be chosen to regulate and/or optimize the supply voltage VDD. Optional Zener diode734may limit the voltage on the BJT714during the charging phase of capacitor746and an attach phase, allowing for a lower voltage for the BJT714.

In open phase of capacitor746, the BJT714may be turned off and line power may directly drive a DC-DC output stage1nthe empty phase of capacitor746, such as when the capacitor746is discharging, the line voltage may be below a voltage on capacitor746. In this phase, Zener diode734may conduct in a forward direction and capacitor746may power a DC-DC converter stage. The voltage on capacitor746is thereby reduced to a value appropriate for a next attach phase.

Power factor and efficiency may be improved by splitting capacitor746into separate capacitors.FIG. 8is a circuit illustrating a dimmer compatibility circuit with two capacitors for attach phase operations according to one embodiment of the disclosure. In circuit800, the BJT714is coupled to capacitors802and804. The BJT714may draw current for an attach phase. After the attach phase, current may be drawn to further charge capacitor802, or may charge capacitor802at the peak of the line in series with capacitor804.

In the circuit800with two capacitors802and804, current for each capacitor may be individually controlled through a pair of transistors (not shown) corresponding to the capacitors802and804.FIG. 9is a circuit illustrating current control for two capacitors with two transistors according to one embodiment of the disclosure. In circuit900, transistors902and904may be used to control the current through capacitors802and804. The circuit900may allow for additional current shaping and a higher power factor and/or efficiency.

More generically, the BJT configurations described above may be used in any glue circuitry of an LED-based light bulb.FIG. 10is a circuit illustrating a drive circuit for an LED-based light bulb. A circuit1000includes a glue path1002coupled in parallel with a power stage1004. The glue path1002may be activated during a time period commencing at the dimmer disconnect time and ending at the rise of a leading-edge phase-cut dimmer. The glue path1002may also be activated at other times. For example, when a LED-based light bulb is coupled to a non-dimming circuit and activated during relatively low voltage portions of the line voltage, the glue path1002may be activated to provide power from the line for the IC controller. In another example, the glue path1002may be activated during a final phase of a trailing-edge dimmer.

The power stage1004may be, for example, a switch-mode power stage, and provide regulated power to light emitting diodes (LEDs)1006. The glue path1002may be configured to maintain a low-impedance path during appropriate portions of a line cycle. Power stage1004may be configured according to one of a buck, boost, flyback, or buck-boost converter topology. The output of power stage1004may be an approximately constant current when LEDs1006are used. In other embodiments, switch-mode power supply1004may be configured to drive a gas discharge lamp system. The brightness of the lamp, such as LED lamp1006or a gas discharge lamp, may generally be varied in conformity with an observed input phase-cut of a dimmer signal.

Referring back toFIG. 2, additional configurations of the base drive circuit212are shown below inFIGS. 11-12.FIG. 11is a base drive circuit having a current-mode charge pump according to one embodiment of the disclosure. Charge pump1100within a base drive circuit212may deliver charge from a supply voltage VDDat input node204to the base node of the BJT210. Charge delivered to the base may be multiplied by a gain of the BJT210to provide a net output power from charge pump circuit1100. In operation of the charge pump circuit1100, there may be two alternating phases: a charge phase and a dump phase. The two phases may alternate at a high switching frequency (e.g., 20 MHz). In the charge phase, the switches1104and1106may be closed, and switches1102,1108, and1110may be open. In the dump phase, switches1102and1108may be closed, and switches1104,1106and1110may be open. The average current delivered by the charge pump1100may be calculated as
C1*fsw*dv,
where C1 is the capacitance of capacitor1112, fsw is the switching frequency for the BJT210, and dv is a difference between a voltage of capacitor1112at the end of the charge phase and a voltage of capacitor1112at the end of the dump phase. When no base current is desirable, switch1110may be closed to disable the charge pump circuit1100, and the other switches1102,1104,1106, and1108may be left in a stable, non-dissipative condition. For example, switches1102and1108may be open and switches1104and1106may be closed.

Another base drive circuit is shown inFIG. 12.FIG. 12is a base drive circuit having a current-mode charge pump according to another embodiment of the disclosure. The charge pump1200of base drive circuit212may include the switches1102and1104and capacitor1112of the charge pump1100. Diodes1202and1204may replace switches1106and1108of charge pump1100. Switch1206may allow disabling of the charge pump1200by shorting the base-emitter junction of the BJT210. Capacitor1112and switches1102,1104, and1206may be internal to an IC controller powered by the supply voltage VDD. In one embodiment, such an IC controller may include a Zener diode, as illustrated in Zener diode762ofFIG. 7, coupled between the supply voltage VDDand a ground to allow extra current generated at the input node204to be discharged to ground.

As described above, a supply voltage VDDmay be generated from the emitter of a bipolar junction transistor (BJT). Charge for the supply voltage VDDmay also be generated from a reverse recovery time (RRT) of the BJT to harvest energy and charge a capacitor for the supply voltage VDD. One circuit for harvesting charge during reverse recovery is shown inFIG. 13.FIG. 13is a circuit illustrating a BJT-based boost stage topology according to one embodiment of the disclosure. Although a boost stage is illustrated, the charge harvesting during reverse recovery may be applied to other power circuitry.

A circuit1300includes a BJT1310. An input voltage VIN, such as a line voltage, may be applied at input node1302and passed to a collector node of the BJT1310through inductor1320. A control circuit1312may be coupled to the BJT1310through a base node and an emitter node of the BJT1310. The BJT1310may be emitter-controlled through switch1314. Reverse recovery of charge from a base node of the BJT1310may be passed through the control circuit1312to output node1304to charge capacitor1350to generate a supply voltage VDD.

During a start-up time for the circuit1300, resistor1322may provide charge to the output node1304to generate supply voltage VDD. After start-up, the BJT1310is emitter-controlled to control power delivery to LEDs1306. The BJT1310may be controlled through the switch1314, which may be a low-voltage field-effect transistor (LV FET) operated from a control signal VPLS. During an on phase of the BJT1310, base current is applied from the control circuit1312to the base node of the BJT1310. The current may be sufficiently high enough to position the operation point of the BJT1310on a boundary of saturation and triode operation.

The on phase is illustrated as time period T1 inFIG. 14.FIG. 14are graphs illustrating currents and control signals for operating a BJT-based boost stage, such as that ofFIG. 13, according to one embodiment of the disclosure. At time1412, the time period T1 begins when a control signal VPLSapplied to the switch1314switches high to enable the switch1314. A collector current ICmay then increase linearly with current through the inductor1320. Additionally, current may be applied to the base node of the BJT1310as shown by a positive iauxcurrent into the base node of the BJT1310. If the provided base current from iauxis less than a minimum required base current

(IB<ICβ),
where IBis current at base of BJT1310, ICis current at collector of BJT1310, and β is a gain of BJT1310, the BJT1310may enter into the linear region of operation. This may increase current loss in the BJT1310. If the base current from iauxis more than a minimum required base current

(IB>ICβ),
the BJT1310may enter into a saturation region of operation. In this operating condition, the current loss in the BJT1310may be reduced as compared to the linear region of operation. However, the power dissipation in the BJT1310may be higher because the base current may be higher. Thus, the operating point of the BJT1310may be selected to be slightly into the saturation region, such that there may be a balance between switching losses of the BJT1310and base current dissipation during the on phase.

Referring back toFIG. 14, at time1414the control signal VPLSswitches to a low signal to turn off the switch1314ofFIG. 13and begin time period T2. When the BJT1310is in saturation region before time1414, the BJT1310may enter a reverse recovery phase to discharge base charge accumulated during T1 at time1414. During time period T2, collector current ICcontinues to linearly increase because the BJT1310is still conducting. The collector current ICpasses through the emitter node of BJT1310and through diode1324to output node1304to charge capacitor1350and generate supply voltage VDD. A variable resistor1330, such as a resistive digital-to-analog converter (DAC), of a reverse recovery path from the BJT1310may be used to control the reverse recovery period T2. In another embodiment, the variable resistor1330may be omitted, and the reverse recovery period T2 controlled by varying a base current applied to the BJT1310from current source1342during time period T1. However, increasing the base current IBmay result in additional power dissipation during time period T1. The variable resistor1330may allow decoupling of a selection of base current for the time period T1 from control of the reverse recovery period T2. Thus, the variable resistor1330may allow control of an amount of charge harvested for the supply voltage VDD.

At time1416, a time period T3 begins during which the BJT1310turns off resulting in a zero collector current IC1404and a zero auxiliary current iaux1406. During time period T3, power is delivered from the input node1302to LEDs1306through the inductor1320.

The effects of varying the resistor1330are illustrated in the graph ofFIG. 15.FIG. 15are graphs illustrating a change in auxiliary current with different resistances in a reverse recovery path according to one embodiment of the disclosure. Varying the resistor1330adjusts a duration of T2, but the time period for T1+T2 may remain fixed. By increasing or decreasing the length of time of T2, total charge transferred to the supply voltage VDDduring time period T2 may be adjusted. By increasing the resistor1330, the reverse recovery time may increase. In the embodiment shown, a T1+T2 time is fixed, resulting in an inductor current reaching the same peak regardless of the value of resistor1330. When the reverse recovery time increases, the amount of energy harvested at the chip supply may increase as shown using the supply current wave, represented by the iauxcurrent wave.

Operation of circuit1300ofFIG. 13may be described mathematically as shown below. A current through the inductor1320may be given by:

During the on phase (time period T1), the inductor current ICmay increase linearly when the BJT1310and switch1314are on. During reverse recovery (time period T2), the voltage across the inductor1320may become Vi−VDD. During an energy delivery to the load, the voltage across the inductor1320may become Vi−VO. For calculating reverse recovery current, several assumptions may be made, including:1) VinVDD; and 2) critical conduction operation mode; and 3) Fixed output power.

Considering the above assumptions, the power output, Pout, of the inductor1320and an average current, IO,AvG, to the output node1304may be calculated as shown below:

Pout=Vout*IO,AVG=ConstantIO,AVG=IPeak*T32*T=Constant,
where T is a time period summed from T1, T2, and T3, and IPeakis a peak current value through the inductor1320. Based on the assumptions and current through inductor1320, IPeakmay be calculated as:

ViL*(T1+T2)=VO-ViL*T3=>Vi=(1-(T1+T2)T)*VO=(1-DutyCycle)*VO⁢IPeak=ViL*(T1+T2),
where Viis the input voltage VIN, and L is an inductor value of the inductor1320. From the above equations a peak current, IPeak, may also be represented as:

The average reverse recovery current to output node1304, IVDD,RR, may then be calculated as:

To harvest energy during reverse recovery for charging the supply voltage VDD, a minimum T2 period may be necessary as defined by the following criteria:

The circuit1300ofFIG. 13may be modified to allow sensing of the collector current and a calculation of reverse recovery charge.FIG. 16is a circuit illustrating a BJT-based boost stage topology with emitter voltage sensing according to one embodiment of the disclosure. For example, circuit1600ofFIG. 16includes an additional node1612for accessing the control circuit1312. The node1612may be coupled to the switch1314. A resistor1602coupled to the node1612may set a voltage at node1612. By monitoring the voltage at node1612, a collector current ICmay be calculated and the ramp rate determined. From the ramp rate, an auxiliary current iauxmay be calculated, based on the equations above, and a controller performing the calculating may then determine a timing interval of operating the VPLScontrol signal.

The circuit1600ofFIG. 16may be modified to provide feedback regarding when the BJT1310turns off.FIG. 17is a circuit illustrating a BJT-based boost stage topology with turn-off detection according to one embodiment of the disclosure. A circuit1700includes control circuit1312coupled to the base and emitter of BJT1310. Coupled to the base node of the BJT1310may be a switch1704operated by control signal VPLS,T2. The switch1704couples the resistor1330and a comparator1706to the base of the BJT1310. A switch1340couples the current source1342to the base node of the BJT1310based on a control signal VPLS,T1. The current source1342may be powered from a supply voltage VDD, such as that generated by the circuit1700through feedback loop216. The current source1342may be, for example, a charge pump as described above with reference toFIGS. 3-6 and 11-12.

The comparator1706may provide detection of when the BJT1310turns off. During a first time period, the base node of the BJT1310may be charged from current source1342when the switch1340is closed and the switch1704is open. During a reverse recovery period, such as time period T2, the switch1704may be closed and the switch1340opened to allow reverse current from the base node of the BJT1310to pass through the resistor1330to ground. The comparator1706compares a voltage across the resistor1330with a reference voltage, which may be close to the ground level. The voltage across the resistor1330will decrease to near ground as the base of the BJT1310is nearing complete discharge and the BJT1310is nearing turn off. The comparator1706may detect this condition and provide an output at node1712.

A controller IC may receive the output of node1712and control the VPLS,T1and VPLS,T2signals and adjust the resistor1330to obtain a desired output voltage VDD. The resistor1330may be increased to increase the duration of T2 but at a decrease of initial inductor peak current, Ip, such that the final inductor peak current, Ipf, remains the same.

A complete system illustrating operation of a LED-based light bulb having the functionality described above, including dimmer compatibility, is shown inFIG. 18.FIG. 18is a block diagram illustrating a dimmer system with a variable resistance device according to another embodiment of the disclosure. A system1800may include a dimmer compatibility circuit1808with a variable resistance device1808aand a control integrated circuit (IC)1808b. The control IC1808bmay include, for example, the transistors and switches disclosed inFIGS. 2-6. In certain embodiments, the transistors and switches disclosed inFIGS. 2-6may be external to the control IC1808b. The dimmer compatibility circuit1808may couple an input stage having a dimmer1804and a rectifier1806with an output stage1810, which may include light emitting diodes (LEDs). The system1800may receive an input from an AC mains line1802.

Although the present disclosure and certain representative advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims. For example, although signals generated by a controller are described throughout as “high” or “low,” the signals may be inverted such that “low” signals turn on a switch and “high” signals turn off a switch. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the present disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.