Systems and methods for improving transient response in H-bridge buck / boost drivers using an integrated matrix manager

Abstract

A method for controlling a compensation circuit (280, 282), the method comprising: at a detection circuit, receiving a set of control signals generated by a control circuit to drive a set of light-emitting diode (LED) switches (112; 214) that control a set of LEDs (110), the set of LEDs (110) being driven by a DC / DC converter (200) coupled to a feedback loop; Using one or more of the control signals in the set of control signals to make a determination as to whether a change in status of one or more of the LEDs (110) in the set of LEDs (110) is imminent; and in response to the determination, using the detection circuit to control the feedback loop to reduce a current overshoot or current undershoot in a current driving the set of LEDs (110).

Description

CROSS REFERENCE TO RELATED PATENT APPLICATIONSThe present application claims priority under 35 U.S.C. § 119(e) to simultaneous and separate U.S. Provisional Patent Application No. 63 / 332,899 filed April 20, 2022 entitled "SYSTEMS AND METHODS FOR IMPROVING TRANSIENT RESPONSE IN SLEW-RATE LIMITED H-BRIDGE BUCK-BOOST DRIVERS" and U.S. Provisional Patent Application No. 63 / 413,541 filed October 5, 2022 entitled "SYSTEMS AND METHODS FOR IMPROVING TRANSIENT RESPONSE H-BRIDGE BUCK-BOOST DRIVERS" and U.S. Provisional Patent Application No. 63 / 441,377 filed January 26, 2023, A method for improving transient response H-BRIDGE BUCK-BOOST DRIVERS USING INTEGRATED MATRIX MANAGER, and a non-prepended U.S. patent application Ser. No. 18 / 131,407, filed Apr. 6, 2023, entitled "SYSTEMS AND METHODS FOR IMPROVING TRANSIENT RESPONSE IN H-BRIDGE BUCK-BOOST DRIVERS USING INTEGRATED MATRIX MANAGER," each of which is a inventor of Sure Hariharan and Ron Vincent Oampo. The disclosures of all of the above applications are incorporated herein in their entirety by reference for all purposes.BACKGROUNDA. Technical FieldThe present disclosure relates generally to systems and methods for current and voltage regulators. More particularly, the present disclosure relates to systems and methods for improving transient response in H-bridge down / up conversion driver applications such as light emitting diode (LED) applications. Relevant disclosures are found, for example, in the documents DE 10 2015 103 293 A1, US 2017 / 0325296 A1 and US 2012 / 0139428 A1. DE 10 2015 103 293 A1 discloses a method for applying an active output voltage discharge for a buck-boost converter. It includes receiving an indication of a changed output voltage request, disabling and re-activating a control loop, and actively discharging the voltage from the output capacitance through the inductor to ground. The voltage is then adapted to a second output voltage. US 2017 / 0325296 A1 discloses a control unit for an LED arrangement having two LED units connected in series. The control unit receives an input signal for the desired output characteristic of the LED arrangement. It determines the duty cycles for the LED units, reduces current based on the largest duty cycles, and adjusts duty cycles accordingly. An output signal controls the LED array and the power supply in the switching mode to achieve the desired output characteristic. US 2012 / 0139428 A1 discloses a device for controlling an electrical load, comprising at least two individual loads connected in series. Each individual load is connected in parallel to a controllable switch and can be switched independently. In addition, a driver stage is present which feeds a current into the electrical load. The controllable switches are controlled by the control unit. A dummy load is connected in series with the single loads.B. BackgroundAdaptive driving beam (ADB) headlights are increasingly preferably used in motor vehicle applications. Generally, an ADB circuit uses an LED driver that supplies regulated current to an array of LEDs to generate light. A matrix manager places shunt switches in parallel with each of the LEDs to turn the LEDs on or off to control a desired light output. A side effect of switching operations, in which the number of LEDs that are turned on in a chain of LEDs is increased and decreased over time, is the introduction of undesirable transients in the output current, which has dead times and thus negatively affects the LED brightness. For comparison, an ideal LED driver would maintain a constant output current regardless of the varying chain voltage.Accordingly, it is desirable to provide systems and methods for various applications, including modern LED driver circuits, that overcome the disadvantages of existing designs and improve the slew rate limited transient response of a circuit, ideally without adversely affecting other circuit parameters.This technical object is achieved by a method for controlling a compensation circuit according to claim 1, a controller according to claim 11 and a detection circuit for controlling a compensation circuit according to claim 20.BRIEF DESCRIPTION OF THE DRAWINGSReferences are made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative and not limiting. Although the invention will be described generally in connection with these embodiments, it should be understood that the scope of the invention is not intended to be limited to these particular embodiments. FIG. 1 is a simplified circuit diagram of an LED driver system utilizing a switching LED driver. FIG. 2 illustrates an exemplary DC / DC converter circuit that utilizes average current mode control and a variable compensation circuit, according to various embodiments of the present disclosure. FIG. 3 illustrates an example H-bridge down / up conversion LED driver circuit that utilizes average current mode control and a variable compensation circuit, according to various embodiments of the present disclosure. FIG. 4 illustrates an H-bridge buck / boost converter circuit that utilizes average current mode control, according to various embodiments of the present disclosure. FIG. 5 illustrates an example H-bridge buck / boost converter circuit that utilizes a detection circuit, in accordance with various embodiments of the present disclosure. FIG. 6 illustrates an example integrated circuit including an LED driver and a matrix manager circuit, in accordance with various embodiments of the present disclosure. FIG. 7 shows simulation results for a converter circuit according to various embodiments of the present disclosure. FIG. 8 is a comparison of experimental results illustrating the effect of average current mode control applied to a switching LED driver circuit, according to various embodiments of the present disclosure. FIG. 9 is a flow diagram of an illustrative process for using edge detection and logic circuitry to control a compensation circuit according to various embodiments of the present disclosure. FIG. 10 is a flowchart of an illustrative process for using a detection circuit to control a compensation circuit according to various embodiments of the present disclosure.DETAILED DESCRIPTION OF THE EMBODIMENTSIn the following description, specific details are set forth for purposes of explanation in order to provide an understanding of the invention. However, it will be understood by those skilled in the art that the invention may be practiced without these details. Furthermore, those skilled in the art will appreciate that embodiments of the present invention described below may be implemented in a variety of ways, such as a process, apparatus, system, apparatus, or method, on a tangible computer readable medium.Components or modules shown in diagrams are illustrative of embodiments of the invention and are not intended to obscure the invention. It will also be appreciated that throughout this discussion, components may be described as separate functional units that may comprise subunits, however, those skilled in the art will appreciate that various components or portions thereof may be divided into separate components or integrated together, including integrated within a single system or component, e.g., a monolithic IC. It should be noted that functions or operations discussed herein may be implemented as components. Components may be implemented in software, hardware, or a combination thereof. Further, connections between components or systems in the figures are not intended to be limited to direct connections. Rather, data between these components may be modified, reformatted, or otherwise altered by intervening components. In addition, additional or fewer compounds may be used. It should also be noted that the terms "coupled," "connected," or "communicatively coupled" are intended to be understood to include direct connections, indirect connections via one or more intervening devices, and wireless connections.References throughout the specification to "one embodiment," "a preferred embodiment," or "embodiments" mean that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention and may be present in more than one embodiment. Moreover, any occurrence of the above-mentioned formulations at various places in the specification does not necessarily refer to the same embodiment or embodiments.The use of certain terms in various places in the specification is illustrative and should not be construed as limiting. A service, function, or resource is not limited to a single service, function, or resource; the use of these terms may refer to a grouping of related services, functions, or resources that may be distributed or aggregated.The terms "include," "including," "comprise," and "comprising" are intended to be open ended terms, and any lists following are examples and are not intended to be limited to the listed items. Any headings used herein are for organization purposes only and are not intended to limit the scope of the specification or claims. Each reference mentioned in this patent document is incorporated herein by reference in its entirety.It should be noted that embodiments described herein are discussed in the context of LED driver circuits, however, those skilled in the art will appreciate that the teachings of the present disclosure are not limited to any particular driver circuit(s), voltage or current regulators, or LED applications, and may likewise be used in other contexts and for driving non-LED loads.In this document, the terms "regulator" and "converter" and the terms "LED string" and "LED array" are used interchangeably. Likewise, the terms "matrix manager" and "matrix control circuit" are used interchangeably. "control circuit" includes microcontrollers, logic elements, amplifiers, comparators, and any other control elements that will be recognized by those skilled in the art. FIG. 1 is a simplified circuit diagram of an LED driver system utilizing a switching LED driver. An LED driver system 100 includes a switch LED driver 102 that drives an LED string 108. As shown in FIG. 1, the LED string 108 includes multiple LEDs (e.g., 110) each controlled by a MOSFET device acting as a switch (e.g., 112) controlled by a matrix manager 504.An output capacitor 106 in the LED driver circuit 100 typically has a larger capacitance value than the capacitance value that would be required for a simple buck LED driver. However, a larger capacitor causes an increase in dead time during operation, e.g., when the LED driver 102 switches from driving a relatively small number of LEDs (e.g., 110) to driving a relatively large number of LEDs. During the dead time, no light is output from the LED string 108 because the output capacitor 106 is charged to the new LED string forward voltage required to regulate the desired load current. Moreover, the resulting transient effect causes a slight drop in the time averaged LED current in the LED driver circuit 100 below the regulation point. As a result, the overall brightness produced by the LED string 108 is slightly reduced.Conversely, when the LED driver 102 switches from driving a relatively high number of LEDs to driving a relatively low number of LEDs, the LED current experiences an overshoot condition in which the LED current exceeds a set point and remains in this state for a relatively longer time, i.e., until the output capacitor discharges to the new LED string voltage. None of these scenarios is desirable because the additional dead time limits the minimum dimming duty cycle of the LED string 108. Further, a longer current overshoot may physically damage some or all of the LEDs in the LED string 108. These problems are exacerbated when multiple LEDs are switched simultaneously. Low cost LED driver systems and corresponding methods that reduce dead time and maintain continuous inductor current in ADB and similar applications are desirable.FIG. 2 illustrates an exemplary DC / DC converter circuit that utilizes average current mode control and a variable compensation circuit, according to various embodiments of the present disclosure. In embodiments, a DC / DC converter 200 includes an H-bridge 220 powered by a power source 270 and including switches 202- 208 and an inductor 210. As shown in FIG. 2, the DC / DC converter 200 may include a resistive-only load 216, error amplifiers 230- 232, comparators 234- 236, clock-based logic circuitry 240- 242, a gate driver 254, and RC compensation networks 280, 282 including various switches, resistors (e.g., 258), and capacitors (e.g., 256).In embodiments, the converter circuit 20 may include two feedback loops, as shown in FIG. 2. A first loop ("inner loop") may include switch 206, error amplifier 230, comparators 234- 236, e.g., a pair of PWM comparators, logic circuitry 240- 242, and gate driver 254. A second loop ("outer loop") may include a switch 202, a resistor 262, the error amplifiers 230- 232, the comparators 234- 236, the logic circuitry 240- 242, and the gate driver 254. As shown, the output of the error amplifier 232 may be used to control the input of the error amplifier 230.In embodiments, once the load 216 conducts current, the inner loop amplifier 230 may generate an error voltage 252, referred to as V COMP between the outer loop and the sensed current flowing through the switch 206. The obtained fault voltage 252 may be input to the pair of PWM comparators 234- 236, whereby the duty cycle of one or more of the switches 202- 208 of the H-bridge 220 may be adjusted to regulate an average current through the switch 206. In embodiments, because the switch 206 is connected in series with the load 216, the feedback arrangement in FIG. 2 may use the average current flowing through the switch 206 to adjust the duty cycle of the switches 202- 208 such that the output voltage is regulated to a value determined by a reference 250 and a voltage divider formed by resistors 262- 264. For example, the average current flowing through the switch 206 may be substantially equal to the current flowing through the load 206 in the steady state.In embodiments, in the regular down conversion mode, for example, the converter circuit 200 may have an input voltage of 12 V and an output voltage of 7 V. In scenarios where the input voltage falls below 7V, the H-bridge circuit 220 enters a boost mode control to properly maintain the output voltage. Because the zero in the right half-plane limits the transition frequency (e.g., to 20 kHz), component values for the compensation circuits 280, 282 are typically chosen such that the compensation circuits 280, 282 may support the worst-case upconversion mode. Advantageously, this not only prevents circuit instabilities in step-up mode, but also provides circuit stability in step-down mode operation. As will be appreciated by those skilled in the art, this approach does not necessarily ensure that the best possible bandwidth is always achieved in both modes. In particular, in the step-down mode, in order to keep the unit gain lower than 1 / 10 of the switching frequency, e.g., 400 kHz, it is preferable that the transition frequency does not exceed, e.g., 40 kHz. However, the presence of the zero in the right half plane in the up-conversion mode may force the up-conversion mode transition frequency to be, for example, 1 / 5 of the frequency of the zero in the right half plane of, for example, 20 kHz (i.e., 4 kHz), thereby causing a loss of a significant amount of bandwidth of 36 kHz in the down-conversion mode operation. Therefore, it would be desirable to have available solutions that allow satisfactory and stable circuit performance in all modes of operation, ideally without loss of bandwidth or adverse effects on other circuit parameters, regardless of the mode in which converter circuit 200 operates at a given time.In particular, it is desirable to have systems and methods available in which the compensation networks 280, 282 of the converter circuit 200 may be independently adjusted for different modes of operation such that, rather than being limited to a design designed to provide protection only against instabilities that may be caused by the worst-case upconversion mode scenario, the maximum bandwidth and thus the fastest transient response may be individually selected for the different modes. In this way, all operating modes and ranges may benefit from increased circuit performance. In various present embodiments, this may be achieved, for example, by modifying the compensation networks 280, 282 or the error amplifiers 230- 232, e.g., by adding one or more switches, such that the feedback loop may use different compensation values that may be switched on and off (i.e., adjusted) depending on circuit conditions and operating mode(s), thereby preventing suboptimal circuit behavior in one mode in favor of improved circuit behavior in another mode.In detail, the switchable compensation networks 280, 282 may be made adjustable according to the operating mode and the specific application, e.g., to increase a transition frequency in each respective operating mode. In embodiments, in response to the DC / DC converter 200 detecting the state in which the H-bridge 220 is currently operating, e.g., whether the H-bridge is operating in the buck mode or the boost mode, the compensation network 280, 282 may be adjusted to archive a desired operating condition in that mode while maintaining a satisfactory bandwidth for that operating mode. As a result, while an optimum bandwidth in the step-up mode would not forcibly serve as the optimum bandwidth in the step-down mode, an optimum bandwidth in the step-down mode can be used without causing instability of the step-up case.In embodiments, the DC / DC converter 200 may receive information about a state of the H-bridge 220 from any controller or logic circuit that may be internal or external to the circuit 200. For example, in embodiments, the controller may compare the ratio of the input and output voltages to determine the state.It should be appreciated that in embodiments, a desired application-specific operating condition for a given state or mode may be determined prior to determining suitable component values for the compensation networks 280, 282. For example, in embodiments, a maximum boost condition, e.g., as defined by the lowest input voltage and the highest input voltage, may be used to select appropriate values for the compensation circuits 280, 282, an effective load resistance, and an output capacitor value that define a boost load pole and a lowest transition frequency for the circuit 200. Once the zero in the right half-plane has been determined, e.g., by using the effective load resistance, the inductance 210, and the duty cycle, the feedback compensation may be configured such that the compensating zero is at approximately the same frequency as the boost load pool and the unit gain frequency is lower than, e.g., 1 / 5 of the zero in the right half-plane. Similarly, a maximum downconversion condition, e.g., defined by the highest input voltage and the lowest input voltage, may be used to select appropriate values for the compensation circuits 280, 282, an effective load resistance, and an output capacitor value, which define a downconversion load pole and the highest transition frequency for the circuit 200. In embodiments, the feedback compensation may be configured such that the compensating zero is at approximately the same frequency as the step-down load pole and the unit gain frequency is lower than, e.g., 1 / 5-1 / 10 of the switching frequency.In embodiments, once the converter circuit 200 determines an operating mode for the H-bridge 220, the converter circuit 200 may switch between, e.g., two preselected compensation settings such that the compensation setting for the down-conversion mode is not limited by the zero in the right half-plane in the up-conversion mode.FIG. 3 illustrates an example H-bridge down / up conversion LED driver circuit that utilizes average current mode control and a variable compensation circuit, according to various embodiments of the present disclosure. In embodiments, the H-bridge down / up conversion LED driver circuit 300 includes the H-bridge 220. For clarity, components similar to those shown in FIG. 2 are labeled in the same manner. For the sake of brevity, a description of their functions will not be repeated here.As shown in the topology of FIG. 3, the H-bridge down / up conversion LED driver circuit 300 includes the LED string 216 that includes LEDs that may each be connected in parallel with a shunt switch (e.g., 214).As shown in FIG. 3, in embodiments, the inner loop may include the switch 206, the error amplifier 230, the comparators 234- 236, e.g., a pair of PWM comparators, the logic circuitry 240- 242, and the gate driver 254. The outer loop may include switch 202, resistor 222, current sense amplifier 224, error amplifiers 230- 232, comparators 234- 236, logic circuitry 240- 242, and gate driver 254. In embodiments, the current sense amplifier 220 and the error amplifier 232 may be used in the outer loop to adjust a desired current through the LED string 216, e.g., as determined by a reference voltage 250, which may be programmable by a user. As shown, the output of the error amplifier 232 may be used to control the input of the error amplifier 230.Similar to the circuit in FIG. 2, in embodiments, once the H-bridge down / up conversion LED driver circuit 300 determines an operating mode for the H-bridge 220, the driver circuit 300 may switch between a number of predetermined compensation settings such that the compensation setting for the down conversion mode is not limited by the zero in the right half-plane of the up conversion mode.FIG. 4 illustrates an H-bridge buck / boost converter circuit that utilizes average current mode control, according to various embodiments of the present disclosure. In embodiments, the H-bridge down / up conversion LED driver circuit 400 includes the H-bridge 220. As shown in the topology of FIG. 4, the H-bridge 220 is powered by a power source 270 and includes switches 202- 208 and inductor 210. The H-bridge down / up conversion LED driver circuit 400 further includes the LED string 216 including LEDs that may each be connected in parallel with a shunt switch (e.g., 214), the output capacitor 212 coupled to a ground potential, the current sense amplifier 224, the error amplifiers 230- 232, the comparators 234- 236 and 246- 248, the clock-based logic circuitry 240- 242, the gate driver 254, a logic device 244, a switch 238, and the RC compensation network 282 including the resistor 258 and the capacitor 256.In embodiments, the inner loop may include the switch 206, the error amplifier 230, the comparators 234- 236, e.g., a pair of PWM comparators, the logic circuitry 240- 242, and the gate driver 254. The outer loop may include switch 202, resistor 222, current sense amplifier 224, error amplifiers 230- 232, comparators 234- 236, logic circuitry 240- 242, and gate driver 254. In embodiments, the current sense amplifier 220 and the error amplifier 232 may be used in the outer loop to adjust a desired current through the LED string 216, e.g., as determined by a reference voltage 250, which may be programmable by a user. As shown, the output of the error amplifier 232 may be used to control the input of the error amplifier 230. As shown in FIG. 4, the switch 238 is coupled between the error amplifier 232 and the outer loop RC compensation network 282. Switch 238 is further coupled to accept programmable high clamping voltage and low clamping voltage levels at the output of error amplifier 232. In operation, the clamping voltage may be adjusted according to, for example, the reference voltage 250 at the noninverting input of the error amplifier 232.In embodiments, once LEDs in the chain 216 conduct a current, the inner loop amplifier 230 may generate an error voltage 252, referred to as V COMP between the outer loop and the sensed current flowing through the switch 206. The obtained fault voltage 252 may be input to the pair of PWM comparators 234- 236, whereby the duty cycle of one or more of the switches 202- 208 of the H-bridge 220 may be adjusted to regulate an average current through the switch 206. In embodiments, because the switch 206 is connected in series with the LED string 216, the feedback arrangement in FIG. 4 may adjust the average current flowing through the switch 206 and the current flowing through the LED string 216 to have substantially the same value. For example, the average current flowing through the switch 206 in the steady state may be substantially equal to the current flowing through the LED string 206.In embodiments, changing load conditions, e.g., due to an LED driver circuit changing from driving an LED string having a relatively small number of LEDs to driving a higher number of LEDs, may cause the LED current to drop substantially to a value of 0 A. This drop, in turn, causes the zero current comparator 248 to output a signal that can be used in embodiments to disconnect the switch 238 from the voltage node 228. As a result, voltage V C at node 228 may be pulled high and may rise to high clamping voltage 260. It should be noted that this is in sharp contrast to the typical behavior of a conventional feedback loop that would respond to the drop in LED current by operating in a slew rate limited range and more linearly increasing the error voltage based on the RC compensation network and the maximum available current output by the error amplifier. The step function like increase in voltage at node 228 may be considered to be caused by a temporary separation of the outer loop, which forces a programmed average current through switch 206 to increase to a relatively higher level, thereby increasing the amount of current available to charge output capacitor 212. This charging, in turn, reduces the dead time, e.g., until the LED string 216 reaches a new target pass string voltage associated with the number of LEDs turned on in the LED string 216. Once the LED string 216 conducts an LED current again, the signal output by the sense amplifier 224 may cause the switch 238 to close, thereby returning the average current control to the closed feedback loop topology. Average current mode control systems and methods herein advantageously maintain the DC regulation point of the voltage at node 228 for a fixed LED current regardless of the input or output voltage. For example, by opening the switch 238, the desired voltage value is maintained across the RC compensation network 280. As an additional advantage, once switch 238 is closed, the voltage at node 228 may return immediately to its previous regulation point prior to opening switch 238 to assume its pre-transient value.In embodiments, a change in load conditions caused by an LED driver circuit changing from driving an LED string with a relatively high number of LEDs to driving a lower number of LEDs may cause the LED current to exhibit current overshoot behavior rather than dead time. The overshoot causes the feedback loop to perform in a similar manner as before, but in the opposite direction. In particular, the overshoot is associated with the output voltage of capacitor 212 being initially too high for the number of LEDs being turned on. Thus, it is desirable to reduce the average current flowing through the switch 206 to prevent excess charge from flowing through the LED string 216 and the capacitor 212 while the capacitor 212 is at a lower LED string voltage in the process of discharging. In embodiments, in an overshoot scenario, the overcurrent comparator 246 may output a signal that may be used to disconnect the switch 238 from the voltage node 228 such that the voltage V C is pulled down to the low clamping voltage 262. Once the overshoot condition decays, switch 238 may close, the voltage at node 228 may return to its previous regulation point, and the closed feedback loop resumes control of LED driver circuit 400.FIG. 5 illustrates an example H-bridge down / up conversion LED driver circuit that utilizes average current mode control, according to various embodiments of the present disclosure. In embodiments, the H-bridge down / up conversion LED driver circuit 500 includes the H-bridge 220. As shown in the topology of FIG. 5, the H-bridge 220 is powered by a power source 270 and includes switches 202- 208 and inductor 210. The H-bridge down / up conversion LED driver circuit 500 further includes the LED string 216 including LEDs that may each be connected in parallel with a shunt switch (e.g., 214), the output capacitor 212 coupled to a ground potential, the current sense amplifier 224, the error amplifiers 230- 232, the comparators 234- 236, the clock-based logic circuitry 240- 242, the gate driver 254, an edge detection and logic circuitry 502, a matrix manager 504, the switch 238, and the RC compensation network 282 including the resistor 258 and the capacitor 256.It should be appreciated that the edge detection and logic circuitry 502 may be implemented as any control circuitry known in the art and may include, for example, a logic decoder circuit. Likewise, the matrix manager 504 may be implemented as any control circuit known in the art. The switch 238 may be implemented as any switch known in the art, including a FET or MOSFET device.In embodiments, the inner loop in driver circuit 500 may include switch 206, error amplifier 230, comparators 234- 236, e.g., a pair of PWM comparators, logic circuitry 240- 242, and gate driver 254. And the outer loop may include at least one of switches 202- 208 (e.g., 202), resistor 222, current sense amplifier 224, error amplifiers 230- 232, comparators 234- 236, logic circuitry 240- 242, and gate driver 254. In embodiments, the current sense amplifier 220 and the error amplifier 232 may be used in the outer loop to adjust a desired current through the LED string 216, e.g., as determined by a reference voltage 250, which may be programmable by a user. As shown, the output of the error amplifier 232 may be used to control the input of the error amplifier 230. As shown in FIG. 5, the switch 238 is coupled between the error amplifier 232 and the outer loop RC compensation network 282. Switch 238 is further coupled to accept programmable high clamping voltage and low clamping voltage levels at the output of error amplifier 232. In operation, the clamping voltage may be adjusted according to, for example, the reference voltage 250 at the noninverting input of the error amplifier 232.In embodiments, once LEDs in the chain 216 conduct a current, the inner loop amplifier 230 may generate an error voltage 252, referred to as V COMP between the outer loop and the sensed current flowing through the switch 206. The obtained fault voltage 252 may be input to the pair of PWM comparators 234- 236, whereby the duty cycle of one or more of the switches 202- 208 of the H-bridge 220 may be adjusted to regulate an average current through the switch 206. In embodiments, because the switch 206 is connected in series with the LED string 216, the feedback arrangement in FIG. 5 may adjust the average current flowing through the switch 206 and the current flowing through the LED string 216 to have substantially the same value. For example, the average current flowing through the switch 206 in the steady state may be substantially equal to the current flowing through the LED string 206.In embodiments, a change in load conditions, e.g., caused by the matrix manager 504 controlling any of the switches 214 to open, such as to transition from driving the LED string with a relatively small number of LEDs to driving a higher number of LEDs, may cause the edge detection and logic circuit 502 to detect an edge. This, in turn, may cause edge detection and logic circuit 502 to output a signal or digital command, e.g., a digital signal, that provides information useful in embodiments to determine whether to disconnect switch 238 from voltage node 228. As a result, voltage V C at node 228 may be pulled high and may rise to high clamping voltage 260. It should be noted that this is in sharp contrast to the typical behavior of a conventional feedback loop that would respond to the drop in LED current by operating in a slew rate limited range and more linearly increasing the error voltage based on the RC compensation network and the maximum available current output by the error amplifier. The step function like increase in voltage at node 228 may be considered to be caused by a temporary separation of the outer loop, which forces a programmed average current through switch 206 to increase to a relatively higher level, thereby increasing the amount of current available to charge output capacitor 212. This charging, in turn, reduces the dead time, e.g., until the LED string 216 reaches a new target pass string voltage associated with the number of LEDs turned on in the LED string 216. Once the LED string 216 conducts an LED current again, the signal output by the sense amplifier 224 may cause the switch 238 to close, thereby returning the average current regulation to the closed loop feedback topology. Average current mode control systems and methods herein advantageously maintain the DC regulation point of the voltage at node 228 for a fixed LED current regardless of the input or output voltage. For example, by opening the switch 238, the desired voltage value is maintained across the RC compensation network 280. As an additional advantage, once switch 238 is closed, the voltage at node 228 may return immediately to its previous regulation point prior to opening switch 238 to assume its pre-transient value.In embodiments, if the matrix manager 504 causes any of the switches 214 to close and thereby transition from driving an LED string having a relatively high number of LEDs to driving a lower number of LEDs, then current overshoot behavior may occur rather than dead time. The overshoot causes the feedback loop to perform in a similar manner as before, but in the opposite direction. In particular, the overshoot is associated with the output voltage of capacitor 212 being initially too high for the number of LEDs that conduct current. Thus, it is desirable to reduce the average current flowing through the switch 206 to prevent excess charge from flowing through the LED string 216 and the capacitor 212 while the capacitor 212 is at a lower LED string voltage in the process of discharging. In embodiments, in an overshoot scenario, edge detection and logic circuit 502 may output a signal that may be used to disconnect switch 238 from voltage node 228 such that voltage V C is pulled down to low clamping voltage 262. Once the overshoot condition decays, switch 238 may close, the voltage at node 228 may return to its previous regulation point, and the closed feedback loop resumes control of LED driver circuit 500.Those skilled in the art will understand that to achieve optimum performance, it would be advantageous if the feedback loop were to predict a priori that a change in state, i.e. switching one or more of the LEDs on or off, is imminent. In embodiments, when the LED driver and matrix manager 504 are implemented in separate integrated circuits, the feedback loop is used to perform a method for determining the new state to which the LED string 216 transitions, e.g., based on an LED current overshoot or undershoot condition. One possible approach is to use a stand-alone matrix manager that can forward information regarding the state of the switches to a stand-alone LED driver, e.g., via dedicated pins and / or a suitable communication protocol. The LED current may be monitored and the voltage V C may be driven to a high clamp state when current undershoot occurs and vice versa to a low clamp state when current overshoot occurs. This approach may introduce a delay between the time the matrix switches (e.g., 214) open and close and the time the feedback loop must react, thereby negatively impacting performance.Thus, unlike existing applications in which the LED drivers and matrix managers are implemented in separate integrated circuits, in embodiments herein, to further improve performance and reduce size, the LED driver circuit 500 and matrix manager 504 may be implemented on the same integrated circuit as illustrated in FIG. 6 as the LED driver circuit and matrix manager 602, including the switches (e.g., 112) that control the LED string 108. In addition to increasing performance, e.g., by reducing signal delays due to time delays, integrated embodiments may advantageously reduce the number of dedicated pins to communicate between two separate circuits or sub-circuit.It is to be understood that the circuit topologies in FIGS. 2-6 are not limited to the design details shown therein or described in the accompanying text. For example, those skilled in the art will understand that resistors (e.g., resistor 258) may be implemented as a set of switchable parallel resistors that may be used to provide a variable resistance of the RC compensation network 280, 282 that may be set to a predetermined resistance by control logic. Likewise, capacitors (e.g., capacitor 256) may be implemented as a bank of parallel variable capacitors. Those skilled in the art will further understand that switch 238 may be implemented as any switch known in the art, including a FET or MOSFET device, and logic device 502 may be implemented as any control circuit known in the art. The compensation networks 280, 282 may be implemented as one or more dedicated compensation networks that may be separately controlled and operated. Those skilled in the art will further appreciate that any number of elements described above may be physically and / or functionally divided into sub-modules or combined in various configurations.Experimental results show that systems and methods disclosed herein achieve relatively short dead times. FIG. 7 shows simulation results for a converter circuit according to various embodiments of the present disclosure. It should be noted that experimental results are provided herein for illustrative purposes and have been performed under specific conditions using a specific embodiment or specific embodiments; accordingly, neither these experiments nor their results are to be used to limit the scope of the disclosure of the present patent document. The diagram 700 shows that a relatively short dead time (denoted by numeral 708) may be achieved using a circuit similar to that shown in FIG. 5. Advantageously, this result can be achieved while maintaining the LED current 704 substantially continuously at about 1 A with a drastic variation in the output voltage 702 of about 17 V to 27 V.FIG. 8 is a comparison of experimental results illustrating the effect of average current mode control applied to a switching LED driver circuit, according to various embodiments of the present disclosure. Diagram 802 in FIG. 8 shows a result for a common circuit that does not use the teachings of the present disclosure, while diagram 805 shows a result for a circuit that does so. As can be readily seen from FIG. 8, the reduction of the dead time is significant for the diagram 805. In FIG. 8, numeral 806 indicates an example improvement associated with a low clamping voltage shown as numeral 262 in FIG. 5. In contrast, numeral 808 indicates an example improvement associated with a high clamping voltage shown as numeral 260 in FIG. 6.FIG. 9 is a flow diagram of an illustrative process for using control signals of an edge detection and logic circuit to control a compensation circuit according to various embodiments of the present disclosure. In embodiments, process 900 may begin at step 902 when a set of control signals, which may be generated by, e.g., a matrix manager and which drive a set of LEDs in a chain of LEDs, is provided to edge detection and logic circuitry. For example, the set of control signals may indicate whether and which switches controlling the LEDs are about to be opened or closed. This information may be used by the edge detection and logic circuitry at step 904 to control a switch, such as switch 238 in FIG. 5, coupled to a feedback loop and controlling a compensation circuit to reduce current overshoot or undershoot in a current driving the LEDs, according to various embodiments set forth herein. Those skilled in the art will appreciate that: (1) certain steps may be optionally performed; (2) steps may not be limited to the particular order set forth herein; (3) certain steps may be performed in different orders; and (4) certain steps may be performed simultaneously.FIG. 10 is a flowchart of an illustrative process for using a detection circuit to control a compensation circuit according to various embodiments of the present disclosure. In embodiments, process 1000 may begin at step 1002 when a detection circuit, e.g., circuit 502 shown in FIG. 5, is used to receive a set of control signals that may have been generated by a control circuit, such as matrix manager 504 in FIG. 5, to drive a set of LEDs. At step 1004, the set of control signals, e.g., their rising edge, may be used to determine whether a change in a status of any of the LEDs driven by a DC / DC converter circuit is imminent. The DC / DC converter circuit may comprise a feedback loop. Finally, at step 1006, in response to the determination, a switch, e.g., coupling the detection circuit to the feedback loop, may be used to control a compensation circuit, also coupled to the feedback loop, to reduce current overshoot or undershoot in a current driving the LEDs.Aspects of the present invention may be encoded on one or more non-transitory computer readable media having instructions for one or more processors or one or more processing units to cause steps to be performed. It should be noted that the one or more non-transitory computer readable media are intended to include volatile and non-volatile memory. It should be noted that alternative implementations are possible, including a hardware implementation or a software / hardware implementation. Hardware-implemented functions may be realized using application specific integrated circuits (ASICs), programmable arrays, digital signal processing circuitry, or the like. Accordingly, the terms in any claims are intended to cover both software and hardware implementations. Likewise, the term "computer-readable medium or media" as used herein includes software and / or hardware having a program of instructions implemented thereon, or a combination thereof. With these implementation alternatives in mind, it should be appreciated that the figures and the accompanying description provide the functional information that would be required by those skilled in the art to write program code (i.e., software) and / or fabricate circuits (i.e., hardware) to perform the required processing.It should be noted that embodiments of the present invention may further relate to computer products having a non-transitory tangible computer readable medium having thereon computer code for performing various computer-implemented operations. The media and computer code may be those specially designed and constructed for the purposes of the present invention, or they may be of the type known or available to those skilled in the relevant art. Examples of tangible computer readable media include, but are not limited to: magnetic media such as hard disks; optical media such as CD-ROMs and holographic devices; magneto-optical media; and hardware devices specifically configured to store or store and execute program code such as ASICs, programmable logic devices (PLDs), flash memory devices, and ROM and RAM devices. Examples of computer code include machine code, such as produced by a compiler, and files containing higher code, which are executed by a computer using an interpreter. Embodiments of the present invention may be implemented in whole or in part as machine executable instructions that may reside in program modules executed by a processing device. Examples of program modules include libraries, programs, routines, objects, components, and data structures. In distributed computing environments, program modules may be physically located in environments that are local, non-local, or both.Those skilled in the art will appreciate that no computing system or programming language is critical to the practice of the present invention. Those skilled in the art will also understand that the above examples and embodiments are exemplary and do not limit the scope of the present disclosure. All permutations, extensions, equivalents, combinations, and improvements thereto, which will become apparent to those skilled in the art upon reading the specification and reviewing the drawings in detail, are intended to be included within the true spirit and scope of the present disclosure. It is also noted that elements of any claims may be arranged differently, including having multiple dependencies, configurations, and combinations.

Claims

A method of controlling a compensation circuit (280, 282), the method comprising: at a detection circuit, receiving a set of control signals generated by a control circuit to drive a set of light emitting diode (LED) switches (112; 214) that control a set of LEDs (110), the set of LEDs (110) being driven by a DC / DC converter (200) coupled to a feedback loop; using one or more of the control signals in the set of control signals to make a determination whether a change in a status of one or more of the LEDs (110) is imminent in the set of LEDs (110); and in response to the determination, using the detection circuit to control the feedback loop to reduce current overshoot or undershoot in a current driving the set of LEDs (110).The method of claim 1, wherein using the detection circuit comprises controlling, in response to the determination, a switch (238) coupling the detection circuit to the feedback loop and / or a compensation circuit (280, 282).The method of claim 1 or 2, wherein the detection circuit and the control circuit are integrated into a single circuit to reduce signal delay or time delay or eliminate a need to use a feedback current to control the switch (238).The method of claim 3, wherein the set of LEDs (110) is integrated into the single circuit.The method of any preceding claim, further comprising using at least one edge of the set of control signals.The method of any preceding claim, wherein the detection circuit controls the feedback loop using an edge detection circuit (502) and / or a logic circuit (502).The method of claim 6, wherein the edge detection circuit (502) comprises a logic decoder.The method of any preceding claim, wherein the set of control signals comprises a digital command.The method of any preceding claim, wherein the control circuitry driving the set of LEDs (110) is a matrix manager circuitry (504).The method of any preceding claim, wherein the DC / DC converter (200) uses an H-bridge configuration to drive the set of LEDs (110).A controller comprising: a control circuit coupled in a feedback loop to a DC / DC converter (200) driving a set of light emitting diodes (LEDs (110)), the control circuit generating a set of control signals; a detection circuit coupled to the control circuit, the detection circuit determining whether a change in a status of one or more of the LEDs (110) in the set of LEDs (110) is imminent in response to receiving one or more control signals in the set of control signals, and in response controlling the feedback loop to reduce current overshoot or undershoot in a current driving the set of LEDs (110).The controller of claim 11, wherein controlling the feedback loop comprises using a switch (238) coupling the detection circuit to the feedback loop and / or a compensation circuit (280, 282).The controller of claim 12, wherein the detection circuit and the control circuit are integrated into a single circuit that performs steps comprising at least one of: reducing a signal delay or a time delay; or eliminating a need to use a feedback current to control the switch.The controller of claim 13, wherein the set of LEDs (110) is integrated into the single circuit.The controller of any of claims 11 to 14, wherein the detection circuit comprises an edge detection circuit (502) and a logic circuit (502).The controller of claim 15, wherein the edge detection circuit (502) comprises a logic decoder.The controller of claim 15 or 16, further wherein the edge detection circuit (502) uses at least one edge of the set of control signals.The controller of any of claims 11 to 17, wherein the set of control signals comprises a digital command.The controller of any of claims 11 to 18, wherein the control circuit is a matrix manager circuit (504).A detection circuit for controlling a compensation circuit (280, 282), the detection circuit comprising: a logic circuit (502); and an edge detection circuit (502) coupled in a feedback loop to a control circuit that generates a set of control signals that drive a current through a set of light emitting diodes (LEDs, 110), wherein the edge detection circuit (502), in response to receiving one or more control signals, uses the logic circuit (502) to determine whether a change in a status of one or more LEDs (110) is imminent and causes a switch (238) to couple the edge detection circuit (502) to a compensation circuit (280, 282) to control the feedback loop and to reduce current overshoot or undershoot in the current.

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