CN116915055A - System and method for improving transient response in an H-bridge buck-boost driver using an integrated matrix manager - Google Patents

Abstract

Systems and methods for controlling compensation circuits are presented. In an embodiment, a detection circuit receives a set of control signals that have been generated by a control circuit for driving a set of Light Emitting Diode (LED) switches. The switches control a set of LEDs driven by a DC-DC converter coupled to a feedback loop that is detachably coupled to the compensation circuit. In an embodiment, the detection circuit determines whether a change in the state of the LED is imminent, and in response, uses a compensation circuit to control the feedback loop in such a way that current overshoot or undershoot in the LED current is reduced.

Description

System and method for improving transient response in an H-bridge buck-boost driver using an integrated matrix manager

Cross Reference to Related Applications

The present application claims priority benefits from 35u.s.c. ≡119 (e) from: co-pending and commonly assigned U.S. provisional patent application No. 63/332,899 entitled "SYSTEMS AND METHODS FOR IMPROVING TRANSIENT RESPONSE IN SLEW-RATE LIMITED H-BRIDGE BUCK-BOOST drive" filed on 4/20/2022; U.S. provisional patent application No. 63/413,541 entitled "SYSTEMS AND METHODS FOR IMPROVING TRANSIENT RESPONSE H-BRIDGE BUCK-BOOST driver" filed on 5 of 2022; U.S. provisional patent application No. 63/441,377 entitled "SYSTEMS AND METHODS FOR IMPROVING TRANSIENT RESPONSE H-BRIDGE BUCK-BOOST DRIVERS USING INTEGRATED MATRIX MANAGER [ systems and methods for improving transient response H-BRIDGE BUCK-boost drivers using an integrated matrix manager ]", filed on 1, 26, 2023; and U.S. non-provisional patent application Ser. No. 18/131,407, titled "SYSTEMS AND METHODS FOR IMPROVING TRANSIENT RESPONSE IN H-BRIDGE BUCK-BOOST DRIVERS USING INTEGRATED MATRIX MANAGER [ systems and methods for improving transient response in H-BRIDGE BUCK-boost drives using an integrated matrix manager ]," filed on 6, 4, 2023, each of which takes Su Leishen. Ha Liha blue and Luo En Wenson-Okatsui as the inventors. The disclosures of all of the above applications are incorporated herein by reference in their entirety for all purposes.

Background

A.Technical Field

The present disclosure relates generally to systems and methods for current and voltage regulators. More specifically, the present disclosure relates to systems and methods for improving transient response in H-bridge buck-boost driver applications, such as in Light Emitting Diode (LED) applications.

B.Background

In automotive applications, adaptive high beam (ADB) headlamps are rapidly becoming popular. In general, ADB circuits use LED drivers to supply regulated current to an LED array to produce light. The matrix manager connects a shunt switch in parallel with each LED to turn the LED on or off to control the desired light output. One side effect of switching operations that increase and decrease the number of LEDs that are turned on in a string of LEDs over time is to introduce an undesirable transient response in the output current, which can appear as dead time and thus negatively impact LED brightness. In contrast, an ideal LED driver will maintain a constant output current, independent of varying string voltages.

It is therefore desirable to have systems and methods for various applications, including modern LED driver circuits, that overcome the drawbacks of existing designs and improve slew rate limited transient response of the circuit without adversely affecting other circuit parameters.

Drawings

Reference will now be made to embodiments of the application, examples of which are illustrated in the accompanying drawings. The drawings are intended to be illustrative, and not limiting. While the application is generally described in the context of these embodiments, it will be understood that it is not intended to limit the scope of the application to these particular embodiments.

Fig. 1 is a simplified circuit diagram of an LED driver system utilizing a switch mode LED driver.

Fig. 2 illustrates an exemplary DC/DC converter circuit utilizing average current mode control and variable compensation circuitry in accordance with various embodiments of the present disclosure.

Fig. 3 illustrates an exemplary H-bridge buck-boost LED driver circuit utilizing average current mode control and variable compensation circuitry in accordance with various embodiments of the present disclosure.

Fig. 4 illustrates an H-bridge buck-boost converter circuit utilizing average current mode control in accordance with various embodiments of the present disclosure.

Fig. 5 illustrates an exemplary H-bridge buck-boost converter circuit utilizing a detection circuit, in accordance with various embodiments of the present disclosure.

Fig. 6 illustrates an exemplary integrated circuit including an LED driver and matrix manager circuit, according to various embodiments of the present disclosure.

Fig. 7 depicts simulation results of a converter circuit in accordance with various embodiments of the present disclosure.

Fig. 8 is a comparison of experimental results showing the effect of applying average current mode control to a switch mode LED driver circuit, according to various embodiments of the present disclosure.

Fig. 9 is a flowchart of an illustrative process for controlling a compensation circuit using edge detection and logic circuits in accordance with various embodiments of the present disclosure.

FIG. 10 is a flowchart of an illustrative process for controlling a compensation circuit using a detection circuit in accordance with various embodiments of the present disclosure.

Detailed Description

In the following description, for purposes of explanation, specific details are set forth in order to provide an understanding of the present application. It will be apparent, however, to one skilled in the art that the application may be practiced without these details. Furthermore, those skilled in the art will appreciate that the embodiments of the application described below may be implemented in a variety of ways, such as a process, an apparatus, a system, a device, or a method, on a tangible computer readable medium.

The components or modules shown in the figures illustrate exemplary embodiments of the application and are intended to avoid obscuring the application. It should also be understood that throughout this discussion, components may be described as separate functional units that may include sub-units, but those skilled in the art will recognize that various components or portions thereof may be divided into separate components or may be integrated together, including integrated in a single system or component (e.g., a monolithic IC). It should be noted that the functions or operations discussed herein may be implemented as components. The components may be implemented in software, hardware, or a combination thereof.

Furthermore, connections between components or systems within the figures are not intended to be limited to direct connections. Rather, the data between these components may be modified, reformatted, or otherwise changed by intermediate components. Moreover, additional connections or fewer connections may be used. It should also be noted that the terms "coupled," "connected," or "communicatively coupled" are to be understood as including direct connections, indirect connections via one or more intermediary devices, and wireless connections.

Reference throughout this specification to "one embodiment," "a preferred embodiment," "an embodiment," or "embodiments" means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment and may be included in more than one embodiment of the present application. Moreover, appearances of the phrases in various places in the specification are not necessarily all referring to the same embodiment or embodiments.

Certain terminology is used throughout this specification in various places for the purpose of description and should not be taken in a limiting sense. The service, function or resource is not limited to a single service, function or resource; the use of these terms may refer to a group of related services, functions, or resources, which may be distributed or aggregated.

The terms "include," "comprising," "includes," and "including" are to be construed as open-ended terms and any listed items thereafter are examples and are not intended to be limited to the listed items. Any headings used herein are for organizational purposes only and are not to be used to limit the scope of the description or the claims. Each reference mentioned in this patent document is incorporated herein by reference in its entirety.

It should be noted that the embodiments described herein are discussed in the context of an LED driver circuit, but those skilled in the art will recognize that the teachings of the present disclosure are not limited to any particular driver circuit, voltage or current regulator, or LED application, and may be used in other contexts as well and to drive non-LED loads.

In this document, the terms "regulator" and "converter" and the terms "LED string" and "LED array" are used interchangeably. Similarly, the terms "matrix manager" and "matrix control circuit" are used interchangeably. "control circuitry" includes microcontrollers, logic elements, amplifiers, comparators, and any other control element recognized by those skilled in the art.

Fig. 1 is a simplified circuit diagram of an LED driver system utilizing a switch mode LED driver. The LED driver system 100 includes a switch mode LED driver 102 that drives an LED string 108. As depicted in fig. 1, LED string 108 includes a plurality of LEDs (e.g., 110), each controlled by a MOSFET device that acts as a switch (e.g., 112) controlled by matrix manager 504.

The output capacitor 106 in the LED driver circuit 100 typically has a capacitance value that is greater than that required for a simple buck LED driver. In operation, however, a larger capacitor may cause an increase in dead time, for example, when the LED driver 102 switches from driving a relatively smaller number of LEDs (e.g., 110) to driving a relatively larger number of LEDs. During the dead time, the LED string 108 does not output light because the output capacitor 106 is being charged to the new target LED string forward voltage required to regulate the desired load current. In addition, the resulting transient effect causes the time-averaged LED current in the LED driver circuit 100 to drop slightly below the regulation point. Thus, the overall brightness produced by the LED string 108 is somewhat reduced.

Conversely, when the LED driver 102 switches from driving a relatively large number of LEDs to driving a relatively small number of LEDs, an overshoot condition occurs in the LED current, in which the LED current exceeds the set point and remains in that condition for a relatively long time, i.e., until the output capacitor discharges to a new LED string voltage. Both of these situations are undesirable because the additional dead time limits the minimum dimming duty cycle of the LED string 108. Further, prolonged current overshoots may cause physical damage to some or all of the LEDs in LED string 108. These problems become more serious if multiple LEDs are switched simultaneously. It is desirable to have a low cost system LED driver system and corresponding method that allows for reduced dead time and maintains continuous inductor current in ADBs and similar applications.

Fig. 2 illustrates an exemplary DC/DC converter circuit utilizing average current mode control and variable compensation circuitry in accordance with various embodiments of the present disclosure. In an embodiment, DC/DC converter 200 includes an H-bridge 220 that is energized by power supply 270 and includes switches 202-208 and an inductor 210. As depicted in fig. 2, DC/DC converter 200 may drive pure resistive load 216, error amplifiers 230-232, comparators 234-236, clock-based logic 240-242, gate driver 254, and RC compensation networks 280, 282, including various switches, resistors (e.g., 258), and capacitors (e.g., 256).

In an embodiment, the converter circuit 200 may include two feedback loops, as depicted in fig. 2. The first loop ("inner loop") may include the switch 206, the error amplifier 230, comparators 234-236 (e.g., a pair of PWM comparators), logic circuitry 240-242, and a gate driver 254. The second loop ("outer loop") may include the switch 202, the resistor 262, the error amplifiers 230-232, the comparators 234-236, the logic circuitry 240-242, and the gate driver 254. As depicted, the output of error amplifier 232 may be used to control the input of error amplifier 230.

In an embodiment, once the load 216 conducts current, the inner loop amplifier 230 may generate an error voltage 252 (in V _COMP Representation). The resulting error voltage 252 may be input to a pair of PWM comparators 234-236, which may set the duty cycle of one or more of the switches 202-208 of the H-bridge 220 to regulate the average current through the switch 206. In an embodiment, since switch 206 is coupled in series with load 216, the feedback arrangement of FIG. 2 may use the average current flowing through switch 206 to adjust the duty cycle of switches 202-208, causing the output voltage to be adjusted to a value determined by reference 250 and the voltage divider formed by resistors 262-264. For example, in steady state, the average current through switch 206 may be substantially equal to the current through load 216.

In an embodiment, in a conventional buck mode, the converter circuit 200 may have an input voltage of, for example, 12V and an output voltage of 7V. In the event that the input voltage drops below 7V, the H-bridge circuit 220 will enter boost mode regulation to properly maintain the output voltage. Since the right half-plane zero limits the crossover frequency (e.g., to 20 kHz), the component values of the compensation circuits 280, 282 are typically selected so that the compensation circuits 280, 282 can accommodate the "worst case" boost mode.

Advantageously, this not only avoids circuit instability in boost mode, but also provides circuit stability in buck 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 types of modes. In particular in buck mode, in order to keep the unity gain below 1/10 of the switching frequency (e.g. 400 kHz), it is preferred that the crossover frequency does not exceed e.g. 40kHz. However, the presence of the right half-plane zero in boost mode may cause the boost mode crossover frequency to be, for example, 1/5 of the right half-plane zero frequency (e.g., 20 kHz), i.e., 4kHz, thus resulting in a sacrifice of bandwidth up to as much as 36kHz during buck mode operation. Thus, the solutions that can be expected are: regardless of the mode in which the converter circuit 200 operates at any given time, satisfactory and stable circuit performance is ideally achieved in all modes of operation without sacrificing bandwidth or adversely affecting any other circuit parameters.

In particular, the systems and methods that are desirable are: in these systems and methods, the compensation networks 280, 282 of the converter circuit 200 may be independently adjusted for different modes of operation, thereby enabling the maximum bandwidth and thus the fastest transient response to be individually selected for the different modes, rather than being limited to designs tailored to prevent only the instabilities that may be caused by the worst case boost mode conditions. In this way, all modes and areas of operation can take advantage of improved circuit performance.

In various embodiments herein, this may be accomplished, for example, by modifying the compensation networks 280, 282 of the error amplifiers 230-232, for example, by adding one or more switches so that the feedback loop may use various compensation values that may be switched freely (i.e., adjusted) depending on circuit conditions and operating mode(s), thereby avoiding sub-optimal circuit performance in one mode while supporting improved circuit performance in another mode.

In detail, the switchable compensation networks 280, 282 may be adapted according to the operation mode and the specific application, for example to increase the crossover frequency in each respective operation mode. In an embodiment, in response to the DC/DC converter 200 detecting a state in which the H-bridge 220 is currently operating (e.g., whether the H-bridge is operating in buck mode or boost mode), the compensation networks 280, 282 may be adjusted to achieve the desired operating conditions in that mode while maintaining a satisfactory bandwidth for that mode of operation. Therefore, although the optimum bandwidth in the step-up mode is not necessarily used as the optimum bandwidth in the step-down mode, the optimum bandwidth in the step-down mode may be used without destabilizing the step-up condition.

In an embodiment, the DC/DC converter 200 may obtain information about the state of the H-bridge 220 from any controller or logic circuitry, which may be internal or external to the circuit 200. In an embodiment, the controller may determine the state, for example, by comparing the ratio of the input voltage and the output voltage.

It is to be understood that in an embodiment, the desired operating conditions specific to the application in a given state or mode may be determined prior to determining the appropriate component values for the compensation networks 280, 282. For example, in an embodiment, a maximum boost condition (defined by, for example, a minimum input voltage and a maximum output voltage) may be used to select appropriate values for the compensation circuits 280, 282, the effective load resistance, and the output capacitor values that define the boost load pole and the minimum crossover frequency for the circuit 200. Once the right half-plane zero is determined (e.g., by using the effective load resistance, inductor 210, and duty cycle), the feedback compensation can be designed such that the compensation zero is at about the same frequency as the boost load pole and the unity gain frequency is less than, for example, 1/5 of the right half-plane zero.

Similarly, the maximum buck condition (which is defined, for example, by the highest input voltage and the lowest output voltage) may be used to select appropriate values for the compensation circuits 280, 282, the effective load resistance, and the output capacitor values that define the buck load pole and the highest crossover frequency for the circuit 200. In an embodiment, the feedback compensation may be designed such that the compensation zero is at about the same frequency as the buck load pole and the unity gain frequency is less than, for example, 1/5 to 1/10 of the switching frequency.

In an embodiment, once the converter circuit 200 determines the operation mode of the H-bridge 220, the converter circuit 200 may switch between, for example, two pre-selected compensation settings in such a way that the compensation settings of the buck mode are advantageously not limited by the right half-plane zero in the boost mode.

Fig. 3 illustrates an exemplary H-bridge buck-boost LED driver circuit utilizing average current mode control and variable compensation circuitry in accordance with various embodiments of the present disclosure. In an embodiment, H-bridge buck-boost LED driver circuit 300 includes H-bridge 220. For clarity, components similar to those shown in fig. 2 are labeled in the same manner. For the sake of brevity, descriptions or functions of components are not repeated herein.

As depicted by the topology in fig. 3, the H-bridge buck-boost LED driver circuit 300 includes an LED string 216 that includes LEDs that each may be connected in parallel with a shunt switch (e.g., 214).

As depicted in fig. 3, in an embodiment, the inner loop may include a switch 206, an error amplifier 230, comparators 234-236 (e.g., a pair of PWM comparators), logic circuitry 240-242, and a 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 an embodiment, the current sense amplifier 224 and error amplifier 232 in the outer loop may be used to set a desired current through the LED string 216, which is determined, for example, by a reference voltage 250, which may be user programmable. As depicted, the output of error amplifier 232 may be used to control the input of error amplifier 230.

Similar to the circuit in fig. 2, in an embodiment, once H-bridge buck-boost LED driver circuit 300 determines the operating mode of H-bridge 220, driver circuit 300 may switch between a plurality of predetermined compensation settings such that the compensation settings for the buck mode are not limited by the right half-plane zero point of the boost mode.

Fig. 4 illustrates an H-bridge buck-boost converter circuit utilizing average current mode control in accordance with various embodiments of the present disclosure. In an embodiment, H-bridge buck-boost LED driver circuit 400 includes H-bridge 220. As depicted by the topology of fig. 4, H-bridge 220 is powered by power supply 270 and includes switches 202-208 and inductor 210. The H-bridge buck-boost LED driver circuit 400 further includes: LED string 216 (which includes LEDs that may each be connected in parallel with a shunt switch (e.g., 214)), output capacitor 212 coupled to ground potential, current sense amplifier 224, error amplifiers 230-232, comparators 234-236 and 246-248, clock-based logic 240-242, gate driver 254, logic 244, switch 238, and RC compensation network 282, which includes resistor 258 and capacitor 256.

In an embodiment, the 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. 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 an embodiment, the current sense amplifier 224 and error amplifier 232 in the outer loop may be used to set a desired current through the LED string 216, which is determined, for example, by a reference voltage 250, which may be user programmable. As depicted, the output of error amplifier 232 may be used to control the input of error amplifier 230. As depicted in fig. 4, switch 238 is coupled between error amplifier 232 and outer loop RC compensation network 282. The switch 238 is further coupled to present programmable high and low clamp voltage levels at the output of the error amplifier 232. In operation, the clamp voltage may be adjusted, for example, based on the reference voltage 250 present at the non-inverting input of the error amplifier 232.

In an embodiment, once the LEDs in string 216 conduct current, inner loop amplifier 230 may generate an error voltage 252 (in V _COMP Representation). The resulting error voltage 252 may be input to a pair of PWM comparators 234-236, which may set the duty cycle of one or more of the switches 202-208 of the H-bridge 220 to regulate the average current through the switch 206. In an embodiment, since the switch 206 is coupled in series with the LED string 216, the feedback arrangement in fig. 4 may adjust the average current through the switch 206 and the current through the LED string 216 to have substantially the same value. For example, in steady state, the average current through switch 206 may be substantially equal to the current through LED string 216.

In an embodiment, for example, a change in load conditions caused by the LED driver circuit switching from driving an LED string having a relatively small number of LEDs to driving a larger number of LEDs may cause the LED current to drop substantially to a value of 0A. This drop in turn causes zero current comparator 248 to output a signal that, in an embodiment, may be used to disconnect switch 238 from voltage node 228. Thus, the voltage V at node 228 _C May be pulled up and up to the high clamp voltage 260. Notably, this is in sharp contrast to the typical behavior of a conventional feedback loop, which reacts to LED current drops by operating in a slew-rate limited region and linearly increasing the error voltage based on the RC compensation network and the maximum available current output by the error amplifier. The step function rise in voltage at node 228 may be considered to be caused by the temporary opening of the outer loop, which causes the programmable 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 dead time, for example, until the LED string 216 reaches a new target forward string voltage associated with the number of LEDs turned on in the LED string 216.Once LED string 216 resumes conducting LED current, the signal output by sense amplifier 224 may cause switch 238 to close, thereby returning control of the average current to a closed feedback loop topology.

The average current mode control system and method herein advantageously maintains a DC regulation point of the voltage at node 228 to achieve a fixed LED current regardless of the input or output voltage. For example, opening the switch 238 may maintain a desired voltage value across the RC compensation network 280. As an additional benefit, once the switch 238 is closed, the voltage at node 228 returns to its previous adjustment point immediately before the switch 238 opens, thereby presenting its previous transient value.

In an embodiment, a change in load conditions caused by switching an LED driver circuit from driving an LED string having a relatively large number of LEDs to driving a smaller number of LEDs may cause the LED current to exhibit current overshoot behavior instead of dead time. The overshoot will cause the feedback loop to behave similarly as before, except in the opposite direction. In particular, the overshoot is associated with the output voltage of the capacitor 212 initially being too high for the number of LEDs that are turned on. Accordingly, it is desirable to reduce the average current through switch 206 to prevent excessive charge from flowing through LED string 216 and capacitor 212 when capacitor 212 is in the process of discharging to a lower LED string voltage. In an embodiment, in the event of an overshoot, the over-current comparator 246 may output a signal that may be used to disconnect the switch 238 from the voltage node 228, thereby causing the voltage V _C Is pulled down to the low clamp voltage 262. Once the overshoot condition subsides, switch 238 may be closed, the voltage at node 228 may return to its previous regulation point, and the closed feedback loop may regain control of LED driver circuit 400.

Fig. 5 illustrates an exemplary H-bridge buck-boost LED driver circuit utilizing average current mode control in accordance with various embodiments of the present disclosure. In an embodiment, H-bridge buck-boost LED driver circuit 500 includes H-bridge 220. As depicted by the topology of fig. 5, H-bridge 220 is powered by power supply 270 and includes switches 202-208 and inductor 210. The H-bridge buck-boost LED driver circuit 500 further includes: LED string 216 (which includes LEDs each of which may be connected in parallel with a shunt switch (e.g., 214)), output capacitor 212 coupled to ground potential, current sense amplifier 224, error amplifiers 230-232, comparators 234-236, clock-based logic 240-242, gate driver 254, edge detection and logic 502, matrix manager 504, switch 238, and RC compensation network 282, which comprises resistor 258 and capacitor 256.

It is to be appreciated that the edge detection and logic circuitry 502 may be implemented as any control circuitry known in the art and include, for example, logic decoder circuitry. Similarly, matrix manager 504 may be implemented as any control circuitry known in the art. The switch 238 may be implemented as any switch known in the art, including FET or MOSFET devices.

In an embodiment, 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 the switches 202-208 (e.g., 202), the resistor 222, the current sense amplifier 224, the error amplifier 230-232, the comparators 234-236, the logic circuitry 240-242, and the gate driver 254.

In an embodiment, the current sense amplifier 224 and error amplifier 232 in the outer loop may be used to set a desired current through the LED string 216, which is determined, for example, by a reference voltage 250, which may be user programmable. As depicted, the output of error amplifier 232 may be used to control the input of error amplifier 230. As depicted in fig. 5, switch 238 is coupled between error amplifier 232 and outer loop RC compensation network 282. The switch 238 is further coupled to present programmable high and low clamp voltage levels at the output of the error amplifier 232. In operation, the clamp voltage may be adjusted, for example, based on the reference voltage 250 present at the non-inverting input of the error amplifier 232.

In an embodiment, once the LEDs in string 216 conduct current, inner loop amplifier 230 may generate an outer loopError voltage 252 (in V _COMP Representation). The resulting error voltage 252 may be input to a pair of PWM comparators 234-236, which may set the duty cycle of one or more of the switches 202-208 of the H-bridge 220 to regulate the average current through the switch 206. In an embodiment, since the switch 206 is coupled in series with the LED string 216, the feedback arrangement in fig. 5 may adjust the average current through the switch 206 and the current through the LED string 216 to have substantially the same value. For example, in steady state, the average current through switch 206 may be substantially equal to the current through LED string 216.

In an embodiment, a change in load conditions caused by, for example, matrix manager 504 controlling any switch 214 to open (such as transitioning from driving a string of LEDs having a relatively small number of LEDs to driving a larger number of LEDs) may cause edge detection and logic circuitry 502 to detect an edge. This in turn may cause the edge detection and logic circuit 502 to output a signal or digital command, for example, a digital signal that may provide useful information in embodiments to determine whether to disconnect the switch 238 from the voltage node 228. Thus, the voltage V at node 228 _C May be pulled up and up to the high clamp voltage 260. Notably, this is in sharp contrast to the typical behavior of a conventional feedback loop, which reacts to LED current drops by operating in a slew-rate limited region and linearly increasing the error voltage based on the RC compensation network and the maximum available current output by the error amplifier. The step function rise in voltage at node 228 may be considered to be caused by the temporary opening of the outer loop, which causes the programmable 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 dead time, for example, until the LED string 216 reaches a new target forward string voltage associated with the number of LEDs turned on in the LED string 216. Once LED string 216 resumes conducting LED current, the signal output by sense amplifier 224 may cause switch 238 to close, thereby returning the regulation of the average current to a closed feedback loop topology.

The average current mode control system and method herein advantageously maintains a DC regulation point of the voltage at node 228 to achieve a fixed LED current regardless of the input or output voltage. For example, opening the switch 238 may maintain a desired voltage value across the RC compensation network 280. As an additional benefit, once the switch 238 is closed, the voltage at node 228 returns to its previous adjustment point immediately before the switch 238 opens, thereby presenting its previous transient value.

In an embodiment, when matrix manager 504 causes any switch 214 to close, transitioning from driving an LED string having a relatively large number of LEDs to driving a smaller number of LEDs, the LED current may exhibit current overshoot behavior instead of dead time. The overshoot will cause the feedback loop to behave similarly as before, except in the opposite direction. In particular, the overshoot is associated with the output voltage of the capacitor 212 initially being too high for the number of LEDs conducting current. Accordingly, it is desirable to reduce the average current through switch 206 to prevent excessive charge from flowing through LED string 216 and capacitor 212 when capacitor 212 is in the process of discharging to a lower LED string voltage. In an embodiment, in the event of an overshoot, edge detection and logic circuit 502 may output a signal that may be used to disconnect switch 238 from voltage node 228, thereby causing voltage V _C Is pulled down to the low clamp voltage 262. Once the overshoot condition subsides, switch 238 may be closed, the voltage at node 228 may return to its previous regulation point, and the closed feedback loop may regain control of LED driver circuit 500.

As will be appreciated by those skilled in the art, it would be beneficial if the feedback loop could know in advance that one or more LEDs are about to change their status, i.e. they are about to be turned on or off, in order to achieve optimal performance. In an embodiment, when the LED driver and matrix manager 504 are implemented in different integrated circuits, a feedback loop is used to perform some method to determine which new state the LED string 216 is changing to (e.g., based on an overshoot or undershoot condition of the LED current). One possible approach is to use a separate matrix tube that can communicate information about the switch state to a separate LED driver, e.g. via dedicated pins and/or an appropriate communication protocolAnd a processor. The LED current can be monitored and the voltage V can be set as soon as a current undershoot occurs _C To a high clamp state, whereas when current overshoot occurs, the voltage may be driven to a low clamp state. This approach may introduce a time difference between the time the matrix switch (e.g., 214) opens and closes and the time the feedback loop must respond, thereby negatively impacting performance.

Thus, unlike existing applications where the LED driver and matrix manager are implemented in different 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 an LED driver circuit and matrix manager 602 that includes a switch (e.g., 112) that controls the LED string 108. In addition to improving performance, for example, by reducing signal delays due to time differences, integrated embodiments may also advantageously reduce the number of dedicated pins used to communicate between two separate circuits or sub-circuits.

It is to be understood that the circuit topologies in fig. 2-6 are not limited to the constructional details shown herein or described in the accompanying text. For example, those skilled in the art will recognize that the resistor (e.g., resistor 258) may be implemented as a set of switchable parallel resistors that may be used to provide a variable resistance value for the RC compensation network 280, 282, i.e., that may be adjusted to a predetermined resistance value by the control logic. Similarly, a capacitor (e.g., capacitor 256) may be implemented as a set of variable capacitors in parallel. Those skilled in the art will further recognize that switch 238 may be implemented as any switch known in the art, including FET or MOSFET devices, and logic circuitry 502 may be implemented as any control circuitry known in the art. The compensation networks 280, 282 may be implemented as one or more dedicated compensation networks that may be individually controlled and operated. Those skilled in the art will further recognize that the various elements described above may be physically and/or functionally divided into sub-modules or combined in various configurations.

Experimental results indicate that the systems and methods disclosed herein can achieve relatively short dead times. Fig. 7 depicts simulation results of a converter circuit in accordance with various embodiments of the present disclosure. It should be noted that the experimental results herein are provided in an illustrative manner and are performed under specific conditions using one or more specific embodiments; accordingly, none of these experiments nor the results thereof should be used to limit the scope of the disclosure of the current patent document. Graph 700 shows that a relatively short dead time (represented by numeral 708) can be achieved using a circuit similar to that shown in fig. 5. Advantageously, this result may be achieved when the output voltage 702 changes sharply from about 17V to 27V while maintaining the LED current 704 substantially continuously at about 1A.

Fig. 8 is a comparison of experimental results showing the effect of applying average current mode control to a switch mode LED driver circuit, according to various embodiments of the present disclosure. Curve 802 in fig. 8 depicts the results of a conventional circuit that does not utilize the teachings of the present disclosure, while curve 805 depicts the results of a circuit that utilizes the present disclosure. As can be readily appreciated from fig. 8, the dead time of curve 805 is significantly reduced. In fig. 8, numeral 806 indicates an exemplary improvement associated with the low clamp voltage depicted by numeral 262 in fig. 5. Instead, numeral 808 indicates an exemplary improvement associated with the high clamp voltage depicted by numeral 260 in fig. 5.

Fig. 9 is a flowchart of an illustrative process for controlling a compensation circuit using control signals of edge detection and logic circuits in accordance with various embodiments of the present disclosure. In an embodiment, process 900 may begin at step 902, when a set of control signals, which may be generated by, for example, a matrix manager and drive a set of LEDs in a string of LEDs, are provided to an edge detection and logic circuit. The set of control signals may indicate, for example, which switches controlling the LEDs are about to open or close. This information may be used by the edge detection and logic circuit to control a switch (such as switch 238 in fig. 5) coupled to the feedback loop and to control the compensation circuit to reduce current overshoot or current undershoot in the current driving the LEDs in accordance with the various embodiments presented herein at step 904. Those skilled in the art will recognize that: (1) certain steps may optionally be performed; (2) The steps may not be limited to the specific order set forth herein; (3) certain steps may be performed in a different order; and (4) some steps may be accomplished simultaneously.

FIG. 10 is a flowchart of an illustrative process for controlling a compensation circuit using a detection circuit in accordance with various embodiments of the present disclosure. In an embodiment, process 1000 may begin at step 1002 when a set of control signals, which may have been generated by a control circuit (e.g., matrix manager 504 in fig. 5) for driving a set of LEDs, is received using a detection circuit (e.g., circuit 502 shown in fig. 5). At step 1004, the set of control signals (e.g., their rising edges) may be used to determine whether the state of any of the LEDs driven by the DC-DC converter circuit is about to change. The DC-DC converter circuit may include a feedback loop. Finally, at step 1006, responsive to the determination, a compensation circuit also coupled to the feedback loop may be controlled using, for example, a switch coupling the detection circuit to the feedback loop in order to reduce current overshoot or current undershoot in the current driving the LEDs.

Aspects of the application may be encoded on one or more non-transitory computer-readable media with instructions for one or more processors or processing units to cause steps to be performed. It should be noted that the one or more non-transitory computer readable media should include volatile memory and non-volatile memory. It should be noted that alternative implementations are possible, including hardware implementations or software/hardware implementations. The hardware implemented functions may be implemented 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. Similarly, the term "one or more computer-readable media" as used herein includes software and/or hardware or a combination thereof having a program of instructions embodied thereon. In view of these alternatives to the embodiments, it will be appreciated that the figures and accompanying description provide functional information that would be required by one 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 application may further relate to computer products with a non-transitory tangible computer-readable medium that have computer code thereon for performing various computer-implemented operations. The media and computer code may be those specially designed and constructed for the purposes of the present application, or they may be of the kind well known or available to those having skill in the relevant arts. Examples of tangible computer readable media include, but are not limited to: magnetic media such as hard disks; optical media such as CD-ROM and holographic devices; a magneto-optical medium; and hardware devices that are specially configured for storing or for storing and executing 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 level code that are executed by a computer using an interpreter. Embodiments of the application may be implemented in whole or in part as machine-executable instructions in program modules that are executed by a processing device. Examples of program modules include libraries, programs, routines, objects, components, and data structures. In a distributed computing environment, program modules may be located in a local, remote, or both environment.

Those skilled in the art will recognize that no computing system or programming language is critical to the practice of the application. Those skilled in the art will recognize that the foregoing examples and embodiments are exemplary and not limiting to the scope of the present disclosure. All permutations, enhancements, equivalents, combinations and modifications thereto that will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings are intended to be included within the true spirit and scope of the present disclosure. It should also be noted that the elements of any claim may be arranged in a variety of ways, including having a variety of dependencies, configurations, and combinations.

Claims (10)

1. A method for controlling a compensation circuit, the method comprising:

at a detection circuit, receiving a set of control signals that have been generated by a control circuit for driving a set of LED switches that control a set of Light Emitting Diodes (LEDs), the set of LEDs driven by a DC-DC converter coupled to a feedback loop;

determining, using one or more control signals of the set of control signals, whether a state of one or more LEDs of the set of LEDs is about to change; and

in response to the determination, the feedback loop is controlled using the detection circuit to mitigate current overshoot or current undershoot in the current driving the set of LEDs.

2. The method of claim 1, wherein using the detection circuit comprises: in response to the determination, a switch coupling the detection circuit to at least one of the feedback loop or compensation circuit is controlled.

3. The method of claim 1, wherein the detection circuit and the control circuit are integrated into a single circuit to reduce signal delay or time difference or eliminate the need to control the switch using feedback current.

4. The method of claim 1, wherein the detection circuit controls the feedback loop by using at least one of an edge detection circuit or a logic circuit.

5. The method of claim 1, wherein the control circuit driving the set of LEDs is a matrix manager circuit.

6. A controller, comprising:

a control circuit coupled in a feedback loop to a DC-DC converter that drives a set of Light Emitting Diodes (LEDs), the control circuit generating a set of control signals;

a detection circuit coupled to the control circuit, the detection circuit responsive to receiving one or more control signals of the set of control signals to determine whether a state of one or more LEDs of the set of LEDs is about to change, and in response, to control the feedback loop to reduce current overshoot or current undershoot in the current driving the set of LEDs.

7. The controller of claim 11, wherein controlling the feedback loop comprises using a switch coupling the detection circuit to at least one of the feedback loop or compensation circuit.

8. 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 signal delay or time difference; or alternatively

Eliminating the need to control the switch using feedback current.

9. The controller of claim 11, wherein the control circuit is a matrix manager circuit.

10. A detection circuit for controlling a compensation circuit, the detection circuit comprising:

a logic circuit; and

an edge detection circuit coupled in a feedback loop to a control circuit that generates a set of control signals that drive current through a set of Light Emitting Diodes (LEDs), the edge detection circuit responsive to receiving one or more control signals to determine whether a state of the one or more LEDs is about to change using the logic circuit, and to cause a switch coupling the edge detection circuit to a compensation circuit to control the feedback loop and reduce overshoot or undershoot in the current.