Fast current response driving circuit with step-down output voltage self-adaptive adjustment

Abstract

The invention discloses a step-down type output voltage self-adaptive regulation fast current response drive circuit, and belongs to the field of LED drive integrated circuits. According to the driving circuit, a dual-mode hybrid topological structure is used, transient response is enhanced in an event driving mode, anode voltage of an LED is adaptively adjusted according to cathode voltage of the LED in combination with a Buck type DCDC converter and a current well unit in an accurate voltage adjusting mode, and high-efficiency output is achieved through high response speed and reduction of invalid margin voltage. The design integrates the power unit, the current well unit, the loop compensation module, the comparator module, the selection module and the driving logic unit, and has the advantages of high efficiency and high response speed.

Description

Technical Field

[0001] The present invention relates to the field of LED driver integrated circuits and the field of power management chips, and particularly relates to a fast current response driving circuit with step-down output voltage adaptive regulation. Background Art

[0002] Wearable devices include smart watches, smart bracelets, etc., and their sales have increased explosively. As intelligent devices for health monitoring, they integrate various optical sensors for measuring biological signals. Among them, LEDs, as input sources of optical signals, are widely used in various wearable devices. This application has very strict requirements on the power consumption and efficiency of the selected chips. An LED driving circuit with low power consumption and high response speed is particularly important for extending the standby time of wearable devices. Event-driven integrated circuits are only turned on when an event is triggered, enabling the chip to maintain an extremely low-power off mode in the idle state.

[0003] Figure 2 As shown in the volt-ampere curve of a common LED, it can be seen that a small voltage change may cause a large current fluctuation. Therefore, a current source is usually used to drive the LED to improve the accuracy of its output.

[0004] There are three classic designs for LED driving circuits as follows. Figure 3 As a traditional Buck-type LED driving circuit, it is widely used in LED driving because of its high efficiency. However, when measuring biological signals, it is desired to use a signal with a low duty cycle and narrow pulse width to improve the efficiency of the entire system. The Buck-type LED driving circuit, due to its low response speed, is not suitable for measuring biological signals in wearable devices. Figure 4 As a traditional linear LED driving circuit, it has the advantages of small size and low static current, and does not require energy storage components, so it has a high response speed. However, due to its low efficiency, it is not suitable for intelligent wearable devices powered by batteries with limited capacity. Figure 5 As a traditional LED driving circuit controlled by a current trap, it is commonly used to drive LEDs for measuring biological signals. In order to make the LED operate within a relatively large output range, the input voltage VDD of the LED is not less than the maximum operating voltage of the LED plus the clearance voltage of the current trap. Therefore, when the LED operating current is low, the LED operating voltage is low, so the high margin voltage in the system causes the efficiency of the driving circuit to decrease. Summary of the Invention

[0005] In view of the advantages and disadvantages of various LED driver integrated circuits, the present invention proposes a fast current response driving circuit with step-down output voltage adaptive regulation, which can adaptively adjust the input voltage of the LED according to the amplitude of the output current, thereby solving the problem of low efficiency under low output load current of the LED, and the driving circuit always maintains high efficiency.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A buck-type output voltage self-adaptive regulation fast current response driving circuit is used to drive an LED load. It adopts a dual-mode hybrid topology structure, enhances the transient response in the event-driven mode, and adaptively regulates the anode voltage of the LED according to the cathode voltage of the LED in the precise voltage regulation mode;

[0008] The fast current response driving circuit includes a power unit, a current trap unit, a loop compensation module, a comparator module, a selection module, and a driving logic unit;

[0009] The power unit is a Buck-type DCDC converter composed of two power MOS transistors, a storage inductor, and a filter capacitor. The anode of the LED is connected to the voltage output terminal of the DCDC converter, and the cathode of the LED is connected to the current trap unit. The LED driving current is regulated by the current trap. At the same time, the cathode voltage of the LED is sampled as the feedback voltage and connected to the loop compensation module. The error is calculated in the loop compensation module between the feedback voltage and the DC bias reference voltage required by the current trap unit. The error signal is compared with the sawtooth wave of the comparator module, and the comparator module outputs a PWM wave; The PWM wave and the event drive are jointly connected to the selection module, the output terminal of the selection module is connected to the driving logic unit, and the output terminal of the driving logic unit controls the on and off of the two power MOS transistors in the power unit.

[0010] As a preference of the present invention, the two power MOS transistors are denoted as power MOS transistor M1 and power MOS transistor M2;

[0011] The positive pole of the power supply is connected to the source terminal of M1 transistor, the drain terminal of M1 transistor and the drain terminal of M2 transistor are connected to one end of the storage inductor, the other end of the storage inductor is connected to one end of the filter capacitor and serves as the voltage output terminal of the DCDC converter, and the negative pole of the power supply, the source terminal of M2 transistor, and the other end of the filter capacitor are grounded.

[0012] As a preference of the present invention, the loop compensation module includes an error amplifier and a compensator bridging the output of the error amplifier and the negative input. The negative input of the error amplifier is connected to the cathode of the LED, and the positive input of the error amplifier is connected to the preset DC bias reference voltage required by the current trap unit.

[0013] Preferably, in the present invention, the positive input of the comparator module is the output voltage of the loop compensation module, and the negative input of the comparator module is a sawtooth wave. When the sawtooth wave voltage is higher than the output voltage of the loop compensation module, the comparator module outputs a low level, the M1 transistor is turned on, the M2 transistor is turned off, and the power supply voltage charges the energy storage inductor and supplies energy to the LED at the same time; when the sawtooth wave voltage is lower than the output voltage of the loop compensation module, the comparator module outputs a high level, the M1 transistor is turned off, the M2 transistor is turned on, and the energy storage inductor discharges to supply energy to the LED.

[0014] Preferably, in the present invention, the selection module uses a multiplexer to select one of two, and its two input terminals are respectively connected to the output voltage of the comparator and the drive event signal; when there is a drive event signal, the event-driven mode is immediately executed, and after the jump condition is met in the event-driven mode, the precise voltage regulation mode is automatically executed.

[0015] Preferably, in the event-driven mode, the M1 transistor is turned on, the M2 transistor is turned off, and the output voltage of the DCDC converter rises. When the output voltage rises to a preset value, the event-driven mode is exited.

[0016] Preferably, in the precise voltage regulation mode:

[0017] When the cathode voltage of the LED is higher than the DC bias reference voltage required by the current trap unit, the output voltage of the loop compensation module rises, the high-level duration of the PWM wave output by the comparator module increases, the low-level duration decreases, the PWM duty cycle rises, the turn-on time of the M1 transistor increases, the turn-on time of the M2 transistor decreases, and the output voltage drops until it drops to the DC bias reference voltage required by the current trap unit and the output becomes stable;

[0018] When the cathode voltage of the LED is lower than the DC bias reference voltage required by the current trap unit, the output voltage of the loop compensation module drops, the high-level duration of the PWM wave output by the comparator module decreases, the low-level duration increases, the PWM duty cycle drops, the turn-on time of the M1 transistor decreases, the turn-on time of the M2 transistor increases, and the output voltage rises until it rises to the DC bias reference voltage required by the current trap unit and the output becomes stable.

[0019] The beneficial effects of the present invention are as follows:

[0020] The present invention dynamically adjusts the output voltage according to the output current of the load LED, and for the LED driven by a narrow pulse width current type, a high driving circuit efficiency can also be achieved at a low load output current. Description of the Drawings

[0021] Figure 1 It is a schematic framework diagram of a buck-type output voltage adaptive regulation fast current response drive circuit.

[0022] Figure 2 It is the voltage-current curve of the LED.

[0023] Figure 3 It is a traditional Buck-type LED driving circuit.

[0024] Figure 4 It is a traditional linear LED driving circuit.

[0025] Figure 5 It is a traditional LED driving circuit controlled by a current trap.

[0026] Figure 6 It is the circuit diagram of a fast current response driving circuit with step-down output voltage adaptive regulation.

[0027] Figure 7 It is the working schematic diagram of the feedback circuit. Specific implementation manners

[0028] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0029] A fast current response driving circuit with step-down output voltage adaptive regulation Figure 1 is the framework schematic diagram of the present invention. A Buck-type DCDC converter is used as the power unit. The anode of the LED is connected to the voltage output terminal of the DCDC converter, and the cathode of the LED is connected to the current trap unit. The driving current of the LED is adjusted by the current trap. At the same time, the cathode voltage of the LED is sampled as the feedback voltage and connected to the loop compensation module. The feedback voltage and the DC bias reference voltage required by the current trap unit calculate the error in the loop compensation module. The error signal is compared with the sawtooth wave of the comparator module, and the comparator module outputs a PWM wave; based on the control gate logic, the opening and closing of two power MOS transistors in the power unit are controlled.

[0030] As Figure 6 shown, the driving circuit includes a power unit, a current trap unit, a loop compensation module, a comparator module, a multiplexer and a driving logic unit. The loop compensation module includes an error amplifier and a compensator bridging the output of the error amplifier and the negative input; the power unit includes a power MOS transistor M1 and a power MOS transistor M2.

[0031] Among them, the positive pole of the power supply is connected to the source terminal of M1, the negative pole of the power supply is grounded, the drain terminal of M1 is connected to the drain terminal of M2, the source terminal of M2 is grounded, both ends of the inductor are respectively connected to the anode of the LED and the drain terminal of M1, both ends of the capacitor are respectively connected to the anode of the LED and the ground, the anode voltage of the LED is the output voltage, the cathode of the LED is connected to the current sink unit, and the driving current of the LED is adjusted by the current sink; the gates of M1 and M2 are connected to the output terminal of the driving logic unit, the cathode of the LED is connected to the negative input of the error amplifier, the positive input of the error amplifier is connected to the preset DC bias reference voltage Vref required by the current sink, the compensator is connected to the positive input and output of the error amplifier, the positive input of the comparator module is connected to the output of the error amplifier, the negative input of the comparator module is connected to the sawtooth wave, the output of the comparator module and the driving event are connected to a multiplexer (MUX) for selecting one of the two, and one of them is selected in different modes, and the output of the MUX is connected to the driving logic unit. The circuit is divided into two modes: event-driven mode and precise voltage regulation mode. The circuit enters the event-driven mode according to the driving event. After meeting the jump-out condition in the event-driven mode, the precise voltage regulation mode is automatically executed.

[0032] In the event-driven mode, the event-driven directly controls the driving logic unit, and the power MOS transistor M1 is in the on state, and the output voltage rises. In this state, the response speed of the driving circuit is fast, and the output voltage can quickly rise to the preset value. However, the output voltage of this mode cannot be precisely adjusted, so there will be unnecessary surplus voltage affecting the system efficiency (LED power / total input power). Therefore, in the present invention, when the output voltage rises to the preset value, it enters the precise voltage regulation mode. In the precise voltage regulation mode, the output voltage is precisely adjusted to the required value through a feedback circuit composed of a loop compensation module, a comparator module, a selection module, and a driving logic unit.

[0033] In the precise voltage regulation mode, the cathode of the LED is used as the feedback point to sample the cathode voltage. The cathode voltage and the preset DC bias reference voltage Vref required by the current sink are used as the inputs of the error amplifier. At the same time, in order to improve the loop stability of the entire system, the error amplifier and the compensator together form a loop compensation module. The output voltage of the loop compensation module is compared with the sawtooth wave of the comparator module to output a PWM wave. When the sawtooth wave voltage is higher than the output voltage of the loop compensation module, the comparator module outputs a low level, the M1 power transistor is turned on, and the M2 power transistor is turned off. The power supply voltage charges the inductor and supplies energy to the LED load at the same time; when the sawtooth wave voltage is lower than the output voltage of the loop compensation module, the comparator module outputs a high level, the M1 power transistor is turned off, and the M2 power transistor is turned on. The inductor discharges to supply energy to the load. Ignoring the influence of small ripples, the output voltage is equal to the input voltage multiplied by the duty cycle of the PWM wave generated by the comparator module. The opening and closing of the power MOS are controlled to achieve the required output voltage.

[0034] When the LED cathode voltage is higher than the DC bias reference voltage Vref required by the current sink, the voltage is reduced to the set target voltage after feedback through the loop compensation circuit module and the comparator module. Specifically, as Figure 7 shown, Output 1 and Output 2 in the figure respectively represent the output voltage of the error amplifier. The output voltage of the error amplifier increases (from Output 1 to Output 2). The output of the error amplifier serves as the positive input of the comparator module. When the output of the error amplifier increases, the high-level duration of the PWM wave output by the comparator module increases, the low-level duration decreases, the PWM duty cycle rises, the on-time of M1 decreases, the on-time of M2 increases, and the output voltage drops. Since the LED current is stabilized to the required current value by the current sink, the voltage across the LED is also a fixed value at this time. The decrease in the output voltage means the decrease in the LED cathode voltage until the cathode voltage drops to the required Vref voltage and the output becomes stable.

[0035] Similarly, when the LED cathode voltage is lower than the DC bias reference voltage Vref required by the current sink, the voltage is increased to the set target voltage after feedback through the loop compensation circuit module and the comparator module. Specifically, the output voltage of the error amplifier decreases. The output of the error amplifier serves as the positive input of the comparator module. When the output of the error amplifier decreases, the high-level duration of the PWM wave output by the comparator module decreases, the low-level duration increases, the PWM duty cycle drops, the on-time of M1 increases, the on-time of M2 decreases, and the output voltage rises. Since the LED current is stabilized to the required current value by the current sink, the voltage across the LED is also a fixed value at this time. The increase in the output voltage means the increase in the LED cathode voltage until the cathode voltage rises to the required Vref voltage and the output becomes stable.

[0036] The content not described in detail in the specification of the present invention belongs to the well-known technology of those skilled in the art. Although the embodiments of the present invention are described in conjunction with the accompanying drawings, various modifications or alterations can be made by those of ordinary skill in the art within the scope of the appended claims.

Claims

1. A fast current response driving circuit with step-down output voltage adaptive regulation, used to drive LED load, characterized in that: Adopting dual-mode hybrid topology, the transient response is enhanced in event-driven mode, and the anode voltage of the LED is adaptively adjusted according to the cathode voltage of the LED in precise voltage regulation mode; The fast current response driving circuit comprises a power unit, a current sink unit, a loop compensation module, a comparator module, a selection module and a driving logic unit; The power unit is a Buck type DCDC converter composed of two power MOS tubes, an energy storage inductor and a filter capacitor. The LED anode is connected to the voltage output end of the DCDC converter, the LED cathode is connected to the current sink unit, the LED driving current is adjusted by the current sink, and the LED cathode voltage is sampled as a feedback voltage to be connected to a loop compensation module. The feedback voltage and the DC bias reference voltage required by the current sink unit are used to calculate the error in the loop compensation module, the error signal is compared with the sawtooth wave of the comparator module, and the comparator module outputs a PWM wave; the PWM wave and the event drive are connected to the selection module together, the output end of the selection module is connected to the drive logic unit, and the output end of the drive logic unit controls the opening and closing of the two power MOS tubes in the power unit.

2. The fast current response driving circuit with step-down output voltage adaptive regulation according to claim 1, characterized in that: The two power MOS tubes are marked as power MOS tube M1 and power MOS tube M2; The positive pole of the power supply is connected to the source end of the M1 tube, the drain end of the M1 tube and the drain end of the M2 tube are connected to one end of the energy storage inductor, the other end of the energy storage inductor is connected to one end of the filter capacitor and serves as the voltage output end of the DCDC converter, and the negative pole of the power supply, the source end of the M2 tube, and the other end of the filter capacitor are grounded.

3. The fast current response driving circuit with step-down output voltage adaptive regulation according to claim 2, characterized in that: The loop compensation module includes an error amplifier and a compensator connected across the error amplifier output and negative input, the negative input of the error amplifier is connected to the LED cathode, and the positive input of the error amplifier is connected to the DC bias reference voltage required by the preset current sink unit.

4. The fast current response driving circuit with step-down output voltage adaptive regulation according to claim 2, characterized in that: The positive input of the comparator module is the output voltage of the loop compensation module, and the negative input of the comparator module is a sawtooth wave. When the sawtooth wave voltage is higher than the output voltage of the loop compensation module, the comparator module outputs a low level, the M1 tube is turned on, the M2 tube is turned off, and the power supply voltage is used to charge the energy storage inductor and supply energy to the LED at the same time; when the sawtooth wave voltage is lower than the output voltage of the loop compensation module, the comparator module outputs a high level, the M1 tube is turned off, the M2 tube is turned on, and the energy storage inductor is discharged to supply energy to the LED.

5. The fast current response driving circuit with step-down output voltage adaptive regulation according to claim 1, characterized in that: The selection module adopts a multiplexer to select one of two, and its two input terminals are respectively connected to the comparator output voltage and the driving event signal; when there is a driving event signal, the event-driven mode is immediately executed, and when the exit condition is met in the event-driven mode, the precise voltage regulation mode is automatically executed.

6. The fast current response driving circuit with step-down output voltage adaptive regulation according to claim 5, characterized in that: In the event-driven mode, the M1 tube is turned on, the M2 tube is turned off, and the output voltage of the DCDC converter rises. When the output voltage rises to a preset value, the event-driven mode is exited.

7. The fast current response driving circuit with step-down output voltage adaptive regulation according to claim 5, characterized in that: In the precise voltage regulation mode described: When the LED cathode voltage is higher than the DC bias reference voltage required by the current sink unit, the output voltage of the loop compensation module increases, the high-level duration of the PWM wave output by the comparator module increases, the low-level duration decreases, the PWM duty cycle increases, the M1 tube opening time increases, the M2 tube opening time decreases, and the output voltage decreases until it drops to the DC bias reference voltage required by the current sink unit, and the output is stable; When the LED cathode voltage is lower than the DC bias reference voltage required by the current sink unit, the output voltage of the loop compensation module decreases, the high-level duration of the PWM wave output by the comparator module decreases and the low-level duration increases, the PWM duty cycle decreases, the M1 tube turn-on time decreases, the M2 tube turn-on time increases, and the output voltage rises until it reaches the DC bias reference voltage required by the current sink unit, and the output is stable.

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