TWM601945U - LED backlight driving circuit and control chip applied in the same - Google Patents

Abstract

This creation provides an LED (Light Emitting Diode) backlight driving circuit and a control chip for the circuit. In the control chip, the reference voltage module receives the analog dimming signal and provides the processed analog dimming signal; the loop compensation module generates the first signal based on the processed analog dimming signal and the LED current detection signal; pulse width The modulating dimming module receives an enable or PWM (Pulse Width Modulation) dimming signal to generate a second signal; the logic control module is based on the first signal, the second signal, and the third signal from the oscillator module Signal and current detection signal to generate a control signal; the drive module generates a drive signal based on the control signal and provides it to the GATE pin; the gate of the internal MOS is connected to the pulse width modulation dimming module, and the drain is connected to the LED pin and The source is connected to the FB pin; the output overvoltage protection module is connected to the CS/OVP pin to receive signals to detect whether the circuit system enters the output overvoltage state.

Description

LED backlight driving circuit and control chip used for the circuit

This creation generally relates to the field of light-emitting diode (LED, Light Emitting Diode) drive circuits, and more specifically to LED backlight drive circuits and control chips used in the circuits.

With the development of LED drive technology, under the premise of ensuring performance, the pursuit of lower cost and higher integration has become the consensus of the industry.

For example, FIG. 1 shows an example of a conventional LED backlight driving scheme 100. In the conventional LED backlight driving scheme 100, in order to achieve loop stability, a resistor R5 and a capacitor C3 for loop compensation need to be set, and in order to achieve pulse width modulation (PWM, Pulse Width Modulation) dimming, it needs to be set Dimming field effect transistor (MOS) Q2, in order to achieve analog dimming, an auxiliary filter capacitor C4 is required. Therefore, in the traditional LED backlight driving solution, more auxiliary devices need to be arranged around the chip, and the chip (for example, chip U) itself needs more functional pins, which increases the system complexity and improves the system cost.

In view of one or more of the above-mentioned problems, this creation provides a novel LED backlight driving circuit and a control chip for the circuit.

According to an aspect of the present creation, a control chip for an LED backlight driving circuit is provided. The control chip includes: a reference voltage module, a loop compensation module, a logic control module, a drive module, an oscillator module, a pulse width modulation dimming module, an output overvoltage protection module, and an internal MOS. The reference voltage module receives the analog dimming signal through the analog dimming signal input pin, and provides the processed analog dimming signal to the loop compensation module; the loop compensation module is based on the processed analog dimming signal and Feedback the LED current detection signal of the pin to generate the first signal; The pulse width modulation dimming module receives the enable or pulse width modulation dimming signal through the enable or pulse width modulation dimming signal input pin to generate a second signal; the logic control module is based on the first signal, the second signal, and the The third signal of the oscillator module and the current detection signal received by the current detection and output overvoltage protection detection pin are used to generate a control signal; the drive module generates a drive signal based on the control signal and provides it to the drive pin; The gate of the internal MOS is connected to the pulse width modulation dimming module, the drain is connected to the LED pin, and the source is connected to the feedback pin; the output overvoltage protection module is connected to the current detection and output overvoltage protection detection pins , To receive the signal to detect whether the circuit system enters the output over-voltage state; when the control chip is used in the LED backlight drive circuit, the power supply pin is connected to the external voltage input terminal to obtain the required power, and the LED load is connected through the LED pin The negative electrode.

According to another aspect of the present creation, an LED backlight driving circuit including the above-mentioned control chip is provided.

100: Traditional LED backlight drive scheme

200: LED backlight drive circuit

310: Reference voltage module

320: Loop compensation module

330: Logic Control Module

340: drive module

350: Oscillator Module

360: PWM dimming module

370: Internal MOS

380: Output overvoltage protection module

410,420,430,440,450: Waveform

C1: Chip power supply capacitor

C2: output filter capacitor

C3: Capacitance

C4: auxiliary filter capacitor

CS/OVP: detection pin

D1: Freewheeling diode

FB: Feedback pin

GATE: drive pin

GND: reference ground pin

HPWM: Analog dimming signal input pin

I _LED : working current

L1: Power inductor

LED: Drain pin

LPWM: enable or pulse width modulation (PWM) dimming signal input pin

Q1: Power power MOS field effect transistor

Q2: Dimming Field Effect Transistor (MOS)

R1: LED current detection resistor

R2, R3: Output overvoltage protection (OVP) resistance

R4: current sense resistor

R5: resistance

S _GATE : drive signal

U: chip

U1: control chip

V _IN : DC power supply

VDD: power supply pin

This creation can be better understood from the following description of the specific implementation of the creation in conjunction with the drawings. Similar reference signs in the drawings generally refer to the same components in different views, in which:

Figure 1 shows an example of a conventional LED backlight driving scheme.

Fig. 2 shows a schematic diagram of an LED backlight driving circuit according to an embodiment of the present creation.

Fig. 3 shows a schematic block diagram of a control chip for an LED backlight driving circuit according to an embodiment of the present creation.

FIG. 4 shows an example signal timing diagram when the LED backlight driving circuit according to the embodiment of the present creation works.

The features and exemplary embodiments of various aspects of the present creation will be described in detail below. In the following detailed description, many specific details are proposed in order to provide a comprehensive understanding of this creation. However, it is obvious to those skilled in the art that this creation can be done without these specific Some details are implemented in the case of details. The following description of the embodiments is only to provide a better understanding of the present creation by showing an example of the present creation. This creation is by no means limited to any specific structures, elements and configurations proposed below, but covers any modification, replacement and improvement of the structures, elements and configurations without departing from the spirit of the creation. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessary obscurity of the creation.

FIG. 2 shows a schematic diagram of an LED backlight driving circuit 200 (in a solid line frame) according to an embodiment of the present creation. The LED backlight driving circuit 200 may include, for example, a control chip U1, a power inductor L1, a power power MOS field effect transistor Q1, a freewheeling diode D1, a chip power supply capacitor C1, an output filter capacitor C2, and an LED current detection resistor R1, output Over Voltage Protection (OVP, Over Voltage Protection) resistors R2 and R3, current detection resistor R4 and so on.

Specifically, as shown in FIG. 2, the control chip U1 may include the following pins, for example:

LPWM pin-also known as enable or pulse width modulation (PWM) dimming signal input pin, configured to receive external enable or PWM dimming signal;

HPWM pin ─ ─ also known as analog dimming signal input pin, configured to receive external analog dimming signal;

FB pin ─ ─ also called feedback pin, is configured to receive LED current detection signal;

LED pin──connect to the drain of the internal MOS of the chip;

The GND pin is the reference ground pin of the control chip U1, which is configured to connect the control chip U1 to the chip ground;

The CS/OVP pin is also called the current detection and output overvoltage protection detection pin, which can play a dual role of current detection and output overvoltage protection.

GATE pin-also called drive pin, is configured to output drive signal.

The VDD pin is the chip power supply pin of the control chip U1.

The LED backlight driving circuit 200 is shown as a Boost circuit (also referred to as a "boost chopper circuit"). One end of the power inductor L1 is configured to be connected to a DC power supply (V _IN ). Optionally, a fuse can be connected between the power inductor L1 and the power supply to protect the circuit. The other end of the power inductor L1 is connected to the positive electrode of the freewheeling diode D1; the negative electrode of the freewheeling diode D1 is connected to one end of the output filter capacitor C2; the other end of the output filter capacitor C2 is grounded.

The gate of the power power MOS field effect transistor Q1 is connected to the GATE pin of the control chip U1, and its drain terminal is connected between the power inductor L1 and the positive pole of the freewheeling diode D1, and its source is connected to the current detection resistor R4 Ground.

A terminal for connecting the positive electrode of the LED load is provided between the negative electrode of the freewheeling diode D1 and the output filter capacitor C2. When the LED backlight driving circuit 200 is used to drive the LED load, the positive electrode of the LED load is connected to this terminal, and the negative electrode of the LED load is connected to the LED pin of the control chip U1. The LED load here may be, for example, an LED lamp used to provide a backlight for devices such as a display screen, or may be other forms of LEDs, which are not specifically limited here.

The VDD pin of the control chip U1 is configured to receive an external DC voltage signal (VDD). The VDD pin of the control chip U1 can be connected to the chip power supply capacitor C1, and the other end of the chip power supply capacitor C1 is connected to the chip ground.

One end of the LED current detection resistor R1 is connected to the FB pin of the control chip U1, and the other end is grounded.

The GND pin of the control chip U1 is connected to the chip ground.

One end of the OVP resistor R2 is connected to the CS/OVP pin of the control chip U1, and the other end is connected between the power inductor L1 and the positive pole of the freewheeling diode D1. One end of the OVP resistor R3 is connected to the CS/OVP pin of the control chip U1, and the other end is connected between the power MOS field effect transistor Q1 and the current detection resistor R4.

The working scene of the LED backlight driving circuit 200 will be further described below in conjunction with FIGS. 3 and 4.

FIG. 3 shows a schematic block diagram of the control chip U1 of the LED backlight driving circuit 200. As shown in the figure, the control chip U1 may include a reference voltage module 310, a loop compensation module 320, a logic control module 330, a driving module 340, an oscillator module 350, a PWM dimming module 360, and an internal MOS 370 , And output overvoltage protection module 380 and so on. The above various modules are only It is an example, and according to actual needs, the control chip U1 may also include other functional modules under appropriate circumstances, which is not specifically limited here.

The reference voltage module 310 receives the analog dimming signal through the HPWM pin, and provides the processed analog dimming signal to the loop compensation module 320.

The loop compensation module 320 generates a first signal based on the processed analog dimming signal and the LED current detection signal from the FB pin.

The PWM dimming module 360 receives the LPWM signal through the LPWM pin, and generates a second signal.

The logic control module 330 is configured to be based on the first signal from the loop compensation module 320, the second signal from the PWM dimming module 360, the third signal from the oscillator module 350, and the CS/OVP trigger The current detection signal received by the pin generates a control signal and outputs the control signal to the driving module 340.

The driving module 340 generates a driving signal based on the control signal and provides it to the GATE pin.

The gate of the internal MOS 370 is connected to the PWM dimming module 360, its drain is connected to the LED pin, and its source is connected to the FB pin.

The output overvoltage protection module 380 is connected to the CS/OVP pin to receive signals to detect whether the circuit system (for example, the LED backlight driving circuit system applying the control chip U1) enters the output overvoltage state.

As shown in Figure 3, the PWM dimming MOS is integrated inside the control chip U1, eliminating the need for analog dimming filter capacitors (such as the auxiliary filter capacitor C4 in Figure 1), and the loop compensation module is set Loop compensation is integrated in the control chip. The control chip U1 reduces the function pins through the multiplexing of CS/OVP, that is, when the power power MOS field effect transistor Q1 is turned on, it detects the power MOS field effect transistor current and performs loop control. When transistor Q1 is turned off, the output voltage is detected. The control chip U1 reduces the function pins and the auxiliary devices around the system, so that the overall volume of the LED backlight driving circuit can be reduced, the system integration level is improved, and the system cost is reduced.

The basic working principle of the LED backlight driving circuit 200 will be described below in conjunction with FIG. 4. Figure 4 shows a timing diagram of the main signals involved in the operation of the LED backlight driving circuit 200 over time. The waveform 410 indicates the chip power supply voltage (VDD) of the control chip U1, and the waveform 420 indicates the enable or PWM dimming signal ( LPWM), the waveform 430 indicates the analog dimming signal (HPWM), the waveform 440 indicates the driving signal (S _GATE ) output at the GATE pin of the control chip U1, and the waveform 450 indicates the operating current of the _LED (I _LED ).

When the LED backlight driving circuit 200 is working, the control chip U1 control system works in a constant current state, and its compensation loop is all integrated inside the chip, for example, the loop compensation module 320 shown in FIG. 3.

The control chip U1 uses the logic control module 330 to control the entire loop based on the LPWM signal received through the LPWM pin, and uses the internal MOS 370 to control the on and off of the LED load to achieve PWM dimming control.

The control chip U1 uses the reference voltage module 310 to convert it into the reference voltage of the output current inside the chip according to the working factor of the analog dimming signal received through the HPWM pin, so that the LED load current follows the working factor of the analog dimming signal Change to complete the analog dimming control.

The system can work in both PWM dimming and analog dimming modes at the same time to flexibly realize various dimming requirements.

The control chip provided by this creation integrates the PWM dimming MOS inside the chip, omitting the auxiliary filter capacitor in the traditional LED backlight driving scheme, and integrates the loop compensation module inside the control chip, and at the same time, through pin multiplexing Reducing the pins of the chip reduces the overall volume of the LED backlight driving circuit, improves system integration, and reduces system cost.

This creation can be realized in other concrete forms without departing from its spirit and essential characteristics. The current embodiment is regarded as illustrative rather than restrictive in all aspects. The scope of this creation is defined by the scope of the attached patent application rather than the above description, and falls within the meaning and equivalent of the scope of the patent application. All changes within the scope are thus included in the scope of this creation.

200: LED backlight drive circuit

C1: Chip power supply capacitor

C2: output filter capacitor

CS/OVP: detection pin

D1: Freewheeling diode

FB: Feedback pin

GATE: drive pin

GND: reference ground pin

HPWM: Analog dimming signal input pin

L1: Power inductor

LED: Drain pin

ENA/LPWM: enable or pulse width modulation (PWM) dimming signal input pin

Q1: Power power MOS field effect transistor

R1: LED current detection resistor

R2, R3: Output overvoltage protection (OVP) resistance

R4: current sense resistor

U1: control chip

V _IN : DC power supply

VDD: power supply pin

Claims (10)

A control chip for LED backlight driving circuit, including: Reference voltage module, loop compensation module, logic control module, drive module, oscillator module, pulse width modulation dimming module, output overvoltage protection module, and internal MOS; The reference voltage module receives the analog dimming signal through the analog dimming signal input pin (HPWM) of the control chip, and provides the processed analog dimming signal to the loop compensation module; The loop compensation module generates a first signal based on the processed analog dimming signal and the LED current detection signal from the feedback pin (FB) of the control chip; The pulse width modulation dimming module receives the enable or pulse width modulation dimming signal through the enable or pulse width modulation dimming signal input pin (LPWM) of the control chip, and generates a second signal; The logic control module is configured to be based on the first signal, the second signal, the third signal from the oscillator module, and the current detection through the control chip and the output overvoltage protection detection guide Pin (CS/OVP) receives the current detection signal to generate the control signal; The driving module generates a driving signal based on the control signal from the logic control module and provides it to the driving pin (GATE) of the control chip; The gate of the internal MOS is connected to the pulse width modulation dimming module, the drain of the internal MOS is connected to the LED pin (LED) of the control chip, and the source of the internal MOS is connected to The feedback pin (FB); The output overvoltage protection module is connected to the current detection and output overvoltage protection detection pin (CS/OVP) to receive a signal to detect whether the circuit system enters an output overvoltage state; and When the control chip is used in an LED backlight driving circuit, the power supply pin (VDD) is connected to the external voltage input terminal to obtain the required power, and the LED pin (LED) is connected to the negative electrode of the LED load. The control chip according to claim 1, further comprising: for connecting the control chip to The reference ground pin (GND) of the chip ground. An LED backlight driving circuit includes: the control chip as described in claim 1 or 2. The LED backlight driving circuit according to claim 3, comprising a first resistor for LED current detection, one end of the first resistor is connected to the feedback pin (FB) of the control chip and the other end is connected to Chip ground; and The loop compensation module of the control chip is configured to ensure that the LED backlight driving circuit operates in a constant current state based on the LED current detection signal of the feedback pin (FB). The LED backlight driving circuit according to claim 3 includes a chip power supply capacitor, one end of the chip power supply capacitor is connected to the power supply pin (VDD) of the control chip and the other end is connected to the chip ground. The LED backlight driving circuit according to claim 3, wherein the LED backlight driving circuit is a Boost circuit, and the LED backlight driving circuit further includes a power inductor, a freewheeling diode, an output filter capacitor, a current detection resistor, and Power electric MOS field effect transistor; Wherein, one end of the power inductor is connected to the input voltage terminal, the other end of the power inductor is connected to the positive electrode of the freewheeling diode, and the negative electrode of the freewheeling diode is connected to the output filter capacitor. One end, the other end of the output filter capacitor is grounded; The gate of the power power MOS field effect transistor is connected to the drive pin (GATE) of the control chip, and the drain of the power power MOS field effect transistor is connected to the inductor and the diode Between the positive poles of the body, and the source of the power power MOS field effect transistor is grounded via the current detection resistor; and Wherein, a terminal for connecting the positive electrode of the LED load is provided between the negative electrode of the freewheeling diode and the output filter capacitor. The LED backlight driving circuit according to claim 6, wherein the logic control module is configured to control the LED backlight driving circuit based on the second signal. The LED backlight driving circuit according to claim 6 is configured to use the internal MOS to control the on and off of the LED load. The LED backlight driving circuit according to claim 6, wherein the reference voltage module is It is configured to convert the analog dimming signal into a reference voltage of the output current inside the control chip according to the working factor of the analog dimming signal, so that the current of the LED load follows the change of the analog dimming signal Work factor changes. The LED backlight driving circuit according to claim 6, further comprising a second resistor and a third resistor: One end of the second resistor is connected to the current detection and output overvoltage protection detection pin (CS/OVP) of the control chip, and the other end of the second resistor is connected to the power inductor and the freewheeling Between the positive poles of the diode; and One end of the third resistor is connected to the current detection and output overvoltage protection detection pin (CS/OVP) of the control chip, and the other end of the third resistor is connected to the power power MOS field effect transistor Between the source and the current detection resistor.

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