CN201388317Y - LCD backlight driver power saving circuit - Google Patents

Abstract

The utility model relates to an LCD backlight drive power-saving circuit, which comprises a DC/DC step-up converter, and several light-emitting diodes (LEDs) and detection resistors are connected in series between the voltage output terminal of the DC/DC step-up converter and the ground. R, the DC/DC boost converter is connected to the reference voltage V _REF , the feedback terminal of the DC/DC boost converter is connected to resistor R1 and resistor R2, the other end of resistor R2 is connected to the calibration voltage V _REG , the standard voltage V _REG The voltage value is greater than the voltage value of the reference voltage V _REF , the other end of the resistor R1 is connected to the connection point of the light-emitting diode LED and the detection resistor R, and the feedback reference voltage of the original DC/DC boost converter is not changed. By adding resistor components and changing The position of the feedback point is used to reduce the voltage drop of the original detection resistor, which improves the efficiency of the power supply as a whole and achieves the effect of saving power.

Description

LCD backlight driver power saving circuit

technical field

The utility model relates to a power-saving circuit, in particular to an LCD backlight driving power-saving circuit, which belongs to the field of electronic technology.

Background technique

Hand-held communication devices such as GSM mobile phones, e-books, PDAs, and color screen LCD backlights of digital cameras are all realized by high-brightness light-emitting diodes. LEDs can make color display more realistic, small in size and long in life. , environmental protection and other advantages, the uniform backlight of a color screen LCD requires 3 to 4 or more white light-emitting diodes LEDs, and driving the light-emitting diodes LEDs requires a constant current source, and the current size is generally 15mA to 20mA.

The current commonly used light-emitting diode LED drive circuit is shown in Figure 1. In the circuit design, a DC/DC step-up converter is required to stabilize the current of the light-emitting diode LED in a constant range for a long period of time. . The voltage output terminal of the DC/DC step-up converter is grounded after being connected in series with multiple light-emitting diodes LED and detection resistor R, and the other end of the detection resistor R is connected to the feedback terminal of the DC/DC step-up converter. The internal or external reference voltage V _REF of the type converter, when the output voltage V _OUT exceeds the sum of the forward voltage drops of the LEDs connected in series, the LED starts, and the brightness of the LED depends on its forward current , The DC/DC boost converter compares the detection voltage across the detection resistor R with the reference voltage V _REF of the DC/DC converter to form a closed feedback loop to control the brightness of the light-emitting diode LED. At this time, the feedback resistor is the detection resistor R. When adjusting the brightness of the light-emitting diode LED, the magnitude of the current is generally changed by adjusting the size of the detection resistor R. The magnitude of the current depends on the size of the feedback resistor and the voltage of the feedback point, I=feedback point voltage V/feedback resistor R, in order to save power, the current must be reduced, and the voltage of the feedback point DC/DC boost converter Generally, it is fixed and not easy to change, so it is necessary to increase the detection resistor R. For the constant current source, the smaller the feedback resistance, the better, and the larger the detection resistance R, the greater the power loss on the detection resistance R.

Utility model content

The problem to be solved by the utility model is to provide an LCD backlight drive power-saving circuit capable of reducing gratuitous loss, high power supply efficiency and saving power energy.

In order to solve the above problems, the technical solution adopted in the utility model is: LCD backlight drive power-saving circuit, the power-saving circuit includes a DC/DC step-up converter, the voltage output terminal of the DC/DC step-up converter Several light-emitting diodes LEDs and detection resistors R are connected in series between the ground and the DC/DC step-up converter connected to the reference voltage V _REF , characterized in that: the feedback termination resistor R1 of the DC/DC step-up converter and resistor R2, the other end of the resistor R2 is connected to the calibration voltage V _REG , the voltage value of the standard voltage V _REG is greater than the voltage value of the reference voltage V _REF , the other end of the resistor R1 is connected to the connection between the light-emitting diode LED and the detection resistor R point.

The utility model adopts the above technical scheme and has the following advantages: without changing the feedback reference voltage of the original DC/DC step-up converter, the voltage drop of the original detection resistor is reduced by adding resistance components and changing the position of the feedback point, so that the battery can be Working under lower voltage output conditions than before, the overall efficiency of the power supply is improved, the working time of the battery is extended, and the effect of power saving is achieved.

Below in conjunction with accompanying drawing and embodiment the utility model is further described.

Description of drawings

Accompanying drawing 1 is the circuit diagram of LCD backlight drive circuit in the prior art;

Accompanying drawing 2 is the LCD backlight driving circuit circuit diagram in the utility model embodiment.

Detailed ways

Embodiment: As shown in accompanying drawing 2, the LCD backlight drive power saving circuit comprises a DC/DC step-up converter, and a plurality of light-emitting diodes LED and detection resistor R are connected in series to the voltage output of the DC/DC step-up converter Between terminal and ground, the DC/DC boost converter is externally connected to the reference voltage V _REF , the feedback terminal is connected to resistors R1 and R2, and the other end of resistor R2 is connected to the calibration voltage V _REG , the voltage value of the calibration voltage V _REG is greater than the reference voltage The voltage value of V _REF , the other end of the resistor R1 is connected to the connection point of the light-emitting diode LED and the detection resistor R, and the voltage value of the feedback end of the DC/DC step-up converter remains unchanged during the working process. There is an operational amplifier inside the DC/DC boost converter, the reference voltage V _REF is connected to the reverse terminal of the operational amplifier, and the feedback terminal is the non-inverting terminal of the operational amplifier. According to the principle of virtual short and virtual break of the operational amplifier, the formula can be obtained: (V _REF −R×I light emitting diode LED)/R1=(V _REG −V _REF )/R2, it can be obtained that the current I light emitting diode LED and the calibration voltage V _REG have a proportional relationship. Adjusting the calibration voltage V _REG can reduce or increase the magnitude of the current.

When adjusting the brightness of the light-emitting diode LED, the calibration voltage V _REG is several times the reference voltage V _REF , the value of the resistor R1 and resistor R2 is generally tens of K to hundreds of K, and the current flowing through it is in the microampere level. The power loss in resistor R1 and resistor R2 is very small. Change the current size of I light-emitting diode LED by changing the size of V _REG . In order to save power, when the current of the light-emitting diode LED is reduced, the size of the detection resistor R remains unchanged, and the power loss is smaller than that of changing the resistance to adjust the brightness. At the same time, since the feedback reference voltage of the DC/DC converter has not changed, the voltage on the detection resistor R is lower than the feedback reference voltage value at this time, the conduction range of the light-emitting diode LED is wider than the original one, and the output of the DC/DC converter The voltage V _OUT can be reduced, so that the battery can work at a lower voltage output than the original condition, and prolong the working time of the battery.

Claims (1)

1, LCD backlight drive power save circuit, described power save circuit comprises a DC/DC boosting type converter, be in series with several LEDs between the voltage output end of DC/DC boosting type converter and the ground and detect resistance R, the DC/DC boosting type converter meets reference voltage V _REF, it is characterized in that: the feedback end connecting resistance R1 of described DC/DC boosting type converter and resistance R 2, another termination calibration voltage V of described resistance R 2 _RFG, described normal voltage V _RFGMagnitude of voltage greater than reference voltage V _REFMagnitude of voltage, the other end sending and receiving optical diode LED of resistance R 1 and the tie point that detects resistance R.

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