CN101742188B - LCD (Liquid Crystal Display)-TV power supply voltage detection circuit - Google Patents

Abstract

The present invention is applicable to the electronic field and provides an LCD-TV power supply voltage detection circuit, including a voltage stabilization control circuit and a switch control circuit connected to the voltage stabilization control circuit, wherein the voltage stabilization control circuit is also connected with an AC voltage detection circuit to detect AC input voltage, the AC voltage detection circuit includes a first rectifier tube, first, second and third pull-up resistors R1, R2, R3 and pull-down resistor R4 connected in series, connected to the third, The precision potentiometer U1 at the node between the fourth resistors R3 and R4 , the first voltage regulator transistor V1 connected to the precise voltage regulator U1 , and the first triode Q1 connected to the first voltage regulator transistor V1 . The AC input voltage is detected by the AC voltage detection circuit, and when the voltage is lower than the minimum AC voltage for reliable operation of the power supply, the power supply of the main circuit of the power supply and the PFC circuit is turned off, thereby achieving the purpose of stopping the power supply and protecting the power supply circuit.

Description

A LCD-TV power supply voltage detection circuit

technical field

The invention belongs to the technical field of televisions, in particular to an LCD-TV power supply voltage detection circuit.

Background technique

At present, LCD-TV (liquid crystal television) has rapidly increased its penetration rate in the market by virtue of its large screen, low thickness and high definition. LCD TV has become more and more popular with many consumers, and its market share has continued to rise. high. However, while the LCD TV market continues to grow and develop, its power supply has also attracted more attention. Because the power supply varies greatly in many areas, the power supply in some areas is insufficient, and the power supply department has to adopt step-down power supply. In some remote areas, the loss is too much, resulting in low AC voltage, which will cause the load to not work normally. At present, most power supply products are designed with a power factor corrector in the circuit. Through its boost function, liquid crystal power supply products can work relatively reliably between the AC input voltage of 110-240Vac, but if the power grid voltage is lower than the AC 110Vac voltage, it will cause the load not to work properly. In the case of long-term load failure, the reliability of the power supply will be reduced and the life of the power supply will be shortened.

Contents of the invention

The purpose of the embodiments of the present invention is to provide a LCD-TV power supply voltage detection circuit, which detects the AC input voltage, and shuts off the power supply of the main circuit of the power supply and the PFC circuit when the voltage is lower than the minimum AC voltage for reliable operation of the power supply, so that the power supply stops working. to protect the power circuit.

The embodiment of the present invention is realized in the following way. An LCD-TV power supply voltage detection circuit includes a voltage stabilization control circuit and a switch control circuit connected to the voltage stabilization control circuit, wherein the voltage stabilization control circuit is also connected with an AC voltage detection circuit to detect AC input voltage, the AC voltage detection circuit includes a first rectifier tube, first, second and third pull-up resistors R1, R2, R3 and pull-down resistor R4 connected in series, connected to the third, The precision potentiometer U1 at the node between the fourth resistors R3 and R4 , the first voltage regulator transistor V1 connected to the precise voltage regulator U1 , and the first triode Q1 connected to the first voltage regulator transistor V1 .

In the embodiment of the present invention, the AC input voltage is detected by the AC voltage detection circuit, and the power supply of the main circuit of the power supply and the PFC circuit is turned off when the voltage is lower than the minimum AC voltage for reliable operation of the power supply, thereby achieving the purpose of stopping the power supply and protecting the power supply circuit.

Description of drawings

Fig. 1 is a schematic block diagram of the LCD-TV power supply voltage detection circuit of the present invention.

Fig. 2 is a schematic circuit diagram of the LCD-TV power supply voltage detection circuit of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Fig. 1 shows the principle block diagram of the LCD-TV power supply voltage detection circuit of the present invention, including a voltage stabilization control circuit and a switch control circuit connected to the voltage stabilization control circuit. Among them, the voltage stabilization control circuit is also connected with an AC voltage detection circuit to detect the AC input voltage. When it is detected that the input AC voltage of the power grid is lower than the reliable voltage, the voltage stabilization control circuit has no voltage output to the main circuit and the PFC circuit. Not working, so the power supply stops working, which plays a role in protecting the power supply.

Fig. 2 shows the circuit schematic diagram of the LCD-TV power supply voltage detection circuit of the present invention, wherein, the AC voltage detection circuit comprises a first rectifier tube, pull-up resistors first, second and third resistors R1, R1, and R1 connected in series. R2, R3 and the pull-down resistor fourth resistor R4, and the first capacitor C1 connected in parallel with the first, second, third, and fourth resistors R1, R2, R3, and R4 connected in series are connected to the third and fourth The precise potential regulator U1 of the node between the four resistors R3 and R4, the first voltage regulator tube V1 and the second rectifier tube D2 connected to the precise potential regulator U1, and the first voltage regulator tube V1 and the second rectifier tube D2 connected to the first transistor Q1. The R foot of U1 is connected to one end of the third resistor R3, and the other end of the third resistor R3 is connected in series with the first and second resistors R1 and R2, and the other end of the first resistor R1 is connected to one end (negative) of the first rectifier tube D1. The other end of a rectifier tube D1 (positive) is connected to the AC signal, and one end of the first capacitor C1 is connected to one end of the first rectifier tube D1 (negative) and the other end is grounded; the R pin of the precise potentiometer U1 is also connected to the fourth resistor R4 One end, the other end of the fourth resistor R4 is connected to the thermal ground, and the R pin of the precision potentiometer U1 is also connected to one end of the sixth resistor R6, and the other end of the sixth resistor R6 is connected to the second rectifier tube D2 (negative). The A pin of the precise potentiometer U1 is grounded, and the K pin of the precise potentiometer U1 is respectively connected to one end of the fifth resistor R5 and one end (negative) of the first regulator tube V1, and the other end of the fifth resistor R5 is connected to the regulator control Circuit, one end (forward) of the first regulator tube V1 is connected to one end of the seventh resistor R7 of the current limiting resistor; one end (forward) of the second rectifier tube D2 is connected to the collector of the first triode Q1, and the first triode Q1 The collector of the first transistor Q1 is also connected to the voltage regulator control circuit, and the base of the first triode Q1 is respectively connected to the other end of the seventh resistor R7 and one end of the bias resistor R8, and the other end of the eighth resistor R8 is grounded; further, the first The emitter of transistor Q1 is grounded.

The voltage stabilization control circuit includes a second transistor Q2, a second capacitor C2 connected to the base of the second transistor Q2, a second voltage regulator transistor V2, and a ninth resistor R9. Wherein, the emitter of the second triode Q2 is connected to Vcc out, and the collector is connected to the fifth resistor R5 of the AC voltage detection circuit. In addition, the collector of the second triode Q2 is also connected to Vcc in, and the base is also connected to Vcc in. Connect to the collector of the first triode Q1 of the AC voltage detection circuit. The ninth resistor R9 is connected to the switch control circuit, and the ninth resistor R9 is also connected to the ground through the tenth resistor R10, and one end of the second capacitor C2 and the second voltage regulator tube V2 is grounded. The switch control circuit includes a photocoupler U2 connected to the voltage stabilization control circuit, a third triode Q3 connected to the photocoupler U2, and an eleventh resistor R11 connected to the base of the third triode Q3 as a bias resistor and Filter capacitor C3. Wherein, the collector of the third triode Q3 is connected to the photocoupler U2, and the emitter is grounded. In addition, the base of the third triode Q3 is also connected to the ON/OF terminal through the twelfth current limiting resistor R12 and the third rectifier D3.

After the ON/OF power-on control signal passes through the twelfth resistor R12 of the current limiting resistor, under the joint action of the eleventh resistor R11 of the bias resistor and the filter capacitor C3, the third triode is saturated and turned on, and its collector is low Level, the light-emitting diode of the photocoupler U2 emits light, the phototransistor is turned on, Vcc in provides a bias voltage to the second transistor Q2 after passing through the ninth resistor R9 and the tenth resistor R10, and the second transistor Q2 Saturated conduction, the emitter has a supply voltage output, and at the same time, because the base of the second transistor Q2 is connected to the second voltage regulator tube V2, the emitter output voltage of the second transistor Q2 is clamped at the second voltage regulator tube Below the regulated voltage of V2.

When the grid power supply voltage meets the working conditions of the LCD-TV power supply (not less than 110Vac), the AC input voltage is bridge-type rectified and sampled by the sampling resistor, and the voltage is greater than or equal to 2.5Vdc, which makes the precise potentiometer U1 turn on , at this moment, the voltage at point K of the precision potentiometer U1 is at a low level, the first voltage regulator tube V1 cannot be broken down by sodium, and no current flows through the first voltage regulator tube V1, so the first triode Q1 is cut off , the base of the second triode Q2 in the voltage stabilizing control circuit is at a high level, the voltage stabilizing control circuit is normal, there is a supply voltage output, and the power supply works normally. And when the AC input voltage is lower than 110Vac (110Vac is used as the reference point for setting parameters), the AC input voltage is rectified by the bridge, and then rectified by the first rectifier tube D1 and the first, second and third pull-up resistors R1 , R2, R3, and the pull-down resistor fourth resistor R4 after sampling, the voltage at the sampling point is less than 2.5Vdc. Under this voltage, the LM431 is turned off. At this time, Vcc in is divided by the fifth resistor R5 and the first voltage regulator tube V1 is filled with sodium Breakdown, the current flows through the first voltage regulator tube V1, and under the joint action of the seventh resistor R7 of the current limiting resistor and the eighth resistor R8 of the bias resistor R8, the first triode Q1 is saturated and turned on. At this time, the first triode The collector of the tube Q1 is at a low level, which pulls down the base potential of the second transistor Q2 in the voltage stabilization control circuit, resulting in abnormal operation of the voltage stabilization control circuit and no VCC out output. The power chip does not work, which causes the power supply to stop working and is in a protection state. In addition, the sixth resistor R6 and the second rectifier D2 form a compensation circuit to prevent the power supply from malfunctioning at the set point (110Vac) due to parameter errors.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (1)

1. a kind of LCD-TV power supply voltage detection circuit, comprise voltage stabilization control circuit, the switch control circuit that connects voltage stabilization control circuit, it is characterized in that: voltage stabilization control circuit is also connected with AC voltage detection circuit to detect AC input voltage, the The AC voltage detection circuit includes the first rectifier tube (D1), the first, second and third pull-up resistors (R1), (R2), (R3) and the fourth pull-down resistor (R4) connected in series , the precision potentiometer (U1) connected to the node between the third and fourth resistors (R3), (R4), the first voltage regulator tube (V1) connected to the precision potential regulator (U1), and the first A first triode (Q1) connected to a regulator tube (V1); The AC voltage detection circuit also includes a compensation circuit composed of a sixth resistor (R6) and a second rectifier tube (D2), wherein one end of the sixth resistor (R6) is connected to the precision potential regulator (U1), and the other end is connected to the second Rectifier tube (D2); A first capacitor (C1) is connected in parallel with the first, second, third and fourth resistors (R1), (R2), (R3) and (R4) connected in series; The collector of the first triode (Q1) is connected to the voltage stabilization control circuit, and the base is respectively connected to the seventh resistor (R7) of the current limiting resistor and the eighth resistor (R8) of the bias resistor, and the eighth resistor (R8) The other end is commonly grounded with the emitter of the first triode (Q1); The voltage stabilizing control circuit includes a second triode (Q2), a second capacitor (C2) connected to the base of the second triode (Q2), a second voltage stabilizing tube (V2) and a ninth resistor (R9 ); The emitter of the second triode (Q2) is connected to Vcc out, the collector is also connected to Vcc in, and the base is connected to the collector of the first triode (Q1) of the AC voltage detection circuit; The switch control circuit includes a photocoupler (U2) connected to the voltage stabilization control circuit, a third transistor (Q3) connected to the photocoupler (U2), and a third transistor (Q3) connected to the base The bias resistor eleventh resistor (R11) and the filter capacitor (C3); The collector of the third transistor (Q3) is connected to the photocoupler (U2), and the emitter is grounded. In addition, the base of the third transistor (Q3) also passes through the current limiting resistor twelfth resistor (R12) , The third rectifier tube (D3) is connected to the ON/OF terminal.

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