CN201307826Y - LCD-TV power supply voltage detecting circuit - Google Patents

Abstract

The utility model discloses an LCD-TV power supply voltage detecting circuit, comprising a PWM master chip, a triode Q2 connected with the PWM master chip, an N-channel MOS pipe Q1 connected with the triode Q2 by a fifth resistance, and a second resistance R2, a third resistance R3 and a fourth resistance R4 which are connected with the grid (G) of the N-channel MOS pipe Q1. The PFC output voltage is detected by a voltage detecting network, under the conditions that the voltage of the electrical network is low and a power factor corrector (PFC) circuit is not started, a switching network composed of the N-channel MOSFET and the PNP triode is cut off by resistance sampling, a power supply circuit is disconnected with power supplying pin positions of PWF IC (DC/DC circuit), and the PWF (DC/DC circuit) circuit stops working, thereby ensuring stability of the power supply and improving the performance of a television.

Description

A LCD-TV power supply voltage detection circuit

【Technical field】

The utility model relates to the technical field of television sets, in particular to an LCD-TV power supply voltage detection circuit applied to an LCD-TV power supply.

【Background technique】

In order to ensure the safety, reliability and durability of the LCD-TV power supply, it is necessary to make it work under the working conditions required by the circuit, but often due to many unpredictable factors (power grid factors or abnormal circuit operation, etc.) condition. For example: the grid power supply is insufficient, the power supply department adopts step-down power supply, or it is located in a remote area, and the loss is too much, resulting in low AC voltage. If the power factor corrector (PFC) circuit does not start at this time, it will cause the load to fail. normal work. In the long run, the magnetic core of the transformer will be saturated, and further, the MOSFET will be broken down and the IC will be damaged, which will cause power failure and cause the instability of the TV. Therefore, the design of the detection circuit is an indispensable and important link.

【Content of utility model】

In order to solve the above problems, the main purpose of this utility model is to provide a LCD-TV power supply voltage detection circuit.

To achieve the above object, the technical solution of the utility model is:

An LCD-TV power supply voltage detection circuit, comprising a PWM main chip, a transistor Q2 connected to the PWM main chip, an N-channel MOS transistor Q1 connected to the transistor Q2 through a fifth resistor R5, and a gate connected to the N-channel MOS transistor Q1 The second, third, and fourth resistors R2, R3, and R4 connected to pole (G).

Further, the second resistor R2 is connected in series with a first resistor R1, and then connected to the PFC output through the diode D1.

Further, the third and fourth resistors R3 and R4 are connected in parallel with the first capacitor C1 to be grounded together with the source (S) of the N-channel MOS transistor Q1.

Further, one end of the fifth resistor R5 is connected to the drain (D) of the N-channel MOS transistor Q1 , and the other end is connected to the base of the triode Q1 .

Compared with the prior art, the LCD-TV power supply voltage detection circuit of the utility model detects the PFC output voltage through the voltage detection network. The switching network composed of N-channel MOSFET and PNP transistor is turned off, so that the power supply circuit is disconnected from the power supply pin of the PWMIC (DC/DC circuit), and the PWM (DC/DC) circuit stops working to ensure the stability of the LCD power supply and improve TV performance.

【Description of drawings】

Fig. 1 is the circuit schematic diagram of the LCD-TV power supply voltage detection circuit of the utility model.

【Detailed ways】

Please refer to Fig. 1, a kind of LCD-TV power supply voltage detection circuit of the utility model mainly utilizes the switch network that N-channel MOS transistor Q1 and three-stage transistor Q2 are combined to carry out the detection of LCD-TV power supply PFC output voltage, including The main PWM chip, the triode Q2 connected to the PWM main chip, the N-channel MOS transistor Q1 connected to the triode Q2 through the fifth resistor R5, and the second and third transistors connected to the gate (G) of the N-channel MOS transistor Q1 , the fourth resistors R2, R3, R4. Wherein, the second resistor R2 is connected in series with a first resistor R1, and then connected to the PFC output through a diode D1; the third and fourth resistors R3, R4 are connected in parallel with the first capacitor C1 and connected to the source of the N-channel MOS transistor Q1 (S ) are commonly grounded; one end of the fifth resistor R5 is connected to the drain (D) of the N-channel MOS transistor Q1, and the other end is connected to the base of the transistor Q1; the sixth resistor R6 is connected in parallel with the second capacitor C2, and one end is connected to the transistor Q1 The other end is connected to the emitter of the triode Q1, and connected to the power supply Vcc through a resistor R7. The transistor Q2 is an NPN transistor, and its collector is connected to the power supply pin of the PWM main chip.

When the power grid is working normally, the output AC is 220V, and the voltage rises to DC 380-400V after bridge rectification and the power factor corrector (PFC) boost circuit in the LCD-TV power supply. At this time, the PFC output voltage is 380-400V After being sampled by the pull-up resistor (the first resistor R1 and the second resistor R2 connected in series) and the pull-down resistor (the third resistor R3), the voltage is within the range of VGS(th) (threshold voltage) of the N-channel MOS transistor Q1, The N-channel MOS transistor Q1 is saturated and turned on, and the drain voltage is pulled to a low potential. After the voltage is limited by the fourth resistor R4, it gives the NPN transistor Q1 a low-potential conduction signal, and the transistor Q1 is saturated and turned on. The VCC power grid supplies the PWM chip ( DC/DC circuit) power supply, the power supply works normally.

When the grid power supply is insufficient, the power supply department adopts step-down power supply, or is located in a remote area, and the loss is too much, resulting in low AC voltage. At this time, the power factor corrector (PFC) circuit of the power supply is not activated. If the main circuit (DC/ DC part) continues to work, the load will work abnormally, and the reliability and durability of the power supply will be reduced in the long run. In this case, we can calculate that the PFC output voltage is about 155V, and select it according to this reference voltage parameters of the sampling circuit. After sampling, the gate voltage of the N-channel MOS transistor Q1 is 1V, which is just at the lower limit of VGS(th). That is to say, if the AC voltage is lower than 110V and the PFC circuit is not activated, the N-channel MOS transistor Q1 is turned off. No low level is provided to the NPN transistor Q1, the power supply of the PWM main chip (DC/DC circuit part) is disconnected, and the power supply has no output, which serves the purpose of protecting the power supply.

Detect the PFC output voltage through the voltage detection network. When the grid voltage is very low and the power factor corrector (PFC) circuit is not started, the switch network composed of N-channel MOS transistor Q1 and PNP transistor Q2 is turned off through resistance sampling. In this way, the power supply circuit is disconnected from the power supply pin of the PWM IC (DC/DC circuit), and the PWM (DC/DC) circuit stops working, so as to protect the power supply.

The best embodiment described above is only to set forth and illustrate the utility model, but is not limited to any specific form disclosed, and many modifications and changes are possible.

Claims (6)

1. LCD-TV voltage detection circuit, comprise the PWM master chip, it is characterized in that: the N-channel MOS pipe (Q1) that also include the triode (Q2) that connects the PWM master chip, is connected by the 5th resistance (R5) with triode (Q2) and be connected with the grid (G) of N-channel MOS pipe (Q1) second, third, the 4th resistance (R2), (R3), (R4).

2. LCD-TV voltage detection circuit as claimed in claim 1 is characterized in that: second resistance (R2) is in series with one first resistance (R1), connects PFC output by diode (D1) then.

3. LCD-TV voltage detection circuit as claimed in claim 2 is characterized in that source electrode (S) common ground of the 3rd, the 4th resistance (R3), (R4) back in parallel with first electric capacity (C1) and N-channel MOS pipe (Q1).

4. LCD-TV voltage detection circuit as claimed in claim 3 is characterized in that: the 5th resistance (R5) end is connected with the leakage level (D) of N-channel MOS pipe (Q1), and the other end links to each other with the base stage of triode (Q1).

5. LCD-TV voltage detection circuit as claimed in claim 4, it is characterized in that: also include the 6th resistance (R6) and second electric capacity (C2), described the 6th resistance (R6) is connected the base stage of triode (Q1) with second electric capacity (C2) back in parallel, one end, the other end connects the emitter of triode (Q1), and connects power Vcc by a resistance (R7).

6. LCD-TV voltage detection circuit as claimed in claim 5 is characterized in that: triode (Q2) is the NPN triode, and its collector electrode is connected to the power supply pin of PWM master chip DC/DC part.

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