CN201041938Y - A kind of LCD-TV power supply undervoltage protection circuit - Google Patents

Abstract

An LCD-TV power supply undervoltage protection circuit, the circuit mainly includes the first, second, third, and fourth resistors, a triode, a capacitor, a diode, and an integrated chip; the bases of the triode are respectively connected to the first and second resistors, and further the first The resistor is connected to the diode, the other end of the diode is connected to the output terminal of the power supply, and the second resistor is grounded; the collector of the triode is respectively connected to the third and fourth resistors, capacitors, and integrated chips, and the fourth resistor and capacitor are both grounded, and the third resistor is connected to the ground. The resistor is connected with the power supply CPU that sends out the control signal, and the emitter of the triode is grounded.

Description

A kind of LCD-TV power supply undervoltage protection circuit

technical field

The utility model relates to the field of electronic technology, in particular to an LCD-TV power supply undervoltage protection circuit.

Background technique

The design of the protection circuit is undoubtedly a very important link in the design of the power supply. It plays a very important role in improving the safety and reliability of the power supply and prolonging the service life of the power supply. When designing the protection circuit, on the one hand, it is necessary to ensure that its functions are perfect and its work is stable and reliable; on the other hand, it should be simple and clear, and avoid complexity.

In order to ensure the overall usability and reliability of the LCD-TV, various state protections, such as overvoltage, overcurrent, and overvoltage, must be implemented in product performance.

The PWM circuits of common LCD-TV power supplies have over-power protection functions, but none or part of them have over-current, over-voltage and under-voltage protections. To realize over-current, over-voltage and under-voltage protection functions, additional circuits are required.

Utility model content

In view of this, the utility model provides an LCD-TV power supply undervoltage protection circuit, which is mainly used in the LCD-TV power supply, and plays a protective role when the output voltage of the power supply is undervoltage, and effectively protects other circuits and devices.

An LCD-TV power supply undervoltage protection circuit, wherein, the LCD-TV power supply undervoltage protection circuit mainly includes first, second, third, and fourth resistors, triodes, capacitors, diodes, and integrated chips; the bases of the triodes are respectively connected to the first 1. The second resistor, further the first resistor is connected to one end of the diode, the other end of the diode is connected to the output end of the power supply, and the second resistor is grounded; the collector of the triode is respectively connected to the third and fourth resistors, capacitors, and integrated chips, Further, both the fourth resistor and the capacitor are grounded, the third resistor is connected to the power supply CPU that sends out the control signal, and the emitter of the triode is grounded.

The integrated chip is connected with the self-locking circuit

Compared with the prior art, the utility model uses the LCD-TV power supply undervoltage protection circuit. When the output voltage is lower than the protection voltage, the diode of the LCD-TV power supply undervoltage protection circuit is cut off, the triode is cut off, and the control signal of the power supply CPU is on the capacitor. Charging, when the capacitor voltage is charged to the conduction voltage of the integrated chip, the integrated chip is turned on, and the integrated chip gives a control signal so that the power supply has no output, so as to protect the output voltage of the power supply when it is undervoltage, and effectively protect other circuits and devices.

Description of drawings

FIG. 1 is a schematic diagram of an LCD-TV power supply undervoltage protection circuit in a preferred embodiment of the present invention.

Detailed ways

In order to make the purpose, technical solution, and advantages of the utility model clearer and clearer, the technical solution of the utility model will be further described in detail below in conjunction with specific embodiments and accompanying drawings.

As shown in Figure 1, it is an LCD-TV power supply undervoltage protection circuit which is a preferred embodiment of the present invention. It mainly uses triodes and diodes to perform LCD-TV power supply undervoltage protection. The LCD-TV power supply undervoltage protection circuit mainly includes Resistors R1, R2, R3, R4, transistor Q1, capacitor C1, diode ZD1, integrated chip IC1.

As shown in Figure 1, the connection relationship of the LCD-TV power supply undervoltage protection circuit is as follows: the base of the triode Q1 is respectively connected to resistors R1 and R2, further resistor R1 is connected to diode ZD1, and further resistor R2 is grounded; The collectors are respectively connected to resistors R3, R4, capacitor C1, and integrated chip IC1, and further, both resistor R4 and capacitor C1 are grounded; the emitter of the triode Q1 is grounded.

LCD-TV output has 24V, 12V, 5V, etc. In Figure 1, U1 is used to represent LCD-TV output, that is, diode ZD1 is connected to the output terminal U1 of LCD-TV power supply, ON/OFF is the CPU control signal, represented by U2, ON/OFF The OFF signal is given by the CPU of the LCD-TV main board. When ON means high level, 24V and 12V should output normally; when OFF means low level, 24V and 12V have no output. The integrated chip IC1 outputs a control signal output, so that the power supply outputs or does not output the voltage U1.

When the output voltage U1 is output normally, when the output voltage of U1 is greater than 18V, the diode ZD1 conducts reversely, and the transistor Q1 conducts at the same time, the ON/OFF signal goes to the ground through the resistor R3 and the transistor Q1, and the integrated chip IC1 does not play a control role. The integrated chip IC1 has no control signal output, and since the integrated chip IC1 has no control signal output, the output of U1 is normal.

When the power supply is working normally, the output voltage U1 is normal. The typical value of U1 voltage is 24V. When the output voltage U1 is less than 18V, it is considered to be undervoltage. In order to prevent damage to the LCD screen of the powered device and the components of the power supply itself, a power module is required. Enter the protection state, that is, undervoltage protection, for which 18V is used as the undervoltage protection point.

When the power supply is working normally, the output voltage U1 is greater than 18V, the reverse conduction of the diode ZD1, and the transistor Q1 is turned on at the same time, the ON/OFF signal goes to the ground through the resistor R3 and the transistor Q1, the integrated chip IC1 does not have a control function, and the integrated chip IC1 No control signal output, because the integrated chip IC1 has no control signal output, so U1 output is normal.

When the power supply is working normally, the output voltage U1 is about 24, which is greater than the undervoltage protection trigger point of 18V. The diode ZD1 is a 15V Zener diode, and the diode ZD1 breaks down due to sodium, and at the same time provides the base current for the transistor Q1, so that the transistor Q1 The BE is turned on, and the ON/OFF signal voltage U2 goes to the ground through the resistor R3 and the transistor Q1. The ON/OFF signal is given by the CPU of the LCD-TV main board, and the output voltage is between 2.5 and 4.2V. The saturation voltage drop of the transistor Q1 Compared with the bottom, it is not enough to turn on the diode of the integrated chip IC1. At this time, the integrated chip IC1 has no control function, and the integrated chip IC1 has no control signal output. Since the integrated chip IC1 has no control signal output, the output of U1 is normal. The integrated chip IC1 is connected to the self-locking circuit. When the diode of the integrated chip IC1 is turned on, the ON/OFF signal voltage U2 is 0V; when the diode of the integrated chip IC1 is not turned on, the ON/OFF signal voltage U2 is 2.5 to 4.2 Between V (the specific value is determined by the CPU).

When the output voltage U1 is less than 18V, diode ZD1 is cut off, transistor Q1 is cut off, U2 charges capacitor C1 through resistor R3, when the voltage of capacitor C1 is charged to the conduction voltage of integrated chip IC1, integrated chip IC1 is turned on, and integrated chip IC1 The control signal is output, (here the capacitor C1 is used to prevent malfunction during normal startup), and the control signal given by the integrated chip IC1 causes the power supply U1 to have no output.

The parameters of the diode ZD1 can be changed, the undervoltage protection point can be adjusted, the capacitor C1 can be changed, the delay time can be adjusted, and malfunctions can be prevented. The component parameters in Figure 1 can be adjusted according to specific applications.

When over-current protection is implemented, it needs to be combined with over-power protection. When the current over-current increases, the output voltage is reduced. When the output voltage U1 reaches the under-voltage protection point, the circuit protection makes U1 have no output.

Although the utility model has been described with reference to the current preferred embodiments, those of ordinary skill in the art should recognize that the above-mentioned preferred embodiments are only used to illustrate the utility model, and are not intended to limit the protection scope of the utility model , any modification, equivalent replacement, improvement, etc. made within the spirit and principle scope of the present utility model shall be included in the protection scope of the utility model.

Claims (2)

1. A kind of LCD-TV power supply undervoltage protection circuit, it is characterized in that: this LCD-TV power supply undervoltage protection circuit mainly comprises the first, two, three, four resistances, triode, electric capacity, diode, integrated chip; The poles are respectively connected to the first and second resistors, further the first resistor is connected to one end of the diode, the other end of the diode is connected to the output end of the power supply, and the second resistor is further grounded; the collector of the triode is respectively connected to the third and fourth resistors, capacitor , an integrated chip, further the fourth resistor and the capacitor are both grounded, the third resistor is connected to the power supply CPU that sends out the control signal, and the emitter of the triode is grounded. 2. The undervoltage protection circuit of LCD-TV power supply according to claim 1, characterized in that: the integrated chip is connected with the self-locking circuit.

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