Overvoltage and overcurrent protection circuit applied to liquid crystal display television power supply system

Abstract

The utility model relates to a liquid crystal display television power supply technology, discloses an overvoltage and overcurrent protection circuit applied to a liquid crystal display television power supply system, effectively solves the overvoltage and overcurrent problems of the television power supply system, and is simple in structure and easy to implement. In the scheme of the utility model, the overvoltage and overcurrent protection circuit is designed behind the switch transformer in the power supply system, and the output of the protection circuit is fed back to the power management chip; the designed protection circuit detects voltage and current output by a power supply system in real time through voltage comparison at the two ends of a sampling resistor and monitoring of a voltage stabilizing diode, and when overcurrent occurs, a comparator outputs a high level to trigger a field effect transistor and an optocoupler to be conducted, so that a protection pin of a power management chip is pulled down, and a power supply is cut off; and when overvoltage occurs, the voltage stabilizing diode is conducted, so that the field effect transistor and the optocoupler are triggered to be conducted, and therefore, the protection pin of the power management chip is pulled down, and the power supply is cut off.

Description

Technical Field

[0001] This utility model relates to LCD TV power supply technology, specifically to an overvoltage and overcurrent protection circuit applied to LCD TV power supply systems. Background Technology

[0002] Currently, LCD TV power supply systems mainly adopt, such as Figure 1 The power supply system shown has an AC input that is converted from AC to DC, controlled by a power management chip, and finally isolated by a switching transformer to output multiple DC voltages, including a 12V power supply for the chassis / audio and a VLED power supply for the backlight.

[0003] On the one hand, when the mechanism / audio malfunctions, the current flowing through the 12V power supply line will increase sharply, causing the switching power supply to overload, resulting in abnormal heating of the power devices, which in turn leads to the failure of the power devices / switching power supply, and may even cause a fire hazard due to abnormal heating of the power devices.

[0004] On the other hand, since the lower limit of the input voltage of the chassis / audio chip is relatively low, when the switching power supply is malfunctioning, such as when the optocoupler secondary is short-circuited or the voltage sampling resistor is abnormal, the 12V output voltage will gradually increase. When the output voltage exceeds the lower limit of the input voltage of the chassis / audio chip, the chassis / audio chip will be damaged. Utility Model Content

[0005] The technical problem to be solved by this utility model is to propose an overvoltage and overcurrent protection circuit for LCD TV power supply systems, which effectively solves the overvoltage and overcurrent problems of TV power supply systems, and has a simple structure and is easy to implement.

[0006] The technical solution adopted by this utility model to solve the above-mentioned technical problems is:

[0007] An overvoltage and overcurrent protection circuit for use in an LCD TV power supply system includes:

[0008] The components include: first to twelfth resistors, first to fifth capacitors, first diode, second diode, Zener diode, field-effect transistor, first integrated circuit, and second integrated circuit;

[0009] The anode of the first diode is connected to the output terminal of the switching transformer in the LCD TV power supply system, the cathode of the first diode is connected to one end of the first resistor, and is connected to the non-inverting input terminal of the first integrated circuit U1 through the second resistor; one end of the first resistor is connected to the anode of the first capacitor, and the other end of the first resistor is connected to the inverting input terminal of the first integrated circuit through the fourth resistor, and is connected to the anode of the second capacitor; the cathodes of both the first capacitor and the second capacitor are grounded.

[0010] The third resistor is connected between the non-inverting input terminal of the first integrated circuit and ground; the fifth resistor is connected between the inverting input terminal of the first integrated circuit and ground.

[0011] The power supply terminal of the first integrated circuit is connected to the positive terminal of the first capacitor through the sixth resistor, grounded through the third capacitor, and connected to the output terminal of the first integrated circuit through the seventh resistor; the output terminal of the first integrated circuit is connected to the gate of the field-effect transistor (FET) through the eighth resistor and the second diode; the fourth capacitor is connected between the positive terminal of the second diode and ground; the tenth resistor and the fifth capacitor are both connected between the gate of the FET and ground; the gate of the FET is also connected to the positive terminal of the first capacitor through the ninth resistor and the Zener diode; the source of the FET is grounded, and the drain is connected to the input of the second integrated circuit; one end of the eleventh resistor is connected to the positive terminal of the first capacitor, and the other end is connected to the second integrated circuit; the output of the second integrated circuit is connected to the protection pin of the power management chip in the LCD TV power supply system through the twelfth resistor.

[0012] Furthermore, the first integrated circuit employs a comparator.

[0013] Furthermore, the second integrated circuit employs an optocoupler.

[0014] The beneficial effects of this utility model are:

[0015] This invention incorporates an overvoltage and overcurrent protection circuit in the power supply system of an LCD TV. Based on this circuit design, the power supply can be quickly cut off in case of overvoltage or overcurrent abnormalities, protecting the safety of the entire TV. The circuit has a simple structure, uses common electronic components, and is not only low in cost but also easy to implement and maintain. Attached Figure Description

[0016] Figure 1 A schematic diagram of a traditional LCD TV power supply system.

[0017] Figure 2 This is a schematic diagram of the improved LCD TV power supply system of this utility model;

[0018] Figure 3 This is a structural diagram of the overvoltage and overcurrent protection circuit in the embodiment;

[0019] The diagram is labeled as follows: R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4 is the fourth resistor, R5 is the fifth resistor, R6 is the sixth resistor, R7 is the seventh resistor, R8 is the eighth resistor, R9 is the ninth resistor, R10 is the tenth resistor, R11 is the eleventh resistor, R12 is the twelfth resistor, C1 is the first capacitor, C2 is the second capacitor, C3 is the third capacitor, C4 is the fourth capacitor, C5 is the fifth capacitor, D1 is the first diode, D2 is the second diode, ZD1 is the Zener diode, Q1 is the MOSFET, U1 is the first integrated circuit, U2 is the second integrated circuit, 12V-A is the positive terminal of C1, 12V-B is the positive terminal of C2, PRO is the protection pin of the power management chip, and T1 is the switching transformer. Detailed Implementation

[0020] This utility model aims to provide an overvoltage and overcurrent protection circuit for LCD TV power supply systems, effectively solving the overvoltage and overcurrent problems in TV power supply systems, and with a simple structure and easy implementation. Its core idea is to design an overvoltage and overcurrent protection circuit after the switching transformer in the power supply system. The output of this protection circuit is fed back to the power management chip, such as... Figure 2 As shown, the designed protection circuit monitors the voltage and current output of the power supply system in real time by comparing the voltage across the sampling resistor and monitoring with a Zener diode. When an overcurrent occurs, the comparator output goes high, triggering the MOSFET and optocoupler to conduct, thereby pulling the protection pin of the power management chip low and cutting off the power supply. When an overvoltage occurs, the Zener diode conducts, thereby triggering the MOSFET and optocoupler to conduct, thereby pulling the protection pin of the power management chip low and cutting off the power supply.

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] Example

[0023] This embodiment mainly provides an exemplary description of the specific implementation method of the overvoltage and overcurrent protection circuit. (See also...) Figure 3 The overvoltage and overcurrent protection circuit in this embodiment includes: first to twelfth resistors R1 to R12, first to fifth capacitors C1 to C5, first diode D1, second diode D2, Zener diode ZD1, field-effect transistor Q1, first integrated circuit U1, and second integrated circuit U2; wherein, the first integrated circuit U1 can be a comparator, such as LM393; and the second integrated circuit U2 can be an optocoupler, such as PC817B.

[0024] In the circuit described above, the anode of the first diode D1 is connected to the output terminal of the switching transformer T1 in the LCD TV power supply system, and the cathode of the first diode D1 is connected to one end of the first resistor R1 and then connected to the non-inverting input terminal +IN A of the first integrated circuit U1 through the second resistor R2. One end of the first resistor R1 is connected to the positive terminal 12V-A of the first capacitor C1, and the other end of the first resistor R1 is connected to the inverting input terminal -IN A of the first integrated circuit U1 through the fourth resistor R4 and then connected to the positive terminal 12V-B of the second capacitor C2. The cathodes of both the first capacitor C1 and the second capacitor C2 are grounded.

[0025] The third resistor R3 is connected between the non-inverting input terminal +IN A of the first integrated circuit U1 and ground; the fifth resistor R5 is connected between the inverting input terminal -IN A of the first integrated circuit U1 and ground.

[0026] The power supply terminal Vcc of the first integrated circuit U1 is connected to the positive terminal (12V-A) of the first capacitor C1 through the sixth resistor R6, and grounded through the third capacitor C3, and connected to the output terminal OUT A of the first integrated circuit U1 through the seventh resistor R7; the output terminal OUT A of the first integrated circuit U1 is connected to the gate of the field-effect transistor Q1 through the eighth resistor R8 and the second diode D2; the fourth capacitor C4 is connected between the positive terminal of the second diode D2 and ground; the tenth resistor R10 and the fifth capacitor C5 are both connected between the gate of the field-effect transistor Q1 and ground; the gate of the field-effect transistor Q1 is also connected to the positive terminal (12V-A) of the first capacitor C1 through the ninth resistor R9 and the Zener diode ZD1; the source of the field-effect transistor Q1 is grounded, and the drain is connected to the input of the second integrated circuit U2; one end of the eleventh resistor R1 is connected to the positive terminal (12V-A) of the first capacitor C1, and the other end is connected to the second integrated circuit U2; the output of the second integrated circuit U2 is connected to the protection pin PRO of the power management chip in the LCD TV power supply system through the twelfth resistor R12.

[0027] The overcurrent protection working principle of the above circuit is as follows:

[0028] When the 12V voltage output from the switching transformer T1 supplies power to the downstream load through the first resistor R1, a voltage difference will be generated across the first resistor R1. The voltage at 12V-A is divided by the second resistor R2 and the third resistor R3, and the corresponding voltage is output to the non-inverting input terminal +IN A of the first integrated circuit U1. The voltage at 12V-B is divided by the fourth resistor R4 and the fifth resistor R5, and the corresponding voltage is output to the inverting input terminal -IN A of the first integrated circuit U1. At the same time, the positive terminal 12V-A of the first capacitor C1 is connected to the Vcc of the first integrated circuit U1 after current limiting by the sixth resistor R6, thus supplying power to U1. The third capacitor C3 is used for Vcc filtering.

[0029] When the voltage at +IN A is higher than the voltage at -IN A, the output terminal OUTA is pulled high by the seventh resistor R7. This level is isolated by the second diode D2 and filtered by the fifth capacitor C5 before being connected to the gate of the field-effect transistor Q1. The drain and source of Q1 are conducting. The voltage at the positive terminal of the second capacitor C2 (12V-B) is current-limited by the eleventh resistor R11 and flows through the diode in the optocoupler. The third and fourth pins of the optocoupler are conducting. The protection pin PRO of the power management chip is pulled low by the twelfth resistor R12, and the power management chip stops working. Conversely, when the voltage at +IN A is lower than that at -IN A, the internal transistor of U1 is turned on, OUTA is pulled low, Q1 is turned off, U2 does not operate, and the power management chip works normally.

[0030] The overvoltage protection working principle of the above circuit is as follows:

[0031] When the voltage at the positive terminal of the first capacitor C1 (12V-A) is higher than the forward voltage of the Zener diode ZD1, ZD1 conducts. The voltage at 12V-A is then divided by resistors R9 and R10 to generate a high level, turning on the MOSFET Q1. This, in turn, pulls the protection pin PRO of the power management chip low through the optocoupler, causing the power management chip to stop working. Conversely, when the 12V-A voltage is lower than the forward voltage of ZD1, ZD1 is cut off, Q1 is cut off, the optocoupler does not activate, and the power management chip operates normally.

[0032] As can be seen, this embodiment, through the above simple circuit structure, forms a reliable overvoltage and overcurrent protection circuit, which can be applied to the power supply system of LCD TVs. It can effectively solve the problems of overvoltage and overcurrent in the output of switching power supplies. The structure is simple, the cost is low, and it is highly feasible.

[0033] Although embodiments of the present invention have been described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, and all such changes and alterations shall not depart from the protection scope of the present invention.

Claims

1. An overvoltage and overcurrent protection circuit applied to a power supply system of a liquid crystal television, characterized in that, include: The first to twelfth resistors (R1~R12), the first to fifth capacitors (C1~C5), the first diode (D1), the second diode (D2), the Zener diode (ZD1), the field-effect transistor (Q1), the first integrated circuit (U1), and the second integrated circuit (U2); The anode of the first diode (D1) is connected to the output terminal of the switching transformer (T1) in the LCD TV power supply system. The cathode of the first diode (D1) is connected to one end of the first resistor (R1) and then connected to the non-inverting input terminal of the first integrated circuit (U1) through the second resistor (R2). One end of the first resistor (R1) is connected to the anode (12V-A) of the first capacitor (C1), and the other end of the first resistor (R1) is connected to the inverting input terminal of the first integrated circuit (U1) through the fourth resistor (R4) and then connected to the anode (12V-B) of the second capacitor (C2). The cathodes of both the first capacitor (C1) and the second capacitor (C2) are grounded. The third resistor (R3) is connected between the non-inverting input terminal of the first integrated circuit (U1) and ground; the fifth resistor (R5) is connected between the inverting input terminal of the first integrated circuit (U1) and ground. The power supply terminal of the first integrated circuit (U1) is connected to the positive terminal (12V-A) of the first capacitor (C1) through the sixth resistor (R6), grounded through the third capacitor (C3), and connected to the output terminal of the first integrated circuit (U1) through the seventh resistor (R7); The output terminal of the first integrated circuit (U1) is connected to the gate of the field-effect transistor (Q1) through the eighth resistor (R8) and the second diode (D2); the fourth capacitor (C4) is connected between the positive terminal of the second diode (D2) and ground; the tenth resistor (R10) and the fifth capacitor (C5) are both connected between the gate of the field-effect transistor (Q1) and ground. The gate of the field-effect transistor (Q1) is also connected to the positive terminal (12V-A) of the first capacitor (C1) through the ninth resistor (R9) and the Zener diode (ZD1); the source of the field-effect transistor (Q1) is grounded, and the drain is connected to the input of the second integrated circuit (U2); one end of the eleventh resistor (R11) is connected to the positive terminal (12V-A) of the first capacitor (C1), and the other end is connected to the second integrated circuit (U2); the output of the second integrated circuit (U2) is connected to the protection pin (PRO) of the power management chip in the LCD TV power supply system through the twelfth resistor (R12).

2. The overvoltage and overcurrent protection circuit for a liquid crystal television power supply system as described in claim 1, characterized in that, The first integrated circuit (U1) employs a comparator.

3. The overvoltage and overcurrent protection circuit for a liquid crystal television power supply system as described in claim 1, characterized in that, The second integrated circuit (U2) employs an optocoupler.

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