CN216751174U

CN216751174U - AC input undervoltage protection circuit

Info

Publication number: CN216751174U
Application number: CN202220163544.XU
Authority: CN
Inventors: 丁峰峰; 李永俊
Original assignee: Sichuan Changhong Electric Co Ltd
Current assignee: Sichuan Changhong Electric Co Ltd
Priority date: 2022-01-21
Filing date: 2022-01-21
Publication date: 2022-06-14
Anticipated expiration: 2032-01-21

Abstract

The utility model relates to the field of AC input undervoltage protection, and provides an AC input undervoltage protection circuit for realizing input undervoltage protection, which comprises: the input undervoltage protection circuit comprises an alternating current power grid input end, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a first diode, a first capacitor, an operational amplifier, a voltage source, a first voltage-regulator tube, an MOS tube and a power supply output end, and input undervoltage protection is realized through the connection relation among all elements.

Description

AC input undervoltage protection circuit

Technical Field

The utility model relates to the field of alternating current input undervoltage protection, in particular to an alternating current input undervoltage protection circuit.

Background

With the high-speed development of economy in China, televisions are more and more popular, but in a part of remote mountainous areas, the situation that a power grid is unstable or even the voltage is low still exists. Many traditional television products do not contain alternating current network voltage detection function, still are working under the condition that input voltage is on the low side, but under this operating condition, the temperature rise of inside device is on the high side, and long-time work can lead to the product to become invalid, brings the reliability problem.

SUMMERY OF THE UTILITY MODEL

In order to realize input undervoltage protection, the utility model provides an alternating current input undervoltage protection circuit.

The technical scheme adopted by the utility model for solving the problems is as follows:

ac input undervoltage protection circuit includes: an input end of an alternating current power grid, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a first diode, a first capacitor, an operational amplifier, a voltage source, a first voltage-regulator tube, an MOS tube and a power output end,

the input end of the alternating current network is respectively connected with one end of a second resistor and the anode of a first diode through a first resistor, the other end of the second resistor is grounded, the cathode of the first diode is respectively connected with one end of the first capacitor and one end of the third resistor, the other end of the first capacitor is grounded, the other end of the third resistor is respectively connected with one end of the fourth resistor and the reference end of the operational amplifier, the other end of the fourth resistor and the anode end of the operational amplifier are both grounded, the cathode end of the operational amplifier is connected with a voltage source through a fifth resistor, the cathode end of the operational amplifier is further connected with one end of a sixth resistor and the negative electrode of the first voltage-regulator tube, the other end of the sixth resistor is grounded, the positive electrode of the first voltage-regulator tube is respectively connected with the grid electrode of the MOS tube and one end of the seventh resistor, the other end of the seventh resistor and the source electrode of the MOS tube are grounded, and the drain electrode of the MOS tube is connected with the power output end.

And the second voltage-stabilizing tube is connected with the reference end and the anode end of the operational amplifier in parallel.

And one end of the second capacitor is connected with the reference end of the operational amplifier, and the other end of the second capacitor is connected with the cathode end of the operational amplifier.

Compared with the prior art, the utility model has the beneficial effects that: the utility model adopts the AC input undervoltage protection circuit to set accurate undervoltage protection points, and when the input voltage is lower than the preset input voltage, the switching power supply IC is closed in time, thereby ensuring the reliability of the product. Meanwhile, the circuit loss can be reduced by adopting a half-wave rectification mode, and the influence on the standby power consumption of the television is small. In addition, compared with the traditional circuit, the voltage hysteresis setting is not needed, the brown in voltage point and the brown out voltage point are basically the same, and the problem of temperature rise balance design during low-voltage input can be better solved.

Drawings

FIG. 1 is a circuit diagram of an AC input under-voltage protection circuit;

fig. 2 is a system configuration diagram of the embodiment.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the utility model and are not intended to limit the utility model.

As shown in fig. 1, the ac input under-voltage protection circuit includes an ac power grid input terminal ACin, a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R10, a first diode D1, a first capacitor C2, an operational amplifier U1, a voltage source V2, a first voltage regulator D7, a MOS transistor Q1, and a power output terminal Vfb,

an input end ACin of an alternating current power grid is respectively connected with one end of a second resistor R2 and an anode of a first diode D1 through a first resistor R1, the other end of the second resistor R2 is grounded, a cathode of the first diode D1 is respectively connected with one end of a first capacitor C2 and one end of a third resistor R3, the other end of the first capacitor C2 is grounded, the other end of the third resistor R3 is respectively connected with one end of a fourth resistor R4 and a reference end of an operational amplifier U1, the other end of the fourth resistor R4 and an anode end of an operational amplifier U1 are both grounded, a cathode end of the operational amplifier U1 is connected with a voltage source V2 through a fifth resistor R5, a cathode end of the operational amplifier U1 is also connected with one end of a sixth resistor R6 and a cathode of a first voltage regulator D387, the other end of the sixth resistor R6 is grounded, an anode of the first voltage regulator D7 is respectively connected with a gate of a MOS tube Q1 and a seventh resistor R87446, the other end of the seventh resistor R10 and the source of the MOS transistor Q1 are grounded, and the drain of the MOS transistor Q1 is connected with the power output end Vfb.

Preferably, the current regulator further comprises a second regulator tube D6, the second regulator tube D6 is connected in parallel with the reference end and the anode end of the operational amplifier U1, and the second regulator tube D6 aims to protect the reference end of the operational amplifier U1 and prevent the surge voltage at the alternating current end from being connected in series to cause the failure of U1.

Furthermore, the current source further comprises a second capacitor C3, one end of the second capacitor C3 is connected with the reference end of the operational amplifier U1, the other end of the second capacitor C3 is connected with the cathode end of the operational amplifier U1, and the second capacitor C3 is a feedback capacitor, so that the normal operation of the feedback loop of the operational amplifier U1 can be ensured.

As shown in fig. 2, in actual use, the ac power grid input terminal ACin is connected to the live line or the neutral line of the ac power grid input terminal, and the power output terminal Vfb is connected to the Vfb pin of the switching power supply IC. The input voltage amplitude of the alternating current mains is reduced after voltage division is carried out through a first resistor R1 and a second resistor R2, alternating current waveforms are changed into direct current voltage waveforms after half-wave rectification and filtering are carried out through a first diode D1 and a first capacitor C2, the direct current voltage waveforms are input to an operational amplifier U1 after voltage division is carried out through a third resistor R3 and a fourth resistor R4, the U1 is a TL431 operational amplifier IC, and the reference end of the operational amplifier U1, namely the reference voltage of a 1 st pin is 2.5V.

When the alternating-current input voltage ratio is lower and is less than a preset under-voltage point, namely the voltage amplitude after voltage division through the first resistor R1, the second resistor R2, rectification, the third resistor R3 and the fourth resistor R4 is less than 2.5V of the reference voltage of the 1 st pin of the operational amplifier U1, the 2 nd pin of the U1 is represented as a high level, the voltage amplitude is the voltage amplitude after the voltage source V2 is subjected to voltage division through the fifth resistor R5 and the sixth resistor R6, the voltage amplitude can be generally set to be greater than 10V during design, the amplitude is still greater than the gate voltage of the NMOS transistor Q1 after voltage reduction through the first voltage-regulator tube D7, the Q1 is conducted, the voltage of the Vfb pin of the switching power supply IC is pulled down through the power output end Vfb, and the switching power supply IC turns off the control signal of the switching transistor at this time, so that the output voltage is zero, and under-voltage protection is realized in time. When the input voltage is higher than a preset under-voltage point, namely the voltage amplitude after the voltage division rectification of R1 and R2 and the voltage division of R3 and R4 is larger than the reference voltage of the No. 1 pin of U1 by 2.5V, the No. 2 pin of U1 is represented as a low level, the voltage of the U1 is smaller than the voltage reduction of the first voltage-regulator tube D7, so that the grid voltage of the NMOS tube Q1 is 0V, the Q1 is cut off, the voltage of the Vfb pin of the switching power supply IC is represented as a high level, the grid voltage provides a direct current supply voltage through the full bridge rectification, and the direct current supply voltage is converted into an output voltage through the switching tube and the transformer by the switching power supply IC to supply power for subsequent equipment.

Claims

1. Alternating current input undervoltage protection circuit, its characterized in that includes: an input end of an alternating current power grid, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a first diode, a first capacitor, an operational amplifier, a voltage source, a first voltage regulator tube, an MOS tube and a power output end,

2. The ac input under-voltage protection circuit of claim 1, further comprising a second regulator tube connected in parallel with the reference terminal and the anode terminal of the operational amplifier.

3. The AC input under-voltage protection circuit according to claim 1 or 2, further comprising a second capacitor, wherein one end of the second capacitor is connected to the reference terminal of the operational amplifier, and the other end of the second capacitor is connected to the cathode terminal of the operational amplifier.