CN207625292U - Power supply switching circuit and television power supply system - Google Patents

Abstract

The utility model discloses a power switching circuit, which comprises a control module and a power switching module; wherein, the control module has an AC voltage detection terminal, a DC voltage detection terminal and a switching control terminal; the power switching module has an AC power input terminal , a DC power input terminal, a switching controlled terminal and a power output terminal; a TV power supply system, including: including a DC power supply module, an AC-DC conversion circuit, a power switching circuit and a TV working module. Realize that when the AC power supply and DC power supply power the TV at the same time, the internal power switching circuit will give priority to using the AC power supply for power supply. The TV power supply system has a DC power supply module, an AC-DC conversion circuit and a power switching circuit, making the TV power supply system compatible with AC. There are two power supply modes: mains power supply and DC power supply.

Description

Power switching circuit and TV power supply system

technical field

The utility model belongs to the field of power supply systems, in particular to a power switching circuit and a television power supply system.

Background technique

At this stage, higher requirements are put forward for the demand for uninterruptible power supply and the diversity of power supply. However, the traditional TV power supply system can only be powered by AC, and it is not compatible with battery or adapter power supply. As a result, the TV will stop working immediately when the power is suddenly cut off; Realizing the optimization of AC power supply when both AC and DC are powered simultaneously causes great inconvenience to users.

Utility model content

The purpose of this utility model is to provide a power switching circuit and a TV power supply system, so that when the AC power supply and the DC power supply power the TV at the same time, the AC power supply is preferentially used through the internal power switching circuit, so that the TV power supply system can be compatible with AC There are two power supply modes: mains power supply and DC power supply.

In order to solve the above technical problems, the embodiment of the utility model provides a power switching circuit, including a control module and a power switching module; wherein, the control module has an AC voltage detection terminal, a DC voltage detection terminal and a switching control terminal; the power supply The switching module has an AC power input terminal, a DC power input terminal, a switching controlled terminal and a power output terminal;

The AC voltage detection end of the control module is connected to the AC power input end of the power switching module, the DC voltage detection end of the control module is connected to the DC power input end of the power switching module, and the switching of the control module The control end is connected to the switching controlled end of the power switching module; the AC power input end of the power switching module is connected to the power output end of the power switching module.

Further, the control module includes: a first resistor, a second resistor, a third resistor, a fourth resistor, a first switch tube, and a second switch tube;

The first end of the first resistor is connected to the AC voltage detection end of the control module, the second end of the first resistor is connected to the first end of the second resistor; the first end of the second resistor terminal is connected to the control terminal of the first switch tube, the second terminal of the second resistor is grounded; the output terminal of the first switch tube is grounded; the first terminal of the third current limiting resistor is connected to the control terminal The DC voltage detection end of the module is connected, the second end of the third resistor is connected to the control end of the second switch tube, and the second end of the third resistor is also connected to the input end of the first switch tube ; The first end of the fourth resistor is connected to the second end of the third resistor, and the second end of the fourth resistor is grounded; the input end of the second switching tube is connected to the switching control of the control module The input terminal of the second switching tube is also connected to the DC voltage detection terminal of the control module, and the output terminal of the second switching tube is grounded.

Preferably, the control module further includes: a first capacitor, a fifth resistor, a sixth resistor, a seventh resistor and an eighth resistor;

The fifth resistor is connected between the second end of the first resistor and the control end of the first switch tube; the sixth resistor is connected between the second end of the third resistor and the second between the control terminals of the switch tube; the seventh resistor is connected between the input terminal of the second switch tube and the switch control terminal of the control module; the eighth resistor is connected to the second switch tube Between the input end and the DC voltage detection end of the control module; the first end of the first capacitor is connected to the first end of the second resistor, and the second end of the first capacitor is connected to the second The second end of the resistor is connected.

Further, the power switching module includes: a switching switch and a first diode;

The control end of the switch is connected to the switched controlled end of the power switching module, the input end of the switch is connected to the DC power input end of the power switching module, and the output end of the switch is connected to the The power output end of the power switching module is connected; the first diode is connected between the AC power input end of the power switching module and the power output end of the power switching module; wherein, the first diode The anode of the first diode is connected to the AC power input terminal of the power switching module, and the negative pole of the first diode is connected to the power output terminal of the power switching module.

Preferably, the power switching module further includes a second diode, a second capacitor and a power supply ground capacitor;

The second diode is connected between the output end of the switch and the power output end of the power switching module; wherein, the anode of the second diode is connected to the output end of the switch, The cathode of the second diode is connected to the power output end of the power switching module; the first end of the second capacitor is connected to the power output end of the power switching module, and the second capacitor of the second capacitor is connected to the power output end of the power switching module. The terminal is grounded; the first terminal of the power supply grounding capacitor is connected to the first terminal of the second capacitor, and the second terminal of the power supply grounding capacitor is grounded.

Preferably, the switch is a P-channel MOS transistor;

The control end of the changeover switch corresponds to the gate of the P-channel MOS transistor, the input end of the changeover switch corresponds to the source of the P-channel MOS transistor, and the output end of the changeover switch corresponds to the gate of the P-channel MOS transistor. The drain of the P-channel MOS transistor.

The embodiment of the utility model also provides a TV power supply system, including: a DC power module, an AC-DC conversion circuit, a power switching circuit and a TV working module;

The DC power supply module has a DC power supply output terminal; the AD-DC conversion circuit has a DC power supply output terminal and an AC power supply input terminal for inputting AC power; the TV working module has a power supply input terminal;

The DC power output end of the DC power supply module is connected to the DC power input end of the power switching circuit; the DC power output end of the AC-DC conversion circuit is connected to the AC power input end of the power switching circuit; the The power output end of the power switching circuit is connected with the power input end of the TV working module.

Further, the TV power supply system further includes an undervoltage and overvoltage protection circuit connected between the DC power output terminal of the DC power supply module and the DC power input terminal of the power switching circuit; wherein, the undervoltage The overvoltage protection circuit includes: an undervoltage detection unit, an overvoltage detection unit and a power-off switch;

The power-off switch has a power input terminal, a switch control terminal and a power output terminal; the overvoltage detection unit has an overvoltage detection terminal and an overvoltage control terminal; the undervoltage detection unit has an undervoltage detection terminal and an undervoltage control terminal. end;

The power input end of the power-off switch is connected to the DC power output end of the DC power module, and the power output end of the power-off switch is connected to the DC power input end of the power switching circuit;

The undervoltage detection terminal of the undervoltage detection unit is connected to the power input terminal of the power-off switch, and the undervoltage control terminal of the undervoltage detection unit is connected to the switch control terminal of the power-off switch; the overvoltage The overvoltage detection terminal of the detection unit is connected to the power input terminal of the power-off switch, and the overvoltage control terminal of the overvoltage detection unit is connected to the switch control terminal of the power-off switch.

Further, the undervoltage detection unit includes a first voltage dividing resistor, a second voltage dividing resistor and a third switch tube;

The first end of the first voltage dividing resistor is connected to the undervoltage detection end of the undervoltage detection unit, and the second end of the first voltage dividing resistor is connected to the first end of the second voltage dividing resistor; The first terminal of the second voltage dividing resistor is connected to the control terminal of the third switching tube, and the second terminal of the second voltage dividing resistor is grounded; the input terminal of the third switching tube is connected to the undervoltage The undervoltage control terminal of the detection unit is connected, the input terminal of the third switch tube is also connected with the undervoltage detection terminal of the undervoltage detection unit, and the output terminal of the third switch tube is grounded.

Further, the overvoltage detection unit includes: a fourth switch tube, a third voltage dividing resistor and a fourth voltage dividing resistor;

The first terminal of the third voltage dividing resistor is connected to the overvoltage detection terminal of the overvoltage detection unit, and the second terminal of the third voltage dividing resistor is connected to the control terminal of the fourth switching tube; the The input terminal of the fourth switch tube is connected to the overvoltage detection terminal of the overvoltage detection unit, and the output terminal of the fourth switch tube is connected to the overvoltage control terminal of the overvoltage detection unit; the fourth divided voltage The first end of the resistor is connected to the second end of the third voltage dividing resistor, and the second end of the fourth voltage dividing resistor is grounded.

Compared with the prior art, the beneficial effect of a power switching circuit and a TV power supply system of the present utility model is that: the power switching module in the power switching circuit is controlled by the control module in the power switching circuit, so that AC power and DC power When supplying power to the backend at the same time, the power switching module blocks the DC power supply and preferentially selects the AC power supply to supply power to the backend, so that when the AC power supply and the DC power supply are simultaneously powered on the TV, the AC power supply is preferentially used through the internal power switching circuit. The TV power supply system has a DC power supply module, an AC-DC conversion circuit and a power switching circuit, so that the TV power supply system is compatible with two power supply modes of AC power supply and DC power supply.

Description of drawings

Fig. 1 is a schematic structural diagram of an embodiment of a power switching circuit provided by the present invention;

Fig. 2 is the circuit schematic diagram of another embodiment of the power switching circuit provided by the utility model;

Fig. 3 is a structural schematic diagram of the TV power supply system provided by the utility model;

Fig. 4 is a schematic circuit diagram of an embodiment of the undervoltage and overvoltage protection circuit in the TV power supply system provided by the utility model.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. example. Based on the embodiments of the present utility model, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the scope of protection of the present utility model.

Referring to Fig. 1, it is a schematic structural diagram of an embodiment of a power switching circuit provided by the present invention, the power switching circuit includes: a control module 10 and a power switching module 20; wherein, the control module 10 has an AC voltage detection terminal, a DC A voltage detection terminal and a switching control terminal; the power switching module 20 has an AC power input terminal, a DC power input terminal, a switching controlled terminal and a power output terminal;

The AC voltage detection end of the control module 10 is connected to the AC power input end of the power switching module 20, the DC voltage detection end of the control module 10 is connected to the DC power input end of the power switching module 20, and the The switching control end of the control module 10 is connected to the switching controlled end of the power switching module 20 ; the AC power input end of the power switching module 20 is connected to the power output end of the power switching module 20 .

It should be noted that the power switching circuit provided by the utility model controls the power switching module in the power switching circuit through the control module in the power switching circuit, so that when the AC power supply and the DC power supply supply power to the rear end at the same time, the power supply The switching module blocks the DC power supply and preferentially selects the AC power supply to supply power to the rear end, so that when the AC power supply and the DC power supply supply power to the TV at the same time, the AC power supply is preferentially used for power supply through the internal power switching circuit.

As shown in FIG. 2 , it is a schematic circuit diagram of another embodiment of the power switching circuit provided by the present invention.

On the basis of the above-mentioned embodiments, the power supply switching circuit provided in this embodiment further optimizes the structure of some functional circuits, as follows:

The control module 10 includes: a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a first switch Q1 and a second switch Q2;

The first end of the first resistor R1 is connected to the AC voltage detection end of the control module 10, the second end of the first resistor R1 is connected to the first end of the second resistor R2; the second The first terminal of the resistor R2 is connected to the control terminal of the first switching tube Q1, the second terminal of the second resistor R2 is grounded; the output terminal of the first switching tube Q1 is grounded; the third current limiting resistor The first end of R3 is connected to the DC voltage detection end of the control module 10, the second end of the third resistor R3 is connected to the control end of the second switching tube Q2, and the second end of the third resistor R3 end is also connected to the input end of the first switch tube Q1; the first end of the fourth resistor R4 is connected to the second end of the third resistor R3, and the second end of the fourth resistor R4 is grounded; The input terminal of the second switching tube Q2 is connected to the switching control terminal of the control module 10, the input terminal of the second switching tube Q2 is also connected to the DC voltage detection terminal of the control module 10, and the second switching tube Q2 is connected to the DC voltage detection terminal of the control module 10. The output end of the switch tube Q2 is grounded.

Preferably, the first resistor R1 and the second resistor R2 form a voltage divider circuit in the control module 10, which is used to adjust the voltage input by the AC voltage detection terminal of the control module 10 so that the first switch The threshold voltage of the conduction of the transistor Q1, the threshold voltage=0.6×(R ₁ +R ₂ )/R ₂ , that is, when the TV is plugged into the AC power supply, the voltage input by the AC voltage detection terminal of the control module 10 starts to rise from 0V, When the voltage rises to the threshold voltage, the voltage at both ends of the second resistor R2 is 0.6V, which just turns on the first switch tube Q1. Similarly, the third resistor R3 and the fourth resistor R4 also form a voltage divider circuit in the control module 10, which is used to adjust the voltage input by the DC voltage detection terminal of the control module 10 so that the second Threshold voltage at which the switch tube Q2 is turned on.

Preferably, the control module 10 further includes: a first capacitor C1, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7 and an eighth resistor R8;

The fifth resistor R5 is connected between the second end of the first resistor R1 and the control end of the first switch tube Q1; the sixth resistor R6 is connected to the second end of the third resistor R3 between the control terminal of the second switching tube Q2; the seventh resistor R7 is connected between the input terminal of the second switching tube Q2 and the switching control terminal of the control module 10; the eighth resistor R8 is connected between the input end of the second switching transistor Q2 and the DC voltage detection end of the control module 10; the first end of the first capacitor C1 is connected to the first end of the second resistor R2, The second end of the first capacitor C1 is connected to the second end of the second resistor R2.

Further, the power switching module 20 includes: a switching switch QM1 and a first diode D1;

The control end of the switch QM1 is connected to the switched controlled end of the power switch module 20, the input end of the switch QM1 is connected to the DC power input end of the power switch module 20, and the switch QM1 The output end is connected to the power output end of the power switching module 20; the first diode D1 is connected between the AC power input end of the power switching module 20 and the power output end of the power switching module 20; Wherein, the anode of the first diode D1 is connected to the AC power input end of the power switching module 20 , and the cathode of the first diode D1 is connected to the power output end of the power switching module 20 .

Preferably, the switching switch QM1 is a P-channel MOS transistor;

The control terminal of the switch QM1 corresponds to the gate of the P-channel MOS transistor, the input terminal of the switch QM1 corresponds to the source of the P-channel MOS transistor, and the output terminal of the switch QM1 Corresponding to the drain of the P-channel MOS transistor.

When the DC power input terminal of the power switching module 20 is connected to power and the AC power input terminal of the power switching module 20 is not connected to power, the switching switch QM1 is controlled to be turned on, because the first diode D1 The presence of the DC power input terminal of the power switching module 20 makes the current connected to the power output terminal of the power switching module 20 output to the load of the power output terminal of the power switching module 20, and the current cannot be reversed to the AC power input terminal of the power switching module 20.

When the AC power input terminal of the power switching module 20 is connected to the power supply, the switching switch QM1 is controlled to be cut off. Since the switching switch QM1 is a P-channel MOS transistor, its cut-off state will form between the drain and the source. Body diode, wherein the drain is the negative pole of the body diode, the AC power input terminal of the power switching module 20 will not flow back current to the DC power input terminal of the power switching module 20 through the body diode, and when switching to AC power input At the moment when the mains power supply is connected to the terminal, because its voltage is too low, the input terminal of the DC power supply can still supply power to the load at the output terminal of the power supply through the body diode.

Preferably, the power switching module 20 also includes a second diode D2, a second capacitor C2 and a power supply grounding capacitor E1; the second diode D2 can prevent the power output terminal of the power switching module from having current when it is connected to an external load back to the power switch module 20 .

The second diode D2 is connected between the output end of the switch QM1 and the power output end of the power switch module 20; wherein, the anode of the second diode D2 is connected to the output end of the switch QM1 The output end of the second diode D2 is connected to the output end of the power switching module 20; the first end of the second capacitor C2 is connected to the output end of the power switching module 20. , the second end of the second capacitor C2 is grounded; the first end of the power supply grounding capacitor E1 is connected to the first end of the second capacitor C2, and the second end of the power supply grounding capacitor E1 is grounded.

The following takes the external load connected to the power supply output end of the power switching module as a TV, and takes "the power supply is an AC power supply, such as a commercial power supply; a DC power supply, such as a battery" as an example to describe the working principle of this embodiment:

When the TV is powered by a DC power supply but not connected to an AC power supply, the AC voltage detection terminal of the control module 10 has no voltage signal input, because the second terminal of the second resistor R2 is grounded to provide control for the first switch tube Q1 terminal low-level signal, the first switching tube Q1 is turned off; the DC voltage detection terminal of the control module 10 detects the voltage signal input and sends a high-level signal to the control terminal of the second switching tube Q2, The second switch tube Q2 is turned on, the input terminal of the second switch tube Q2 is connected to the DC voltage detection terminal of the control module 10, and the second switch tube Q2 is grounded because the output terminal of the second switch tube Q2 is connected to the ground. The high level of the input terminal of the tube Q2 is pulled low, causing the switching control terminal of the control module 10 to output a low level; the switching controlled terminal of the power switching module 20 receives a low level signal, so that the switching switch When QM1 is turned on, the DC power input end and the power output end of the power switching module 20 are turned on, and the DC power supplies power to the rear end.

When the TV is powered by a DC power supply and plugged into an AC power supply, the AC voltage detection terminal of the control module 10 detects a voltage signal input and sends a high-level signal to the control terminal of the first switching tube Q1, so that the first switching tube Q1 A switch tube Q1 is turned on, because the output terminal of the first switch tube Q1 is grounded and the level input to the control terminal of the second switch tube Q2 is pulled down, so that the second switch tube Q2 is turned off, because the first switch tube Q2 The input end of the two switching tubes Q2 is connected to the DC voltage detection end of the control module 10, so that the switching control end of the control module 10 outputs a high level signal to the switching controlled end of the power switching module 20, resulting in the The switching switch QM1 is cut off, the DC power input end of the power switching module 20 is not connected to the power output end, and the DC power supply does not supply power to the rear end; since the AC power input end of the power switching module 20 is switched with the power supply When the power output terminal of the module 20 is connected, the AC power supply supplies power to the rear end through the first diode D1, that is, when the AC power supply and the DC power supply supply power to the rear end at the same time, the control module 10 controls the power switching module 20 to block the DC For power supply, AC power supply is preferred to supply power to the rear end.

As shown in Figure 3, the embodiment of the utility model also provides a TV power supply system, including: a DC power supply module 301, an AC-DC conversion circuit 302, a power switching circuit 303 and a TV working module 304;

The DC power supply module 301 has a DC power supply output terminal; the AD-DC conversion circuit 302 has a DC power supply output terminal and an AC power supply input terminal for inputting AC mains power; the TV working module 304 has a power supply input terminal;

The DC power output end of the DC power supply module 301 is connected to the DC power input end of the power switching circuit 303; the DC power output end of the AC-DC conversion circuit 302 is connected to the AC power input end of the power switching circuit 303 Connection; the power output end of the power switching circuit 303 is connected to the power input end of the TV working module 304 .

Preferably, the TV working module 304 includes: a backlight, that is, a constant current circuit powered by a light bar inside the TV, a TV main chip as the core and peripheral audio and video processing circuits and ports; the AD-DC conversion circuit 302 will The AC power of the AC mains is converted into a 12V power output from the output terminal of the DC power supply.

Further, the TV power supply system further includes an undervoltage and overvoltage protection circuit 305 connected between the DC power output terminal of the DC power supply module 301 and the DC power input terminal of the power switching circuit 303;

As shown in Figure 4, it is a schematic circuit diagram of an embodiment of the undervoltage and overvoltage protection circuit 305 in the TV power supply system provided by the present invention; wherein, the undervoltage and overvoltage protection circuit 305 includes: an undervoltage detection unit 30. Overvoltage detection unit 40 and power-off switch Q5;

The power-off switch Q5 has a power input terminal, a switch control terminal and a power output terminal; the overvoltage detection unit 40 has an overvoltage detection terminal and an overvoltage control terminal; the undervoltage detection unit 30 has an undervoltage detection terminal and Undervoltage control terminal;

The power input end of the power-off switch Q5 is connected to the DC power output end of the DC power module 301, and the power output end of the power-off switch Q5 is connected to the DC power input end of the power switching circuit 303;

The undervoltage detection terminal of the undervoltage detection unit 30 is connected to the power input terminal of the power-off switch Q5, and the undervoltage control terminal of the undervoltage detection unit 30 is connected to the switch control terminal of the power-off switch Q5; The overvoltage detection terminal of the overvoltage detection unit 40 is connected to the power input terminal of the power-off switch Q5, and the overvoltage control terminal of the overvoltage detection unit 40 is connected to the switch control terminal of the power-off switch Q5.

Further, the undervoltage detection unit 30 includes a first voltage dividing resistor RD1, a second voltage dividing resistor RD2, a third switch tube Q3, a Zener diode D3, a resistor R9 and a resistor R10;

The first terminal of the first voltage dividing resistor RD1 is connected to the undervoltage detection terminal of the undervoltage detection unit 30, and the second terminal of the first voltage dividing resistor RD1 is connected to the negative pole of the Zener diode D3; The anode of the Zener diode D3 is connected to the first terminal of the second voltage dividing resistor RD2; the first terminal of the second voltage dividing resistor RD2 is connected to the control terminal of the third switching transistor Q3, and the The second terminal of the second voltage dividing resistor RD2 is grounded; the input terminal of the third switch tube Q3 is connected to the undervoltage control terminal of the undervoltage detection unit 30 through the resistor R10, and the input terminal of the third switch tube Q3 The resistor R9 is also connected to the undervoltage detection terminal of the undervoltage detection unit 30 , and the output terminal of the third switching transistor Q3 is grounded.

Further, the overvoltage detection unit 40 includes: a fourth switch tube Q4, a third voltage dividing resistor RD3 and a fourth voltage dividing resistor RD4;

The first terminal of the third voltage dividing resistor RD3 is connected to the overvoltage detection terminal of the overvoltage detection unit 40, the second terminal of the third voltage dividing resistor RD3 is connected to the control terminal of the fourth switching tube Q4 connection; the input terminal of the fourth switch tube Q4 is connected to the overvoltage detection terminal of the overvoltage detection unit 40, and the output terminal of the fourth switch tube Q4 is connected to the overvoltage control terminal of the overvoltage detection unit 40 connected; the first end of the fourth voltage dividing resistor RD4 is connected to the second end of the third voltage dividing resistor RD3, and the second end of the fourth voltage dividing resistor is grounded.

When the undervoltage and overvoltage protection circuit 305 is working, when the voltage of the power input terminal of the power-off switch Q5 decreases, the voltage detected by the undervoltage detection terminal of the undervoltage detection module 30 becomes smaller, and the voltage flowing through the undervoltage detection terminal becomes smaller. The current of the second voltage dividing resistor RD2 in the undervoltage detection unit 30 decreases, and the voltage U _RD2 at both ends of the second voltage dividing resistor RD2 also decreases thereupon; since the overvoltage voltage point is greater than the undervoltage voltage point, In the overvoltage detection unit 40, when the voltage at the power input terminal of the power-off switch Q5 drops below the undervoltage voltage point, the voltage U _RD3 at both ends of the third voltage dividing resistor RD3 of the overvoltage detection unit 40 is smaller than the fourth The turn-on threshold of the switching tube Q4, the fourth switching tube Q4 is cut off, so the overvoltage detection unit 40 does not participate in controlling the power-off switch Q5;

When the voltage at the power input terminal of the power-off switch Q5 drops below the undervoltage voltage point, the voltage U _RD2 at both ends of the second voltage dividing resistor RD2 of the undervoltage detection unit 30 is smaller than the conductance of the third switching transistor Q3. threshold, the third switching tube Q3 is turned off, and at this time, the level of the undervoltage control terminal of the undervoltage detection unit 30 is pulled up through the resistors R10 and R9 in the undervoltage detection unit 30, so that the first The input terminal of the three switch tubes Q3 gives a high-level signal to the undervoltage control terminal of the undervoltage detection unit 40; after the switch control terminal of the power-off switch Q5 receives the high-level signal, the power-off switch Q5 Turning on to off, so that the power output terminal of the power-off switch Q5 does not supply power to the rear end, and through the mutual cooperation between the under-voltage detection unit 30, the over-voltage detection unit 40 and the power-off switch Q5, the power supply circuit is realized. Undervoltage protection function.

When the undervoltage and overvoltage protection circuit 305 works normally, that is, when the voltage at the power input terminal of the power-off switch Q5 is greater than the undervoltage voltage point and less than the overvoltage voltage point, the third voltage dividing resistor of the overvoltage detection unit 40 The voltage U _RD3 at both ends of RD3 is less than the turn-on threshold of the fourth switching tube Q4, the fourth switching tube Q4 is cut off, the overvoltage detection unit 40 does not participate in controlling the power-off switch Q5, and the undervoltage detection The voltage U RD2 at both ends of the second voltage dividing resistor _RD2 of the unit 30 is greater than the conduction threshold of the third switching tube Q3, and the third switching tube Q3 is turned on. Since the output end of the third switching tube Q3 is grounded, the The high level of the input terminal of the third switching transistor Q3 is pulled low, causing the undervoltage control terminal of the undervoltage detection unit 30 to output a low level, so that the power-off switch Q5 is turned on, and the power-off switch Q5 is turned on. The power output end of the switch Q5 normally supplies power to the rear end.

When the undervoltage and overvoltage protection circuit 305 is working, when the voltage of the power input terminal of the power-off switch Q5 rises, the voltage detected by the overvoltage detection terminal of the overvoltage detection module 40 becomes larger, and the voltage flowing through The current of the third voltage dividing resistor RD3 in the overvoltage detection module 40 increases; when the voltage of the power input terminal of the power-off switch Q5 rises above the overvoltage voltage point, the overvoltage detection unit 40 The voltage U RD3 at both ends of the third voltage dividing resistor _RD3 is greater than the turn-on threshold of the fourth switch tube Q4, the fourth switch tube Q4 is turned on, and the transition is given through the input terminal of the fourth switch tube Q4. The high-level signal of the overvoltage control terminal of the voltage detection unit 40; because the overvoltage voltage point is greater than the undervoltage voltage point, the undervoltage detection unit 30 will rise above the overvoltage voltage point when the voltage at the power input terminal of the power-off switch Q5 , the voltage U _RD2 across the second voltage dividing resistor RD2 of the undervoltage detection unit 30 is greater than the conduction threshold of the third switching transistor Q3, the third switching transistor Q3 is turned on, and the undervoltage detection unit Both the resistor R10 and the resistor R9 in 30 are pull-up resistors, so that the switch control terminal of the final power-off switch Q5 receives a high-level signal, and the power-off switch Q5 changes from on to off, so that the power-off switch Q5 The output end of the power supply does not supply power to the rear end, and the overvoltage protection function of the power supply circuit is realized through the mutual cooperation between the undervoltage detection unit 30 , the overvoltage detection unit 40 and the power-off switch Q5 .

In summary, the beneficial effects of a power switching circuit and a TV power supply system of the present invention are: the power switching module in the power switching circuit is controlled by the control module in the power switching circuit, and the AC power and the DC power are simultaneously connected to each other. When the back end supplies power, the power switching module blocks the DC power supply and preferentially selects the AC power supply to supply power to the back end, so that when the AC power supply and the DC power supply power the TV at the same time, the internal power switching circuit preferentially uses the AC power supply for power supply, and the TV power supply The system has a DC power supply module, an AC-DC conversion circuit and a power switching circuit, so that the TV power supply system is compatible with two power supply modes of AC power supply and DC power supply.

The above is a preferred embodiment of the present utility model, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present utility model, some improvements and modifications can also be made, these improvements and modifications It is also regarded as the protection scope of the present utility model.

Claims (10)

1. A power switching circuit, characterized in that, comprises a control module and a power switching module; wherein, the control module has an AC voltage detection terminal, a DC voltage detection terminal and a switching control terminal; the power switching module has an AC power input terminal, DC power input terminal, switching controlled terminal and power output terminal; The AC voltage detection end of the control module is connected to the AC power input end of the power switching module, the DC voltage detection end of the control module is connected to the DC power input end of the power switching module, and the switching of the control module The control end is connected to the switching controlled end of the power switching module; the AC power input end of the power switching module is connected to the power output end of the power switching module. 2. The power switching circuit according to claim 1, wherein the control module comprises: a first resistor, a second resistor, a third resistor, a fourth resistor, a first switch tube, and a second switch tube; The first end of the first resistor is connected to the AC voltage detection end of the control module, the second end of the first resistor is connected to the first end of the second resistor; the first end of the second resistor terminal is connected to the control terminal of the first switch tube, the second terminal of the second resistor is grounded; the output terminal of the first switch tube is grounded; the first terminal of the third resistor is connected to the control module The DC voltage detection end is connected, the second end of the third resistor is connected to the control end of the second switch tube, and the second end of the third resistor is also connected to the input end of the first switch tube; The first end of the fourth resistor is connected to the second end of the third resistor, and the second end of the fourth resistor is grounded; the input end of the second switching tube is connected to the switching control end of the control module , the input terminal of the second switch tube is also connected to the DC voltage detection terminal of the control module, and the output terminal of the second switch tube is grounded. 3. The power switching circuit according to claim 2, wherein the control module further comprises: a first capacitor, a fifth resistor, a sixth resistor, a seventh resistor and an eighth resistor; The fifth resistor is connected between the second end of the first resistor and the control end of the first switch tube; the sixth resistor is connected between the second end of the third resistor and the second between the control terminals of the switch tube; the seventh resistor is connected between the input terminal of the second switch tube and the switch control terminal of the control module; the eighth resistor is connected to the second switch tube Between the input end and the DC voltage detection end of the control module; the first end of the first capacitor is connected to the first end of the second resistor, and the second end of the first capacitor is connected to the second The second end of the resistor is connected. 4. The power switching circuit according to claim 1, wherein the power switching module comprises: a switching switch and a first diode; The control end of the switch is connected to the switched controlled end of the power switching module, the input end of the switch is connected to the DC power input end of the power switching module, and the output end of the switch is connected to the The power output end of the power switching module is connected; the first diode is connected between the AC power input end of the power switching module and the power output end of the power switching module; wherein, the first diode The anode of the first diode is connected to the AC power input terminal of the power switching module, and the negative pole of the first diode is connected to the power output terminal of the power switching module. 5. The power switching circuit according to claim 4, wherein the power switching module further comprises a second diode, a second capacitor and a power supply grounding capacitor; The second diode is connected between the output end of the switch and the power output end of the power switching module; wherein, the anode of the second diode is connected to the output end of the switch, The cathode of the second diode is connected to the power output end of the power switching module; the first end of the second capacitor is connected to the power output end of the power switching module, and the second capacitor of the second capacitor is connected to the power output end of the power switching module. The terminal is grounded; the first terminal of the power supply grounding capacitor is connected to the first terminal of the second capacitor, and the second terminal of the power supply grounding capacitor is grounded. 6. The power switching circuit according to claim 4 or 5, wherein the switching switch is a P-channel MOS transistor; The control end of the changeover switch corresponds to the gate of the P-channel MOS transistor, the input end of the changeover switch corresponds to the source of the P-channel MOS transistor, and the output end of the changeover switch corresponds to the gate of the P-channel MOS transistor. The drain of the P-channel MOS transistor. 7. A TV power supply system, characterized in that it includes a DC power supply module, an AC-DC conversion circuit, a power switching circuit and a TV working module; The power switching circuit is the power switching circuit described in any one of claims 1 to 6; The DC power supply module has a DC power supply output terminal; the AC-DC conversion circuit has a DC power supply output terminal and an AC power supply input terminal for inputting AC mains power; the TV working module has a power supply input terminal; The DC power output end of the DC power supply module is connected to the DC power input end of the power switching circuit; the DC power output end of the AC-DC conversion circuit is connected to the AC power input end of the power switching circuit; the The power output end of the power switching circuit is connected with the power input end of the TV working module. 8. The television power supply system according to claim 7, further comprising an undervoltage and overvoltage protection device connected between the DC power output end of the DC power supply module and the DC power input end of the power switching circuit. circuit; wherein, the undervoltage and overvoltage protection circuit includes: an undervoltage detection unit, an overvoltage detection unit and a power-off switch; The power-off switch has a power input terminal, a switch control terminal and a power output terminal; the overvoltage detection unit has an overvoltage detection terminal and an overvoltage control terminal; the undervoltage detection unit has an undervoltage detection terminal and an undervoltage control terminal. end; The power input end of the power-off switch is connected to the DC power output end of the DC power module, and the power output end of the power-off switch is connected to the DC power input end of the power switching circuit; The undervoltage detection terminal of the undervoltage detection unit is connected to the power input terminal of the power-off switch, and the undervoltage control terminal of the undervoltage detection unit is connected to the switch control terminal of the power-off switch; the overvoltage The overvoltage detection terminal of the detection unit is connected to the power input terminal of the power-off switch, and the overvoltage control terminal of the overvoltage detection unit is connected to the switch control terminal of the power-off switch. 9. The TV power supply system according to claim 8, wherein the undervoltage detection unit comprises a first voltage dividing resistor, a second voltage dividing resistor and a third switch tube; The first end of the first voltage dividing resistor is connected to the undervoltage detection end of the undervoltage detection unit, and the second end of the first voltage dividing resistor is connected to the first end of the second voltage dividing resistor; The first terminal of the second voltage dividing resistor is connected to the control terminal of the third switching tube, and the second terminal of the second voltage dividing resistor is grounded; the input terminal of the third switching tube is connected to the undervoltage The undervoltage control terminal of the detection unit is connected, the input terminal of the third switch tube is also connected with the undervoltage detection terminal of the undervoltage detection unit, and the output terminal of the third switch tube is grounded. 10. The TV power supply system according to claim 8, wherein the overvoltage detection unit comprises: a fourth switching tube, a third voltage dividing resistor and a fourth voltage dividing resistor; The first terminal of the third voltage dividing resistor is connected to the overvoltage detection terminal of the overvoltage detection unit, and the second terminal of the third voltage dividing resistor is connected to the control terminal of the fourth switching tube; the The input terminal of the fourth switch tube is connected to the overvoltage detection terminal of the overvoltage detection unit, and the output terminal of the fourth switch tube is connected to the overvoltage control terminal of the overvoltage detection unit; the fourth divided voltage The first end of the resistor is connected to the second end of the third voltage dividing resistor, and the second end of the fourth voltage dividing resistor is grounded.