CN206164076U - Short-circuit protection circuit and switching power supply circuit - Google Patents

Abstract

The utility model discloses a short-circuit protection circuit, comprising: an output current feedback pin connection end, a first diode, a voltage dividing circuit, a first switch tube, an overvoltage trigger protection pin connection end and a high-level power supply end ; The output current feedback pin connection terminal is connected to the anode of the first diode; the voltage divider circuit includes a high voltage input terminal, a ground terminal and a voltage divider node; the high voltage input terminal is connected to the first two The negative pole of the pole tube, the ground terminal is grounded, the voltage dividing node is connected to the control terminal of the first switch tube; the first end of the first switch tube is connected to the high-level power supply terminal; the first switch tube is connected to the high-level power supply terminal; A second end of a switch tube is connected to the connection end of the overvoltage trigger protection pin. The utility model also discloses a switching power supply circuit using the short circuit protection circuit. By implementing the utility model, the output can be stopped when the load is short-circuited, thereby protecting the dimming switch tube.

Description

A short circuit protection circuit and switching power supply circuit

technical field

The utility model relates to the field of electronic technology, in particular to a short-circuit protection circuit and a switching power supply circuit.

Background technique

In electronic products, white LEDs are increasingly being used as backlights for display screens. In recent years, many product designers hope that the brightness of white LEDs can be changed accordingly in different applications. Therefore, between the two output terminals of the LED driving power supply, in addition to connecting the LED load, a switch tube is added to control the current flowing through the LED load. The output current is chopped through the switching characteristics of the switching tube, so that the LED light source is continuously turned on and off, and the light characteristics of the LED can be changed by adjusting the duty ratio of the switching tube. In order to achieve constant current, a sampling resistor is usually connected, that is, the LED load, the switch tube and the sampling resistor are connected in series and connected in parallel between the output terminals of the drive power supply, and the voltage at both ends of the sampling resistor is collected to adjust the output current to achieve constant current. Purpose.

However, this kind of driving power has defects. When the LED load is short-circuited, the output voltage is borne by the switch tube, which is easily damaged due to excessive power consumption. At the same time, the current passes through the LED load, the switching tube and the sampling resistor instantaneously, and a high voltage spike will be formed at both ends of the sampling resistor, and the switching tube is also easily damaged.

Utility model content

The purpose of the utility model is to provide a short-circuit protection circuit and a switching power supply circuit, which can stop the output when the load is short-circuited, thereby protecting the dimming switch tube.

In order to achieve the above object, the utility model provides a short circuit protection circuit, comprising: output current feedback pin connection end, first diode, voltage divider circuit, first switching tube overvoltage trigger protection pin connection end and high voltage Flat power supply terminal;

The output current feedback pin connection end is connected to the anode of the first diode;

The voltage divider circuit includes a high voltage input terminal, a ground terminal and a voltage divider node; the high voltage input terminal is connected to the cathode of the first diode, the ground terminal is grounded, and the voltage divider node is connected to the first diode A control terminal of a switch tube;

The first end of the first switch tube is connected to the high-level power supply end; the second end of the first switch tube is connected to the overvoltage trigger protection pin connection end.

Implementing the utility model has the following beneficial effects:

The short circuit protection circuit provided by the utility model can make the first diode conduct when there is a high current peak at the connection end of the output current feedback pin, and load the high voltage on the voltage dividing circuit, and the voltage of the voltage dividing node will be The first switch tube is turned on, so that the overvoltage trigger protection pin is connected to the high-level power supply terminal to obtain overvoltage and trigger the protection mechanism. When applied to switching power supply circuits, when the LED load is short-circuited, the electrolysis instantly discharges through the LED load, the dimming switch tube and the output current sampling resistor, turning on the first switch tube, and triggering the switching power supply chip to turn off the output by overvoltage, thereby protecting the dimming switch. Optical switch tube.

Further, the voltage dividing circuit also includes a first resistor and a second resistor;

The first terminal of the first resistor is connected to the high voltage input terminal, the second terminal of the first resistor is connected to the first terminal of the second resistor, and the second terminal of the second resistor is connected to the ground terminal .

Further, the short circuit protection circuit further includes a first capacitor, the first end of the first capacitor is connected to the control end of the first switching transistor, and the second end of the first capacitor is grounded.

Further, the first switch transistor is an N-type field effect transistor;

The gate of the N-type field effect transistor is the control terminal of the first switch transistor, the drain of the N-type field effect transistor is the first end of the first switch transistor, and the source of the N-type field effect transistor is It is the second end of the first switching tube.

The utility model also provides a switching power supply circuit, including a power supply input terminal, a voltage conversion circuit, an LED load input terminal, an LED load output terminal, a second switching tube, a sampling resistor, a switching power supply chip, a PWM control circuit and the above-mentioned short circuit protection circuit;

The switching power supply chip includes an overvoltage trigger protection pin, a drive output pin, and an output current feedback pin;

The voltage conversion circuit includes a voltage conversion input terminal, a voltage conversion output terminal and a switch control terminal; the power supply input terminal is connected to the voltage conversion input terminal, and the voltage conversion output terminal is connected to the LED load input terminal; the switch The drive output pin of the power chip is connected to the switch control terminal;

The LED load output end is connected to the first end of the second switch tube, the second end of the second switch tube is connected to the first end of the sampling resistor, and the second end of the sampling resistor is grounded; The output end of the PWM control circuit is connected to the control end of the second switching tube; the first end of the sampling resistor is connected to the output current feedback pin;

The output current feedback pin connection end of the short circuit protection circuit is connected to the first end of the sampling resistor; the overvoltage trigger protection pin connection end is connected to the overvoltage trigger protection pin.

In the switching power supply circuit provided by the utility model, when the LED load is short-circuited, the electrolysis instantly discharges through the LED load, the dimming switch tube and the output current sampling resistor, so that the first switch tube is turned on, and the switching power supply chip is triggered to turn off the output by overvoltage, thereby Protect the dimmer switch tube.

Further, the voltage conversion circuit is a non-isolated voltage conversion circuit.

Further, the voltage conversion circuit further includes an inductor, a second diode, a third switch tube and a second capacitor;

The first end of the inductance is connected to the voltage conversion input end, the second end of the inductance is connected to the anode of the second diode, and the cathode of the second diode is connected to the voltage conversion output end;

The control end of the third switch tube is connected to the switch control end, the first end of the third switch tube is connected to the anode of the second diode, and the second end of the third switch tube is grounded;

A first end of the second capacitor is connected to the voltage conversion output end, and a second end of the second capacitor is grounded.

Further, the switching power supply circuit further includes a third diode, the anode of the third diode is connected to the first end of the sampling resistor, and the cathode of the third diode is connected to the sampling resistor. second end.

Description of drawings

Fig. 1 is the structural representation of the short-circuit protection circuit that the utility model provides;

Fig. 2 is a structural representation of an embodiment of the switching power supply circuit provided by the utility model;

FIG. 3 is a schematic structural diagram of a short circuit protection circuit in the switching power supply circuit shown in FIG. 2 .

detailed description

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 the short circuit protection circuit provided by the utility model; the short circuit protection circuit provided by the utility model includes: the output current feedback pin connection terminal FB1, the first diode D1, the voltage divider circuit 101, the first A switch tube Q1, an overvoltage trigger protection pin connection terminal OVP1 and a high-level power supply terminal 12V;

The output current feedback pin connection terminal FB1 is connected to the anode of the first diode D1;

The voltage divider circuit 101 includes a high voltage input terminal, a ground terminal and a voltage divider node; the high voltage input terminal is connected to the cathode of the first diode D1, the ground terminal is grounded, and the voltage divider node is connected to the control terminal of the first switch tube Q1;

A first end of the first switching tube Q1 is connected to a high-level power supply terminal 12V; a second end of the first switching tube Q1 is connected to an overvoltage trigger protection pin connection terminal OVP1.

When there is a high current peak at the connection terminal FB1 of the output current feedback pin, the first diode D1 is turned on, and the high voltage is applied to the voltage divider circuit 101, and the voltage of the voltage divider node turns on the first switch tube Q1, Therefore, the overvoltage trigger protection pin connection terminal OVP1 is connected to the high-level power supply terminal 12V, that is, the overvoltage is obtained and the protection mechanism is triggered.

Referring to Fig. 2, it is a schematic structural diagram of an embodiment of a switching power supply circuit provided by the present invention; the switching power supply circuit of this embodiment includes a power supply input terminal VBL, a voltage conversion circuit 201, an LED load input terminal LED+, and an LED load output terminal LED-, second switch tube Q2, sampling resistor, switching power supply chip U1, PWM control circuit 202 and short circuit protection circuit 203; wherein, the sampling resistor includes resistors RS1-RS3, and the short circuit protection circuit 203 adopts the above-mentioned overvoltage trigger protection mechanism short circuit protection circuit.

The switching power supply chip U1 includes an overvoltage trigger protection pin OVP, a drive output pin GATE, and an output current feedback pin FB; those skilled in the art know that the overvoltage trigger protection pin OVP is used to close the The output of the drive output pin GATE; the output current feedback pin FB is used to receive the sampling information of the output current, so that the switching power supply chip U1 adjusts the output of the drive output pin GATE according to the sampling information to achieve the purpose of constant current or constant voltage;

The voltage conversion circuit 201 includes a voltage conversion input terminal, a voltage conversion output terminal and a switch control terminal; the power supply input terminal is connected to the voltage conversion input terminal, and the voltage conversion output terminal is connected to the LED load input terminal; the switching power supply chip U1 The drive output pin GATE of the switching power supply chip U1 is connected to the switch control terminal; that is, the drive output pin GATE of the switching power supply chip U1 controls the switch in the voltage conversion circuit;

The LED load output terminal LED- is connected to the first terminal of the second switching tube Q2, the second terminal of the second switching tube Q2 is connected to the first terminal of the sampling resistor, and the second terminal of the sampling resistor is grounded; the output terminal VOUT of the PWM control circuit 202 Connect the control end of the second switching tube Q2; the first end of the sampling resistor is connected to the output current feedback pin FB; in the switching power supply circuit of this embodiment, after the electrical signal at the power input end passes through the voltage conversion circuit, the output voltage passes through the LED load, the second The second switch tube Q2 and the sampling resistor are grounded; the PWM control circuit 202 controls the second switch tube. Obviously, the PWM control circuit 202 can change the effective value of the output current and the LED load by adjusting the duty ratio of the second switch tube Q2. light characteristics;

The output current feedback pin connection end FB1 of the short circuit protection circuit 203 is connected to the first end of the sampling resistor; the overvoltage trigger protection pin connection end OVP1 is connected to the overvoltage trigger protection pin OVP. When the LED load is short-circuited, the electrolysis instantly discharges through the LED load, the dimming switch tube (that is, the second switch tube Q2) and the output current sampling resistors RS1~RS3, so that the first switch tube is turned on, and the switching power supply chip is triggered to turn off the output by overvoltage , thus protecting the second switching tube.

Since the short-circuit protection circuit of the output part of the switching power supply circuit needs to be connected to the pin of the switching power supply chip of the input part, that is, needs a common ground, the voltage conversion circuit of this embodiment is a non-isolated voltage conversion circuit. In one of the optional implementation manners, the voltage conversion circuit 201 further includes an inductor L1, a second diode D2, a third switching transistor Q3 and a second capacitor C2;

The first terminal of the inductor L1 is connected to the voltage conversion input terminal, the second terminal of the inductor L2 is connected to the anode of the second diode D2, and the cathode of the second diode D2 is connected to the voltage conversion output terminal;

The control end of the third switch tube Q3 is connected to the switch control terminal, the first end of the third switch tube Q3 is connected to the anode of the second diode D2, and the second end of the third switch tube Q2 is grounded; preferably, the third switch tube The second end of Q2 is grounded through the fourth resistor R4, and the voltage at the first end of the fourth resistor can be collected as feedback information and transmitted to the input current feedback pin CS of the switching power supply chip U1, so that the switching power supply chip U1 Adjust the output of the GATE pin;

A first end of the second capacitor C2 is connected to the voltage conversion output end, and a second end of the second capacitor C2 is grounded.

The above-mentioned voltage converting circuit is a BOOST boosting circuit, which can realize a boosting effect. In other implementation manners, voltage conversion circuits of other topologies may be used to replace the BOOST booster circuit according to actual needs.

In one of the optional implementation manners, the switching power supply circuit further includes a third diode D3, the anode of the third diode D3 is connected to the first end of the sampling resistor, and the third diode D3 The negative electrode of is connected to the second terminal of the sampling resistor. The third diode D3 can prevent a large current from flowing through the sampling resistor when the output is short-circuited, causing the sampling resistor to burn out.

Referring to FIG. 3 , it is a schematic structural diagram of the short circuit protection circuit 203 in the switching power supply circuit shown in FIG. 2 . The short-circuit protection circuit adopts the short-circuit protection circuit in FIG. 1 with an overvoltage trigger protection mechanism, so its working principle for realizing short-circuit protection will not be repeated here.

The voltage dividing circuit in the short circuit protection circuit 203 also includes a first resistor R1 and a second resistor R2; the first end of the first resistor R1 is connected to the high voltage input end, and the second end of the first resistor R1 is connected to the first end of the second resistor R2. terminal, and the second terminal of the second resistor R2 is connected to the ground terminal. In other implementation manners, other components and structures may be used to achieve voltage division to achieve better circuit effects, for example, voltage regulator tubes and resistors are used to achieve voltage division.

In addition, the short circuit protection circuit 203 further includes a first capacitor C1, the first end of the first capacitor C1 is connected to the control end of the first switch C1, and the second end of the first capacitor C1 is grounded. The first capacitor C1 filters the control terminal of the first switch transistor Q1.

As a preferred implementation manner, the first switching transistor Q1 is an N-type field effect transistor;

The grid G of the N-type field effect transistor is the control terminal of the first switching transistor Q1, the drain D of the N-type field effect transistor is the first end of the first switching transistor Q1, and the source S of the N-type field effect transistor is It is the second terminal of the first switching transistor Q1. In other embodiments, the first switching tube Q1 can also be replaced by an NPN transistor or other three-terminal control switching device or its derivatives. In different applications, depending on the actual circuit power consumption, cost, driving power and The parameter matching of the drive control components of the switch tube requires reasonable selection and setting. The selection and setting of the switch tube is a common design process in the prior art, and will not be repeated here.

The short circuit protection circuit provided by the utility model can make the first diode conduct when there is a high current peak at the connection end of the output current feedback pin, and load the high voltage on the voltage dividing circuit, and the voltage of the voltage dividing node will be The first switch tube is turned on, so that the overvoltage trigger protection pin is connected to the high-level power supply terminal to obtain overvoltage and trigger the protection mechanism. When applied to switching power supply circuits, when the LED load is short-circuited, the electrolysis instantly discharges through the LED load, the dimming switch tube and the output current sampling resistor, turning on the first switch tube, and triggering the switching power supply chip to turn off the output by overvoltage, thereby protecting the dimming switch. Optical switch tube.

The above are the preferred embodiments of the present utility model, and 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 deformations can also be made, and these improvements and deformations are also considered It is the protection scope of the utility model.

Claims (8)

1. a kind of short-circuit protection circuit, it is characterised in that include：Output current feedback pin connection end, the first diode, partial pressure Circuit, first switch pipe, over-pressed trigger protection pin connection end and high level feeder ear；

The output current feedback pin connection end connects the positive pole of first diode；

The bleeder circuit includes high voltage input terminal, earth terminal and partial pressure node；The high voltage input terminal connection the described 1st The negative pole of pole pipe, the earth terminal ground connection, the control end of first switch pipe described in the partial pressure Node connectedness；

The first end of the first switch pipe connects the high level feeder ear；The second end connection of the first switch pipe is described Over-pressed trigger protection pin connection end.

2. short-circuit protection circuit as claimed in claim 1, it is characterised in that the bleeder circuit also includes first resistor and the Two resistance；

The first end of the first resistor connects the high voltage input terminal, and the second end connection of the first resistor is described second electric The first end of resistance, the second end of the second resistance connects the earth terminal.

3. short-circuit protection circuit as claimed in claim 1 or 2, it is characterised in that the short-circuit protection circuit also includes first Electric capacity, the first end of first electric capacity connects the control end of the first switch pipe, the second end ground connection of first electric capacity.

4. short-circuit protection circuit as claimed in claim 1 or 2, it is characterised in that the first switch pipe is N-type field effect Pipe；

The grid of the N-type field effect transistor is the control end of the first switch pipe, and the drain electrode of the N-type field effect transistor is described The first end of first switch pipe, the source electrode of the N-type field effect transistor is the second end of the first switch pipe.

5. a kind of switching power circuit, it is characterised in that including power input, voltage conversion circuit, LED load input, LED load outfan, second switch pipe, sampling resistor, switching power source chip, pwm control circuit and as Claims 1-4 appoint Short-circuit protection circuit described in one；

The switching power source chip includes over-pressed trigger protection pin, drives output pin, output current feedback pin；

The voltage conversion circuit includes voltage conversion input, voltage conversion outfan and switch control terminal；The power supply is defeated Enter the end connection voltage conversion input, the voltage conversion outfan connects the LED load input；The switch electricity The driving output pin of source chip connects the switch control terminal；

The LED load outfan connects the first end of the second switch pipe, the second end connection institute of the second switch pipe State the first end of sampling resistor, the second end ground connection of the sampling resistor；The outfan connection described the of the pwm control circuit The control end of two switching tubes；The first end of the sampling resistor connects the output current feedback pin；

The output current feedback pin connection end of the short-circuit protection circuit connects the first end of the sampling resistor；The overvoltage Trigger protection pin connection end connects the over-pressed trigger protection pin.

6. switching power circuit as claimed in claim 5, it is characterised in that the voltage conversion circuit is non-isolation type voltage Change-over circuit.

7. switching power circuit as claimed in claim 5, it is characterised in that the voltage conversion circuit also include inductance, the Two diodes, the 3rd switching tube and the second electric capacity；

The first end of the inductance connects the voltage conversion input, and the second end of the inductance connects second diode Positive pole, the negative pole of second diode connects the voltage conversion outfan；

The control end of the 3rd switching tube connects the switch control terminal, the first end connection of the 3rd switching tube described the The positive pole of two diodes, the second end ground connection of the 3rd switching tube；

The first end of second electric capacity connects the voltage conversion outfan, the second end ground connection of second electric capacity.

8. the switching power circuit as described in any one of claim 5 to 7, it is characterised in that the switching power circuit is also wrapped Include the 3rd diode, the positive pole of the 3rd diode connects the first end of the sampling resistor, the 3rd diode it is negative Pole connects the second end of the sampling resistor.