TWI399630B - Current restrictor - Google Patents

Description

Current limiter

The present invention relates to a power supply circuit, and more particularly to a current limiter for use in a weak current circuit.

At present, most portable electronic products are powered by batteries, and charging circuits for charging are also provided in electronic products. The charging circuit is controlled by an internal microprocessor of the electronic product. When the charging function is activated, the microprocessor sends a control signal to the charging circuit, and the charging circuit connects the received external power source to the battery according to the control signal to charge the battery.

However, when the charging circuit is turned on to the external power source and the battery, a large inrush current is usually generated, and this inrush current easily causes damage to components or batteries in the charging circuit.

In view of this, it is necessary to provide a current limiter that can avoid inrush current.

A current limiter is configured to control the on and off of the power supply through the current limiter according to the control signal, the current limiter includes: a buffer unit, a first switch unit and a second switch unit, wherein the buffer unit is configured to receive the control signal And controlling the first switch unit to be gradually turned on; the first switch unit is used for controlling by its own gradual conduction The second switching unit is gradually turned on; the second switching unit is configured to receive an input of the power source and gradually increase the output of the power source under the control of the first switching unit.

The current limiter controls the first switching unit and the second switching unit to be gradually turned on by the buffer unit, thereby preventing the second switching unit from receiving an input current and generating an inrush current when conducting, thereby ensuring circuit safety.

100‧‧‧ Controller

204‧‧‧First switch unit

200‧‧‧ current limiter

206‧‧‧Second switch unit

300‧‧‧Battery

208‧‧‧Filter unit

202‧‧‧buffer unit

Q1‧‧‧Triode

R1‧‧‧matching resistor

R4‧‧‧voltage resistor

R2‧‧‧discharge resistor

Q2‧‧‧ Field Effect Transistor

R3‧‧‧Charging resistor

L1‧‧‧Inductance

C1‧‧‧ snubber capacitor

C2‧‧‧First filter capacitor

20‧‧‧Signal input

C3‧‧‧Second filter capacitor

30‧‧‧Power input

40‧‧‧Power output

1 is a block diagram of a charging system of a preferred embodiment.

2 is a detailed block diagram of the current limiter shown in FIG. 1.

FIG. 3 is a specific circuit diagram of the current limiter shown in FIG. 1.

Please refer to FIG. 1 , which is a structural diagram of a charging system 10 according to a preferred embodiment, including a controller 100, a current limiter 200 and a battery 300, which are sequentially connected.

The controller 100 is configured to generate and send a control signal to the current limiter 200 to activate the charging function. The control signal is usually a high level signal, and the control signal generation may be generated automatically according to a user operation or after the electronic product is connected to the charger. The current limiter 200 is configured to receive power and transmit the power to the battery 300 according to the control signal.

Please refer to FIG. 2 , which is a specific module diagram of the current limiter 200 shown in FIG. 1 , including a buffer unit 202 , a first switching unit 204 , a second switching unit 206 , and a filtering unit 208 .

The buffer unit is configured to receive the control signal 202 and control the first switch unit 204 to be gradually turned on.

The first switching unit 204 is configured to gradually turn the second switching unit 206 on and off by its own gradual conduction and turn-off.

The second switching unit 206 is configured to receive an input of the power source and utilize its own gradual conduction characteristic when conducting, to gradually increase the output current to a stable value.

The filtering unit 208 is configured to filter and output the current output by the second switching unit 206 to provide battery charging or other circuits.

Please refer to FIG. 3 , which is a specific circuit diagram of the current limiter 200 shown in FIG. 1 . The buffer unit 202 includes an input matching resistor R1, a discharge resistor R2, a charging resistor R3, and a snubber capacitor C1. The first switching unit 204 is a triode Q1. The second switching unit 206 includes a voltage dividing resistor R4 and a P channel enhanced field effect transistor Q2. The filtering unit 208 includes an inductor L1 and a first filter capacitor C2 and a second filter capacitor C3. The current limiter 200 further includes a signal input terminal 20, a power input terminal 30, and a power output terminal 40.

The input matching resistor R1 is connected between the signal input terminal 20 and the base of the transistor Q1. The charging resistor R3 and the snubber capacitor C1 are connected in series and then connected in parallel with the discharge resistor R2 between the base of the transistor Q1 and the ground. The emitter of the transistor Q1 is grounded. The collector of the transistor Q1 is connected to the power supply input terminal 30 via a voltage dividing resistor R4. The source of the field effect transistor Q2 is connected to the power supply input terminal 30, and the gate of the field effect transistor Q2 is connected to the collector of the transistor Q1. The drain of field effect transistor Q2 is coupled to power supply output 40 via inductor L1. The first filter capacitor C2 and the second filter capacitor C3 are respectively connected between the two ends of the inductor L1 and the ground.

After the high level control signal is input from the signal input terminal 20, the charging resistor is first used. R3 charges the snubber capacitor C1. As the amount of charge of the snubber capacitor C1 increases, the voltage of the base of the triode Q1 gradually increases, thereby causing the transistor Q1 to be gradually turned on. Further, because Q1 is gradually turned on and the input of the power supply at the power input terminal 30, the current on the voltage dividing resistor R4 is gradually increased, that is, the voltage difference between the gate and the source of the field effect transistor Q2 is gradually increased, thereby making the field The effect transistor Q2 is gradually turned on, and the output current of the drain is gradually increased. Finally, the filter circuit composed of the first filter capacitor C2, the second filter capacitor C3, and the inductor L1 is filtered and output from the power output terminal 40. After the power is turned off, the power on the snubber capacitor C1 can be discharged by the charging resistor R3 and the discharging resistor R2 to prepare for the next buffering.

In this way, by the charging buffer function of the snubber capacitor C1, the control signal for converting the high-level control signal into a voltage gradually increasing is supplied to the subsequent switching unit, so that the respective switching units are gradually turned on, and the output current is gradually increased to avoid the impact. The generation of current ensures the safety of the circuit.

It is to be understood by those skilled in the art that the above embodiments are only intended to illustrate the invention, and are not intended to limit the invention, as long as it is within the spirit of the invention Changes and modifications are intended to fall within the scope of the invention.

200‧‧‧ current limiter

202‧‧‧buffer unit

204‧‧‧First switch unit

206‧‧‧Second switch unit

208‧‧‧Filter unit

Claims (9)

A current limiter is configured to control the on and off of the power supply through the current limiter according to the control signal, wherein the current limiter comprises: a buffer unit, a first switch unit and a second switch unit, wherein the buffer unit is used for Receiving the control signal and controlling the first switch unit to be gradually turned on; the first switch unit is configured to gradually control the second switch unit to be turned on by its own gradually conducting; the second switch unit is configured to receive an input of the power source and The output of the power supply is gradually increased under the control of the first switching unit. The current limiter of claim 1, wherein the current limiter further comprises a control signal input end for receiving the control signal, the buffer unit comprises a snubber capacitor and a discharge resistor, the control signal input end and the first The switch unit is connected, and the snubber capacitor is connected in parallel with the discharge resistor between the control signal input terminal and the ground. The current limiter of claim 2, wherein the buffer unit further comprises a charging resistor, the charging resistor is connected in series with the snubber capacitor and then connected in parallel with the discharging resistor. The current limiter of claim 2, wherein the buffer unit further comprises an input matching resistor connected between the signal input end and the first switching unit. The current limiter of claim 1, wherein the first switch unit is a triode, the base thereof is connected to the signal input end, the emitter is grounded, and the collector is connected to the second switch unit. The current limiter of claim 1, wherein the current limiter further comprises The power input end is for receiving power, the second switch unit comprises a voltage dividing resistor and a field effect transistor, and the voltage dividing resistor is connected between the power input end and the first switching unit, the source and the gate of the field effect transistor The poles are respectively connected at both ends of the voltage dividing resistor, and the drain of the field effect transistor is used for the output of the power source. The current limiter of claim 6, wherein the field effect transistor is a P channel enhanced field effect transistor, and a source of the field effect transistor is connected between the voltage dividing resistor and the power input end. The gate of the field effect transistor is connected between the voltage dividing resistor and the first switching unit. The current limiter of claim 1, wherein the current limiter further comprises a filtering unit and a power output end, the filtering unit is located between the second switching unit and the power output end, and is configured to use the second switching unit The output current is filtered and output. The current limiter of claim 8, wherein the filtering unit comprises an inductor, a first filter capacitor and a second filter capacitor, wherein the inductor is respectively connected to the second switch unit and the power output, the first filter capacitor And the second filter capacitor is respectively connected in parallel between the two ends of the inductor and the ground.