TWI445273B - Over current protection circuit - Google Patents

Description

Overcurrent protection circuit

The present invention relates to a protection circuit, and more particularly to an overcurrent protection circuit.

The overcurrent generated by the electronic device during startup or when the load circuit changes not only affects the normal operation of the entire electronic device, but may even cause damage to the entire system. Therefore, it is necessary to design an appropriate overcurrent protection circuit in the electronic device, to limit the current to prevent the overcurrent from damaging the entire system, and limiting the current can also help to reduce the size of the power supply. Conventionally, the error amplifier can be used to detect whether the load current is too large at the input end of the switching power supply, and according to the detection result, an overcurrent control signal required by the system is generated to control the current input to the load.

FIG. 1 is a schematic diagram of a conventional overcurrent protection circuit 100. The overcurrent protection circuit 100 is coupled between a power input terminal Vin and a load 101 for controlling a switch 104. The overcurrent protection circuit 100 includes a current detection circuit 103 and a control unit 106. The switch is implemented as an N-type transistor 104. The magnitude of the current I on the power supply path 105 varies with the load 101. When the current detecting circuit 103 detects that the current I of the power supply path 105 is at a limited value, the control unit 106 will pass the N-type transistor 104. The state is set to be fully turned on, that is, the gate voltage of the N-type transistor 104 is controlled to a high level state. The magnitude of the current of the N-type transistor 104 is related to the voltage difference between its gate and source. Therefore, once the current detecting circuit 103 detects an overcurrent condition of the power supply path 105, the control unit 106 reduces the voltage difference between the gate and the source by lowering the gate voltage of the N-type transistor 104, thereby limiting the amount of current that can be transmitted through the N-type transistor 104 to the load 101.

It is an object of the present invention to provide an effective and stable overcurrent protection circuit.

According to an aspect of the present invention, an overcurrent protection circuit is provided. The overcurrent protection circuit is coupled to the current path between the output of a switch and a load. The overcurrent protection circuit includes a first overcurrent detection unit, a second overcurrent detection unit, and a control unit. The first overcurrent detecting unit is coupled between the current path and a first voltage for outputting a first control signal according to the current on the current path. The second overcurrent detecting unit is coupled between the current path and a second voltage for outputting a second control signal according to the current on the current path. The control unit is coupled to the first overcurrent detecting unit and the second overcurrent detecting unit, and controls the switch according to the first control signal or the second control signal to reduce the current on the current path.

In one embodiment, the switch is a transistor, and the transistor is coupled to a power input terminal, and the source terminal of the transistor is coupled to the current path.

In an embodiment, the control unit further includes: a gate voltage supply circuit, a first N-type transistor, and a second N-type transistor, wherein the first N-type transistor is coupled to the gate of the transistor Extremely, the gate terminal of the first N-type transistor receives the first control signal, the second terminal of the second N-type transistor is coupled to the gate terminal of the transistor, and the gate terminal of the second N-type transistor receives the second control signal.

In one embodiment, the first overcurrent detecting unit further includes: a first amplifier, a third N-type transistor, a first resistor, and a second resistor. The first amplifier has a positive terminal, a negative terminal and an output terminal; the positive terminal and the negative terminal of the first amplifier are sequentially coupled to the current path according to the current direction on the current path, and the third N-type transistor The gate is coupled to the output of the first amplifier, and the third N-type transistor is coupled to the positive terminal of the first amplifier; the first resistor couples the positive terminal of the first amplifier to the current path; The source terminal of the type transistor is coupled to the first voltage through the second resistor, wherein a first control signal is generated when a current flows through the second resistor.

In one embodiment, the second overcurrent detecting unit further includes: a second amplifier, a first P-type transistor, a second P-type transistor, a third resistor, and a fourth resistor. The second amplifier has a positive terminal, a negative terminal and an output terminal, and the negative terminal and the positive terminal of the second amplifier are sequentially coupled to the current path according to the current direction on the current path; the first P-type transistor The gate terminal is coupled to the output end of the second amplifier, the first terminal of the first P-type transistor is coupled to the positive terminal of the first amplifier, and the source terminal of the first P-type transistor is coupled to the second voltage; the second P-type battery Forming a current mirror circuit with the first P-type transistor, wherein a gate terminal of the second P-type transistor is coupled to an output terminal of the second amplifier, and a source terminal of the second P-type transistor is coupled to the second voltage; a third resistor coupling the positive terminal of the second amplifier to the current path; a second terminal of the second P-type transistor is coupled to the fourth resistor, wherein the second control is generated when a current flows through the fourth resistor signal.

In one embodiment, when the current path generates an overcurrent, the third N-type transistor outputs a first current according to the overcurrent at the source terminal of the third N-type transistor. Generating the first current when the first current flows through the second resistor And controlling a signal to turn on the first N-type transistor to change a gate voltage of the switch to reduce a current on the current path.

In one embodiment, when the current path generates an overcurrent, according to the overcurrent, the first P-type transistor outputs a second current through the current mirror structure at the drain of the second P-type transistor. The second current flows through the fourth resistor to generate the second control signal to turn on the second N-type transistor to change the gate voltage of the switch to reduce the current on the current path.

In summary, the present invention couples at least one first overcurrent detecting unit and a second overcurrent detecting unit to the current path connected to the load to provide overcurrent protection. By setting the operating voltages of the first overcurrent detecting unit and the second overcurrent detecting unit, the starting timing and protection range of the two overcurrent detecting units can be determined to provide more comprehensive protection.

The following description of the preferred embodiments of the invention is in the

Fig. 2 is a schematic illustration of an overcurrent protection circuit in accordance with an embodiment of the present invention. The overcurrent protection circuit 200 of the present invention is coupled between the output end of a switch 204 and a load end 211. The overcurrent protection circuit 200 includes a first overcurrent detection unit 201, a second overcurrent detection unit 202, and a control unit 203. In the following embodiments, the switch 204 is implemented as an N-type transistor to illustrate the application of the present invention. However, in other embodiments, the switch can also be implemented as a P-type transistor. The switch 204 is coupled to the power input terminal 210 for receiving an input. The input voltage Vin is coupled to a current path 205 for providing an output voltage Vout to the load terminal 211 for supplying power to a load 212. The first overcurrent detecting unit 201 is coupled to the current path 205 for outputting a first signal S1 corresponding to one of the currents flowing through the current path 205. The second overcurrent detecting unit 202 is also coupled to the current path 205 for outputting a second signal S2 corresponding to one of the currents flowing through the current path 205. The control unit 203 is coupled to the first overcurrent detecting unit 201 and the second overcurrent detecting unit 202. When the first signal S1 or the second signal S2 is received, a control signal is outputted to the switch 204. The gate terminal is used to drive the switch 204 to reduce the current flowing through the current path 205 for overcurrent protection.

Fig. 3 is a circuit diagram of an overcurrent protection circuit according to an embodiment of the present invention. According to the present invention, the control unit 303 includes a first N-type transistor 3031, a second N-type transistor 3032, and a gate voltage supply circuit 3033. When the current path 305 does not have an overcurrent, the switch 304 is controlled by the gate voltage. Supply circuit 3033 provides a voltage to control the amount of current that switch 304 transmits to current path 305. Conversely, when an overcurrent occurs in the current path 305, the first overcurrent detecting unit 301 generates the first signal S1, or the second overcurrent detecting unit 302 generates the second signal S2 to respectively control the first N type The crystal 3031 or the second N-type transistor 3032 is turned on, so as to drive the switch 304 to reduce the current flowing through the current path 305 to achieve the purpose of overcurrent protection, wherein the first overcurrent detecting unit 301 and the second overcurrent detecting unit 302 The mode of operation is as follows.

The first overcurrent detecting unit 301 includes a first amplifier 3011, a first resistor 3012, a third N-type transistor 3013, and a second resistor 3014. Wherein, the first amplifier 3011, the first resistor 3012, and the third N The transistor 3013 and the second resistor 3014 form a negative feedback relationship, and the first overcurrent detecting unit 301 pulls the positive and negative terminals of the first amplifier 3011 to the equipotential by utilizing the characteristics of the overall negative feedback. . The output of the first amplifier 3011 is coupled to the gate of the third N-type transistor 3013, and the positive and negative terminals of the first amplifier 3011 are coupled to the current path 305, and the first amplifier 3011 is based on the current. The I1 direction sequentially couples the positive and negative terminals to the current path 305. The source of the third N-type transistor 3013 is coupled to the voltage Vss through the resistor 3014, and the drain of the third N-type transistor 3013 is coupled to the positive terminal of the first amplifier 3011.

In one embodiment, the current path 305 has a path resistance Rs, and the currents flowing through the path resistance Rs and the first resistor 3012 are current I1 and current I2, respectively, and the magnitudes of the current I1 and the current I2 are equal to the path resistance Rs and The ratio of the first resistor 3012 is related. When the current increases in the current path 305, that is, the current I1 flowing through the path resistance Rs is increased, the current I2 is relatively increased due to the characteristics of the negative feedback. And the positive terminal and the negative terminal of the first amplifier 3011 are sequentially coupled to the current path 305 according to the flow direction of the current I1, so that the output terminal of the first amplifier 3011 outputs a high level potential to turn on the third N-type transistor 3013. The increased current I2 is transmitted to the second resistor 3014 via the turned-on third N-type transistor 3013 for generating the first signal S1, that is, across the voltage level on the second resistor 3014, when the voltage level is greater than When the initial voltage of the first N-type transistor 3031 in the control unit 303 is turned on, the first N-type transistor 3031 is turned on, and the gate voltage of the switch 304 is pulled down to achieve the purpose of overcurrent protection. When the gate voltage of the switch 304 is pulled down to a specific value, the output voltage Vout also drops to a specific voltage, so that the second overcurrent detecting unit 302 is activated.

The second overcurrent detecting unit 302 includes a second amplifier 3021, a third resistor 3022, a fourth resistor 3025, and a current mirror circuit formed by the first P-type transistor 3023 and the second P-type transistor 3024. . The second amplifier 3021, the third resistor 3022, the current mirror circuit and the fourth resistor 3025 form a negative feedback relationship, and the second overcurrent detecting unit 302 utilizes the characteristics of the overall negative feedback to apply the second amplifier. The positive and negative ends of 3021 are pulled to the equipotential. The output of the second amplifier 3021 is coupled to the gate terminals of the first P-type transistor 3023 and the second P-type transistor 3024, and the positive and negative terminals of the second amplifier 3012 are coupled to the current path 305, and The second amplifier 3011 couples the negative and positive terminals to the current path 305 in sequence according to the current I1 flowing on the current path 305. The source of the first P-type transistor 3023 and the second P-type transistor 3024 is coupled to the voltage Vdd, the first terminal of the first P-type transistor 3023 is coupled to the positive terminal of the second amplifier 3021, and the second P-type is The top of the crystal 3024 is coupled to the fourth resistor 3025.

In one embodiment, the current path 305 has a path resistance Rs, and the currents flowing through the current path 305 and the third resistor 3022 are current I1 and current I3, respectively, and the magnitudes of the current I1 and the current I3 are equal to the path resistance Rs and The ratio of the third resistor 3022 is related. When the current increases in the current path 305, that is, the current flowing through the path resistance Rs is increased by I1, the current I3 is relatively increased due to the negative feedback characteristic. And because the second amplifier 3021 sequentially couples the negative terminal and the positive terminal to the current path 305 according to the current direction, so that the output terminal of the second amplifier 3012 outputs a low level potential to turn on the first P-type transistor 3023 and the second. P-type transistor 3024. And since the first P-type transistor 3023 and the second P-type transistor 3024 form a current mirror circuit, the increased current I3 is also formed in equal proportion to the second P-type battery. The drain of the crystal 3024 is used to generate the second signal S2, that is, across the voltage level on the fourth resistor 3025. When the voltage level is greater than the initial voltage of the second N-type transistor 3032 in the control unit 303. The second N-type transistor 3032 is turned on, and the gate voltage of the switch 304 is pulled down to achieve the purpose of overcurrent protection.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention, and the present invention can be modified and modified without departing from the spirit and scope of the present invention. The scope is subject to the definition of the scope of the patent application attached.

100‧‧‧Overcurrent protection circuit

101‧‧‧Load circuit

103‧‧‧ Current detection circuit

104‧‧‧N type transistor

105‧‧‧Power supply path

106‧‧‧Control unit

200‧‧‧Overcurrent protection circuit

201 and 301‧‧‧First overcurrent detection unit

202 and 302‧‧‧Second overcurrent detection unit

203 and 303‧‧‧ control units

204 and 304‧‧‧ switches

205 and 305‧‧‧ current paths

210‧‧‧Power input

211‧‧‧Load side

212‧‧‧load

3011‧‧‧First amplifier

3012‧‧‧First resistance

3013‧‧‧ Third N-type transistor

3014‧‧‧second resistance

3021‧‧‧second amplifier

3022‧‧‧ Third resistor

3023‧‧‧First P-type transistor

3024‧‧‧Second P-type transistor

3025‧‧‧fourth resistor

3031‧‧‧First N-type transistor

3032‧‧‧Second N-type transistor

3033‧‧‧gate voltage supply circuit

Rs‧‧‧ path resistance

I1, I2 and I3‧‧‧ current

S1‧‧‧ first signal

S2‧‧‧ second signal

The above and other objects, features, advantages and embodiments of the present invention will become more apparent and understood.

Fig. 2 is a schematic diagram showing an overcurrent protection circuit according to an embodiment of the present invention.

Fig. 3 is a circuit diagram showing an overcurrent protection circuit according to an embodiment of the present invention.

200‧‧‧Overcurrent protection circuit

201‧‧‧First overcurrent detection unit

202‧‧‧Second overcurrent detection unit

203‧‧‧ a control unit

204‧‧‧Switch

205‧‧‧ Current path

210‧‧‧Power input

211‧‧‧Load side

212‧‧‧load

Claims (9)

An overcurrent protection circuit is coupled between a switch output end and a load current path, and includes at least: a first overcurrent detecting unit coupled between the current path and a first voltage for The current on the current path outputs a first control signal; a second overcurrent detection unit is coupled between the current path and a second voltage for outputting a second control signal according to the current on the current path; And a control unit coupled to the first overcurrent detecting unit and the second overcurrent detecting unit, and controlling the switch according to the first control signal or the second control signal to reduce current on the current path. The overcurrent protection circuit of claim 1, wherein the switch is a transistor, wherein the transistor is coupled to a power input terminal, and the source terminal of the transistor is coupled to the current path. The overcurrent protection circuit of claim 2, wherein the control unit further comprises: a gate voltage supply circuit coupled to the gate terminal of the transistor; a first N-type transistor, the first The anode of the N-type transistor is extremely coupled to the gate terminal of the transistor, the gate terminal of the first N-type transistor receives the first control signal; and a second N-type transistor, the second N-type transistor汲 Extremely coupled to the gate terminal of the transistor, the gate terminal of the second N-type transistor receives the first Two control signals. The overcurrent protection circuit of claim 3, wherein the first overcurrent detection unit further includes: a first amplifier having a positive terminal, a negative terminal, and an output terminal, wherein the first The positive and negative terminals of the amplifier are sequentially coupled to the current path according to the current direction on the current path; a third N-type transistor, the gate terminal of the third N-type transistor is coupled to the first amplifier An output terminal of the third N-type transistor is coupled to the positive terminal of the first amplifier; a first resistor coupling the positive terminal of the first amplifier to the current path; and a second resistor The source terminal of the third N-type transistor is coupled to the first voltage through the second resistor, wherein the first control signal is generated when a current flows through the second resistor. The overcurrent protection circuit of claim 4, wherein the second overcurrent detection unit further comprises: a second amplifier having a positive terminal, a negative terminal, and an output terminal, wherein the second The negative terminal and the positive terminal of the amplifier are sequentially coupled to the current path according to the current direction on the current path; a first P-type transistor, the gate terminal of the first P-type transistor is coupled to the second amplifier An output terminal, the first terminal of the first P-type transistor is coupled to the positive terminal of the first amplifier, and a source terminal of the first P-type transistor is coupled to the second voltage; A second P-type transistor and the first P-type transistor form a current mirror circuit, wherein a gate terminal of the second P-type transistor is coupled to the output end of the second amplifier, the second P-type transistor The source is extremely coupled to the second voltage; a third resistor couples the positive terminal of the second amplifier to the current path; and a fourth resistor, the second P-type transistor is coupled to the pole A four resistor, wherein the second control signal is generated when a current flows through the fourth resistor. The overcurrent protection circuit of claim 5, wherein when the current path generates an overcurrent, the third N-type transistor outputs a source at the source terminal of the third N-type transistor according to the overcurrent. The first current. The overcurrent protection circuit of claim 6, wherein the first current flows through the second resistor to generate the first control signal to turn on the first N-type transistor to change a gate voltage of the switch. , reducing the current on the current path. The overcurrent protection circuit of claim 5, wherein when the current path generates an overcurrent, the first P-type transistor is transmitted through the current mirror structure to the second P-type according to the overcurrent The drain of the crystal outputs a second current. An overcurrent protection circuit as described in claim 8 of the patent application, The second current is generated when the second current flows through the fourth resistor to turn on the second N-type transistor to change the gate voltage of the switch to reduce the current on the current path.