JPH0659910U - Overcurrent protection circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] It becomes possible to return to the normal state without a large current again when returning after protection operation due to overcurrent. A second output transistor and an overcurrent detection means for detecting the first and second overcurrents are provided in parallel with the first output transistor, and the first output transistor is stopped when the overcurrent is detected. Therefore, the protection current is supplied to the load.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an overcurrent protection circuit used in a stabilized power supply circuit.

[0002]

[Prior art]

 FIG. 4 shows an embodiment of a conventional overcurrent protection circuit. In the figure, 1 is a reference voltage source, 2 is a differential amplifier, 3 is an overcurrent detection circuit, 4 is an input terminal, 5 is an output terminal, 6 is a ground terminal, Q1 is a first output transistor, Q3 and Q8 are A P-type MOS transistor, Q7 is an N-type MOS transistor, and R1, R2, R3, and R4 are resistors. The drain of the first output transistor Q1 is connected to the input terminal 4, and the gate is connected to the output of the differential amplifier 2, the source of the transistor Q3, and the gate of Q8. Further, the output terminal 5 is connected to the source, the resistors R 1 and R 2 are connected in series to the output terminal 5, and the other end is grounded. Its midpoint is connected to the non-inverting input of the differential amplifier 2. Further, the input terminal 4 is connected to the drains of the transistors Q3 and Q8, the drain of the transistor Q7 via the resistor R4 and the gate of Q3, and the source of the transistor Q7 is connected to the output terminal 5 and the gate of the transistor Q7 via the resistor R3. And connected to the source of Q8. On the other hand, the reference voltage source 1 is connected to the inverting input of the differential amplifier 2. The transistors Q7 and Q8 and the resistor R3 form an overcurrent detection circuit 3.

With such a configuration, the output voltage output with respect to the input voltage is divided by the voltage dividing ratio of the resistors R1 and R2, fed back to the differential amplifier 2, and compared with the voltage of the reference voltage source 1. The gate voltage of the first output transistor Q1 is controlled to stabilize the voltage. When a large load is applied to the output terminal 5, a large current flows through the first output transistor Q1 due to the increase in the output current, and at the same time, the current flowing through the transistor Q8 and the resistor R3 also increases, and the voltage across the resistor R3 changes. When the voltage exceeds the threshold voltage of Q7, the transistor Q7 turns on. As a result, since the transistor Q3 is turned on, the gate voltage of the first output transistor Q1 becomes "H" and turned off, and the current is cut off to protect the circuit.

[0004]

[Problems to be solved by the device]

 However, the circuit having the above characteristics has a problem that a large current flows again to the output when returning after the protection operation due to the overcurrent. An object of the present invention is to solve the above problems and to provide an overcurrent protection circuit that can return to a normal state without a large current flowing even when returning.

[0005]

[Means for Solving the Problems]

 The overcurrent protection circuit of the present invention is provided with a second output transistor in parallel with the first output transistor and an overcurrent detection means for detecting an overcurrent of the first and second output transistors. The first output transistor is stopped, and the protection circuit is supplied to the load by the second output transistor.

[0006]

[Action]

 With this configuration, the first output transistor is instantaneously stopped at the time of overcurrent, the output current value is rapidly reduced, and the power supply circuit is protected. After the overcurrent is detected, the protection current continues to flow to the load by the second output transistor, so it is possible to return to the normal state without supplying a large current when returning.

[0007]

【Example】

 FIG. 1 shows an explanatory view of the present invention. In the figure, the same reference numerals as those in FIG. 4 indicate the same or corresponding ones, and Q2 is a second output transistor. Connect the drains of the first and second output transistors to the input terminal and the sources to the output terminal in parallel, connect the gates to the overcurrent detection circuit, and connect the gates of the first and second output transistors. It was configured to control the voltage. In the operation of this circuit, the output current flowing in the first and second output transistors Q1 and Q2 is detected by the overcurrent detection circuit 3 in the normal state, and when the overcurrent is detected, the transistor Q3 is turned on, Output transistor Q1 is turned off. As a result, the output voltage and output current are instantaneously reduced. However, the second output transistor Q2 remains ON, the protection current is supplied to the load, and the output current flowing through the second output transistor Q2 is detected by the overcurrent detection circuit 3 during the recovery operation. Therefore, it shows a different characteristic from that at the time of overcurrent detection, and returns to the normal state without returning to the overcurrent value. This operating state is shown in FIG.

FIG. 2 shows an embodiment of the overcurrent protection circuit of the present invention. In the figure, the same reference numerals as those in FIGS. 1 and 4 denote the same or corresponding parts. Q4 is an N-type MOS transistor, Q5, Q6 and Q9 are P-type MOS transistors, Q10, Q11 and Q12 are inverters, and R5 is a resistor. is there. A second output transistor is provided in parallel with the first output transistor. The drains of the first and second output transistors Q1 and Q2 are connected to the input terminal 4 and the sources are connected to the output terminal 5, and the first output transistor is connected. The gate of the transistor Q1 is connected to the output of the differential amplifier 2, the source of the transistor Q3 and the gate of Q9 via a transmission gate composed of transistors Q4 and Q5. The gate of the second output transistor Q2 is connected to the output of the differential amplifier 2 and the gate of the transistor Q8. Further, the sources of the first and second output transistors Q1 and Q2 are connected to the output terminal 5, the resistors R1 and R2 are connected in series to the output terminal 5, and the other end is grounded. The intermediate point is connected to the non-inverting input of the differential amplifier 2. The input terminal 4 is connected to the drains of the transistors Q6, Q8, Q9 and the drain of the transistor Q7 and the gate of Q6 via the resistor R4. The source of the transistor Q7 is connected to the output terminal 5 and the transistor via the resistor R3. It is connected to the gate of Q7 and the sources of Q8 and Q9. Inverters Q10, Q11, Q12 are connected in series to the source of the transistor Q6, and are grounded via a resistor R5. The output of the inverter Q10 is connected to the gate of the transistor Q3. On the other hand, the reference voltage source 1 is connected to the inverting input of the differential amplifier 2. The transistors Q4, Q5, Q6, Q7, Q8, the inverters Q10, Q11, Q12, and the resistors R3, R4, R5 constitute the overcurrent detection circuit 3.

In the operation of this circuit, the output currents of the first and second output transistors Q1 and Q2 are detected by the transistors Q8 and Q9 and the resistor R3, and both transistors Q8 and Q9 are turned on in the normal state. Has become. When the output currents of the first and second output transistors Q1 and Q2 increase due to the fluctuation of the load at the output terminal, the currents flowing through the transistors Q8 and Q9 and the resistor R3 also increase. When the voltage across the resistor R3 rises and reaches an overcurrent value, the transistor Q7 turns on. Following this, the potential of the resistor R4 decreases and becomes equal to or higher than the threshold voltage of the transistor Q6, and the transistor Q6 is turned on. When the transistor Q6 is turned on, the potential of the resistor R5 changes from the ground voltage Vss to the input voltage Vin, the input of the inverter Q12 changes from "L" to "H", and the inverters Q11 and Q10 are sequentially inverted. The output of the inverter Q11 becomes "H", the output of Q10 becomes "L", the transmission gate composed of the transistors Q4 and Q5 is turned off, and the output of the inverting amplifier 2 is not added to the gate of the first output transistor Q1. . At the same time, the transistor Q3 is turned on, so that the first output transistor Q1 and the transistor Q9 are completely turned off, and the output current is reduced to protect the circuit. In this protection state, since the output current of the second output transistor Q2 is detected by the transistor Q8 and the resistor R3, the protection current becomes the maximum value at the time of restoration, and a large current does not flow. In the reset operation, when the potential of the resistor R3 becomes less than the threshold voltage of the transistor Q7, the transistor Q7 turns off, Q6 turns on, the inverters Q10, Q11, Q12 invert, and Q4, Q5 turn on, Q3 OFF. Then, the operation returns to the normal state again, and the output is supplied by the first and second output transistors Q1 and Q2.

[0010]

[Effect of device]

 As explained above, by providing the second output transistor in parallel with the first output transistor and detecting the overcurrent, it is possible to easily distinguish the overcurrent value and the return current at the time of recovery. The circuit can be returned to the normal state without sending a large current to the output side. Further, the output current value in the overloaded state can be easily set by combining the output transistors.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a circuit according to the present invention.

FIG. 2 is an embodiment of the circuit of the present invention.

FIG. 3 is a graph showing the operation of the circuit in FIG.

FIG. 4 is a conventional overcurrent protection circuit.

[Explanation of sign]

 1 Reference voltage source 2 Differential amplifier 3 Overcurrent detection circuit 4 Input terminal 5 Output terminal Q1 First output transistor Q2 Second output transistor

Claims (1)

[Scope of utility model registration request] 1. A stable device comprising a first output transistor for controlling an input voltage, and a control means for controlling a gate voltage of the first output transistor so that the negatively fed back output voltage becomes equal to a constant reference voltage. In an overcurrent protection circuit provided with an overcurrent detection means for protecting the circuit when the overcurrent of the integrated power supply circuit, a second output transistor is provided in parallel with the first output transistor, and An overcurrent protection circuit comprising: an overcurrent detection means for detecting an overcurrent; when detecting an overcurrent, the first output transistor is stopped, and a protection current is supplied to a load by the second output transistor.