JPH0625910U - Overcurrent protection circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] In a DC power supply circuit for high current output that combines a stabilizing circuit and a transistor for regulators, minimizes power loss when an overcurrent condition occurs due to a load short circuit or the like. And an overcurrent prevention circuit for automatically returning to a normal energized state when an abnormal state on the load side is resolved. [Structure] The voltage detection circuit 3 detects a drop in the output voltage due to a short-circuit of the load 2, etc., and stabilizes as [Q3 OFF → Q4 ON → Q2 OFF] due to the Q3 base voltage drop in the output control circuit 4. Circuit 1 and regulator transistor Q1 are turned on simultaneously
Set to FF. On the other hand, the return pulse generation circuit 5 outputs a return pulse with a short duration to the base of Q3.
If the abnormal state remains, the voltage detection circuit 3 cannot obtain a predetermined voltage and thus does not contribute to the recovery, and when the abnormality of the load 2 is resolved, the normal energized state is restored.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an overcurrent prevention circuit, which detects a overcurrent state in a DC power supply circuit for a large current output that combines a stabilizing circuit and a transistor for a regulator, shuts off the current, and eliminates an abnormal state. It relates to a circuit configuration that automatically restores energization operation.

[0002]

[Prior art]

 Generally, when a DC power supply circuit rectifies a commercial power source and supplies a DC constant voltage to an electronic device, ripples are included even if a smoothing capacitor is used, and the voltage fluctuation increases as the electronic device is used. The DC voltage obtained from the rectifying / smoothing circuit is stabilized by using a stabilizing circuit. In recent years, a stabilization circuit with a dedicated IC is commercially available, and a method of variably setting the output voltage by selecting the value of an external resistor is used.

However, if the output current of the DC power supply circuit is up to about 1 A, the output of the stabilizing circuit can be used as it is, but it is necessary to pass a current (for example, 10 to 20 A) higher than that. In this case, since the current capacity is insufficient, the circuit configuration that combines the above-mentioned stabilizing circuit and transistor for regulator is adopted. FIG. 2 shows a typical circuit thereof. For example, the reference voltage between the terminals bc of the stabilizing circuit 1 is 1.25V, and the output voltage Vo is Vo = 1.25 × when the resistance R1 is 100 to 500Ω. It is given by (1 + R2 / R1), and the current required by load 2 is supplied by stabilizing circuit 1 and PNP transistor Q1 for the regulator while maintaining its constant voltage output. Capacitor C1 is provided to remove the ripple included on the input side, and capacitors C2 and C3 connected to input terminal a and output terminal b of stabilizing circuit 1 prevent abnormal oscillation. It is provided in.

In the above circuit, the PNP transistor Q1 must have a collector-emitter withstand voltage characteristic sufficiently larger than the voltage obtained by subtracting the minimum value Vomin of the output voltage from the maximum value Vimax of the rectified voltage. Since the collector current Ic must flow the maximum value of the output current Io, the collector loss Pcmax is Pcmax ≥ (Vimax-Vomin) × Iomax. There must be.

By the way, when the load 2 is short-circuited, assuming that the DC current amplification factor of the PNP transistor Q1 is h _FE , a current approximately h _FE times the limiting current by the stabilizing circuit 1 and a voltage substantially equal to the input voltage are obtained. The power given as the product of becomes the power loss Pc in the PNP transistor Q1, and a very large power loss occurs.

Therefore, the output current is detected, and when a preset current value is exceeded, the output current is shifted to a constant current state, or the current-voltage characteristic is a so-called fold-back characteristic, and the output current is changed to the rated current. A current limiting circuit that suppresses the current to 1/2 to 1/3 is often provided.

[0007]

[Problems to be solved by the device]

 However, in the case of a large-current DC power supply circuit with an output current of about 10 A or more, when the load is short-circuited, the above-mentioned transition control to the constant current state and fold-down control are used to limit the current. However, the power loss in the regulator transistor is extremely large, and it is often the case that the power loss is more than double that in normal operation. Even if the current is limited, the load is energized, which may cause a secondary accident such as ignition.

On the other hand, the power loss can be considerably reduced by controlling the current to about 1/5 to 1/10 of the rated current by the fold-back type control, but conversely, the short circuit of the load is eliminated. At times, it is extremely difficult to automatically recover, and it is necessary to provide a reset button and manually recover.

Therefore, the present invention, in a DC power supply circuit for high current output, which combines a stabilizing circuit and a transistor for a regulator, immediately cuts off the output current when an overcurrent condition is caused by a short circuit of a load or the like. It was created for the purpose of providing an overcurrent prevention circuit that can return to the normal operation state when the abnormal condition on the load side is eliminated, with almost no power loss.

[0010]

[Means for Solving the Problems]

 The present invention relates to a DC power supply circuit that outputs a large current with a regulator transistor while maintaining a constant output voltage with a stabilization circuit, and a voltage detection circuit that detects the output voltage and a detection voltage of the voltage detection circuit. An output control circuit that turns off the stabilization circuit and the transistor for the regulator when the value is below a certain value, and a signal with a duration of 0.1 seconds or less as a switching signal from the OF control state to the ON control state of the output control circuit The present invention relates to an overcurrent prevention circuit, which is provided with a return signal generation circuit that intermittently outputs the signal at intervals of 1 second to 10 seconds.

[0011]

[Action]

 The output voltage drops when an overcurrent flows, such as when a load is short-circuited.However, the output voltage is detected by the voltage detection circuit, and if the detected voltage drops below a certain value, the output control circuit stabilizes. Turn off the circuit and regulator transistor. In the present invention, unlike the current limiting method, the output current does not flow because the current is completely cut off, and the power loss in the stabilizing circuit and the transistor for the regulator becomes extremely small.

On the other hand, in the output control circuit, once the stabilization circuit and the transistor for the regulator are turned off, a signal to start them up is required, and a complete start-up recovers from the abnormality on the output side. Must be done at the time. In the present invention, the return signal that the return pulse generation circuit always outputs causes the output control circuit to automatically perform the return operation.The return signal has a duration of 0.1 seconds or less and an output interval of 1 second. It is set to 10 seconds. This is because the stabilization signal and the transistor for the regulator are temporarily turned on each time by the return signal, so the power loss will be large if the return signal has a long duration and a short output interval. Then, when the load side recovers to the normal state, when the output control circuit turns on the stabilization circuit and the transistor for the regulator by the above-mentioned return signal, the voltage detection circuit detects a voltage larger than a certain value. , Restore the normal energized state.

[0013]

【Example】

 Hereinafter, an embodiment of the present invention will be described in detail with reference to FIG. This figure shows an electric circuit diagram when the overcurrent protection circuit of the present invention is applied to the DC power supply circuit shown in FIG. 2, in which a voltage detection circuit 3, an output control circuit 4, and a return signal generation circuit 5 are provided. There is a feature in that.

Here, the voltage detection circuit 3 is composed of a series circuit composed of a constant voltage diode D1 and a resistor R5 and a protection resistor 6, and the Zener voltage of the constant voltage diode D1 is about 1/1 of the output voltage under normal conditions. It is set to about 2. The output control circuit 4 is composed of three switching NPN transistors Q2, Q3, Q4, base bias resistors R8, R9, and ripple removal capacitors C5, C6. The detection voltage of the voltage detection circuit 3 is Input to the base of transistor Q3. The recovery signal generation circuit 5 includes an oscillator 5a composed of a multivibrator, a buffer NPN transistor Q5, a base bias resistor R10, a collector load resistor R11, a time constant circuit (capacitor C8 and resistor R12), and two rectifiers. It is composed of diodes D2 and D3 for output and outputs a pulse with a period of about 1 to 10 seconds and a duration of about 0.1 seconds to the base of the transistor Q3 of the output control circuit 4.

The DC power supply circuit operates as follows. First, when the load 2 is in a normal state and the stabilizer circuit 1 and the transistor Q1 for regulator are normally energized, a reverse current flows in the constant voltage diode D1 of the voltage detection circuit 3. Since a predetermined positive voltage is obtained from the terminal of the resistor R5, the transistor Q3 of the output control circuit 4 is in the ON state. When the transistor Q3 is ON, the base voltage of the transistor Q4 becomes almost 0V, the transistor Q4 is OFF, and the base of the transistor Q2 to which the collector of the transistor Q4 is connected is biased via the resistor R8. Since the voltage is applied as it is, the transistor Q2 is also turned on. Then, in that state, the base of the PNP transistor Q1 for the regulator is connected to the collector of the transistor Q2 of the output control circuit 4, so the bias voltage is applied as is via the resistor R4, while maintaining the ON state. Supply a large current to the output side.

On the other hand, when an abnormality occurs on the output side such as when the load 2 is short-circuited, the output voltage decreases, and the reverse current does not flow in the constant voltage diode D1 of the voltage detection circuit 3, so that the resistance R5 The terminal voltage of becomes 0V.

Therefore, the base current stops flowing through the transistor Q3 of the output control circuit 4, and the transistor Q3 is turned off. Then, when the transistor Q3 is turned off, the bias voltage is applied as it is to the base voltage of the transistor Q4 via the resistor R9, and the transistor Q4 is turned on. When the transistor Q4 is turned on, the base of the transistor Q2 is grounded, so the transistor Q2 is turned off and the power supply to the input terminal a of the stabilization circuit 1 is stopped, and the stabilization circuit 1 Turns off. Further, the transistor Q1 for the regulator is a PNP type, and the collector current of the transistor Q2 corresponds to the base current of the transistor Q1. Therefore, when the transistor Q2 is turned off, the transistor Q1 is also turned off at the same time.

By the above operation, when the output voltage drop is detected, the power supply transistor Q2 to the stabilizing circuit 1 and the regulator transistor Q1 are turned off at the same time, and the current supply to the output side is cut off. As a result, the power loss in both transistors Q1 and Q2 is negligible. In addition, secondary current accidents such as ignition can be prevented because the current does not flow to the load 2.

By the way, even in the current cutoff state, the return signal generation circuit 5 outputs the return pulse to the base of the transistor Q3 at a cycle of about 1 to 10 seconds. That is, the oscillator 5a outputs a pulse to the base of the buffer transistor Q5 at the above-mentioned period, and the pulse obtained from the collector of the transistor Q5 is maintained for about 0.1 second by the time constant circuit (C8, R12) and the diode D2. It is output as a positive voltage recovery pulse. Therefore, the base voltage of the transistor Q3 temporarily rises each time the reset pulse is input, and the output control circuit 4 turns on (Q3 is ON → Q4 is OFF → Q2 is ON) and the regulator transistor Q1 is also ON. However, if an abnormal condition such as a short circuit continues on the load 2 side, the output of the voltage detection circuit 3 remains 0V, and since the duration of the return pulse is short, the original state (current cutoff state) ) Return to. Then, the power loss at this time is only a very small loss because the output condition of the return pulse is set as described above, and does not affect the load 2 in the abnormal state.

On the other hand, when the abnormal condition on the load side is resolved, the operation of the stabilizing circuit 1 and the regulator transistor Q1 which are temporarily raised by the above-mentioned return pulse causes normal operation from the voltage detecting circuit 3 to the base of the transistor Q3. The same voltage as during operation is applied, and transistor Q3 maintains the ON state. As a result, the transistor Q4 in the output control circuit 4 is kept in the OFF state and the transistor Q2 is kept in the ON state, the regulator transistor Q1 is kept in the ON state, and the entire DC power supply circuit returns to the normal current supply state.

The diode D3 is inserted so that the voltage generated in the voltage detection circuit 3 in a normal state is not applied to the return signal generation circuit 5 side to cause a malfunction. Further, in this embodiment, the normal resistor R8 is used for the base bias of the transistor Q2, but if it is a constant current element, heat generation due to the current flowing when the transistor Q4 is turned on can be avoided. it can.

[0022]

[Effect of device]

 The overcurrent prevention circuit of the present invention has the following effects due to the above configuration. In a DC power supply circuit in which a regulator transistor outputs a large current while maintaining a constant output voltage with a stabilization circuit, if an abnormal condition such as an overcurrent occurs due to a load short circuit, the output current is immediately cut off. The power loss is minimized, and it is possible to automatically return to the normal energized state when the load side abnormality is resolved. Therefore, it is possible to suppress the power consumption due to the continuation of the overcurrent state, prevent the secondary occurrence of the load and the deterioration of the transistor for the regulator. Can be moved to.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram when an overcurrent prevention circuit of the present invention is applied to a DC power supply circuit.

FIG. 2 is an electric circuit diagram of a conventional large current output DC power supply circuit in which a stabilizing circuit and a transistor for a regulator are combined.

[Explanation of symbols]

1 ... Stabilization circuit, 2 ... Load, 3 ... Voltage detection circuit, 4 ... Output control circuit, 5 ... Return signal generation circuit, 5a ... Oscillator, C1 to C3, C5
~ C8 ... Capacitor, D1 ... Constant voltage diode, D2, D3 ... Rectifying diode, Q1 ... PNP transistor for regulator, Q2-Q5 ... NPN transistor, R1-R6, R8-R12 ... Resistor.

Claims (1)

[Scope of utility model registration request] 1. A direct current power supply circuit in which a regulator transistor outputs a large current while holding a constant output voltage in a stabilizing circuit and a voltage detection circuit for detecting the output voltage, and a detection voltage in the voltage detection circuit is constant. If the output voltage is below the value, the stabilization circuit and the transistor for the regulator are turned off.The output control circuit switches the control circuit from the OFF control state to the ON control state.
An overcurrent prevention circuit comprising a return signal generation circuit for intermittently outputting a signal of a second or less at an interval of 1 to 10 seconds.