JPH0534029Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] This invention is incorporated into a stabilized power supply device of the series dropper type or switching regulator type, and is used to stabilize the power supply when the load current reaches an overcurrent state. The present invention relates to an overcurrent protection circuit for a stabilized power supply device that stops power supply to a load.

[Conventional technology]

As is well known, the above-mentioned regulated power supply is widely used as a DC power supply for various electronic circuits and devices, but it is necessary to protect the regulated power supply and its load circuit when overcurrent occurs for some reason. An overcurrent protection circuit is provided to ensure this. This protection circuit constantly monitors the load current flowing from the regulated power supply to the load, and normally stops power supply to the load when the load current reaches an overcurrent state, and when the regulated power supply enters this power supply stop state, The stopped state continues until the power to the stabilized power source is turned off and then turned on again. A conventional example of a stabilized power supply incorporating such an overcurrent protection circuit is shown in FIG.

The stabilized power supply shown in Figure 2 is of a series dropper type equipped with a transistor 5 for output voltage control, and receives a DC input voltage Vi and supplies a constant output voltage Vo to the load. The overcurrent protection circuit shown surrounded by a dashed line in the figure is incorporated. In this example, the input voltage Vi is AC power supply 1
Input AC voltage from circuit 100 and transformer 2
The half-wave AC voltage transformed through the diode 3
The current is rectified by the capacitor 4 and smoothed by the capacitor 4. The control transistor 5 has its collector and emitter connected in series with a load, and its base connected to a Zener diode 6. This Zener diode 6 connects to the input voltage via a resistor 7.
It is always conductive in response to Vi, and by applying the Zener voltage to the base of the control transistor 5, the base voltage and thus the output voltage Vo are stabilized. As is well known, when the value of the input voltage Vi fluctuates, the control transistor 5 changes its collector-base voltage accordingly, thereby changing the output voltage Vo to the Zener diode 6.
The control transistor 5 is held at a constant value lower than the Zener voltage by the base-emitter voltage of the control transistor 5. Capacitor 8 is provided to further stabilize this output voltage Vo.

As an overcurrent protection circuit, it is necessary to detect the overcurrent state of the load current, and for this purpose, a detection resistor 11 is inserted into the load current circuit, and the overcurrent detection transistor 12 is connected between its emitter and base. It receives the voltage across the detection resistor 11. Therefore, when the load current becomes overcurrent, the detection transistor 12 turns on and applies the input voltage Vi to the series circuit of resistors 13 and 14 connected to its collector.
On the other hand, since the thyristor 15 is connected in parallel with the Zener diode 6 and the voltage across the resistor 13 is applied as its power supply voltage, when the detection transistor 12 turns on, the thyristor 15 also turns on immediately and the Zener diode 6 Makes Zener voltage short circuit. As a result, the base potential of the control transistor 5 decreases, so the control transistor becomes almost cut off and the output voltage Vo disappears.
Therefore, power supply to the load is stopped. Due to this power supply stop, the load current naturally disappears, and the detection transistor 12 is turned off, but the thyristor 15 remains on, so that the power supply stop state is maintained. To release this stopped state, as described above, the input voltage Vi of the AC power supply 1 or the stabilized power supply is once turned off and then turned on again.

[Problem that the invention attempts to solve]

The conventional overcurrent protection circuit described above has a simple configuration and reliable operation, but when a capacitive load is connected to a regulated power supply, the transient overcurrent that flows for a very short time to charge the capacitance However, there is a problem in that the power supply operation as a stabilized power source is stopped in response. The capacitor 8 is of course connected to absorb such transient overcurrent, but if the capacitance of the load is larger than the capacitance of the capacitor 8, the power supply may be stopped by mistake. . To eliminate this problem, capacitor 8
You can increase the capacitance Co considerably, or insert a reactor L to suppress the rise of the load current as shown in Figure 2. Therefore, in order to prevent false stoppages for all loads, it is necessary to use fairly large ones for all loads, and the size is large for this type of stabilized power supply. In the end, this is a very uneconomical solution.

Another solution is to connect a capacitor C in parallel to the power supply drive resistor 14 of the thyristor 15 as shown in the figure, thereby delaying the rise of the power supply drive voltage after the detection transistor 12 is turned on. Therefore, the power supply stop operation of the stabilized power source can be delayed slightly. With this method, by simply adding a small-capacity capacitor C, it is possible to delay the operation of stopping the power supply of the stabilized power supply for a short period of time through which a large current flows to charge the capacitance of the load, thereby eliminating the problem of erroneous stopping. Solvable. However, if the operation of stopping the power supply of the stabilized power source is delayed even slightly, the circuit elements constituting the stabilized power source will be overloaded, albeit for a short time, until the power supply is stopped. Sensitive to this overload are, for example, the aforementioned control transistors. In other words, when a very capacitive load is connected to a regulated power supply, a large current flows immediately after the connection to charge the capacitance, and the output terminals of the regulated power supply are effectively short-circuited. and its output voltage is almost 0
become. Therefore, at this time, the entire input voltage is applied between the collector and emitter of the control transistor. In other words, the collector of the control transistor
The full input voltage is applied between the emitters, and at the same time a large short-circuit current flows between them. Furthermore, a zener voltage is applied to the base of the control transistor for setting a normal output voltage value. As is well known, such conditions are the most severe conditions from the standpoint of the transistor's ASO (safe operating area), and there is no guarantee that the transistor will not be damaged under these conditions. The only option is to reduce the short-circuit current to a minimum or shorten the short-circuit time of the output terminal of the stabilized power supply, and therefore the loads connected to the stabilized power supply are actually limited to those with a not-too-large capacitance. It will end up being put away.

The present invention solves these problems and prevents erroneous power supply interruptions even when a large capacitive load is connected to a stabilized power supply, and also eliminates overcurrents that do not place unnecessary burdens on the stabilized power supply. The purpose is to obtain a protection circuit.

[Means for solving problems]

The purpose or problem is to provide an overcurrent detection circuit that detects the overcurrent state of the load current and issues an overcurrent detection signal as an overcurrent protection circuit for a stabilized power supply, and to continuously receive the detection signal from the overcurrent detection circuit. a time-limited circuit that issues a power supply stop command after a predetermined time limit has elapsed; a power supply stop circuit that receives a stop command from the time-limited circuit and causes a stabilized power supply to stop power supply to the load; A current limiting circuit is provided to reduce the supply current value,
When the load current enters an overcurrent state, the current limiting circuit operates to limit the load current value, and then the power supply stop circuit completely stops the power supply to the load based on the stop command from the time limit circuit. resolved.

[Effect]

As can be seen from the above configuration, the present invention uses a time limit circuit to delay the operation of stopping the power supply of the stabilized power supply when an overcurrent occurs, but this alone is not sufficient for a short time when a capacitive load is connected. However, a large short-circuit current can place an unnecessary burden on the circuit elements in the stabilized power supply, so a current limiting circuit is built into the stabilized power supply to limit the load until the stabilized power supply stops supplying power. Also use means to limit the current value or current limit.

This current limiting circuit can take various specific configurations.For example, the simplest method is to insert a resistor in series with the load current circuit, keep this resistor short-circuited by a transistor, and use an overcurrent detection circuit to detect overcurrent. When a current is detected, the transistor may be turned off in response to a detection signal. Alternatively, if the stabilized power supply is a series dropper type as mentioned above, a control transistor is already inserted in series with the load current circuit, so this can be used to control the detection signal from the overcurrent detection circuit. The voltage between the collector and emitter may be increased accordingly, and for this purpose, for example, as in the embodiment described later, the voltage between the base and emitter may be increased to bypass the base current of the control transistor when an overcurrent occurs. Transistor circuits can be connected.

As described in the above configuration, the time limit circuit is designed to issue a stop command to the power supply stop circuit after a predetermined time period has passed if it continues to receive the detection signal from the overcurrent detection circuit, making it compact and small in capacity. Although this time limit circuit can be configured with circuit elements, in order to make the time limit value generated by this time limit circuit as accurate as possible in implementing the present invention, a capacitor is simply added as described in the section of the prior art. In addition, for example, as described in the embodiment described later, a time limit circuit is constructed of a Zener diode that conducts in response to an overcurrent detection signal, and a series circuit of a resistor and a capacitor connected in parallel to the Zener diode. It is desirable to issue a voltage as a stop command. The overcurrent detection operation of the overcurrent detection circuit is inevitably an analog operation due to its principle, and for example, the operating point tends to fluctuate due to temperature drift of the detection transistor included in it, and the characteristics of each transistor tend to vary. The time setting operation is also affected by this, and the set time limit value tends to fluctuate over time and vary from circuit to circuit. However, if the circuit is configured as above, the Zener diode first conducts due to the detection signal, and then Since the driving voltage for the time setting circuit formed as a series circuit of a resistor and a capacitor is established as the Zener voltage, fluctuations and variations in the set time period can be almost eliminated. Another reason that tends to cause fluctuations and variations in the set time is the operating threshold of the power supply stop charge; for example, the operating threshold of the thyristor gate mentioned above may have temperature drift or variations from thyristor to thyristor. . The time change in the charging voltage of the capacitor in the time-limited circuit that drives this gate is exponential, and the gate is driven at the point where the time change becomes quite gradual, so the gate operation threshold is If there are fluctuations or dispersions in the values, there will be large fluctuations or dispersions in the set time limits accordingly. Therefore, in a preferred embodiment of the present invention, a Zener diode is connected in series with the gate to apparently increase the operating threshold. At this time, by selecting the Zener voltage of the Zener diode to be higher than the operating threshold of the gate, the timer circuit can be set by absorbing the effects of fluctuations in the operating threshold of the gate due to temperature drift and variations from thyristor to thyristor. The time limit value can be stabilized.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG. The stabilized power supply shown in Fig. 1 is
An input circuit 100 that receives voltage from an AC power source 1 via a switch 1a, and two output circuits 200 and 3 connected to it via a transformer 2 in this example.
This is a switching regulator consisting of 00. Output circuit 200 of these is itself 1
This is a stabilized power supply, and in this example, it is configured as a series dropper type stabilized power supply. Built-in protection circuit. Another output circuit 300, which is shown simply in the figure, does not necessarily have a function as a stabilized power supply by itself, and its output voltage Vo3 is connected to the control circuit 50 and the input circuit 100.
It is stabilized by the cooperative action of Therefore, the output voltage Vo3 of the output circuit 300 is given to the control circuit 50 as an actual voltage value and compared with its target value Va. The control circuit 50 issues a switching command SS to the input circuit 100 so that the actual value Vo3 becomes equal to the target value Va, and opens and closes the switching circuit 102 included therein. Input circuit 1
00 converts the AC voltage from the AC power supply 1 into a DC voltage by a rectifier diode 101 shown in a simplified manner, receives the switching command SS from the control circuit 50 via the transformer 103, and sends it to the switching circuit 102.
The switching circuit 102 is opened and closed at an on-off ratio specified by the switching command, and an exciting current is supplied to the primary side of the transformer 2. Both output circuits 2
00 and 300 receive an induced voltage from the secondary side separately provided in the transformer 2 excited by this input circuit 100.

In this way, the output voltage of the output circuit 300
Vo3 is stabilized by the operation of the control circuit 50,
On the other hand, in the output circuit 200, the induced voltage on the secondary side of the transformer 2 is rectified and smoothed by the diode 3 and the capacitor 4, so that the input voltage is stabilized based on the output voltage Vo3 of the output circuit 300.
It receives Vi and further stabilizes its output voltage Vo by operating as a series dropper type stabilized power supply according to the load condition. In addition,
In many cases, a means for detecting overcurrent is provided in the output circuit 300 on the reference side, so to speak, but if the protection operation is performed independently when an overcurrent occurs, there is a risk that other output circuits will be adversely affected. Even if the detection means is incorporated, the detection signal is rather given to the control circuit 50, and by turning off the switching circuit 102 of the input circuit 100 by the switching command SS, the operation of the entire switching regulator is stopped. It is normal to do so. Therefore, the protection circuit according to the present invention is suitable for being incorporated into the output circuit 200 on the driven side when the switching regulator includes a plurality of output circuits as in this embodiment. In addition,
The output voltage Vo3 of the output circuit 300 on the reference side is often set to 5V at the TTL level, and the output voltage Vo3 of the output circuit 200 on the driven side is usually higher than this, for example, 30 to 40V.

The protection circuit according to the present invention incorporated in the stabilized power supply or output circuit 200 is the overcurrent detection circuit 1.
0, a time limit circuit 20, a power supply stop circuit 30, and a current limit circuit 40, each of which is shown surrounded by a dashed-dotted line in the figure. The overcurrent detection circuit 10 includes, as in the conventional case, a detection resistor 11 with a low resistance value inserted in series in the load current path, a detection transistor 12 that receives the voltage across the resistor between its emitter and base, and a resistor 13 connected to its collector. When overcurrent is detected, the detection signal DS is sent to the timer circuit 20.
give to Zener diode 2 in timer circuit 20
1 receives this detection signal DS, conducts the resistor 13 as its series resistor, generates a constant Zener voltage almost independent of the value of the input voltage Vi and the characteristics of the detection transistor 12, and connects the resistor 22 and capacitor 23. to the series circuit. The stop command ST is taken from the charging voltage of the capacitor 23, and in this embodiment, the power supply stop circuit 30 is made up of a thyristor 31.
A Zener diode 25 is connected in series with the gate of the thyristor 31. The resistor 24 connected in parallel to the capacitor 23 is a discharge resistor with a relatively high resistance value. For example, when a capacitive load is connected to the output terminal of the output circuit 200, the overcurrent is reduced within a short time and the output circuit is Capacitor 2, which is in a half-charged state when the operation of the capacitor 2 has not stopped.
It plays the role of discharging 3. The operation of the time limit circuit 20 and the power supply stop charge 30 will be explained below using some formulas.

The zener voltage of zener diodes 21 and 25 is
Vz1, Vz2, the resistance value of the resistor 22 is R, the capacitance value of the capacitor 23 is C, the operating threshold of the power supply of the thyristor 31 is Vg, the charging current for the capacitor 23 is i, and the charging voltage is v, then the following formula holds true.

Vz1=R・i+(1/C)・∫idt v=(1/C)・∫idt However, t is time. Solving this, we get v=Vzl·{1-exp(-t/τ)} with time constant τ=R·C, and if the time limit for charging voltage v to reach Vz2+Vg is T, the following equation is obtained.

T=τ・lnVz1/Vz1−(Vz2+Vg) Typical values in the above formula are Vz1=15~16V,
Vz2=3V, Vg=1V, R=10kΩ, C=1μF, τ
= 10 mS, and 20 to 30 mS is selected as the time limit T.

The current limiting circuit 40 in this embodiment is a transistor that is inserted between the control transistor 5 and the output terminal, and receives the voltage between the base and emitter of a resistor 41 having a low resistance value inserted in series in the load current path. 42, and when the load current enters an overcurrent state, the transistor 42 becomes conductive and its collector-emitter circuit is connected in parallel between the base and emitter of the control transistor 5.
By bypassing the base current of control transistor 5, the voltage drop between the collector and emitter of control transistor 5 is increased to limit the load current. This operation will be explained below using some formulas. For simplicity, the charging state of the capacitor Co of the capacitor 8 is ignored, the load capacitance value is Cl, and the voltage between the collector and emitter of the control transistor 5 (saturation value) is
When Vt is the resistance value of the resistors 11 and 41, R1 and R2 are the resistance values of the resistors 11 and 41, I is the load current, and Vo is the instantaneous value of the output voltage, the following equation holds true.

Vi=R1・I+Vt+R2・I+Vo I・t=Cl・Vo Furthermore, if the voltage between the base and emitter of the transistor 42 is Vbe, then R2・I=Vbe from the on-operation condition of the transistor 42, so it is set by the time limit circuit 20. The limit load capacity at which the overcurrent condition is resolved within the time limit T
Cl is set as t=T in the above equation, and becomes Cl=T/R2.Vbe/Vi-Vt-(1+R1/R2).Vbe. As a numerical example, Vi=30~40v, Vt=0.7
~1.2V, Vbe=0.6V, R1=0.3Ω, R2=0.2Ω
Then, Cl=400 to 500μF. In reality, the capacitor 8 built into the stabilized power supply has a capacity of 100 to 200 μF, and since this is already charged before the load is connected, the load capacity should be increased by that much, but it is safe. Therefore, even if this factor is ignored, even if a load with a capacitance of around 500 μF is connected, an erroneous stop will not occur, and if the load capacitance value is allowed up to this level, there will be no problem in practice. .

In the protection circuit according to the present invention configured as described above, even if a load with a large capacitance is suddenly connected to a stabilized power source, the current limiting circuit 40 operates first to charge the capacitance of the load, thereby stabilizing the load. By limiting the short-circuit current value flowing to the output terminal of the stabilized power supply, the load on circuit elements in the stabilized power supply such as the control transistor 5 is reduced and protected from damage. On the other hand, the time limit circuit generates an accurate set time during this period, and after the elapse of this time limit, the power supply operation of the stabilized power supply is stopped via the power supply stop circuit, but the cause of overcurrent is only due to the capacity of the load. In this case, as long as the capacitance value is, for example, up to about 500 μF as described above, a normal power supply state to the load can be maintained without causing an erroneous stop. According to the present invention, although the protection operation of such a circuit is actually quite complicated, it is possible to determine the values of the circuit elements constituting the protection circuit using a relatively simple calculation method as described above. Convenience arises.

In the above embodiments, the series dropper type stabilized power source was exclusively explained, but the present invention may be applied to stabilized power sources of different types and formats as appropriate within the scope of the present invention. Of course, a similar effect can be obtained by incorporating a current protection circuit.

[Effect of idea]

As explained above, according to the present invention, the overcurrent protection circuit, which is built into the stabilized power supply and causes the stabilized power supply to stop supplying power to the load when the load current reaches an overcurrent state, is configured to an overcurrent detection circuit that detects the state and issues an overcurrent detection signal;
a time limit circuit that issues a power supply stop command after a predetermined time period has elapsed if a detection signal continues to be received from the overcurrent detection circuit; and a power supply stop circuit that receives a stop command from the time limit circuit and causes the stabilized power source to stop supplying power to the load. , a current limiting circuit that reduces the power supply current value to the load according to the overcurrent state of the load current, and when the load current enters the overcurrent state, the current limiting circuit operates first to limit the load current value. After that, the power supply stop circuit completely stops power supply to the load based on the stop command from the timer circuit, so even if a large capacitive load is suddenly connected to the stabilized power supply, the timer circuit will stop the power supply. The operation of the stabilized power supply will not be stopped by mistake within the predetermined time period that is set, and furthermore, due to the operation of the current limiting circuit, unnecessary burdens will not be placed on the circuit elements in the stabilized power supply within this time period, such as transistors, etc. circuit elements are completely protected from damage. Of course, if the overcurrent is caused by a cause other than the capacitance of the load, the timed operation of the timer circuit ensures that the operation of the stabilized power supply is stopped after the timer elapses.

Furthermore, as can be seen from the description of the embodiments, by combining the time limit circuit and current limit circuit according to the present invention, it is possible to increase the time limit value of the time limit circuit, the load current limit value of the current limit circuit, and the load that can be connected to the stabilized power supply. When setting or selecting the capacitance value, etc., it is possible to easily and accurately determine the circuit constants in the protection circuit, which is a great convenience in design. Furthermore, by adopting a desirable aspect of the present invention, even if the characteristics of circuit elements such as transistors and thyristors in the protection circuit fluctuate due to temperature drift or there are considerable variations between circuit elements, the characteristics will be largely unaffected by this. It is possible to cause the time limit circuit to generate a time limit as designed without any problems, and to perform the protection operation accurately.

Furthermore, if the protection circuit of the present invention is applied to each driven output circuit of a switching regulator having multiple output circuits, each output circuit can be operated independently without any substantial effect on the operation of other output circuits. can be protected exactly as described above.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a switching regulator type stabilized power supply incorporating an overcurrent protection circuit for a stabilized power supply according to the present invention, and Figure 2 is a regulated power supply incorporating an overcurrent protection circuit according to the prior art. FIG. In the figure, 1... AC power supply, 2... Transformer, 3... Rectifying diode, 4... Smoothing capacitor, 5... Control transistor, 6... Zener diode for output voltage setting, 7... Resistor, 8...Capacitor for output voltage stabilization, 10...Overcurrent detection circuit, 11...
Detection resistor, 12...Detection transistor, 13, 1
4...Resistor, 15...Thyristor, 20...Time limit circuit, 21...Zena diode, 22...Resistance for time limit setting, 23...Capacitor for time limit setting, 2
4...Discharge resistor, 25...Zena diode, 3
0...Power supply stop charge, 31...Thyristor constituting the power supply stop charge, 40...Current limit circuit, 41
...Resistor, 42...Transistor, 50...Switching regulator control circuit, 100...Switching regulator input circuit, 101...
Rectifier diode, 102... switching circuit,
103...Switching command transformer, 200...
...Stabilized power supply or switching regulator output circuit on the driven side, 300...Reference side output circuit of the switching regulator, C...Capacitance value of time limit setting capacitor 23, Cl...Capacitance value of load,
Co...Capacitance value of output voltage stabilization capacitor 8,
DS...Overcurrent detection signal, I...Load current, i...
... Charging current of time limit setting capacitor 23, R...
Resistance value of the time limit setting resistor 22, R1...Resistance value of the detection resistor 11 of the overcurrent detection circuit, R2...Resistance value of the resistor 41 of the current limiting circuit, ST...Stop command,
T... Generation time limit of the time limit circuit, t... Time, τ...
Time constant of the time limit setting circuit, v...Charging voltage of the time limit setting capacitor 23, Vbe...Base-emitter voltage of the transistor 42 of the current limit circuit, Vg
...Thyristor gate operating threshold of power supply stop charge, Vi...Input voltage to stabilized power supply, Vo...
The output voltage of the stabilized power supply or output circuit 100,
Vo3...output voltage of the output circuit 300, Vt...collector-emitter voltage of the control transistor,
Vz1...Zena voltage of the Zener diode 21 of the time limit circuit, Vz2...Zena voltage of the Zener diode 25 of the time limit circuit.

Claims (1)

[Scope of Claim for Utility Model Registration] 1. A protection circuit that is incorporated in a stabilized power supply and causes the stabilized power supply to stop supplying power to the load when the load current reaches an overcurrent state, which protects the stabilized power supply from overcurrent. an overcurrent detection circuit that detects an overcurrent detection signal and issues an overcurrent detection signal; a time limit circuit that issues a power supply stop command after a predetermined time period has elapsed if the detection signal from the overcurrent detection circuit continues to be received; and a time limit circuit that issues a stop command from the time limit circuit. It is equipped with a power supply stop circuit that stops the power supply to the load to the stabilized power supply when the load current reaches the overcurrent state, and a current limit circuit that reduces the power supply current value to the load according to the overcurrent state of the load current. A stabilized power supply device characterized in that when a current limiter operates, a current limiting circuit first operates to limit the load current value, and then a power supply stop circuit completely stops power supply to the load based on a stop command from a time limit circuit. Overcurrent protection circuit for use. 2 Utility Model Registration Claims In the protection circuit as set forth in claim 1, the time limit circuit comprises a Zener diode that becomes conductive upon receiving an overcurrent detection signal, and a series circuit of a resistor and a capacitor connected in parallel to the Zener diode, An overcurrent protection circuit for a stabilized power supply device, characterized in that a capacitor voltage is issued as a stop command. 3. An overcurrent protection circuit for a stabilized power supply device, characterized in that a discharge resistor is connected in parallel to the capacitor in the protection circuit according to claim 2 of the utility model registration claim. 4. In the protection circuit described in claim 1 of the utility model registration claim, the stabilized power source is a series dropper type stabilized power source, and the transistor for controlling the output voltage is connected between the collector and the emitter in series with the load. An overcurrent protection circuit for a stabilized power supply device, characterized in that the output voltage is set by a Zener diode connected to the base. 5. In the protection circuit as set forth in claim 4 of the utility model registration, the power supply stop charge consists of a thyristor connected to the base of a control transistor so as to short-circuit a Zener diode, and the gate of the thyristor is connected to a time-limiting circuit. An overcurrent protection circuit for a stabilized power supply device, characterized in that the overcurrent protection circuit is configured to issue a stop command. 6. In the protection circuit according to claim 5 of the utility model registration, the operating threshold of the thyristor is increased by a Zener diode connected in series with the gate of the thyristor and receiving a stop command. Current protection circuit. 7. In the protection circuit set forth in claim 4 of the utility model registration, the current limiting circuit connects an overcurrent detection resistor connected in series to the load on the load side of the control transistor and the voltage across the detection resistor to a base-emitter circuit. An overcurrent protection circuit for a stabilized power supply device, comprising a transistor that bypasses the base current of a control transistor through its collector-emitter circuit when conducting. 8 Utility Model Registration The overcurrent protection circuit for a stabilized power supply device according to claim 1, wherein a capacitive load is connected as a load of the stabilized power supply. 9 Utility Model Registration In the protection circuit according to claim 1, the stabilized power supply is a switching regulator comprising one input circuit and a plurality of output circuits each outputting a different output voltage, An overcurrent protection circuit for a stabilized power supply device, characterized in that a protection circuit is incorporated in a driven side output circuit that is different from a reference side output circuit for control operation in which a switching circuit in an input circuit is controlled by the output voltage. .