JPH0728532A - Overload protection circuit for regulated power supply - Google Patents

Abstract

(57) [Abstract] [Purpose] An automatic restart function at overload for a stabilized power supply that uses the voltage of the capacitor 10 that is charged by the input voltage Vi at startup to the control power supply voltage Vc that feeds the control system 10 etc. Grant. [Structure] The starting circuit 30 monitors the control power supply voltage Vc, and when it reaches a predetermined threshold value, the control power supply voltage Vc is applied to the control system 10 etc. via the power feed switch 23 to output the stabilized power supply. When the overload detection circuit 40 having a predetermined timed operation characteristic detects an overload condition, the output operation is stopped and the voltage control circuit 50 causes the capacitor 20 to
Is discharged to lower the control power supply voltage Vc once and then recovered at a predetermined speed. When the control power supply voltage Vc is recovered to the threshold value vr of the starting circuit 30, the output operation of the stabilized power supply is restarted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stabilized power source such as a switching power source, in which the voltage of a capacitor charged by an input voltage at the time of startup is used as a control power source voltage for a control system of an output voltage. The overload protection circuit of.

[0002]

2. Description of the Related Art In a stabilized power supply widely used for supplying a constant voltage to various electronic circuits and electronic devices, a control power supply voltage for a control system of an output voltage cannot be obtained at the time of starting the power supply. In many cases, the capacitor is charged with the input voltage and the voltage is used, and it is attached to the output voltage control system in order to safely protect it from an abnormal condition such as overload caused by a short circuit on the load side. It is customary to incorporate protection circuits. A conventional example of such a stabilized power supply will be briefly described below with reference to FIG.

The stabilized power supply shown in FIG. 4 (a) is a switching power supply. The rectifier circuit 1 in the upper left part of the figure rectifies the AC voltage and the power supply capacitor 2 smoothes and stabilizes the input voltage Vi. The primary coil 3a of the transformer 3 of the buck type or the like is rectified by the diode 6 to rectify the AC induced voltage of the secondary coil 3b of the transformer 3 while interrupting the current flowing through it by the switching transistor 4 as usual, and the output capacitor. The output voltage Vo is stabilized and then output as the output voltage Vo.

The control system 10 shown in the lower part of FIG. 4 (a) comprises an error amplifier 11 for detecting and amplifying the difference between the actual value Sa of the output voltage Vo and the reference voltage Vr, and transforming its output with a resistor 5. Comparator 12 for comparing with the detected value of the primary current of the device 3, high frequency oscillator 13 for designating the switching cycle, and flip-flop 14 which is set by the output and reset by the output of the comparator 12, the actual value as usual The transistor 4 is set to PW by the switching command Sw which is the output of the flip-flop 14 so that Sa is always equal to the reference value Vr.
It is designed to be turned on and off by the M control method. In order to generate the control power supply voltage Vc to be supplied to the control system 10 etc. before or during the startup of the stabilized power supply, the capacitor 20 charged by the input voltage Vi through the resistor 21 is provided, and after the startup is completed, the transformer 20 is provided. The AC voltage of the auxiliary coil 3c of No. 3 is rectified by the diode 22 to make this control power supply voltage Vc. Zener diode 23
Is for preventing an abnormal rise in the control power supply voltage Vc.

A starting circuit 30 is provided to control the control system 10 and smoothly start the stabilized power supply. This start-up circuit 30 monitors the control power supply voltage Vc, which
As shown in Fig. 4 (b), the charge of 20 causes the output to go high when it rises and reaches the threshold value vr.
a is enabled, the output of the high-frequency oscillator 13 is applied to the flip-flop 14, and the switching command Sw shown in FIG. 4 (c) is output to the transistor 4, thereby starting the switching operation of the stabilized power supply, and if the control is performed thereafter. When the power supply voltage Vc is abnormally lowered for some reason, the output is made low to stop the switching operation, and at the same time the auxiliary output is made high to hold the flip-flop 14 in the reset state via the OR gate 14b.

After activation of the stabilized power supply, the control power supply voltage Vc changes to a power supply from the auxiliary coil 3c side after a slight fluctuation as shown in FIG. 4 (b), and is usually slightly lower than the threshold value vr. It is maintained at a constant value, and the control system 10
Thus, a constant output voltage Vo is supplied to the load while controlling the actual value Sa of FIG. 4 (d) to be equal to the reference value Vr. If the stabilized power supply becomes overloaded due to a short circuit on the load side during this operation, the actual value Sa will change to the specified threshold value as shown in Fig. 4 (d).
Since it drops below Vt, the overload detection circuit for this detection
As this 40, a comparator is provided in this conventional example, and when the output of the error amplifier 11 rises abnormally and exceeds the set value V4 given according to the threshold value Vt, a high overload detection signal.
Generate So.

In addition, in the example shown in the figure, an overvoltage detection circuit 60 for the control power supply voltage Vc is provided, and its comparator 61
To the control power supply voltage Vc via the Zener diode 62 and a very low set value V6, and when the control power supply voltage Vc exceeds the Zener voltage of the Zener diode 62, a high overvoltage detection signal is generated and the above-mentioned overload detection signal is generated. It is given to the OR gate 63 with So. The holding circuit 64 that receives the output is for storing an abnormal state, and is set when one of both detection signals is high, and the high output keeps the flip-flop 14 in the reset state through the OR gate 14b to switch the stabilized power supply. Stop the operation. After this operation stop, the power supply from the auxiliary coil 3c side is cut off and the control power supply voltage Vc rises due to the charging of the capacitor 20, but the Zener diode 23 limits this to the Zener voltage Vz as shown in FIG. 4 (b). .

[0008]

Even with the above-mentioned prior art, it is possible to stop the stabilizing power supply and protect it safely when it is overloaded. However, once the operation is stopped, it will remain in the stopped state, so that the operation can be restarted. Has the problem of requiring artificial activation. This may be desirable for complete protection, but as is well known, most overloads are only temporary, so the regulated power supply will automatically be activated after a certain time has elapsed since an emergency stop. In many cases it is more convenient to restart. However, since the above-mentioned control system and protection circuit of the stabilized power supply are usually incorporated in a small integrated circuit chip,
If the automatic restart function is incorporated into this, the circuit becomes more complicated and the chip size needs to be increased, and the constant current consumption of the protection circuit increases, which tends to reduce the power efficiency of the stabilized power supply.

A main object of the present invention is to solve such a problem and to provide an automatic restart function to an overload protection circuit of a stabilized power supply with a circuit configuration as simple as possible, which is secondary but important. The purpose is to reduce the constant power consumption of the stabilized power supply.

[0010]

According to the protection circuit of the present invention, the control power supply is different from the stabilized power supply whose control power supply voltage is the voltage of the capacitor charged by the input voltage at the start-up as described above. When a voltage is received and it reaches a predetermined threshold value, the control circuit starts the output operation of the stabilized power supply, the overload detection circuit that detects the overload state of the stabilized power supply, and the overload detection A voltage control circuit that discharges the capacitor to lower the control power supply voltage once and then recovers it at a predetermined speed is provided, and when the overload occurs, the output operation of the stabilized power supply is stopped and the control power supply voltage is lowered by the voltage control circuit. This is accomplished by restarting the output operation of the regulated power supply when the control power supply voltage later recovers to the threshold value of the starting circuit.

It is desirable that the above-mentioned start-up circuit has two threshold values, a threshold value when the control power supply voltage rises and a lower threshold value when the control power supply voltage falls. In addition, it is desirable that the detection operation of the overload detection signal circuit has a slight time limit, for example, a short time limit of about several tens of μS, in order to prevent unnecessary protection operation. Further, when the overload detection circuit detects an overload state, it is advantageous to stop the power supply to the control system to stop the output operation of the stabilized power supply in order to reduce the power consumption.

In the voltage control circuit, in addition to a circuit that discharges the capacitor to detect the control power supply voltage when overload is detected,
A voltage control capacitor that starts charging at a predetermined speed is provided on condition that the control power supply voltage has dropped below the threshold value of the starting circuit due to discharge, and the control power supply voltage is restored at a predetermined speed according to the increase in the charging voltage. Is good. Further, this voltage control circuit is provided with a holding circuit for storing the fact that the overload state is detected by the overload detection circuit and starting the voltage control action thereof, which is triggered by the overload detection signal to start the operation. It is composed of a current circuit and a current mirror circuit that receives the constant current as a reference current and feeds back the driven current to the constant current circuit to keep it in an operating state, and the current flows in this holding circuit only after receiving an overload detection signal. It is better to do so.

Further, the above-mentioned start-up circuit is also configured as a holding circuit which is composed of a constant current circuit and a current mirror circuit and which is supplied with power by the control power supply voltage, and the constant current circuit is provided with a first voltage barrier from the control power supply voltage. The trigger current is injected to start the operation, and the constant current operates the current mirror circuit, and the feedback current through the second voltage barrier lower than the first voltage barrier keeps the constant current circuit in the operating state. ,
It is preferable that the holding state be entered when the control power supply voltage rises above the first voltage barrier and the holding state be released when the control power supply voltage falls below the second voltage barrier. It is advantageous to stop or reduce the current injection into the constant current circuit through the first voltage barrier by the output of the driven current of the current mirror circuit when the starting circuit configured as the holding circuit enters the holding state. is there.

[0014]

In the stabilized power supply in which the voltage of the capacitor charged by the input voltage at startup is used as the control power supply voltage, conventionally, when the output operation is stopped at the time of overload as described with reference to FIG. Although the control power supply voltage was higher than that during operation because the capacitor was charged due to the power supply being cut off, in the present invention, the voltage control circuit according to the configuration of the preceding paragraph is provided to discharge and control the capacitor after the output operation is stopped. Contrary to the conventional method, the power supply voltage is once lowered and then restored at a predetermined speed, and the output operation of the stabilized power supply is performed when the control power supply voltage is restored to the threshold value by using the start circuit. Resume. As a result, in the present invention, it is possible to provide the overload protection circuit with the automatic restart function of the stabilized power supply with a relatively simple circuit configuration.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration example of a stabilized power supply incorporating the overload protection circuit of the present invention and waveform examples of main signals related thereto, FIG. 2 shows a voltage control circuit, and FIG. 3 shows a configuration example of a starting circuit. . 1 corresponding to those in FIG. 4 are designated by the same reference numerals, and the description of the overlapping portions will be appropriately omitted. Although the stabilized power supply is a switching power supply in the illustrated embodiment, the present invention can of course be applied to other cases.

The structure of the main circuit of the stabilized power supply and the power supply circuit for the control power supply voltage Vc shown in FIG. 1 (a) is the same as that of FIG. 4 (a), and the control system 10 thereof has the structure of FIG. 4 (a). flip flop
It is the same except that the AND gate 14a and the OR gate 14b provided on the input side of 14 are omitted. Instead, in the embodiment of FIG. 1 (a), the power feeding switch 24 is inserted in the power feeding path of the control power source voltage Vc to the circuit portion surrounded by the chain line including the control system 10 and the overvoltage detecting circuit 40. .

The start-up circuit 30 uses the control power supply voltage Vc as in the conventional case.
Is monitored and when a predetermined threshold value is reached, the power supply switch 24 is turned on by the output S3 to supply power to the control system 10 to start the output operation of the stabilized power supply. As shown in Fig. 4, the control power supply voltage Vc has a hysteresis characteristic with a rising threshold value vr and a lower falling threshold value vd, and when the control power supply voltage Vc falls below the threshold value vd, the power supply switch
Turn off 24 to stop the output operation of the stabilized power supply.

When the stabilized power supply is activated, the capacitor 20 is charged by the input voltage Vi through the resistor 21, and the control power supply voltage
When Vc rises as shown in FIG. 1 (b) and reaches the rising threshold value vr of the starting circuit 30, the output S3 turns on the power supply switch 24 to start the control system 10, and the control system 10 starts operating. The transistor 4 is controlled to be turned on / off by the switching command Sw of), and the output operation of the stabilized power supply is started. Immediately after the start of the operation, the control power supply voltage Vc temporarily drops as shown in FIG. 1 (b), but the power supply from the auxiliary coil 3a of the transformer 3 immediately starts to settle to a constant value. Even when the control power supply voltage Vc temporarily drops, the starting circuit 30 outputs the output S3.
It is preferable to set the threshold vd at the time of the fall to a low value, for example, about one half of the threshold vr at the time of the rise, in order to reliably maintain the high state of.

In the normal operating state after the start-up, the output voltage Vo of the stabilized power source is the actual value Sa in FIG.
The error amplifier 11 is controlled so as to be equal to the reference value Vr. In the overload detection circuit 40, the actual value Sa indicates the overload condition due to a short circuit of the load during this operation as shown in Fig. 1 (d).
Is detected from the abnormal lowering below the threshold value Vt as described above, and in this embodiment, the output of the error amplifier 11 is abnormally increased by the comparator 41 to the set value V4 or more and the overload state is detected, A high overload detection signal So is output after a short time period indicated by t4 in Fig. 1 (e), which is set by the attached timer circuit 42 so as not to start the unnecessary protection operation in response to the momentary overload. To do. It is preferable that a small capacitor is incorporated in the timer circuit 42 as shown in the figure so that the timer circuit 42 usually has a time period of about several tens of μS.

The voltage control circuit 50 that receives this overload detection signal So is the most characteristic part of the circuit of the present invention. First, the capacitor 20 is discharged in response to the overload detection signal So to lower the control power supply voltage Vc once. After that, the operation of recovering at a predetermined speed set in advance is performed. Figure 1
A concrete circuit of the voltage control circuit 50 shown as a block in (a) is shown in FIG. 2. The circuit configuration and operation will be described below with reference to this. As shown in the figure, the voltage control circuit 50 in this embodiment includes a holding circuit 51 that receives an overload detection signal So and stores an overload state, and a voltage operation circuit 52 that changes the control power supply voltage Vc based on its operation. , Which are complementary bipolar circuits, each of which is supplied with a control power supply voltage Vc.

The holding circuit 50 is an npn whose bases are commonly connected.
A constant current circuit composed of transistors 71 and 72, in which an emitter resistor 71c is connected to a multi-emitter transistor 71,
A current mirror circuit composed of pnp transistors 73, 74, and 75 connected to a common base is provided, and the reference current of the transistor 71 in the constant current circuit is received by the reference transistor 73 of the current mirror circuit. A resistor 77 for preventing malfunction due to noise intrusion is connected to the constant current circuit on the emitter side, and a transistor 76a is connected to the collector side for compensating the change in the base current due to this connection. Similarly, a noise prevention resistor 77 and a base current compensation transistor 77a are connected to the emitter side and the collector side, respectively.

The above-mentioned overload detection signal So is stored in this holding circuit 50.
Is applied to the base of a transistor 76a connected to the collector of the transistor 72 on the side of the constant current circuit, and its high causes a base current to be injected into the transistors 71 and 72 to turn them on to start the operation of the constant current circuit. As a result, the current mirror circuit also receives a constant current from the reference transistor 73 and starts operating, and supplies a current from the driven transistor 74 side to the transistor 72 to keep the constant current circuit operating even after the overload detection signal So disappears. Therefore, the holding circuit 50 is in the holding state. As described above, the holding circuit 50 is preferably configured to consume the current only after receiving the overload detection signal So. In the illustrated example, the output S5 is taken out from the transistor 75 on the driven side of the current mirror circuit. Further, in order to release the holding circuit 50 from the holding state, for example, a transistor 78 which receives a reset pulse RP generated in response to the rising of the output S3 of the starting circuit 30 is provided so as to draw the current flowing from the transistor 74 to the transistor 72.

In the voltage control circuit 52, pnp transistors 81 and 82, which are the driven side of the current mirror circuit of the holding circuit 51, are provided, and a pnp transistor 83 whose base and emitter are connected to the collectors thereof is provided, and its collector is provided. An npn transistor 84 connected to the base and the base is provided to connect the collector to the control power supply voltage Vc and the emitter to the discharge resistor 85, respectively. Further, for example, a series circuit of two diodes 86 and a capacitor 87 is connected to the collector of the transistor 81 or the base of the transistor 83, and an npn transistor 88 is connected in parallel to the latter so as to short-circuit the same and connected to the base. The output S3 of the starting circuit 30 described above is provided.

Since the output S3 of the starting circuit 30 is high during normal operation, the capacitor 87 is short-circuited. In this state, when the holding circuit 51 of the voltage control circuit 50 operates in response to the overload detection signal So, the voltage operation circuit Since current is supplied from the transistors 81 and 82 of 52, the transistor 83 is turned on, and then the transistor 84 is also turned on to rapidly discharge the capacitor 20 through the discharge resistor 85. As a result, the control power supply voltage Vc drops below the lower threshold value vd of the starting circuit 30 within a short time as shown in FIG. 1 (b), but the forward voltage of the diode 86 remains without being short-circuited. Therefore, the control power supply voltage Vc does not drop below that level and causes the holding circuit 51 to maintain the holding state.

As described above, the control power supply voltage Vc is the start circuit 30.
When the output voltage S3 of the starting circuit 30 changes to low and the power supply to the control system 10 is cut off as described above, the switching command Sw stops as shown in FIG. 1 (c). .
At the same time, the transistor 88 of the voltage operation circuit 52 of FIG. 2 is turned off to release the short-circuited state with respect to the capacitor 87, and thereafter the capacitor 87 is charged by the current supplied from the transistor 81, and the control power supply voltage is changed according to the charged state. Vc rises at a constant speed as shown in Fig. 1 (b). When the control power supply voltage Vc again reaches the higher threshold value vr of the starting circuit 30, the control system 10 is supplied with power by the output S3 being high as in the case of the first starting, as shown in FIG. 1 (c). Restarts the stabilized power supply by restarting the output of the switching command Sw. At the same time, the voltage control circuit 50 returns to the initial state by the reset pulse RP. Note that the time t5 shown in Fig. 1 (b) from the stop of the stabilized power supply to the restart is the supply current of the transistor 81 and the capacitor depending on the application and need.
It is usually set within the range of tens of mS to a few seconds by the capacitance of 87.

In the embodiment shown in FIG. 1A, an overvoltage detecting circuit 60 for the control power supply voltage Vc is provided in addition to the above. This is achieved by using, for example, the comparator 61 and the Zener diode 62 shown in FIG.
May be configured in combination. The high detection output S6 may be given to the complementary control input of the power feed switch 24 via the OR gate 24a to turn it off, for example, as shown by the broken line in the figure, but in this embodiment, this output S6 is supplied to the starting circuit 30. The operation of the stabilized power supply is stopped by giving it and resetting it. When the operation is stopped by the output S6 of the overvoltage detection circuit 60, the automatic restart as described above is not performed.

Finally, a concrete circuit configuration example and operation of the starting circuit 30 will be described with reference to FIG. Figure 3 (a) and Figure 3 (b)
Are circuit examples that are different from each other, but both are voltage control circuits
Since there are many common parts with the holding circuit 51 of 30, corresponding parts are designated by the same reference numerals. Like the holding circuit 51, the starting circuit 30 includes a constant current circuit and a current mirror circuit, each of which is composed of a complementary transistor supplied with the control power supply voltage Vc, as in the case of the holding circuit 51.

In the starting circuit 30 shown in FIG. 3A, the control power supply voltage is
A path for injecting a base current into the transistors 71 and 72 of the constant current circuit from the Vc side through the first voltage barrier, for example, the two Zener diodes 91, the series resistor 91a, and the emitter-base of the npn transistor 92, When the control power supply voltage Vc is higher than the above-mentioned higher or rising threshold value vr set by the first voltage barrier, the constant current circuit is started to be inserted between the transistors 73 and 71. Second
This operating state is maintained by feeding back the current from the current mirror circuit to the constant current circuit via the Zener diode 93 for the voltage barrier. In this state, a high output S3 is taken out from the driven side transistor 75 of the current mirror circuit.
Further, in this holding state, the transistor 92 is turned on to bypass the above-mentioned injection current via the Zener diode 91.

After that, when the control power supply voltage Vc falls below the lower falling threshold value vd set by the second voltage barrier, the feedback current from the current mirror circuit to the constant current circuit cannot be maintained and the system is started. Circuit 30 is released or reset from hold. Further, a transistor 78 similar to that shown in FIG. 2 is provided so that the starting circuit 30 can be reset at any time by the overvoltage detection signal S6.

In the starting circuit 30 shown in FIG. 3 (b), the control power supply voltage is
The base current is directly injected from Vc to the transistors 71 and 72 of the constant current circuit through the Zener diode 91, the series resistor 91a and the diode 94, and after the starter circuit 30 is in the holding state, the pnp transistor 95 and its Series resistance 95
The other point is the same as the circuit of FIG. 3A, except that the npn transistor 96 is turned on by a to bypass the injection current. Of course, the threshold vr when the control power supply voltage Vc rises is determined by the Zener diode 91.
It is also the same that vd can be set independently by the Zener diode 93. The diode 94 serves to prevent the base currents of the transistors 71 and 72 from leaking out when the starting circuit 30 is held.

The stabilized power supply of FIG. 1 (a) configured as described above has the above-mentioned automatic restart function at the time of overload,
It has the feature of low power consumption. That is, as can be seen from the above description, the voltage control circuit 50 and the overvoltage detection circuit 60 do not consume any power during the normal operation of the stabilized power supply, and the main circuit as well as the control system 10 does not operate while the operation is stopped or interrupted. And the overload detection circuit 40 cuts off the supply of the control power supply voltage Vc and does not consume power. As a result, regardless of the automatic restart function, the power consumption is the same as or less than the conventional one, and the power conversion efficiency of the stabilized power supply can be improved.

The present invention is not limited to the above embodiments, and the present invention can be implemented in various modes. For example, in the embodiment, the startup circuit is used after restarting after overload or after detecting overvoltage.
Although the output operation of the stabilized power supply is stopped via 30, the voltage control circuit 50 is shown as indicated by the broken line in Fig. 1 (a).
The output operation may be stopped by directly applying the output S5 and the overvoltage detection signal S6 of the above, or the overload detection signal So to the power supply switch 24 to turn it off. Further, when the output is stopped by the overvoltage detection signal S6, the voltage control circuit 50 is not operated, so that the control power supply voltage Vc is the Zener diode.
Although it rises to the voltage set in 23, even if the voltage rise function at this time is limited to a lower limit by using the voltage limiting function of the Zener diode in the starting circuit 30 and the voltage operating function of the voltage control circuit 50. Good.

[0033]

As described above, in the overload protection circuit according to the present invention, the control power supply voltage is monitored by the stabilized power supply that uses the voltage of the capacitor charged by the input voltage at startup as the control power supply voltage. Start circuit that causes the control system to start the output operation of the regulated power supply when the voltage reaches a predetermined threshold, an overload detection circuit that detects the overload state of the stabilized power supply with a predetermined time characteristic, and an overload If a voltage control circuit that discharges the capacitor to lower the control power supply voltage once and then recovers it at a predetermined speed is detected when is detected, the output operation of the stabilized power supply is stopped and then temporarily lowered when overloaded. By restarting the output operation of the stabilized power supply by the starter circuit when the control power supply voltage is restored to the threshold value of the starter circuit, the circuit configuration of the stabilized power supply is made more complicated than before. It is possible to provide the overload protection circuit with the automatic restart function of the stabilized power supply without causing it.

When an overload condition is detected, the power supply to the control system and the overvoltage detection circuit is stopped to stop the output operation of the stabilized power supply, or the holding circuit of the voltage control circuit is triggered by the overload detection signal. In a preferred embodiment of the present invention, which is composed of a constant current circuit that starts operating and a current mirror circuit that receives the constant current as a reference current and returns a driven current to the constant current circuit, in a normal operation of the stabilized power supply. Eliminates the power consumption of the voltage control circuit, etc., and the power consumption of the control system and the overload detection circuit while the operation is stopped.The power consumption of the stabilized power supply with the automatic restart function is the same as or less than the conventional one. The power conversion efficiency can be improved by suppressing the power consumption.

Further, the starting circuit is set to the first from the control power supply voltage.
Holding with a constant current circuit that starts operation by the current injected through the voltage barrier, and a current mirror circuit that starts operation by the constant current and holds the constant current circuit in the operating state by the feedback current through the second voltage barrier According to the embodiment configured as a circuit, the threshold value of the starting circuit when the control power supply voltage rises is set independently of each other by the first voltage barrier by the first voltage barrier, and thus accurately set. can do.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an overload protection circuit of the present invention.
(a) is a circuit diagram of a stabilized power supply incorporating it, (b) is a control power supply voltage, (c) is a switching command,
The figure (d) is the actual value of the output voltage, and the figure (e) is a waveform diagram showing the overload detection signal.

FIG. 2 is a circuit diagram showing a specific configuration example of a voltage control circuit.

FIG. 3 shows a specific configuration example of a starter circuit, and is shown in FIGS.
[Fig. 3] is a circuit diagram of its different configuration example.

FIG. 4 is a diagram showing an overload protection circuit according to the related art.
(a) is a circuit diagram of a stabilized power supply incorporating it, (b) is a control power supply voltage, (c) is a switching command,
FIG. 3D is a waveform diagram showing the actual value of the output voltage.

[Explanation of symbols]

10 Control system for stabilized power supply 20 Capacitor for control power supply voltage 21 Resistor for charging capacitor 24 Power supply switch for control system 30 Start circuit 40 Overload detection circuit 41 Comparator for overload detection 42 For overload detection signal Timer circuit 50 Voltage control circuit 51 Holding circuit that constitutes voltage control circuit 52 Voltage operation circuit that constitutes voltage control circuit 71,72 Transistor for constant current circuit of start circuit 73,74 Transistor for current mirror circuit of start circuit 84 Capacitor Discharge transistor 87 Capacitor for operating control power supply voltage 91 Zener diode as first voltage barrier for starter circuit 93 Zener diode as second voltage barrier for starter circuit Sa Actual value of output voltage So Overload detection signal Sw Switching command S3 Start circuit output S5 Voltage control circuit holding circuit output Vc Control power supply voltage vd Start circuit lower High threshold of the output voltage vr starting circuit of the input voltage Vo regulated source have values Vi stabilized power supply

Claims (7)

[Claims] 1. A circuit for protecting a stabilized power supply, which uses a voltage of a capacitor charged by an input voltage at the time of start-up as a control power supply voltage, from overload, and monitors the control power supply voltage to obtain a predetermined threshold value. When the overload condition is reached, the control circuit starts the output operation of the stabilized power supply, the overload detection circuit that detects the overload condition of the stabilized power supply, and discharges the capacitor when the overload is detected. And a voltage control circuit that once reduces the power supply voltage and then recovers it at a predetermined speed,
The output operation of the stabilized power supply is restarted when the control power supply voltage is restored to the threshold value of the start circuit after the output operation of the stabilized power supply is stopped at the time of overload and the control power supply voltage is lowered by the voltage control circuit. An overload protection circuit for a stabilized power supply characterized by the above. 2. An overload protection circuit for a stabilized power supply according to claim 1, wherein the detection operation of the overload detection circuit is timed. 3. The voltage control according to claim 1, wherein the voltage control circuit starts charging at a predetermined speed on condition that the control power supply voltage has dropped below the threshold value of the starting circuit due to discharge of the capacitor. An overload protection circuit for a stabilized power supply, characterized in that a capacitor is provided and the control power supply voltage is restored at a predetermined speed in response to an increase in the charging voltage. 4. The circuit according to claim 1, wherein a holding circuit is provided in the voltage control circuit for storing a fact that the overload detection circuit has detected an overload condition and starting a voltage control operation. It consists of a constant current circuit that starts operation when triggered by a load detection signal, and a current mirror circuit that receives the constant current as a reference current and feeds back the driven current to the constant current circuit to keep it in an operating state. An overload protection circuit for a stabilized power supply, characterized in that current consumption occurs only after receiving a detection signal. 5. The constant current circuit according to claim 1, wherein the starter circuit is triggered by a current injected from the control power supply voltage through the first voltage barrier to start operation, and operates by the constant current. And a current mirror circuit for starting and maintaining a constant current circuit by a feedback current through a second voltage barrier lower than the first voltage barrier, and configured as a holding circuit fed by a control power supply voltage. The stabilized power supply is characterized in that when the power supply voltage rises above the first voltage barrier, the holding state is entered, and when the control power supply voltage drops below the second voltage barrier, this holding state is released. Overload protection circuit. 6. The circuit according to claim 5, wherein current is injected into the constant current circuit through the first voltage barrier by the output of the driven current of the current mirror circuit when the holding circuit as the starting circuit enters the holding state. An overload protection circuit for a stabilized power supply, which is characterized in that it is configured to stop. 7. The circuit according to claim 1, wherein when the overload detection circuit detects an overload state, the power supply to the control system is stopped to stop the output operation of the stabilized power supply. Characteristic overload protection circuit for stabilized power supply.