JPH08234852A - Overload protecting system for stabilized power source - Google Patents

Abstract

PURPOSE: To rationally perform protection countermeasure suitable for overload state when the light overload caused by load fluctuation or the like or the heavy overload caused by load short-circuiting, etc., is applied to a stabilized power source. CONSTITUTION: An auxiliary output voltage Vc of a stabilized power source 60 is always monitored by a voltage monitoring means 30 and when that voltage rises to a prescribed threshold value after start, an operation of a control system 10 of the stabilized power source 60 is started. In the first overload state in which that voltage Vc is lowered under a first critical value by load short- circuiting, etc., the operation of the control system 10 is stopped until the stabilized power source 60 is started again by the manual operation of an input switch 1 or the like and a normal output voltage Vo of the stabilized power source 60 is monitored by an overload detecting means 40 built in the control system 10. In the second overload state in which that voltage Vo is lowered to a second critical value by load fluctuation, etc., the operation of the control system 10 is temporarily stopped by operating a voltage control means 50 by an overload signal So and then automatically started again later after the lapse of a prescribed time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for protecting a stabilized power supply such as a switching power supply from an overload condition caused by a short circuit on the load side or an overcurrent.

[0002]

2. Description of the Related Art In a stabilized power supply that supplies a constant voltage to an electronic circuit or electronic device, an overload detection circuit is incorporated to protect from overload, and when the overload state is detected, the operation of the control system is stopped. It is customary to eliminate the output voltage. That is, in the conventional overload protection system, a stabilized power supply,
For example, an overload detection circuit is incorporated along with a control system of a PWM method, which normally controls the opening and closing of switching transistors so that the actual value of the output voltage of the switching power supply always matches the target value, and the output voltage value is constantly adjusted to a predetermined value. It is possible to eliminate the overload condition by comparing the limit value and generating a detection signal when it falls below the limit value, and in response to this, immediately stop the switching transistor opening / closing operation by the control system and eliminate the output voltage. It is customary.
At this time, it is customary to switch the switching command to be given to the switching transistor from the control system to the OFF command in response to the overload detection signal, thereby eliminating the output voltage of the stabilized power supply.

[0003]

However, in the above-mentioned conventional overload protection system, once an overload condition occurs, it is a very slight transient and even if it is resolved after a short time, the stabilized power supply is generated. It is inconvenient that the output operation of is completely stopped. Therefore, the inventor of the present case is
In 5-174585, we proposed an overload protection circuit that temporarily stops the output operation of the stabilized power supply during an overload and then restarts it after a predetermined time period.

However, when this new protection system is actually applied to a stabilized power supply, the operation of stopping and restarting the output of the stabilized power supply is repeated when a severe overload condition such as a load short-circuit continues. It turns out that there are points. It is of course desirable to stop the operation of the stabilized power supply as quickly as possible under a severe overload condition. Especially, if the output is stopped and restarted during that condition, it is stable. The power supply may be damaged.

Further, when the input voltage received by the stabilized power supply is interrupted, a drop in the output voltage accompanying it is detected as an overload state, and the output operation is likely to be stopped and restarted, and the interruption or the slight overload state is short. In the case of time, it is desirable to let the stabilized power supply maintain the output operation. For this purpose, it is necessary to give some time limit to the operating characteristics of the overload detection circuit, but in severe overload conditions, there is a contradiction with the demand to stop the output operation as quickly as possible as described above. . An object of the present invention is to solve such a problem and to provide an overload protection system capable of rationally protecting a stabilized power supply in both a light overload state and a heavy overload state.

[0006]

According to the overload protection system of the present invention, the above-mentioned object is to control the auxiliary output voltage of the regulated power supply by the voltage monitoring means when it rises to a predetermined threshold value. The system starts the output operation of the stabilized power supply, and stops the operation of the control system in the first overload state where the output voltage of the stabilized power supply drops below the first limit value, and causes the overload detection means to monitor the regular output voltage of the stabilized power supply. The second limit value is detected, the second overload condition is detected, and the operation of the control system is stopped according to the first overload condition until the stabilized power supply is restarted.
In addition, it is achieved by temporarily stopping according to the second overload state and then automatically restarting after a predetermined time.

Incidentally, the auxiliary output voltage of the stabilized power source having the above-mentioned structure is supplied to the control system as its control power source voltage,
Moreover, it is advantageous to set the first limit value so that the operation of the control system is stopped in the first overload state, and when the stabilized power supply is started, the control resistance is controlled by the input voltage as in the usual case. It may be started up by charging the capacitor via. Further, in the method of the present invention, it is preferable to incorporate the overload detection means described above in the control system, and it is necessary to set a predetermined time period for the detection operation in case of a very short power failure or a slight overload. Accordingly, it is advantageous in preventing unnecessary protection operation.

The voltage monitoring means referred to in the method of the present invention is
A constant current circuit triggered by the current injected from the auxiliary power supply voltage through the voltage barrier for threshold setting and starting operation,
It is configured as a state holding circuit including a current mirror circuit that starts operation with the constant current output and keeps the constant current circuit in the operating state by the feedback current through the voltage barrier for setting the first limit value, and by appropriately setting the voltage barrier. It is preferable that the auxiliary power supply voltage value has a history characteristic in operation. The threshold and the voltage barrier for the first limit value are preferably set by the Zener breakdown voltage of the Zener diode, respectively.

In order to recover the output operation of the stabilized power supply after it is temporarily stopped at the time of a slight overload, as described above, the voltage of the capacitor charged by the input voltage at startup is supplied to the control system as the control power supply voltage. In the case of a charging power supply, it is advantageous to incorporate a voltage control means to recover the control power supply voltage by discharging the capacitor once in the second overload state, lowering it once, and then charging it at a predetermined speed.

As the voltage control means, a discharge resistor connected to the control power supply voltage capacitor to discharge it in the second overload state, and the auxiliary output voltage lowered to the first limit value of the voltage monitoring means by the discharge. It is preferable to recharge the discharged capacitor while recovering the control power supply voltage in accordance with the increase in the charging voltage of the control capacitor by using a voltage operation circuit including a control capacitor that sometimes starts charging. Further, the voltage control means is provided with a holding circuit for storing the fact that the second overload state is detected by the overload detection means and starting the voltage control operation, and feeding the control power supply voltage to the control system according to the operation. It is advantageous to turn off. The holding circuit for this purpose is a constant current circuit that is triggered in the second overload state to start the operation, and a current mirror circuit that receives the driven current as a reference current and feeds back the driven current to the constant current circuit to maintain the operating state. Is advantageous, and the operation of the holding circuit is preferably canceled on condition that the control power supply voltage is recovered after the second overload state is resolved.

[0011]

According to the present invention, the method of protecting the stabilized power supply should be distinguished between a severe overload state such as a load short circuit and a slight overload state such as when the load fluctuates, and both overload states are detected. Paying attention to the fact that the method should be different originally,
The former is detected as the first overload state and the second overload state is distinguished from the abnormal reduction in the auxiliary output voltage of the stabilized power supply, and the latter is detected as the normal output voltage reduction. (1) In the overload state, the stabilized power supply is stopped until it is restarted, and in the second overload state, it is temporarily stopped and then automatically restarted after a predetermined time period, thereby achieving the above-mentioned intended purpose. .

[0012]

Embodiments of the present invention will be described with reference to the drawings. 1 is a circuit diagram showing a switching power supply device as an example of a stabilized power supply to which a protection system according to the present invention is applied, FIG. 2 is a waveform diagram of main signals related to the embodiment of FIG. 1, and FIG. 3 is a voltage monitoring means. FIG. 4 is a circuit diagram showing an example of the configuration of FIG. 4, and FIG. 4 is a circuit diagram showing an example of the configuration of the voltage control means. In the embodiment described below, the auxiliary output voltage of the stabilized power supply is used as the control power supply voltage for the control system, and at startup, it is started by the capacitor charged by the input voltage.
The present invention is not limited to such an aspect and can be implemented in various forms.

The upper part of FIG. 1 shows the main circuit of a switching power supply device as a stabilized power supply 60. As usual, the input switch 1 receives an AC voltage and the AC voltage is converted into a DC input voltage Vi. Rectifier circuit 2, capacitor 3 for smoothing and stabilizing this input voltage Vi, input voltage
In the example of the figure that receives Vi, a flyback type transformer 4, a switching transistor 5 shown in the lower right part of the figure that interrupts the current flowing in its primary coil 4a, a series resistor 6 for detecting the current, and a transformer Diode 7 for rectifying the pulsating voltage induced in the secondary coil 4b of the device 4 into a DC output voltage Vo
In addition, a capacitor 8 for stabilizing the output voltage Vo is included in this.

The control system 10 shown in the lower part of the figure by being surrounded by a chain line
Usually controls the output voltage Vo to be constant, but in the method of the present invention, it is desirable to incorporate the overload detection means 40 as shown in the figure. In order to control the output voltage Vo constant, in the illustrated example, the error amplifier 1 that receives the actual value Sa and amplifies the difference from the reference voltage Vr as the target value, and the output of the error transistor 1 by the resistor 6 A comparator 12 for comparing with the detected value of the current, an oscillator 13 for generating a clock that determines the cycle of PWM control, and a flip-flop 14 that is set according to the clock and reset by the output of the comparator 12 are provided. The switching command output from the flip-flop 14 so that the actual value Sa is always equal to the reference voltage Vr.
The transistor 5 is turned on / off by Sw.

The auxiliary output voltage Vc of the stabilized power supply 60, which is the control power supply voltage for operating the control system 10, is
The pulsating voltage generated in the auxiliary coil 4c is rectified by the diode 20 and stabilized by the capacitor 21, and when the stabilized power supply 60 is activated, the capacitor 21 is activated by the resistor 22 to raise the control power supply voltage Vc. It is charged by the input voltage Vi via. In the method of the present invention, the charging current via the starting resistor 22 is preferably set to about 100 μA, which is much smaller than the current consumption of the control system 10 when the current consumption is 10 mA, for example. Furthermore, the Zener diode 23 is connected in parallel with the capacitor 21 in order to prevent the control power supply voltage Vc from abnormally rising due to the input voltage Vi which is normally orders of magnitude higher than that. The auxiliary output voltage Vc as the control power supply voltage generated in this way is given to the control system 10 via the power supply switch 24 controlled by the voltage monitoring means 30 and the voltage control means 50 described later.

The voltage monitoring means 30 constantly monitors the auxiliary output voltage Vc and switches the logic state of the output S3 according to the value thereof. In this embodiment, the output S3 is the auxiliary output voltage Vc.
The operation has a hysteresis characteristic such that it becomes high when Vc is equal to or higher than a predetermined threshold value and becomes low when Vc is equal to or lower than a lower first limit value. Therefore, in this embodiment, when the stabilized power supply 60 is activated, the capacitor 21 is charged from the input voltage Vi side, and when the auxiliary output voltage Vc rises to the threshold of the voltage monitoring means 30, its output S3 becomes high, and Accordingly, the power supply switch 24 is turned on and the auxiliary output voltage Vc is given to the control system 10 as the control power supply voltage, so the stabilized power supply 50 starts the output operation, and then the auxiliary output voltage is caused by a severe overload such as a load short circuit. In the first overload state in which Vc drops below the first limit value, the output S3 switches to low. In the circuit example shown in the figure, the flip-flop 25 is set by the output S3 being high, and the Q switch outputs the power supply switch 24.

As described above, the overcurrent detecting means 40 is the control system 10.
In the present invention, the value of the output voltage Vo is monitored, and in the present invention, an overload detection indicating a second overload state, which is a slight overload when the output voltage Vo drops to the second limit value due to a load change or the like, is detected. Generate signal So. In the example of the overcurrent detecting means 40 shown in the figure, the comparator 41 is caused to detect the second overload state when the output of the error amplifier 11 rises to the set value V4, and the timer circuit 42 maintains this state for a predetermined time period. The overload detection signal So is output only when this is done. The timer circuit 42 incorporates a small capacitor, which is shown in the figure,
It is preferable to set a time limit of about several hundred μS, which can prevent the unnecessary protection operation from being started in response to an overload condition for a very short time.

In the present invention, the stabilized power supply is provided in the second overload state.
Since the output operation of 50 is once stopped and then restarted, voltage control means 50 is provided for that purpose. In the example shown in the figure, this is composed of a holding circuit 51 that receives the overload detection signal So and stores the second overload state, and a voltage operation circuit 52 that operates the auxiliary output voltage Vc during its operation. The operation of the control system 10 is stopped, and the voltage operating circuit 52 causes the capacitor 21 to
Is discharged to reduce the auxiliary output voltage Vc, and then the auxiliary output voltage Vc is charged at a predetermined speed to recover the auxiliary output voltage Vc and restart the operation of the control system 10. In the illustrated example, when the holding circuit 51 is in the holding state, the holding output S5 resets the flip-flop 25 to turn off the power feeding switch 24 to cut off the feeding of the auxiliary output voltage Vc to the control system 10.

The stabilized power supply of FIG. 1 configured as described above.
The operation of 60 will be described with reference to the waveform chart of FIG. Input voltage when the stabilized power supply 60 is started by turning on the input switch 1.
The capacitor 21 is first charged by Vi and the auxiliary output voltage Vc
Rises as shown in FIG. 2 (a), and when the voltage monitoring means 30 reaches the threshold value Vt, the output S3 of the voltage monitoring means 30 becomes high and the power supply switch 24 is turned on. Upon receiving Vc, the operation is started, and the transistor 5 is controlled to open / close by the switching command Sw shown in FIG. 2 (b). As a result, the output voltage Vo of the stabilized power supply 60, and thus its actual value Sa, rises as shown in FIG. 2 (c). After the start, the auxiliary output voltage Vc is measured by the voltage monitoring means 30 as shown in FIG. 2 (a).
Settles to a value slightly lower than the threshold value Vt of. Further, the output voltage Vo after startup, and therefore the actual value Sa thereof, is constantly controlled by the control system 10 so as to always match the value of the reference voltage Vr described above, as shown in FIG. 2 (c).

When a severe overload condition such as a load short circuit occurs, the auxiliary output voltage Vc rapidly decreases from this statically determined value as shown in the right side portion of FIG. 2 (a), and the first limit value of the voltage monitoring means 30.
Below V1. This is the first overload state in the present invention, and the output S3 of the voltage monitoring means 30 changes from high to low in this state. The operation of the control system 10 may be stopped by turning off the power supply switch 24 according to the change of the output S3.
In the overload state, the auxiliary output voltage Vc drops significantly and the control system
Since the operation of 10 is substantially stopped, in this embodiment, the control system is
The power supply to 10 is not particularly stopped, and in response to this, the first limit value V1 of the voltage monitoring means 30 is set below the voltage value at which the control system 10 stops operating.

When the operation of the control system 10 is stopped as described above, the switching command Sw of FIG. 2 (b) is of course stopped, and at the same time, the actual value Sa of the output voltage Vo of FIG. 2 (c) disappears. Note that in the circuit example of FIG. 1, the control system 10 stops operating after the occurrence of the first overload state, but its current consumption remains, which is much larger than the charging current flowing from the input voltage Vi side to the capacitor 21 as described above. Since it is large, the auxiliary output voltage Vc is
As shown by v1 in (a), it takes a very low constant voltage value.

As can be seen from the above, according to the present invention, after the occurrence of the first overload condition, which is a severe overload condition, the control system 10 is stopped and the output voltage Vo of the stabilized power supply 60 is left to disappear. In order to restart the output operation, the stabilized power supply 60 must be restarted, that is, the input switch 1 must be turned off and then turned on. In contrast,
When the above-mentioned second overload condition which is a slight overload condition occurs, the operation of the stabilized power supply 60 is once stopped and then automatically restarted after a predetermined time period. FIG. 2D and subsequent figures show this operation for the second overload state. Fig. 2 (d)
The actual value Sa of the output voltage Vo is controlled so that it matches the value of the reference voltage Vr.In a normal operating state after starting the stabilized power supply 60, the actual value Sa drops due to some cause such as load fluctuation. When the second limit value V2 set by the above-mentioned V4 in the overload detection means 40 is dropped as shown in the central portion of FIG. 2 (d), the overload detection means 40 sets it to the second overcurrent state. If it is determined that it continues for the time t4 set in the timer circuit 42, the overload signal So shown in FIG.
Give to.

The voltage control means 50 stores the occurrence of the second overcurrent state in the holding circuit 51, and then turns off the power supply switch 24 by the holding output S5 being high, as described above, and the auxiliary output voltage Vc Since the power supply to the control system 10 is cut off and its operation is stopped, the switching command Sw of FIG. 2 (f) stops, the output voltage Vo disappears, and its actual value Sa of FIG. 2 (d) also becomes 0.
become. At the same time, the voltage control circuit 52 of the voltage control means 50 starts to operate and discharges the capacitor 21 as described above.
As shown in the middle part of (g), the auxiliary output voltage Vc is lowered to the first limit value V1 of the voltage monitoring means 30 or less in this embodiment, and then the auxiliary output voltage Vc is charged again at a predetermined speed. Restore Vc.

The voltage monitoring means 30 keeps its output S3 low when the auxiliary output voltage Vc falls below the first limit value V1. As described above, the auxiliary output voltage Vc recovers and the right side of FIG. 2 (g) is reached. As shown in the part, when the threshold value Vt is reached, the output S3 is made high and the power supply switch 24 is turned on. As a result, the control system
10 restarts the operation and issues the switching command Sw of FIG. 2 (f), and in response to this, the actual value Sa of the output voltage Vo of FIG. 2 (e) rises. In this way, the control system 10 is controlled according to the second overload state.
Fig. 2 (g) until the operation of is stopped and then restarted.
Time t5 is set by the rate at which capacitor 21 is recharged.

In the stabilized power supply 60 of FIG. 1 whose operation has been described above, the power supply switch 24 is connected to the output S3 of the voltage monitoring means 30.
And the flip-flop by the holding output S5 of the voltage control means 50.
It is configured to be turned on and off via 25, which is, of course, desirable to ensure operation, but to simplify the configuration, the flip-flop 25 is omitted and the power supply switch 24 is directly connected to the output S3 or S5. It can also be controlled.

Finally, referring to FIGS. 3 and 4, voltage monitoring means
A specific configuration example of the voltage control means 30 and the voltage control means 50 will be described. Figure 3 (a)
Since different configurations of the voltage monitoring means 30 shown in FIG. 3 (b) and the holding circuit 51 in the voltage control means 50 in FIG. 4 have many common parts, the corresponding parts are designated by the same reference numerals. Both FIG. 3 and FIG. 4 are bipolar circuits which are composed of complementary transistors and are fed from the auxiliary output voltage Vc.

The voltage monitoring means 30 of FIG. 3A is composed of npn transistors 71 and 72 connected to a common base, and a constant current circuit in which an emitter resistor 71c is connected to a transistor 71 having a multi-emitter structure, and a common base connection. pnp transistor
A current mirror circuit composed of 73, 74, and 75 is provided, and the constant current by the transistor 71 of the constant current circuit is given to the reference transistor 73 of the current mirror circuit, and the current of the driven side transistor 74 of the current mirror circuit is supplied to the transistor 72 of the constant current circuit. Is configured to return to. A resistor 76 is connected to the constant current circuit on the emitter side to prevent malfunction due to noise, and a transistor 76a is used to compensate for the change in the base current due to this.
Is connected to the collector side, and similarly, a noise prevention resistor 77 and a base current compensation transistor 77a are connected to the current mirror circuit side on the emitter side and the collector side, respectively.

Furthermore, in the example shown for the voltage barrier for setting the threshold value Vt, two Zener diodes 91 and
A current path for injecting the base current from the auxiliary output voltage Vc side to the transistors 71 and 72 of the constant current circuit via the emitter-base of the npn transistor 92 is provided so that when the auxiliary output voltage Vc is higher than the threshold Vt, a constant current path is provided. The current is fed back to the constant current circuit from the current mirror circuit via the Zener diode 93 for the voltage barrier for starting the current circuit and setting the first limit value V1 between the transistors 73 and 71. Hold the operating state. In this holding state, the output S3 is taken out from the driven side transistor 75 of the current mirror circuit, and the transistor 92 is turned on to bypass the above-mentioned injection current via the Zener diode 91.

In this state, when the auxiliary output voltage Vc drops to the first limit value V1 set by the Zener diode 93 or less, the feedback current from the current mirror circuit to the constant current circuit is narrowed, so the constant current decreases. , The current of the current mirror circuit also decreases and the output S3 switches from high to low. Thus, the voltage monitoring means 30 is configured as a kind of state holding circuit having a history operation characteristic with respect to the voltage value of the auxiliary power supply voltage Vc.

In the voltage monitoring means 30 of FIG. 3 (b), the base current is directly injected from the auxiliary output voltage Vc into the transistors 71 and 72 of the constant current circuit through the Zener diode 91, the series resistor 91a and the diode 94, and The pnp transistor 95 and its series resistance 95
3A, except that the npn transistor 96 is turned on by a to bypass the injection current, and the configuration and circuit operation of the other parts are the same. The diode 94 serves to prevent leakage of the base currents of the transistors 71 and 72 when the voltage monitoring means 30 is held.

The holding circuit 51 shown on the left side of the voltage control means 50 of FIG. 4 has a circuit configuration similar to that of the voltage monitoring means 30 of FIG. 3, and includes a constant current circuit including transistors 71 and 72, a transistor 73, A current mirror circuit including 74, 75, etc. is provided so that the current of the former transistor 71 flows to the latter reference side transistor 73, and the current of the latter driven side transistor 74 is fed back to the former transistor 72. There is.

The overload signal So by the overload detection means 40 is given to the base of the transistor 76a on the collector side of the transistor 72 of the constant current circuit of the holding circuit 51, and the high current injects the base current into the transistors 71 and 72. The constant current circuit and then the current mirror circuit. As a result, the holding circuit 51 enters a holding state in which the second overload state is stored, the driven transistor 75 of the current mirror circuit issues a high holding output S5, and the voltage operating circuit 52 starts operating. A transistor 78 is provided in order to release the holding circuit 51 from the holding state, and a reset pulse RP generated when the output S3 of the voltage monitoring means 30 rises to high is applied to the base of the transistor 78 to turn on the current mirror. The feedback current flowing from the transistor 74 of the circuit to the transistor 72 of the constant current circuit is extracted.

In the voltage operating circuit 52 shown on the right side of FIG. 4, pnp transistors 81 and 82, which are driven sides of the current mirror circuit of the holding circuit 51, and a transistor 83 whose base and emitter are connected to the collectors of both, respectively, The collector of the transistor 84 is connected to the auxiliary output voltage Vc, and the emitter of the transistor 84 is connected to the discharge resistor 85. Further, a series circuit of, for example, two diodes 86 and a capacitor 87 is connected to the collector of the transistor 81, and a short-circuit transistor 88 is connected in parallel to the latter, and the output S3 of the voltage monitoring means 30 is given to the base thereof.

This output during normal operation of the stabilized power supply 60
Since S3 is high, the capacitor 87 is short-circuited. When the holding circuit 50 operates by receiving the overload signal So in this state, current is supplied from the transistors 81 and 82 and the transistor 87 receives the current.
83 is turned on, and then the transistor 84 is also turned on to rapidly discharge the capacitor 21 for the auxiliary output voltage Vc through the discharge resistor 85. As a result, the auxiliary output voltage Vc drops below the first limit value V1 of the voltage monitoring means 30 within a short time, but the forward voltage of the diode 86 always remains without being short-circuited, so that the auxiliary output voltage Vc is as shown in FIG. As shown in (g), the voltage does not drop below that value, which ensures the minimum voltage necessary for the holding circuit 51 to maintain the holding state even when the auxiliary output voltage Vc is lowered.

On the other hand, when the auxiliary output voltage Vc drops below the first limit value V1 of the voltage monitoring means 30, its output S3 switches to low, and the transistor 88 in the voltage operating circuit 52 turns off accordingly and the capacitor Since the short-circuit state for 87 is released, the capacitor 87 is immediately charged by the current supplied from the transistor 81 after the auxiliary output voltage Vc drops to the above-mentioned minimum value, and the capacitor 21 is charged according to the charged state.
Since it is also charged, the auxiliary output voltage Vc rises again at a predetermined speed as shown in FIG. 2 (g).

The voltage control means 50 of FIG. 4 configured as described above stops the output operation of the stabilized power supply 60 by the holding output S5 of the holding circuit 51 which receives the overload signal So indicating the second overload state. Then, the auxiliary output voltage Vc is once lowered by the voltage operating circuit 52, then raised at a predetermined speed, and when the value reaches the threshold value Vt of the voltage monitoring circuit 30, the output S3 of the high level stabilizes the power supply 60. The output operation of can be restarted. The time t5 shown in FIG. 2 (g) from the stop of the output operation of the stabilized power supply 60 to the restart thereof can be easily set by the supply current of the transistor 81 and the electrostatic capacitance of the capacitor 87 depending on the application, and is usually It is recommended to set this within the range of several tens of mS to several seconds.

The stabilized power supply 60 of FIG. 1 incorporating the voltage monitoring means 30 and the voltage control means 50 constructed as shown in FIG. 3 and FIG. 4 has a feature that the power consumption is particularly small. That is, the current flowing through the starting resistor 22 during normal operation is very small, and the voltage control means 50 consumes no power and does not consume the first load state unless the second overload state occurs, as can be seen from the above description. This is because the power consumption of the voltage monitoring means 30 and the control system 10 is reduced while the output operation of the stabilized power supply 60 is stopped after the occurrence of the second load state.

Note that the case where the flip-flop 25 is omitted from the circuit of the stabilized power supply 60 shown in FIG. 1 will be additionally described. Of course, in this case, the power supply switch 24 may be directly controlled by the output S3 of the voltage monitoring means 30. Further, after the second overload condition occurs, the auxiliary output voltage Vc is lowered by the operation of the voltage control means 50 and the operation of the control system 10 is stopped, so that the holding output of the voltage control means 50 as in the circuit of FIG. There is no particular need to turn off the power supply switch 24 by S5.

Further, when the auxiliary output voltage Vc drops after the occurrence of the first overload state or the like, the feedback current flowing from the current mirror circuit in the voltage monitoring means 30 of FIG. 3 to the constant current circuit via the Zener diode 93 decreases. However, since a small feedback current continues until the accumulated charge in the capacitor 21 almost disappears, the holding state of the voltage monitoring means 30 cannot be immediately solved, and the electrostatic discharge of the capacitor 21 is mainly caused before the release or reset. It usually takes several hundred mS to several seconds depending on the capacity. Utilizing this, if the AC input power of the stabilized power supply 60 is interrupted for a short time, or if the input switch 1 is turned off within a short time due to vibration or erroneous operation and power supply is interrupted, the auxiliary output voltage Vc It is possible to prevent the unnecessary protection operation from being immediately started in response to the decrease. For this reason, the margin time to be given to the voltage monitoring means 30 until the holding state is released can be easily set within the above range, for example, by the capacitance of the capacitor 21.

[0040]

As described above, in the overload protection system of the present invention, when the auxiliary output voltage of the stabilized power supply is monitored by the voltage monitoring means and the operating threshold value is reached, the control system outputs the output of the stabilized power supply. In the first overload state where the first limit value is lowered after the start, the operation of the control system is stopped until the stabilized power supply is restarted, and the regular output voltage of the stabilized power supply is monitored by the overload detection means. By causing the second overload state to be detected when the current limit value has dropped to the second limit value, the operation of the control system is temporarily stopped, and then automatically restarted after a predetermined time, the following effects can be achieved. .

(A) First, which is a severe overload such as a load short circuit
Depending on whether it is an overload state or a second overload state, which is a slight overload due to load fluctuation, in the former case, it will be stopped until the restart, and in the latter case, it will be automatically stopped and then restarted to stabilize. It is possible to reasonably provide the optimized power supply with protection suitable for an overload condition. That is, in the first overload state, the operation of the control system is stopped to most reliably protect the stabilized power supply from a severe overload such as a load short circuit, and in the second overload state, the operation of the control system is temporarily stopped. By restarting later, the stabilized power supply can be continued without being disturbed by a temporary overload while protecting it from a slight overload such as load fluctuation.

(B) By detecting the first overload state from the drop in the auxiliary output voltage and the second overload state from the drop in the regular output voltage, the two overload states are substantially independent of each other. By the optimally set limit value, it is possible to detect accurately and at the timing according to each overload state, and to provide a reasonable protection to the stabilized power supply. (c) When the regulated power supply is operating, the voltage monitoring means releases it from the holding state when the auxiliary output voltage drops due to short-term power interruption of the AC input power supply or short interruption of power supply due to input switch vibration or erroneous operation. It is possible to prevent the output operation of the stabilized power supply from being stopped or interrupted due to a wasteful protection operation triggered by a short-term power failure or interruption of power supply, because the time until it is set can be appropriately set according to the application.

The embodiment of the present invention in which the auxiliary output voltage, which is a standard for detecting the first overload state, is supplied to the control system of the stabilized power supply as the control power supply voltage is simplified in configuration of the stabilized power supply. In addition to the above, there is an advantage that the operation of the control system can be surely stopped according to the first overload state. The embodiment in which the overload detection means is incorporated into the control system responds to the first overload state which is a heavy overload by stopping the operation of the control system, and hence the overload detection means, when the first overload state occurs. There is an advantage that the protection operation can be surely prioritized. An embodiment in which the detection operation of the overload detection means has a predetermined time period is
This is advantageous in preventing a wasteful protection operation in response to a slight overload within a very short period of time and reliably prioritizing detection of the first overload state, which is a severe overload.

A constant current circuit for starting the voltage monitoring means used in the method of the present invention, triggered by the current injected from the auxiliary power supply voltage through the voltage barrier for setting the threshold value,
The embodiment configured as a kind of state holding circuit including a current mirror circuit which starts operation at the constant current output and keeps the constant current circuit in the operating state by the feedback current through the voltage barrier for setting the first limit value is a voltage Monitoring means threshold and first
This has the advantages that the limit values can be set accurately independently of each other, the operation history characteristics suitable for the auxiliary power supply voltage value can be provided, and the above-mentioned release time from the holding state can be set appropriately.

A holding circuit for receiving the overload signal and storing the second overload state is provided in the voltage control means for temporarily stopping and then recovering the output operation of the stabilized power supply according to the second overload state. Is a normal current circuit for a stabilized power supply, in which a constant current circuit that is triggered by an overload signal to start operation and a current mirror circuit that receives the constant current as a reference current and feeds back a driven current to the constant current circuit are provided. There is an advantage that the power consumption by the voltage control means can be eliminated during the normal operation. Further, a discharge resistor for discharging the capacitor for the auxiliary output voltage in the second overload state in the voltage operation circuit of the voltage control means, and charging when the auxiliary output voltage is lowered to the first limit value of the voltage monitoring means by the discharge. The embodiment in which the control capacitor for starting is provided has the advantage that the auxiliary output voltage can be quickly lowered once and its recovery speed can be set accurately.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a switching power supply device as an example of a stabilized power supply to which an overload protection system according to the present invention is applied.

2 is a waveform diagram of main signals associated with the regulated power supply of FIG.

FIG. 3 is a circuit diagram showing a circuit configuration example of the voltage monitoring means, and FIGS. 3A and 3B are circuit diagrams showing different configuration examples thereof.

FIG. 4 is a circuit diagram showing a circuit configuration example of voltage control means.

[Explanation of symbols]

4c Auxiliary coil of transformer for auxiliary output voltage 10 Control system for stabilized power supply 20 Rectifier diode for auxiliary output voltage 21 Capacitor for auxiliary output voltage 22 Starting resistor for charging capacitor 24 Feed switch for control system 30 Voltage monitoring means 40 Overload detection means 41 Comparator for overload detection 42 Timer circuit for overload signal 50 Voltage control means 51 Holding circuit for voltage control means 52 Voltage operation circuit for voltage control means 60 Stabilized power supply or switching power supply 71 , 72 Voltage monitoring means and holding circuit constant current circuit transistor 73,74 Voltage monitoring means and holding circuit current mirror circuit transistor 84 Capacitor discharging transistor 85 Capacitor discharging resistance 87 Capacitor for operating auxiliary output voltage 91 Zener diode for setting threshold value of voltage monitoring circuit 93 Zener diode for setting first limit value of voltage monitoring circuit -Diode Sa Actual value of output voltage So Overload signal Sw Switching command S3 Output of voltage monitoring means S5 Holding output of holding circuit of voltage control means Vc Auxiliary output voltage Vo Output voltage of stabilized power supply Vt Threshold value of voltage monitoring means V1 First limit value of voltage monitoring means V2 Second limit value of overload detection means

Claims (10)

[Claims] 1. An auxiliary output voltage of a stabilized power supply is monitored by a voltage monitoring means, and when it rises to a predetermined threshold value, a control system starts the output operation of the stabilized power supply, and
In the first overload state where the voltage drops below the limit value, the operation of the control system is stopped, the overload detection means monitors the regular output voltage of the stabilized power supply, and when it decreases to the second limit value, the second
Detects an overload condition, stops the operation of the control system until the stabilized power supply is restarted according to the first overload condition, and temporarily stops according to the second overload condition, and then automatically after a predetermined time Overload protection system for stabilized power supply, which is characterized in that it is restarted. 2. The system according to claim 1, wherein the auxiliary output voltage is supplied to a control system of the stabilized power supply as a control power supply voltage, and the auxiliary output voltage is controlled in a first overload state where the power supply voltage drops below a first limit value. An overload protection system for a stabilized power supply, characterized in that a first limit value is set so that the operation of the system is stopped. 3. The constant current circuit according to claim 1, wherein the voltage monitoring means starts its operation by being triggered by a current injected from the auxiliary power supply voltage through a voltage barrier for setting a threshold, and the constant current circuit. It has a current mirror circuit that starts operation by a constant current and keeps the constant current circuit in an operating state by a feedback current that passes through a voltage barrier corresponding to the first limit value, and has an operation history characteristic with respect to the auxiliary power supply voltage value. An overload protection system for a stabilized power supply characterized by being configured as a state holding circuit. 4. The overload protection system for a stabilized power supply as claimed in claim 3, wherein a Zener diode is used as a voltage barrier. 5. The overload detection according to claim 1, wherein a voltage of a capacitor charged through a starting resistor by an input voltage is supplied as a control power supply voltage to the control system when the stabilized power supply is started. When the second overload is detected by the means, the voltage control means discharges the capacitor to temporarily lower the control power supply voltage and then charges it at a predetermined speed to recover the control power supply voltage and restart the operation of the control system. An overload protection system for a stabilized power supply characterized by the above. 6. The discharge resistor according to claim 5, wherein the auxiliary output voltage is supplied to the control system as a control power supply voltage, and the voltage control means is connected to a capacitor for the control power supply voltage in a second overload state. And a control capacitor that starts charging at a predetermined rate on condition that the control power supply voltage has dropped below the first limit value of the voltage monitoring means due to its discharge, and the charging voltage of the control capacitor An overload protection system for a stabilized power supply, characterized in that a capacitor after discharging is charged at a predetermined speed while recovering the control power supply voltage according to the rise. 7. The system according to claim 5, further comprising a holding circuit for storing the fact that the second overload state is detected by the overload detection means and starting the voltage control operation in the voltage control means. A constant current circuit that starts the operation of the holding circuit triggered by the second overload state; 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 the operating state. An overload protection system for a stabilized power supply, which is characterized by being configured from. 8. An overload protection system for a stabilized power supply according to claim 7, wherein the power supply to the control system of the control power supply voltage is cut off in accordance with the operation of the holding circuit. 9. The stabilized power supply according to claim 7, wherein the operation of the holding circuit is released on condition that the control power supply voltage is recovered after the second overload condition is resolved. Overload protection method. 10. The overload protection system for a stabilized power source according to claim 1, wherein an overload detection means is incorporated in a control system.