JPH09308237A - Direct-current power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reliability and safety of a direct-current power supply, which is used as a power supply to various electronic equipment, for output short-circuiting. SOLUTION: When the smoothing voltage, obtained by connecting a rectifying smoothing circuit comprising a diode 19 and an electrolytic capacitor 18 to the primary auxiliary winding 4b of a transformer 4, falls below the operating voltage of a control circuit 10 during the operation of the control circuit 10, the capacitor 13 of a second control circuit 10a is charged. When the capacitor 13 is charged to a certain level, a triac 11 is driven to discharge the electrolytic capacitor 9, and a switching element 5 is stopped by means of the control circuit 10 to interrupt an output on the secondary side. Thus, the secondary side is protected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power supply device used as a power supply for various electronic devices.

[0002]

2. Description of the Related Art A conventional DC power supply device will be described with reference to the circuit diagram of FIG. According to the figure, 1 is an AC power source, which is connected to one end of an electrolytic capacitor 3 via a bridge diode 2 which serves as a rectifier.

Reference numeral 4 denotes a transformer, one end of a primary winding 4a of which is connected to the positive side of the electrolytic capacitor 3 and the other end of which is connected to the other end of the electrolytic capacitor 3 via a switching element 5. There is.

An electrolytic capacitor 21 is connected to the secondary winding 4c of the transformer 4 via a diode 20, and a load 22 is connected in parallel to the electrolytic capacitor 21.

An electrolytic capacitor 24 is connected to the secondary winding 4d of the transformer 4 via a diode 23, and a load 25 is connected in parallel with the electrolytic capacitor 24.
Is connected.

4b is a primary auxiliary winding of the transformer 4,
By connecting to the electrolytic capacitor 9 via the diode 8 and connecting the control circuit 10 to the electrolytic capacitor 9, the primary auxiliary winding 4 is connected to the control circuit 10.
Power is supplied from b. Reference numeral 20 a denotes a temperature detecting sensor for the diode 20, which is input to the control circuit 10. An error amplifier 27 detects a load voltage applied to the load 25, and inputs a potential difference from the reference voltage 26 to the control circuit 10.

The electrolytic capacitor 9 and the power source 1 are connected via a series circuit of a diode 6 and a resistor 7,
Power is supplied to the control circuit 10 when the DC power supply device is started.

The operation of the DC power supply device having the above configuration will be described. When the switching element 5 is turned on by the output of the control circuit 10, energy is stored in the transformer 4 from the electrolytic capacitor 3, and when the switching element 5 is off, the energy stored in the transformer 4 is transferred to the secondary winding 4c,
It is emitted from 4d and is rectified and smoothed by the diodes 20 and 23 and the electrolytic capacitors 21 and 24 to become a DC voltage. Further, the output voltage of the load 25 is detected, and the error amplifier 27 compares and amplifies it with the reference voltage 26 and feeds it back to the control circuit 10.
The ON period of the switching element 5 is controlled by this feedback signal, and the voltage applied to the load 25 and the load 22 is always kept constant.

[0009]

When one of a plurality of loads is short-circuited, the output concentrates on the short-circuited load, and in such a state, the diodes 20 and 23 on the secondary side are abnormal. The one with a rating higher than necessary was used so that it would not generate heat. Also, the diode 2
When the temperature detection sensor 20a is attached to 0 and a detection temperature is reached, a detection signal is sent from the temperature detection sensor 20a to the control circuit 10 to stop the oscillation of the switching element 5 to prevent thermal destruction.

Further, the switching element 5 and the diode 2
In order to prevent 0 and 23 from being thermally destroyed, a large heat radiating plate is attached to them, which is a factor of increasing the size and cost of the DC power supply device.

The present invention has been made in view of the above points, and an object thereof is to provide a small-sized and inexpensive DC power supply device.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is designed such that the secondary side is short-circuited while the control circuit is operating in the primary auxiliary winding of the transformer instead of the temperature detecting sensor.
When the smoothing voltage of the primary auxiliary winding becomes lower than the operating voltage of the control circuit, the capacitor of the rectifying / smoothing circuit for the control circuit, which is composed of a diode and a capacitor for supplying power to the control circuit, is discharged to perform the control. A second control circuit for stopping the operation of the circuit is provided.

With the above circuit configuration, a short circuit state of the output is detected from the voltage of the primary auxiliary winding of the transformer, the control circuit is stopped and the output is shut off, so that the diode on the secondary winding side is thermally destroyed. Since the temperature of the secondary winding of the transformer will not rise and insulation breakdown will not occur, the temperature detection sensor can be deleted and the secondary side diode can be made more heat resistant than conventional ones. This contributes to cost reduction.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention is
A series circuit of a switching element and a primary winding of a transformer is connected to the power supply, and one or more output terminals are connected to the secondary winding of the transformer through a rectifying and smoothing circuit of a diode and a capacitor, and the primary auxiliary winding of the transformer is connected. A control circuit for controlling the switching element is connected to the line through a rectifying / smoothing circuit for a control circuit of a diode and a capacitor, and another rectifying / smoothing circuit including another diode and another capacitor in the primary auxiliary winding of the transformer. When the smoothed voltage becomes lower than the operating voltage during the operation of the control circuit, the capacitor of the rectifying / smoothing circuit for the control circuit is discharged to stop the switching element. Since it is configured by the second control circuit including the circuit, the voltage of the primary auxiliary winding of the transformer is controlled by the second control circuit. Since the short circuit condition of the force is detected and the control circuit is stopped and the output is cut off, the diode on the secondary winding side is not thermally broken or the temperature of the secondary winding of the transformer is raised, so that the insulation breakdown is prevented. Since the temperature detection sensor can be deleted and the secondary side diode that does not have high heat resistance can be used, it contributes to downsizing and cost reduction of the device.

The invention according to claim 2 of the present invention is claim 1
As the second control circuit of the described DC power supply device, another rectifying / smoothing circuit including another electrolytic capacitor connected to the primary auxiliary winding and another diode, another transistor connected to the control circuit, and Zener diode connected between the base of the transistor and the other rectifying and smoothing circuit,
When a parallel circuit of a resistor and a capacitor connected in parallel with the transistor and a triac connected to the parallel circuit and connected to the electrolytic capacitor of the rectifying / smoothing circuit for the control circuit are connected, Stop the control circuit,
It is possible to cut off the output and use an inexpensive secondary-side diode, and it is possible to reduce the size and cost of the device without requiring excessive measures for heat dissipation.

The invention described in claim 3 of the present invention is the same as that in claim 2
In addition to the configuration described above, the voltage of the Zener diode is set to be substantially the same as the stop voltage of the control circuit, and it is possible to cope with an instantaneous stop of the power supply.

An embodiment of the DC power supply device of the present invention will be described with reference to the circuit diagram of FIG. The same parts as those of the conventional technique are designated by the same reference numerals, and the description thereof will be omitted and only different points will be described.

The difference is that a second control circuit 10a for controlling the control circuit 10 is provided in place of the temperature detecting sensor 20a used in the prior art. The control circuit 10a includes another rectifying / smoothing circuit including another electrolytic capacitor 18 connected to the primary auxiliary winding 4b and another diode 19, another transistor 15 connected to the control circuit 10, and this transistor 15 Zener diode 16 connected between the base of the other and the other rectifying / smoothing circuit, a parallel circuit of a resistor 14 and a capacitor 13 connected in parallel with the transistor 15, and a rectifying / smoothing circuit for a control circuit connected to the parallel circuit. Triac 1 connected to electrolytic capacitor 9 in the circuit
1 and 1. Note that 12 and 17 are resistors. Further, the control circuit 10 is configured to output to the resistor 12 during operation and stop output to the resistor 12 during non-operation.

Next, the operation will be described. Since the normal operation is the same as in the prior art, it is omitted, and only the case where the secondary load side is short-circuited will be described. When the load 22 is short-circuited, the voltage of the secondary winding 4c of the transformer 4 decreases, and In proportion to this, the voltage of the primary auxiliary winding 4b of the transformer 4 drops, and the voltage of the electrolytic capacitor 18 drops to a voltage at which the Zener diode 16 does not conduct. As a result, the transistor 15 is turned off and the capacitor 13 is charged by the resistor 12. The voltage of the capacitor 13 rises,
When the triac 11 operates, the voltage of the electrolytic capacitor 9 becomes lower than the stop voltage of the control circuit 10, the control circuit 10 stops, the switching element 5 is turned off, and the output is cut off.
By shutting off the switching operation, the transformer 4 and the diode 20 are protected against overheat.

When returning again, the short circuit of the load 22 is released, the power source 1 is disconnected, the electrolytic capacitor 9 is discharged,
When the power supply 1 is turned on again after the holding current of the triac 11 is exhausted, the electrolytic capacitor 9 is charged by the resistor 7 and the control circuit 10 operates when the starting voltage of the control circuit 10 is reached, and the capacitor 13 starts charging by the resistor 12. At the same time, since a voltage is generated from the primary auxiliary winding 4b of the transformer 4, the primary auxiliary winding 4 of the transformer 4 is added to the electrolytic capacitor 18.
The voltage of b is charged and the Zener diode 16 becomes conductive,
Since the transistor 15 is turned on, the capacitor 13 is not charged, the triac 11 does not operate, and the control circuit 10 continues normal operation.

When a momentary power failure occurs in the power supply 1, the control circuit 10 stops when the voltage of the electrolytic capacitor 9 drops to the stop voltage of the control circuit 10, but the control circuit 10 stops. Until transistor 1
By setting the voltage of the Zener diode 16 to be substantially the same as the stop voltage of the control circuit 10 so that 5 continues to be turned on, the triac 11 is set not to operate in response to an instantaneous power failure.

Therefore, when the power supply 1 is restored, the electrolytic capacitor 9 is charged by the resistor 7 and when the voltage exceeds the stop voltage of the control circuit 10, the control circuit 10 operates and the capacitor 1
3 starts charging from the resistor 12 but at the same time a voltage is generated from the primary auxiliary winding 4b of the transformer 4 so that the electrolytic capacitor 18 is charged with the voltage of the primary auxiliary winding 4b of the transformer 4 and the Zener diode 16 becomes conductive. Transistor 15
Is turned on, the capacitor 13 is not charged, the triac 11 does not operate, and the operation of the control circuit 10 is maintained. That is, for the momentary power failure or the like, the second control circuit 10
Since a does not operate with respect to the control circuit 10, the DC power supply device keeps driving.

[0023]

As described above, according to the present invention,
When the output is short-circuited, the output is stopped, so there is no need for a temperature detection sensor that is difficult to attach to heat-generating components.
Further, the operating temperature rating of the heat-generating component and the heat dissipation plate can be lowered as compared with the conventional one, and the device can be downsized.

Further, when the output is short-circuited, the output is not continued and is cut off, so that a secondary failure is not induced and the reliability and safety of the device incorporating the DC power supply device is improved. is there.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of a DC power supply device of the present invention.

FIG. 2 is a circuit diagram of a conventional DC power supply device.

[Explanation of symbols]

 1 power supply 2 bridge diode 3,9,18 electrolytic capacitor 4 transformer 4a primary winding 4b primary auxiliary winding 4c, 4d secondary winding 5 switching element 6,8,19,23 diode 7,12,14,17 Resistance 10 Control circuit 10a Second control circuit 11 Triac 13 Capacitor 16 Zener diode 22, 25 Load 26 Reference voltage 27 Error amplifier

Claims (3)

[Claims] 1. A power supply is connected to a series circuit of a switching element and a primary winding of a transformer, and one or more output terminals are connected to a secondary winding of the transformer through a rectifying and smoothing circuit of a diode and a capacitor. A control circuit for controlling the switching element is connected to the primary auxiliary winding of the transformer through a rectifying / smoothing circuit for a control circuit of a diode and a capacitor, and another diode and another capacitor are connected to the primary auxiliary winding of the transformer. If another smoothing rectifying / smoothing circuit is connected, and this smoothing voltage becomes lower than this operating voltage during the operation of the control circuit, the capacitor of the rectifying / smoothing circuit for the control circuit is discharged to control the control circuit to stop the switching element. A DC power supply device comprising a second control circuit including the other rectifying / smoothing circuit described above. 2. A second control circuit, another rectifying / smoothing circuit including another electrolytic capacitor connected to the primary auxiliary winding and another diode, another transistor connected to the control circuit, and this transistor. Zener diode connected between the base and the other rectifying / smoothing circuit, a parallel circuit of a resistor and a capacitor connected in parallel with the transistor, and a capacitor of the control circuit rectifying / smoothing circuit connected to this parallel circuit. The DC power supply device according to claim 1, wherein the DC power supply device is formed of a triac. 3. The DC power supply device according to claim 2, wherein the voltage of the Zener diode is set to be substantially the same as the stop voltage of the control circuit.