JPH066712Y2 - Switching power supply - Google Patents

Description

Detailed Description of the Invention A. Field of Industrial Application The present invention relates to a switching power supply.

B. SUMMARY OF THE INVENTION The present invention connects the positive side of one rectifier circuit that obtains a DC output to a positive bus bar, the negative side of the other rectifier circuit to a negative bus bar, and connects both buses to a common bus bar in common.
In a switching power supply provided with a stabilizing circuit or the like connected to both bus lines, a plus voltage protection circuit is formed by connecting the cathode of the first Zener diode and the emitter of the first transistor to the plus bus line, and By forming a negative voltage protection circuit by connecting the anode of the second Zener diode and the emitter of the second transistor to the negative bus, a sharp operating characteristic can be obtained by the amplifying action of the PNP transistor and the NPN transistor. It was made possible.

C. 2. Description of the Related Art In a switching power supply, a switching transformer is used to supply DC power intermittently supplied to the primary side coil by controlling the on / off ratio of a switching element, and the output of the secondary side coil is rectified to generate DC power. There is something to gain. Such a switching power supply is generally provided with an overvoltage protection circuit to protect the circuit from overvoltage. FIG. 3 is a circuit diagram showing an example of a switching power supply using such an overvoltage protection circuit. In this figure, reference numeral 1 is a rectifier, and two input sides of this rectifier 1 are connected to an AC power supply AC. A primary side coil 2a of a switching transformer 2 and a switching element 3 are connected in series to the DC output side of the rectifier 1, and a smoothing capacitor 4 is connected in parallel to this output side. Reference numeral 5 is a control oscillator, and the output voltage of the rectifier 1 is input to the input side of the oscillator 5 via a resistor R1. Further, the control oscillator 5 controls the on / off ratio of the switching element 3 to flow an intermittent current to the primary coil 2a of the switching transformer 2,
AC power is induced in the secondary coils 2b1, 2b2, ... 2bn. When the switching element 3 is a transistor, its base voltage is controlled.

Secondary coils 2b1 and 2b2 of the switching transformer 2
Are provided with rectifier circuits 6a and 6b to obtain a DC output.
Also, the positive side of the rectifier circuit 6a is connected to the positive bus A to obtain a positive potential, and the negative side of the rectifier circuit 6a and the positive side of the rectifier circuit 6b are commonly connected to the common bus C to obtain OV. In addition, the minus side of the rectifier circuit 6b is the minus bus bar B
To get a negative potential.

Although the description of the secondary coil 2bn (n is a natural number of 3 or more) and thereafter is omitted, the secondary coil 2b1,
It is provided similarly to 2b2. Reference numeral 7 is a constant voltage circuit. In this constant voltage circuit 7, the positive voltage of the rectifier circuit 6a is input, and the deviation between the positive voltage and the set voltage is amplified.
Reference numeral 8 denotes an insulating photocoupler, which inputs a detection signal to the control oscillator 5 via the photocoupler 8 to control the on / off ratio of the switching element 3 so that the output voltages of the rectifier circuits 6a and 6b become constant. To do. Reference numeral 20 is a zener diode for overvoltage detection and protection.
The cathode side of 0 is connected to the plus bus A, and the anode side is connected to the common bus C via the resistor R2 and the light emitting diode 11D which is the light emitting element of the photocoupler 11 to form a plus voltage protection circuit. When the voltage A exceeds the Zener voltage, an electric current is passed through the resistor R2 and the light emitting diode 11D of the photocoupler 11. 12
Is a thyristor, and this thyristor 12 controls the gate by the on-current flowing from the phototransistor 11T which is a light receiving element to lock the control oscillator 5. Also,
Reference numeral 21 is a Zener diode.
Is connected to the common bus bar C, the anode side is connected to the minus bus bar B via the resistor R3, the light emitting diode 22D of the photocoupler 22, and the photocoupler 22.
The phototransistor 22T is the Zener diode 20.
When the voltage of the negative bus bar B becomes a negative overvoltage and becomes equal to or higher than the Zener voltage of the Zener diode 21, it is connected to both ends of the resistor R3.
A current is passed through the light emitting diode 22D of the photocoupler 22,
The phototransistor 22T is turned on to make the zener diode 2
0 is short-circuited, a current is passed through the photocoupler 11 to control the thyristor 12, and the control oscillator 5 is locked.

D. Problems to be Solved by the Invention In such a switching power supply, when it has both positive and negative buses as described above, it is composed of a Zener diode 20, 21, a photocoupler 22 and the like to detect an overvoltage of its output and protect it. It is composed of a voltage protection circuit, a negative voltage protection circuit, a thyristor 12 for locking the control oscillator 5, and the like.

However, since the overvoltage on the negative voltage protection circuit side has a different polarity, it is not easy to connect it to the positive voltage protection circuit side.
As shown in the figure, Zener diodes 20 and 21, resistance R
2, R3, and the photocoupler 22 are used for coupling with the previous circuit. Therefore, in such a switching power supply, the photocoupler 22 must be used for coupling, which increases the cost. In addition, since the constant voltage characteristic of the Zener diode is highly dependent on the DC value, there is a problem that it is difficult to obtain a stable operating voltage.

Therefore, an object of the present invention is to provide a switching power supply in which the number of photocouplers used is reduced and the first and second transistors are used to obtain sharp operating characteristics by their amplifying action.

E. Means for Solving the Problems As a means for solving the above problems, according to the present invention, a direct current output side of a rectifier is connected to a series circuit composed of switching elements connected in series with a primary coil of a switching transformer, A plurality of coils are provided on the secondary side of the switching transformer, and a rectifier circuit is provided on at least two of the secondary coils, and the negative side of one rectifier circuit and the positive side of the other rectifier circuit are common. Connect to the common bus, connect the plus side of the one rectifier circuit to the plus bus, and connect the minus side of the other rectifier circuit to the minus bus to determine the deviation between the voltage of the plus bus and the set voltage. Detected by the voltage circuit,
In the switching power supply in which the control oscillator is driven by the deviation to control the on / off ratio of the switching element, the first and second Zener diodes and the first and second diodes are connected in series and common to each other. The common busbar is connected to the connection point, the cathode side of the first Zener diode is connected in series to the plus busbar through the first and second resistors, and the anode side of the second Zener diode is connected in series. It is connected to the minus bus through the third and fourth resistors, the base is connected to the common connection point of the first and second resistors, the emitter is connected to the plus bus, and the collector is the first bus.
A first transistor connected to the cathode side of the diode, the base is connected to the common connection point of the third and fourth resistors, the emitter is connected to the minus bus, and the collector is the anode side of the second diode. A second transistor connected to the thyristor, the cathode side of the first diode and the anode side of the second diode are connected to the input side of the photocoupler, and the output side of the photocoupler is connected to the gate of the thyristor. It is characterized in that the control oscillator is locked by turning on and off.

F. Action When an overvoltage occurs on the plus bus bar, the first Zener diode of the plus voltage protection circuit is turned on, the base current of the first transistor flows, and this transistor is turned on, the plus bus line, the first transistor, the photocoupler,
A current flows through the common bus through the second diode, and the photocoupler locks the control oscillator through the thyristor to protect the circuit from overvoltage.

Also, when the negative bus becomes overvoltage, the second Zener diode of the negative voltage protection circuit conducts, the base current of the second transistor flows, and this transistor conducts, the common bus, the first diode, and the photocoupler. A current flows through the negative bus through the second transistor, and the photocoupler locks the control oscillator through the thyristor to protect the circuit from overvoltage.

G. Embodiment Next, an embodiment of the present invention will be described with reference to FIG.

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

Since this switching power supply has the same configuration as the conventional switching power supply, the switching transformer circuit, the switching element control circuit, etc., the same reference numerals are given and description thereof is omitted, and overvoltage detection and protection different from the conventional switching power supply are performed. Only the circuit will be described in detail.

In FIG. 1, reference numeral 13 is a first Zener diode, and this diode 13 has resistors R3 and R2, which are third and second resistors on the cathode side between the positive bus A and the common bus C.
To the plus bus A, and the anode side is connected to the common bus C. A first transistor 14 is a PNP transistor, and this transistor 14 is connected in parallel with the first Zener diode 13, and when the first Zener diode 13 becomes conductive, the current flows through the photocoupler 11 and the second coupler. Common bus C through the diode D2 of
An electric current flows through. In this device, a positive voltage protection circuit is formed by the first Zener diode 13, the first transistor 14, the photocoupler 11, the second diode D2 and the like. Reference numeral 15 is a second Zener diode, which is connected between the common bus C and the negative bus B, and has a cathode R of the common bus C and an anode R of a second and fourth resistance R.
It is connected to the minus bus B via 5 and R6. 16
Is a second transistor which is an NPN transistor,
This transistor 16 is connected in parallel with the second Zener diode 15 and
Is conducted, the current flows through the first diode D1, the photocoupler 11, and the resistor R7, and a current flows through the minus bus B. In this device, a negative voltage protection circuit is formed by the second Zener diode 15, the NPN transistor 16, the first diode D1, the photocoupler 11 and the resistor R7. Reference numeral 103 denotes a plus other channel coupling line, which is provided with a plus other channel coupling busbar 103a so that the circuits can be connected in parallel in the same manner. The cathode side of the first diode D1 is connected to the plus other channel coupling line 103, and the anode side thereof is connected to the common bus C. 104 is a minus other channel coupling line,
As with the plus other channel coupling line 103, a minus other channel coupling busbar 104a is provided,
Similar circuits can be connected in parallel. The cathode side of the second diode D2 is connected to the common bus C, and the anode side thereof is connected to the minus other channel coupling line 104.

Next, the operation of this embodiment will be described. Plus bus A
When an overvoltage occurs, the first Zener diode 13 becomes conductive, whereby a current flows to the emitter side and the base side of the first transistor 14, and the base current makes the first transistor 14 conductive. When the first transistor 14 becomes conductive, the resistor R4 and the photocoupler 11 are connected.
A current flows through the common bus bar C through the light emitting diode 11D and the second diode D2. When a current flows through the light emitting diode 11D of the photocoupler 11, the phototransistor 11T
Operates to control the gate of the thyristor 12 to lock the control oscillator 5 and stop the oscillation. When the control oscillator 5 is locked, the switching transformer 2
Since no voltage is induced in the secondary coil 2b1 of No. 2, an overvoltage is not generated in the plus bus A.

Also, with respect to the minus overvoltage of the minus bus B, the second Zener diode 15 becomes conductive, and due to this conduction, a current flows through the resistor R5 to the base of the second transistor 16, and the base current causes the second transistor 16 to flow. 16
Conducts. When the transistor 16 is turned on, the current flows through the common bus C, the first diode D1, the photocoupler 11, the resistor R7, and the second transistor 16 to the negative bus B.
Current flows through. Then, when a current flows through the photocoupler 11, the gate of the thyristor 12 is controlled to lock the control oscillator 5 and suppress a negative overvoltage, as described above.

FIG. 2 is a characteristic diagram showing the relationship between the overcurrent and the output current of the voltage protection circuit. The vertical axis represents the current flowing to the photocoupler 11, and the horizontal axis represents the plus bus A (indicated as A terminal voltage in FIG. 2). Is taking the voltage of. Vs on the horizontal axis indicates a set voltage value in a normal state, and Vo indicates an overvoltage set value. Thus, it can be seen that when the overvoltage set value is exceeded, the transistor operates with a sudden rise.

As described above, according to this embodiment, the switching power supply having the overvoltage protection circuit having the sharp operating characteristic can be obtained by the amplifying action of the transistor. Further, in the device of this embodiment, similar circuits can be connected in parallel by the plus and minus other channel coupling lines 103 and 104.

H. Effects of the Invention According to the present invention as described above, the switching power supply having the overvoltage protection circuit having the sharp operating characteristic can be obtained by the amplifying action of the first transistor and the second transistor. In addition, the same circuit can be connected in parallel by the other channel coupling line, and the overvoltage protection of many channels can be performed at the same time.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a characteristic diagram showing an embodiment of the present invention, and FIG. 3 is a circuit diagram showing an example of a conventional switching power supply. 2 ... Switching transformer, 2a ... Primary coil,
2b1, 2b2, 2bn ... secondary coil, 3 ... switching element, 5 ... control oscillator, 7 ... constant voltage circuit, 11 ... photocoupler, 13 ... first Zener diode, 14 ... 1 transistor, 15 ... second
Zener diode, 16 ... second transistor.

Claims (1)

[Scope of utility model registration request] 1. A direct current output side of a rectifier is connected with a series circuit composed of switching elements connected in series with a primary side coil of a switching transformer, and a plurality of coils are provided on the secondary side of the switching transformer. A rectifier circuit is provided on at least two of the secondary coils, and the negative side of one rectifier circuit and the positive side of the other rectifier circuit are commonly connected and connected to a common bus bar, and the positive side of the one rectifier circuit is connected. To the plus bus, the minus side of the other rectifier circuit is connected to the minus bus, respectively, the deviation between the voltage of the plus bus and the set voltage is detected by a constant voltage circuit,
In the switching power supply in which the control oscillator is driven by the deviation to control the on / off ratio of the switching element, the first and second Zener diodes and the first and second diodes are connected in series and common to each other. The common busbar is connected to the connection point, the cathode side of the first Zener diode is connected in series to the plus busbar through the first and second resistors, and the anode side of the second Zener diode is connected in series. It is connected to the minus bus through the third and fourth resistors, the base is connected to the common connection point of the first and second resistors, the emitter is connected to the plus bus, and the collector is the first bus.
A first transistor connected to the cathode side of the diode, the base is connected to the common connection point of the third and fourth resistors, the emitter is connected to the minus bus, and the collector is the anode side of the second diode. A second transistor connected to the thyristor, the cathode side of the first diode and the anode side of the second diode are connected to the input side of the photocoupler, and the output side of the photocoupler is connected to the gate of the thyristor. The switching power supply is characterized in that the control oscillator is locked by turning on and off.