JPH05300740A - Switching power supply - Google Patents

Abstract

PURPOSE:To contrive to simplify a positive-negative electronic switch by connecting a constant-voltage rectifier path capacity-coupling positive-negative output ends with the output end of a switching transformer and earthing the middle point of the rectifier path and by connecting one output end with an output part via switching element and earthing the other output end via Zener diode. CONSTITUTION:When a control input terminal Trg1 is at a low level, a negative voltage is generated at the output end (b) of a diode D1 and a positive voltage is generated at the output end (c) of a diode D2. Then, when a control input terminal Trg2 is at a low level, a photocoupler PC is turned OFF and the positive potential of point (e) is outputted from an output part Vout. Subsequently, when the control input terminal Trg2 is brought to high level or open, the photocoupler PC is turned ON, both voltages of the positive potential of the point (e) and the negative potential of the output end (b) are simultaeously outputted from the output part Vout and the positive voltage at the point (e) is lower than the absolute value of the negative voltage of the output end (b) of the diode D1 so that the negative voltage is outputted from the output end Vout.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to switching power supplies.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 2, a power source for charging a drum or the like of a copying machine has a control circuit g and a switching circuit for driving a switching transistor tr between an input section i and an output section v. A rectifier circuit h including a transformer t, a diode f, and the like is provided symmetrically, and one of the rectifier circuits h is received by the input from the trigger terminal j to the control circuit g.
The output voltage from the output part v is switched between positive and negative by driving.

Further, as shown in FIG. 3, a tap m is provided at the midpoint of the secondary winding k of the switching transformer t connected to the rear of the control circuit g and the switching circuit to ground it, and both ends of the winding k are grounded. To each of which a diode f is connected, and the output end of each diode f is used as a positive / negative output end.

[0004]

However, the structure shown in FIG. 2 requires two sets of switching transformers t, a rectifier circuit h, a control circuit g, etc., and has a complicated structure, resulting in a high manufacturing cost. There is.

Further, the structure shown in FIG. 3 also has a disadvantage that the winding of the switching transformer t and the bobbin for the winding are complicated because the intermediate tap m and the like are required.

[0006]

According to the present invention, a voltage doubler rectifier circuit is connected to the output terminal of a switching transformer, the positive and negative output terminals of the circuit are capacitively coupled, the middle point of the capacitive coupling is grounded, and the positive and negative terminals are connected to each other. We do not provide a switching power supply characterized in that one of the output terminals is connected to the output section of the same power supply via a switching element, and the other output terminal is connected to the output section while being grounded via a Zener diode. It is what

[0007]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a switching power supply A according to the present invention.
, T is a switching transformer, R1 to R13 are resistors, Q1 to Q3 are transistors, PC is a photocoupler, and D1 to
D3 is a diode, ZD is a zener diode, IC is a control integrated circuit that also functions as a transistor Q3 drive, and Trg1 and 2 are control signal input terminals.

Therefore, the DC input terminal Vin and the ground terminal G
When a DC voltage is applied between ND and the control signal input terminal Trg1 is low level, the integrated circuit for control turns ON / OFF the transistor Q3 to generate AC in the primary winding T1 of the switching transformer T. Then, the required induction AC voltage is excited in the secondary winding T2.

The AC voltage thus excited is rectified by the voltage doubler rectifier circuit S2 composed of the diodes D1 and D2 connected to one end of the secondary winding T2, and the outputs of the diodes D1 and D2 are capacitively coupled. It is smoothed by the capacitors C1 and C2 and output from the output section Vout. However, in the present invention, since the midpoint a of the capacitors C1 and C2 is grounded,
A negative voltage is output from the output terminal b of the diode D1 and a positive voltage is output from the output terminal c of the diode D2.

The positive / negative output voltage is made variable by feeding back the voltage at the output terminal b of the diode D1 to the control integrated circuit at the voltage at the voltage dividing point d of the resistors R6 and R8.

Then, at the output end b of the diode D1 which outputs a negative voltage, a photocoupler as a switching element Sw is provided.
The output of the diode D2, which outputs a positive voltage, is grounded through the Zener diode ZD while the PC is connected so that the output can be turned ON / OFF, and the voltage is stabilized.

As described above, since the upper limit of the positive voltage is regulated by the Zener diode ZD, the positive voltage at the point e is lower than the absolute value of the negative voltage of the output terminal b of the diode D1.

In the switching power supply A, when the control signal input terminal Trg1 is set to low level, the diode D1
Negative voltage is generated at the output end b of the diode D2 and the output end c of the diode D2
Generates a positive voltage.

In such a state, the control signal input terminal Tr
When g2 is set to Low level, the photocoupler PC is turned off and the positive voltage at point e is output from the output section Vout.

When the control signal input terminal Trg1 is set to low level and the control signal input terminal Trg2 is set to high level or open, the photocoupler PC is turned on, and the positive voltage at the point e and the output terminal Vout and the output terminal are output. Both the negative voltage of b and the voltage are output at the same time, and as described above,
Since the positive voltage at the point e is lower than the absolute value of the negative voltage at the output terminal b of the diode D1, the output from the output section Vout becomes a negative voltage. In this case, the Zener diode ZD
A voltage is applied in the opposite direction, but the current is blocked by the diode D3 that also serves as temperature compensation.

Therefore, the voltage output from the output portion Vout can be switched between positive and negative by switching the control signal input to the control signal input terminal Trg2.

[0018]

As described above, the switching power supply that requires positive / negative switching of the output voltage is connected to the output terminal of the switching transformer by the voltage doubler rectifier circuit, and the positive / negative output terminals of the circuit are capacitively coupled to each other. By grounding the middle point and connecting both output terminals while interposing the switching element at either the positive or negative output terminal, the switching element
By turning on / off, the positive and negative voltages can be switched and output from the output section of the same power supply.

Particularly in the present invention, a switching transformer,
Only one set of rectifier circuit and control circuit is required, and the transformer secondary winding only needs a single winding, and the winding bobbin is also simple, which simplifies the structure of the switching power supply and reduces costs. It has the effect of enabling it.

[Brief description of drawings]

FIG. 1 is a conceptual circuit diagram showing a configuration of a switching power supply according to the present invention.

FIG. 2 is a conceptual circuit diagram showing a configuration of a conventional switching power supply.

FIG. 3 is a conceptual circuit diagram showing a configuration of a conventional switching power supply.

[Explanation of symbols]

 A Switching power supply a Middle point S2 Double voltage rectifier circuit Sw Switching element T Switching transformer Vout Output section

Claims (1)

[Claims] 1. A voltage doubler rectifier circuit is connected to the output terminal of a switching transformer, the positive and negative output terminals of the circuit are capacitively coupled, the midpoint of the capacitive coupling is grounded, and either the positive or negative output terminal is switched. A switching power supply characterized in that it is connected to the output section of the same power source with an element interposed, and the other output terminal is connected to the output section while being grounded via a Zener diode.