JPH07303373A - Power supply - Google Patents

Abstract

(57) [Abstract] [Purpose] In a power supply device configured as a switching regulator, the ripple current of each output winding on the secondary side of a transformer can be adjusted so that each smoothing capacitor has the same life. [Structure] A plurality of secondary windings n2 and n3 provided in an output transformer T1 of a forward type switching power supply device.
In the output circuit, the inductance element L2 having a small value is interposed between the diode D1 and the choke coil L1 of at least one circuit. Then, the inductance element L2 moves the ripple current of the circuit to another output circuit and adjusts the ripple current of each output circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device used in a copying machine, a printer or the like, and more particularly to a power supply device configured as a multi-output switching regulator.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram showing a configuration of a conventional power supply device configured as a forward type switching regulator. In the figure, T1 is a multi-output output transformer, one of its primary winding n1 is connected to the power supply terminal of voltage Vin, and the other is connected to the drain of switching element Q1. The source is connected to the return terminal of the power supply.

Secondary winding n2 of the output transformer T1
n3 is connected to the multi-winding choke coil L1 through rectifying diodes D1 and D3 and flywheel diodes D2 and D4. The other side of the choke coil L1 is connected to the smoothing capacitors C1 and C2.
Reference numeral 1 denotes a PWM control circuit for feedback control, which controls the on / off ratio of the switching element Q1 via the pulse transformer 2 so that the output voltage V2 becomes a desired voltage.

Here, the multi-winding choke coil L1 is used.
If the winding ratio of each winding is not selected at the same winding ratio as the winding ratio of the secondary windings n2, n3 of the output transformer T1, the balance between the windings will be lost and it will be as if it were a transformer. Energy is transferred between the windings, and the regulation of the output voltages V1 and V2 is disturbed. Therefore, the choke coil L1 is manufactured with the same winding ratio as the transformer T1.

In the power supply device configured as described above,
The output relationship is V1> V2, the number of turns of the choke coil L1 is NL2, NL3, and the secondary windings n2, n of the transformer T1.
When the number of turns of 3 is N2 and N3, N2: N3 = NL2:
It becomes NL3. At this time, considering the ripple current of each winding of the choke coil L1, the inductance ratio of NL2 and NL3 is NL2 ↑ 2: NL3 ↑ 2. Thereby,
When the ripple current ratio is calculated, Irip (NL2): I
rip (NL3) ≈V1: V2.

That is, a large ripple current flows through the capacitor C2 having a lower voltage, and this tendency becomes more remarkable as the voltage difference increases. For example, with a 24V power supply for a motor or the like and a 5V power supply for a logic circuit, a ripple current of about 5 times flows into a capacitor, and therefore a smoothing capacitor on the 5V side requires an element having a ripple current withstand capacity of 5 times. It is uneconomical.

[0007]

Since the conventional power supply device is configured as described above, a large difference occurs in the ripple current flowing in each secondary winding of the transformer, and the life of the smoothing capacitor varies. There was a problem that it was uneconomical.

The present invention has been made by paying attention to the above problems, and the magnitude of the ripple current flowing in each winding on the secondary side of the transformer can be adjusted, and the life of the smoothing capacitor of each output can be shortened. The purpose is to obtain a power supply device that is the same and can minimize the total cost of capacitors.

[0009]

A power supply device according to the present invention is a forward type switching power supply device in which a plurality of secondary side windings of an output transformer are provided with a plurality of winding choke coils. An inductance element is connected in series with one or a plurality of windings.

Another power supply device of the present invention is a flyback type switching power supply device, wherein an inductance element is connected in series with one or a plurality of windings of a plurality of secondary windings of a flyback transformer. It was done.

[0011]

According to the present invention, in the forward type switching power supply device, an inductance element connected in series with the winding of the choke coil on the secondary side of the output transformer causes a current to flow to each secondary winding of the output transformer. The magnitude of the ripple current is adjusted.

According to the present invention, in a flyback type switching power supply device, an inductance element connected in series with the secondary winding of the flyback transformer causes a current to flow to each secondary winding of the flyback transformer. The magnitude of the ripple current is adjusted.

[0013]

1 is a circuit diagram showing the configuration of an embodiment of the present invention, and the same reference numerals as those in FIG. 2 indicate the same components.
This power supply device is configured as a forward-type switching power supply device in which a plurality of secondary windings n1 and n2 of an output transformer T1 are provided with a plurality of winding choke coils L1.

A switching element Q1 controlled by a PWM control circuit 1 via a pulse transformer 2 is connected to the primary winding n1 of the output transformer T1, and the secondary windings n2 and n3 are respectively connected. , Rectifying diode D
1, D3, flywheel diodes D2, D4, winding of multi-winding choke coil L1 and smoothing capacitor C
1 and C2 are connected. Further, an inductance element L2 having a small inductance value is connected in series with the winding of the choke coil L1 connected to the secondary winding n2.

Here, in the device of FIG. 1, an inductance element L2 is added to the circuit of the secondary winding n2 of the output V1 of FIG. 2, and the inductance value of the inductance element L2 is that of the choke coil L1. It is sufficiently small compared to the value. Further, here, V1 << V2.

In the power supply device configured as described above, the ripple current of the circuit of the output V1 is moved to the circuit of the output V2 by the inductance element L2 connected in series with the choke coil L1, and the secondary side winding n2. , N3 adjusts the magnitude of the ripple current. Therefore, by optimally setting the value of the inductance L2, it is possible to make the smoothing capacitors C1 and C2 of the outputs of the secondary windings n2 and n3 have the same life and to minimize the total capacitor cost. .

Although the inductance element L2 is connected to one winding of the choke coil L1 in the above example, an inductance element may be connected to both windings to adjust the ripple current. Transformer T1
Even if there are more secondary side windings, it is sufficient to connect an inductance element that adjusts the ripple current to one or more windings of the choke coil connected to them.

As another embodiment of the present invention, it may be applied to a flyback type switching power supply device. In this case, in the circuit of FIG. 1, the output transformer T1 is a flyback transformer, and the flywheel diodes D2 and D4 and the choke coil L1 of the secondary windings n2 and n3 are also used.
However, the inductance element may be connected in series with one or more of the plurality of secondary windings of the flyback transformer.

Even with such a configuration, the ripple current of each output can be adjusted as in the above-described embodiment, the smoothing capacitors can have the same life, and the total capacitor cost can be minimized. it can.

[0020]

As described above, according to the present invention,
Since the inductance element is connected in series with the choke coil and the secondary winding of the transformer, the magnitude of the ripple current flowing in each secondary winding of the transformer can be adjusted,
The smoothing capacitors for each output have the same life, and the total capacitor cost can be minimized.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing a configuration of a conventional example.

[Explanation of symbols]

 T1 output transformer n1 secondary winding n2 secondary winding L1 choke coil L2 inductance element C1 smoothing capacitor C2 smoothing capacitor

Claims (2)

[Claims] 1. A forward-type switching power supply device comprising a plurality of secondary side windings of an output transformer having a plurality of winding choke coils interposed therebetween, wherein an inductance element is provided in series with one or a plurality of windings of the choke coil. A power supply device characterized by being connected with. 2. A flyback type switching power supply device, wherein an inductance element is connected in series with one or a plurality of secondary windings of a flyback transformer.