JPS5822579A - Switching power source - Google Patents

Abstract

PURPOSE:To contrive to reduce noise of an electric power source for switching by a method wherein input/output lead out wires of a transformer are made to pass through the hollow parts of closed magnetic path cores manufactured of a soft magnetic material. CONSTITUTION:The ring-type cores 13 are supplemented to the input/output windings 1, 3 of the transformer 2. Accordingly noise to be overlapped on the input/output windings 1, 3 of the transformer 2 and noise to be radiated from the transformer 2 are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching power supply, and more particularly to a low-noise switching power supply having a combination transformer that reduces output terminal noise, input terminal leakage noise, and radiation noise.

In conventional switching power supplies, a method as shown in FIG. 1, FIG. 2, or FIG. 5, for example, has been adopted in order to reduce noise superimposed on the output voltage. In the figure 1
is the input winding, 2 is the transformer core, 3 is the output winding, 4 is the first
A shield plate, 5 a second shield plate, 6 a switching transistor, 7 a capacitor, 8 a third shield plate, 9
．． 10 is a rectifier, 11 is a bee yoke coil, and 12 is a capacitor. In the case of the single shield shown in Figure 1, there is no reduction effect on high frequency component noise contained in the input winding, and in the case of the double shield shown in Figure 2, the input winding is It has no effect on noise superimposed on line 1 and mixed in. Also, in the transformer having the triple shield structure shown in FIG. 3, the input winding 1. There is a drawback that there is no effect of reducing high frequency component noise contained in the current flowing through the output winding 3. The present invention eliminates all the drawbacks of the conventional switching power supply using a shielded transformer between input and output windings, reduces noise superimposed on the input and output windings, and reduces noise radiated from the transformer and input/output lead wires. The purpose of the present invention is to provide a switching power supply with a new configuration that reduces .

In order to achieve the above object, the present invention is characterized in that input/output lead wires of a transformer are passed through a hollow portion of a closed magnetic circuit core made of a soft magnetic material.

The present invention will be described in detail below based on examples.

Embodiments of the present invention are shown in FIGS. 4 and 5. In the figure,
13 and 14 are ring-shaped magnetic cores, and the same reference numerals indicate the same parts. In the embodiment shown in FIG. 4, the input/output windings 1.
It has a structure in which a ring-shaped magnetic core 13 is inserted into each lead wire 1.3, and has a large reduction effect on line-to-line noise superimposed on the input/output winding 1.3. Furthermore, since the noise with many high frequency components superimposed on the input/output winding 1.3 is reduced, the noise radiated from the input/output winding 1.3 and the transformer can also be reduced. In the embodiment shown in FIG. 5, a ring-shaped magnetic core 14 is inserted into each of the input and output windings 1.3 in pairs, and this method is applicable to each of the input and output windings 1.3. It shows a great reduction effect on noise propagating between the ground and the earth. Furthermore, by having both the structures shown in Figures 4 and 5, it is possible to obtain both effects at the same time, reducing noise superimposed on the output voltage in the switching power supply, noise leaking from the input line, and noise from the transformer. It is also possible to reduce radiated noise.

Ring cores 13 and 14 in Figure 4 or M5
We will explain the effects of Figure 6 shows the equivalent circuit of the transformer shown in Figure 4. In the figure, 15 is a resistor, 16 is a normal mode circuit, and the same reference numerals indicate the same parts.

The equivalent circuit of the ring-shaped magnetic core is represented by a series circuit of a resistor 15 and a normal mode choke 16, and the noise superimposed on the input/output winding is caused by the line capacitance of the transformer winding and the normal mode choke 16. It is blocked by the constructed filter circuit and consumed by the resistor 15. In FIG. 5, the equivalent circuit is shown in FIG. 7, which has the same effect as reducing noise propagating between the input/output windings and ground.

The ring-shaped magnetic core used is about 1001 cFIz to 3
A large noise reduction effect can be obtained by selecting a material (for example, Mn-Zn ferrite, Ni-Zn ferrite, amorphous material, dust core, etc.) that gives a large loss to high frequencies of about 0 MI (z).

As is clear from the above description, according to the present invention, it is possible to reduce the noise superimposed on the input/output windings of the transformer and the noise radiated from the transformer by simply adding a ring-shaped magnetic core. In particular, this method is extremely effective in realizing a low-noise switching power supply.

[Brief explanation of the drawing]

Figures 1, 2, and 3 are circuit diagrams of a transformer in a conventional switching power supply, and Figures 4 and 5 are circuit diagrams of a transformer of the present invention.
Main part circuit diagram showing an example, Figure 6 is an equivalent circuit diagram of Figure 4,
FIG. 7 is an equivalent circuit diagram of FIG. 5. DESCRIPTION OF SYMBOLS 1... Input winding, 2... Transformer magnetic core, 3... Output winding, 4... Mu (1 shield plate, 5... 2nd seal) plate, 6... Switching Transistor, 7...
Condenser ν゛, 8... Third shield plate, 9... Rectifier, 1o... Rectifier, 11... Choke coil,
12... Capacitor, 13 River ring-shaped magnetic core, 14...
・Ring-shaped magnetic core, 15... Resistor, 16... Normal mode choke, 17... Resistor, 18... Como 21
Illustration 2 Illustration S Group O b Illustration 7 Illustration

Claims (1)

[Claims] 1. A switching power supply having at least one transformer, characterized in that input/output lead wires of the transformer are passed through the hollow portion of a soft magnetic material closed magnetic circuit core having a hollow portion. Switching power supply. 2. The switching power supply according to claim 1, wherein the magnetic core is used independently for each terminal lead-out line of the input/output lead-out line. (v) The respective pairs of input lead-out wires or output lead-out wires of the transformer are oriented so that the directions of the magnetic fields generated in the magnetic core by each lead-out wire are almost opposite and have approximately the same magnitude. 2. A switching power supply according to claim 1, wherein said magnetic core is commonly penetrated through said magnetic core. 4゜ Each of the terminal lead-out lines of the input/output lead-out wires is individually provided through the magnetic core, and each pair of the input lead-out wires or the output lead-out wires is also provided with an individual magnetic core penetrated therethrough. A switching power supply according to claim 1, characterized in that: