JPS58102509A - Pulse transformer for switching power source - Google Patents

Abstract

PURPOSE:To produce no pulse induced voltage or cancel the pulse induced voltage between foil facing faces and to improve noise containment effect by a method wherein the initial winding ends of the primary and the secondary electrostatic shield foil are used as a reference potential and the point where induced pulse potential becomes the same level is permitted to connect to the reference potentials at the primary and the secondary circuits. CONSTITUTION:Connection wires 29, 29' are connected to the point producing no pulse in the primary circuit, for example, the minus terminal of a capacitor C4, and connection wires 28, 28' are similarly connected to the point producing no pulse, for example, the minus terminal of an electrolytic capacitor C5. In this way, a common mode noise at the primary side returns to the minus terminal of the electrolytic capacitor C4 through the primary winding 4 and the primary electrostatic shield foil 9, 9' and is contained in the inside. Similarly, common mode noise at the secondary side returns to the minus terminal of the electrolytic capacitor 5 through the secondary shield foil 8, 8' and is contained in the inside. The level of a noise source eN to the ground in the primary and the secondary circuits is remarkably reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pulse transformer for a switching power supply for transforming the rectified voltage of a pulsed commercial power supply.

Figure 1 shows an example of a switching power supply circuit using this Tanuki pulse transformer, including a line filter CI,
C2, Ll, L2. Image power is supplied to the double-wave rectifier circuit D1 through C3, and this rectified voltage is smoothed by an electrolytic capacitor C4, converted into high-frequency pulses by a switching circuit SW1, and transformed by a transformer T1. The transformed secondary output of this transformer T1 is connected to the diode D2.
The DC voltage is rectified by a choke L3 and an electrolytic capacitor C5 to generate a predetermined DC voltage. Note that D3 is a flywheel diode of choke L3, and C6 and C7 are line filters. Such a circuit configuration makes it possible to reduce the size and weight of the stain source, but on the other hand, in order to rectify and switch the commercial power supply voltage such as 100V, a cylindrical frequency voltage of 100V to several 100V is always installed on the primary side of the transformer T1. (The disadvantage is that common mode noise sources are generated on the negative side and secondary side.These noise sources are
As shown in FIG. 2, the transformer TIQ is voltage-divided and coupled by the capacitance of the primary and secondary windings, etc., and becomes a common noise source eN for the input terminals, and the input side filters Ll, L2 .
The voltages are divided by CI, C2 and the filters C6 and C7 and sent out to the outside, that is, to the power supply line and load, as negative-order common mode noise and second-order common mode noise, respectively. Therefore, in order to suppress the transmission of these noises to the outside, it is necessary to increase the capacitance of the filter capacitors CI, C2, C6, and C7 connected to the frame earths F, G, and, as a result, the The leakage current of the commercial power supply increases, making it particularly difficult to adopt for ME equipment due to safety concerns.

According to Japanese Patent Application No. 56-77055, two sheets of shield foil are interposed between the primary and secondary windings via an insulator, and when used, these foils are placed on the primary side. This problem can be solved by connecting each of the points in the secondary side circuit where no pulse occurs. That is, as a result, the common mode noise is confined inside, and the level of the noise source eN explained in FIG. 2 is greatly reduced.

An object of the present invention is to further develop the above-described invention and provide a pulse transformer for a switching power supply that can further reduce the transmission of pulse noise to the outside world.

That is, according to the above invention, since the electrostatic shielding foil is wound around the core, an electromotive force due to electromagnetic induction corresponding to the number of turns (usually one) of the button is generated between the winding start and end of the foil. If there is a pulse potential difference between the opposing storage capacities, the difference voltage may become the noise source eH in FIG. 2. Therefore, according to the present invention, in order to prevent the generation of such new noise sources e)i and achieve complete noise containment,
- With the starting end of the winding of the electrostatic shielding foil on the next and secondary side as a reference potential, the point where the induced pulse potential is at the same level can be connected to the reference potential (point where no pulse occurs) of the primary and secondary side circuits. .

As a result, the pulse induced voltage does not occur between the opposing surfaces of the foil, or even if it occurs, it is canceled out on the entire opposing surface of the foil, and no new noise source eH is generated, further improving the noise containment effect of the electrostatic shielding foil. do.

Next, the present invention will be explained based on the illustrated embodiment.
°・;A secondary winding 3 is first wound around the inner piece of the Σ1 type core 1 with an insulating paper 2 in between, and a primary winding 4 is concentrically wound on the outside. Insulator 5 between wires 3 and 4
Interposed secondary electrostatic shield? V38 and - next working power shield foil 9 are inserted through EK papers 6 and 7, respectively, and are wound. - Another secondary winding 3' is wound on the outside of 4 in the next winding, and these windings @ 4.3'
Similarly, an insulating paper 7' and a next-side electrostatic shielding foil 9 are placed in between.
', an insulator 5', a secondary electrostatic shielding foil 8', and an insulating paper 6' are wound in this order, and both secondary windings 3, 3' are connected to each other at their winding start and end ends. By doing so, a parallel circuit is formed. And these electrostatic shielding foils,
s; 9.9' winding end 1g, 1g-19°19'
The positions of both the starting and ending ends are aligned in the direction perpendicular to the foil winding direction, and the starting and ending parts of each are insulated from each other by insulating paper (not shown). Also of each! ? Connecting wires 28, 28', 29.29' are soldered to the electric shield holes s, s', 9.9' in the same manner and led out.

When using a 1F14 pulse transformer for switching power supply such as Jin's as transformer T1 in Fig. 1, connecting wire 2
9.29' is the point where no pulse occurs in the secondary circuit, for example, the negative terminal of capacitor C4 and the connecting wire 2.
Similarly, 8.28' is connected to a point where pulses do not occur, such as the negative terminal of electrolytic capacitor C5. As a result, the negative side common mode noise returns to the negative side terminal of the electrolytic capacitor C4 through the primary winding #4 and the negative side electrostatic shield foil 9.9', and is confined in N tyq Sv. Similarly, the common mode noise on the secondary side returns to the negative terminal of the electrolytic capacitor C5 through the secondary shield foil 8.8' and is confined inside. The level of the noise source eN relative to ground in the primary and secondary circuits explained in FIG. 2 is greatly reduced.

Furthermore, a pulse electromotive force equivalent to one turn of the #mirrored coil is induced in the electrostatic shield W38, 8-9, 9'; Since it is connected and the current position is -1, the opposing W! 38.9
Or, the voltages of the induced pulses relative to the reference potential on the opposite sides of the foils 8 and 9' change in proportion to the amount of winding, but are the same, and there is no potential difference between the opposing surfaces of the foil over all the winding positions. New occurrences of noise sources e% are avoided.

θ) - The lead-out position B of the secondary electrostatic shield foil 22 with respect to the lead-out position A of the connection wire of the secondary-side electrostatic shield foil 21 corresponds to the deviation of the winding starting ends a and b. Due to the shift, the pulse electromotive force point is the same when viewed from the winding start end. As a result, as is clear from FIG. Up to the end of the side (-η ~ π), a relative pulse electromotive force V is generated due to counter-dissipation, and after that, as a secondary side, the relative pulse electromotive force difference between the two ships is inconceivable over the entire electrostatic shielding foil. In addition, if the overlapping part is not large when winding the electrostatic shielding foil, the insulator intervening between the two windings will function effectively as an electrostatic shield between the secondary and secondary windings. Considering Figures 7 and 8 on the side, if point 6 or the winding direction is a furnace, point d becomes the actual winding start end.

Note that the present invention can also be applied to cases where parallel secondary windings are not provided, or where the core is pot-shaped.

[Brief explanation of drawings]

Fig. 1 is an example of a circuit of a switching power supply, Fig. 2 is an explanatory diagram of a route for sending common mode noise to the outside in the circuit of Fig. 1, Fig. 3 is a longitudinal cross-sectional view of a pulse transformer for a switching power supply according to the present invention, and Fig. 4 The figure is a cross-sectional view of the transformer according to FIG. 3, FIGS. bl. 3, 3': Secondary winding 4 2 primary winding set 5, 5'
: Insulator 2.6.6; 7.7' : Absolute IIR paper 8, 8' : Secondary electrostatic shielding foil 9, 9' Secondary electrostatic shielding foil 18, 1g-19, 19' : Volume Round end 28, 28; 29.29': Connection line 10th Lt 212 5N3 group 40 1st boar 5e; 21 *6 [2nd group 7
80

Claims (1)

[Claims] A pulse switching power supply in which a primary winding and a secondary winding are concentrically wound around a common core, and an electrostatic shielding foil, an insulator, and another electrostatic shielding foil are sequentially wound between the two windings. A pulse transformer for a switching power supply, characterized in that, in the transformer, connection lines are respectively led out from pulse electromotive force points at the same level when viewed from the winding start end of the foil.