JPS5880719A - Noise preventing circuit for switching regulator - Google Patents

Abstract

PURPOSE:To prevent the noise of a switching regulator and to eliminate a radio fault to an electronic device, by connecting a heat sink of a control transistor and an electrostatic/magnetic shield to a stable potential point of an oscillating circuit which is separated from the earth lines of the AC input side and the rectified ouput side respectively. CONSTITUTION:A control transistor TR21 is provided to an oscillating circuit of a switching regulator, and the ON/OFF of the TR21 is controlled by the oscillating frequency. At the same time, a capacitor C is connected between the input terminals of voltage V0. The base of the TR21 is connected to a plus terminal via a resistance R1, and the collector of the TR21 is connected to the primary side of a transformer 23 as well as to a series circuit of a resistance R2 and a diode D. The joint of the R2 and the primary side of the transformer 23 is connected to the plus terminal, and the secondary side of the transformer 23 is connected to a rectifying circuit. Then a heat sink 22 of the TR21 and magnetic/ electrostatic shields 24 and 25 of the transformer 23 connected to a stable potential point of an oscillating circuit which is separated from the earth lines of the input side and the rectified output side respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a switching regulator that oscillates an AC power input by the on/off operation of a control transistor and guides it to a transformer and a rectifier circuit to generate a constant DC voltage. “This is a switching regulator miscellaneous TF rainproof circuit that prevents the occurrence of ♀.

The configuration of a general switching regulator is shown in the block diagram of FIG. Rectifying circuit 1. Alternating current (AC) power source is passed through noise filter 1. After leading to P,2 and rectifying,
The oscillation circuit lIF+3 is caused to oscillate at an oscillation frequency of 20 KIIz or higher. Next, this oscillation circuit 3
A transformer 4 converts the output to a predetermined AC level, and a rectifier circuit 5 generates a predetermined direct current (DC) constant voltage. This D c I(:1) is supplied to a load 6 connected to a rectifier circuit 5 .

In such a switching regulator, since the switching AC voltage 13F is oscillated at a high voltage of 1°l and at a high frequency, a switching control transistor (not shown) included in the oscillation circuit 3 is required. Radiated radio waves were emitted from the heat sink installed in the system, which became a source of noise. This radiated radio wave iJ was a high frequency wave having a switching frequency, and coupled with the primary and secondary lines of the transformer 40, it induced noise that caused the switching regulator to malfunction.

Furthermore, this noise causes radio wave interference that causes electrical equipment such as televisions and radios to malfunction, thus hindering the use of switching regulators in household equipment. Furthermore,
This emitted radiated radio wave coupled with the AC cord became a noise voltage that entered the general power line, interfering with the normal operation of electrical equipment connected to this power line.

Conventionally, the following noise prevention measures have been taken to prevent the occurrence of double noise.

As a first measure, a noise filter 1 was inserted on the AC input side as shown in FIG. In this case, although the noise filter 1 had the effect of attenuating the noise component on the line to which it was inserted, it had no effect on the interference caused by the radiated radio waves. As a second measure, the heat sink provided on the control transformer, the electrostatic shield and magnetic shield provided on the transformer 4 are connected to the AC input side housing ground (
FG) system ground line or signal grounding on the DC output side (S
C) Connected to the system ground line. In this case, it was effective when the impedance of the FG system or SC system was very low, but when the impedance of these lines was high, these ground lines became antennas and induced noise, resulting in the opposite effect. In view of the above points, this invention
Width QJ emitted from the heat sink provided in the control transistor
It is an object of the present invention to provide a switching regulator noise prevention circuit capable of reducing main radio waves and preventing noise generation in a switching regulator.

In order to achieve the object described in item 1, this invention provides an electrostatic shield and a magnetic shield provided on a heat sink and a transformer provided in a control transistor in a switching regulator. It is characterized in that each ground line on the output side of the rectifier circuit connected to the side is connected to a stable potential point of the oscillation circuit, which is separated from the ground line.

Hereinafter, an embodiment of a switching regulator to which the noise prevention circuit according to the above-mentioned noise prevention circuit is applied will be explained with reference to the drawings.

The switching regulator according to this embodiment has the configuration shown in FIG. 1 above. FIG. 2 shows the connection relationship between an oscillation circuit and a transformer that constitute a part of this switching regulator. This oscillation circuit is a control transistor 21
The control transistor 21 oscillates at a switching frequency that turns it on and off. ! In addition, a capacitor C is connected between the input terminals, and the base of the control transistor 21 is connected to the (f) side of the input terminal via a resistor R1, and the emitter is connected to the (-) side of the input terminal.

Further, the collector of the transistor 21 is connected to the (-) side of the input terminal via a series circuit of a resistor R2 and a diode D. The voltage between this series circuit is introduced into the primary side of the transformer 23.

In the second oscillation circuit and transformer configuration, a heat sink 22 is provided to protect the control transistor 21 from overheating, and an electrostatic shield 25 and a magnetic shield are provided to prevent external noise from being induced in the transformer 23. A shield 24 is provided. Furthermore, a heat sink 22 and an electrostatic shield 25
, and the magnetic shield 24 are connected to the emitter of the control transistor 21 by a wiring paulownia, and are electrically connected to the emitter, but are separated from the aforementioned AC input side FG system ground line and DC output side SG system ground line. and insulate. Note that the heat sink 22 is insulated from the collector of the transistor 21.

The switching operation of the oscillation circuit in the second configuration will be explained below.

When the current I2 flows to the base of the control transistor 21 through the resistor R1 and the transistor 21 is turned on, the current 11 flows to the primary side of the transformer 23 and a voltage determined by the winding ratio of the transformer 23 is excited on the secondary side. . This excitation voltage is guided to a rectifier circuit (not shown) to obtain a predetermined constant DC voltage.

At this time, the collector voltage generated at the collector of the transistor 21 has a waveform shown in the waveform example shown in FIG.

In other words, this collector voltage has a rising peak value of 320V, an average peak value of 210V, and a cycle of 50M5, and is a switching AC voltage with a high potential and high frequency as described above. It is. Although the heat sink 22 of the transistor 21 is insulated from the collector, a collector voltage is induced by the capacitor coupling, and the aforementioned radiated radio waves are emitted from the heat sink 22. but,
Since the heat sink 22 is electrically connected to the emitter of the transistor 21, that is, the stable potential point of the oscillation circuit, the collector voltage induced by the above-mentioned capacitor coupling is reduced.
The generation of radiated radio waves is suppressed.

Since the transistor 21 and the heat sink 22 form a closed loop together with the twisted contenzer C, the radiated radio waves and A
Noise voltage due to compression with the C power supply line is reduced. Similarly, since the shield potential of the electrostatic shield 25 and the magnetic shield 24 is the emitter potential of the transistor 21, the noise voltage induced by the compres- sion between the radiation voltage and the primary and secondary sides of the transformer 23 is reduced.

Further, since the emitter of the transistor 21 is separated and insulated from the AC input side ground line and the DC output side ground line, it has the effect of preventing noise even when the impedance of these ground lines is high.

As shown in Figure 2, according to the switching regulator noise prevention circuit of Origin 1, with a simple configuration, the radiated radio waves emitted from the heat sink provided in the control transistor are reduced, and the induced noise is reduced. It has an excellent noise prevention effect that can be made extremely small.

In addition, since the noise from the switching regulator is reduced, it does not cause radio interference to electrical equipment such as televisions and radios, and devices that incorporate a switching regulator can be used at home. The range is expanded.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of a general switching regulator, Fig. 2 is a circuit diagram showing the connection relationship between the oscillation circuit and the transformer in a switching regulator to which the noise prevention circuit related to the +311 is applied, and Fig. 3 is a collector voltage waveform diagram for explaining the effect of FIG. 2. 2.5... Rectifier circuit, 3... Oscillation circuit, 4.23
...transformer, 21...control transistor, 22...heat sink,
24... Magnetic shield, 25... Electrostatic shield. Applicant Sharp Co., Ltd. Agent Patent Attorney Hisainu Komori

Claims (1)

[Claims] (1) Rectifying and controlling AC power source power) - An oscillation circuit containing a transistor oscillates at a predetermined frequency, and the output of this oscillation circuit is led to the primary side of a transformer to convert it to an output of a predetermined level. In a switching regulator that generates a constant DC voltage from a rectifier circuit connected to the secondary side of a transformer, the heat sink provided on the control transistor, the electrostatic shield and magnetic shield provided on the transformer are connected to A switching regulator noise prevention circuit connected to a stable potential point of the oscillation circuit separated from each ground line on the power input side and the output side of the rectifier circuit.