Switching power supply for household REA. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Switching power supply for household REA. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power Supplies

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A single-ended voltage converter with a single-sided switch was chosen to power household electronic equipment with a power of 35...40 W. Converters of this type are currently most widely used in household and industrial equipment.

Switching power supply for household electronic equipment
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Among single-ended voltage converters, the single-ended one with "reverse" switching on of the rectifier diode (Fig. 1) is extremely simple, the principle of operation of which is as follows.

When the transistor VT1 is open, a linearly increasing current flows through the inductance of the primary winding 13-19 of the transformer TV1. In the magnetic circuit of the transformer, energy is stored in the form of a magnetic flux. In the winding III of the TV1 transformer, a voltage of such polarity is induced, at which the VD11 diode is in a non-conducting state, and the voltage on the load is maintained only due to the energy of the capacitor C9, charged in the previous cycle.

After closing the transistor VT1, the current flowing through the winding I of the transformer TV1 is interrupted. Since the magnetic flux in the magnetic circuit of the transformer cannot instantly disappear, then an EMF of self-induction is induced on the winding III of the transformer, the polarity of which is opposite to the voltage that existed on it before the transistor closed.

Diode VD11 opens, and along the resulting circuit: terminal 14 of the transformer TV1, open diode VD11, capacitor C9, output filter LL1, C10, power supply load, terminal 20 of the transformer, current flows.

Thus, the second stage begins - the transfer of energy stored in the form of a magnetic field to the load and charging the capacitor C9. However, part of the magnetic flux is closed in air, bypassing the secondary winding. This flux is determined by the leakage inductance. The energy stored in it at the accumulation stage is not transferred to the load and is compensated by the damping circuit R11C6VD9.

In a single-cycle circuit, the transformer magnetic circuit operates in the mode of a partial magnetization cycle. If the magnetizing current is large enough, then the magnetic induction reaches a saturation level, and the inductance of the primary winding of the transformer drops sharply. This causes a sharp increase in the current of the transistor VT1. To avoid saturation, a gap of up to 2 mm is introduced into the magnetic circuit. Thus, in a single-cycle voltage converter, it is necessary to be very careful in choosing the transistor VT1 and the transformer TV1.

The "heart" of the "flyback" single-cycle voltage converter is the DA1 microcircuit - the PWM controller.

A typical switching circuit and characteristics of the TDA4605 can be found in [1-3]. The transformer from the power supply module MP-403: TPI-8-1 was used as a pulse transformer, as well as two secondary windings 14-18 and 16-20, connected in series. Each winding consists of four PEVTL-0,35 conductors connected in parallel.

At a current density of 5 A / mm2, the secondary winding current reaches 1,7 A. With the inclusion of the transformer TV1 indicated in the diagram and a load power of 40 W, the conversion frequency is 33 kHz. If the voltage in the secondary winding is insufficient for the pulse source to enter the operating mode, a characteristic sound ("tsikka") will be heard, due to the periodic switching on of the starting mode. To facilitate the start-up mode, it is desirable to turn on a button with normally closed contacts between the output of the power source and the load. If it is difficult for the unit to enter the operating mode, it is necessary to briefly press it, thereby facilitating the start of the power source.

Some integrated circuits have a maximum supply voltage of 18 V. By adjusting the resistor R6, and if necessary R5, you can set the desired voltage.

Can be used as a secondary winding 11-7. At the input of the pulsed source, it is necessary to turn on the noise suppression filter. You can use a standard one from a television receiver, consisting of a DF110PTs inductor and capacitors 2200x630 V (2 pcs.) And one 0,1 μFCh630 V.

When connecting to the network, reliable switching elements (toggle switches, switches) should be used. The unit, together with the noise suppression filter, is connected to the network through a 1 A fuse. All elements of the switching power supply are mounted on a printed circuit board made of one-sided foil fiberglass with dimensions of 100×80 mm and a thickness of 1,5 mm (Fig. 2).

Switching power supply for household electronic equipment

Resistors of the MLT type are used in the source, the variable resistor R6 is imported, small-sized. Electrolytic capacitor C1 from SAMSUNG, the rest are also imported, C9 is desirable for an operating temperature of 105 ° C. Capacitors C2, C4, C8 type K73-9; C3, C7, C10 imported, small-sized. Throttle LL1 industrial type DM-2,4. If there is an increased level of ripple at the output of the source, then it is necessary to use a choke with a large inductance, calculated according to the method given in the relevant literature, or turn on another LC filter at the output. To reduce losses in the rectifier at a high conversion frequency, a diode with a Schottky barrier was used as a VD11 diode. With the worst result, you can apply KD213.

The oscillogram on the 14th output of the transformer relative to the 20th output is shown in fig. 3.

Switching power supply for household electronic equipment

Transistor VT1 and diode VD11 are each placed on a ribbed heat sink with dimensions of 40×25 mm. A pulsed power supply assembled from known-good radio elements practically does not require adjustment. In order to reduce interference from the power supply, it is desirable to place it in a metal case with ventilation holes for cooling. It should be borne in mind that the switching power supply is galvanically connected to the network, it operates completely silently and, if handled carelessly, can cause electric shock.

References:

Chips for switching power supplies and their application: Ref. - M.: DODEKA, 1997.
Lukin N.V., Koryakin-Chernyak S.L. Nodes and modules of modern TVs. - K .: Science and technology, 1995.
Kosenko V., Kosenko S., Fedorov V. Reverse pulse IP//Radio. - 1999 - No. 12. - S. 40-41.

Author: O.V. Belousov

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