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Miniature switching power supply, 220/27 volts 25 watts. Encyclopedia of radio electronics and electrical engineering

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The dimensions of the proposed switching power supply (SMPS) allow you to place it in a matchbox. This SMPS differs from a similar device primarily in that it has a 2,5 times higher maximum output power.

It was possible to obtain such parameters thanks to the use of a specialized TOP200YAI microcircuit. This microcircuit contains a built-in overheating protection system with a shutdown threshold of 145 ° C and a circuit for limiting the output current at a level of 415 ... 585 mA.

The schematic diagram of the device is shown in the figure.

Main Specifications

Supply voltage AC, V.....230±15%
Supply voltage frequency, Hz.....40...400
Conversion frequency, kHz.....100
Output voltage, V.....27
Maximum load power. Tue, no more.....25
Efficiency, %.....85

The diode bridge VD1 rectifies the alternating mains voltage, and the capacitor C2 smoothes out the ripple of the rectified voltage. Thermistor RK1 with a negative temperature coefficient of resistance limits the pulse of the charging current of the capacitor C2, which prevents the failure of the diode bridge VD1 at the moment the SMPS is connected to the network. Capacitor C1 reduces the level of interference entering the network from the pulse converter. The converter itself is assembled on a DA1 chip and a T1 pulse transformer. The limiting diode VD2 protects the microcircuit from self-induction voltage pulses that occur on the primary winding of the transformer T1. The auxiliary rectifier on the VD3 diode is designed to provide power to the low-current components of the DA1 chip. The Schottky diode VD4 rectifies the impulse voltage on the output winding III of the transformer T1, and the capacitor C4 smoothes the ripple of the rectified voltage.

In the device, you can use a constant resistor C2-22, C2-23. MLT thermistor - any of the SCK series with a resistance under normal conditions of 33. .68 ohms. Oxide capacitors - small imported, capacitor C1 - DEBB33D222KA2B or CD220025V. We replace the RS206 diode bridge with W08M, KVR08 2W08 DB157, RB157, RC207 bridges. W10M, 2W10M RS207, SF12 diode - on SF11. ES1B ER1B, MUR120. MURS110. UV4002. limiting diode 1.5KE350CA - on 1.5KE300CA R6KEZOOCA or SMBJ200CA. Instead of the Schottky diode 31DQ10, diodes E0VQ100, SB3100, SB5100 can be used.

For the manufacture of a pulse transformer T1, a B18 magnetic circuit made of ferrite 2000NM with a gap of 0,15 ... 0.25 mm was used. Winding (160 turns) and winding II (21 turns) are wound with PEV-2 wire. PETVM. PETV-2. PET-200-l with a diameter of 0,1 mm, and 3 - 37 turns of the same wire with a diameter of 0,51 mm. Three layers of Teflon or Mylar tape are laid between the windings. The microcircuit must be installed on a heat sink with a surface area of about 26 cm2, while it is desirable to use a heat-conducting paste, for example, KPT-8. The heat sink is an aluminum plate 0,8 mm thick, 8 mm wide and 162 mm long, which is curved and fixed around the perimeter of the PCB.

The device does not need adjustment and, provided there are no errors in the installation and use of serviceable components, it starts working immediately.

Author: Moskatov E.

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