This miniature power pack sits in the battery compartment handheld radios, calculators and other miniature electronic equipment where they need to be connected to AC power. After capacitor C1, Zener diode V1 and V2 (see diagram) we obtain the rectified current voltage of 15 V. It is used to supply voltage to the transistor V4. During the negative half-wave current of the diode V3 returns to the power supply portion stored in the power transformer.
Thanks to the transformer T1, the output of the circuit is completely isolated from the network. But if the transistor V4 and the Zener diode V1 to supply radiators, our power supply will not be afraid of a short circuit at the output or prolonged operation at idle.
Since the conversion rate of more than 13 kHz, the ferrite armored core is possible at very small sizes. The primary winding is wound simultaneously with two wires Ø 0,17 mm and contains 100×2 turns. The winding II has 50 turns of the same wire. To eliminate interference by the transmitter, the power supply need to be shielded.
Foreign domestic ВС109 model transistor KT315 or КТ342 with any alphabetic index. Д815Д Zener diodes Д225Б — D226 D or Д208 — Д211 (V2), Д202, Д206 (V3, V5). At 9 volts the number of turns of the secondary winding of T1 should be increased to 75.