Switching power supply.
This source can be used to power any load capacity of up to 20 watts and has smaller dimensions than those who work with step-down transformer at a frequency of 50 Hz.
Switching power supply made by the scheme one-cycle pulse high-frequency transducer. Schematic diagram of pulsed electric power supply is shown in Fig1. Transistor VT1 collected oscillator operating at a frequency of 20 ... 40 kHz (depending on settings). The frequency is adjusted capacitance C5. Elements VD5, VD6 and C6 form a chain running oscillator.
In the secondary circuit after the bridge rectifier is the usual linear regulator on the chip, which allows you to have a fixed output voltage, regardless of changes in the input network (187 ... 242 V).
In the scheme used capacitors: C1, C2-type K73-16 for 630 in; C3 - 50-29 at 440; C4 - K73-17V to 400 V; C5 - K10-17, C6 - K53-4A at 16 V C7 and C8-type K53-18 to 20 V. Resistors can be arbitrary. Zener VD6 can be replaced by KS147A.
Pulse transformer T1 is performed on the ferrite core M2500NMS-2 or M2000NM9 size Sh5h5 (cross-section of the core at the location of the coil 5x5 mm with a gap in the center). Rewinding made wire marks PEL-2. 1.2 The winding contains 600 turns of wire diameter 0.1 mm, 3.4 - 44 coil diameter 0,25 mm, 5-6 - 10 turns in the same wire as the primary winding.
Fig. 1. Switching power supply. Electrical circuit power supply to 15 W
If necessary, the secondary windings may be several (in the diagram shows only one), and for the oscillator is necessary to observe polarity phase windings of 5.6 in accordance with the scheme.
Setting the converter is to obtain a steady excitation oscillator when changing the input voltage from 187 to 242 B. Elements requiring the selection, followed by an asterisk "*". Resistor R2 can have a nominal value of 150 ... 300 kOhm, and the capacitor C5 - 6800 ... 15000 pF. To reduce the size of the converter in case of smaller withdrawn in the secondary circuit of power denominations electrolytic filter capacitors (C3, C7 and C8) can be reduced. Their size is related to load capacity ratio:
P - power in the circuit load, W;
Um - the peak value of the rectified voltage (for current input line voltage 242 V amplitude is 342 V);
Fc - frequency network for the calculation of C3, it takes 50 Hz;
DU - the maximum scope rectified voltage allowable for the applicable type of capacitor (taken from the book: so for 50-29 he is 10 ... 14%, ie 34 V).
The frame structure of pulsed power source should include the installation of the transistor and the stabilizer D1 on the radiators, as well as shielding the entire circuit to reduce radiated interference.
First Source library.espec.ws. Ed. 02.06. VF Gainutdinov