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12V 5A switched power supply

     This switched power supply operates on the principle of the flyback inverter. As the power switch MOSFET is used. The 470k resistor is charging the gate of the MOSFET and makes it start to open. Positive feedback makes the MOSFET fully open quickly. This primary of the transformer is then connected to 325V and the core begins to gather energy. This also increases the primary current and voltage drop across the 0R22 current sensing resistor. When the drop reaches 0.5 V, the transistor KC507 opens and reduce the voltage on the MOSFET gate. MOSFET starts to close and the feedback makes it quickly turn off completely, the polarity of the voltage on the windings is reversed. The collected energy in the transformer core is transferred to the electrolytic filter capacitor at the output. When the output voltage reaches its nominal value zener diode begins to open and current flows through 4N35 optocoupler LED. The optocoupler transistor hus begins to open and increase the voltage at the base of KC507. It thus turns on at lower drop on 0R22, MOSFET opens to a shorter period and the transmitted power is reduced sufficiently, the output voltage does not grow any more. The circuit is short-circuit proof, because current sensor (0R22 with KC507) never let MOSFET peak current to be greater than 2.27 A. The transformer has a ferrite core, secondary winding is wound using four wire diameter of 0.6 mm, the other windings are wound using 0.4 mm wire . Voltage stabilization is made using optocoupler and zener diode. Maximum deviation of output voltage is 4%. This switched power supply can be easily modified for other voltages. (Changes only ZD zener diode voltage and the number of secondary turns at the same ratio.)

     Warning! Switching supply is not for beginners, because most of its circuits are connected to fatal mains voltage. When bad design, the mains voltage can reach the output! Capacitors can remain charged to dangerous voltage even after disconnected from mains. Everything you do at your own risk, for any injury to health or property I do not take responsibility.

The schematic of the 12V 5A switched power supply

Completed switched power supply (some parts are at the bottom of the PCB)

Not intended for lamas!