Bismillah Electronic

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Power supply circuit

This circuit is a Switching Mode Power Supply (SMPS) designed to convert high-voltage AC (85–265V) into a regulated 12V DC, 1A output. It uses a flyback converter topology centered around the LNK625DG integrated circuit.

Core Stages and Components
Input Rectification and Filtering:The AC input is rectified by a bridge of four 1N4007 diodes (D1–D4).The high-voltage DC is filtered by capacitors C1 and C2 and inductor L1, which also help reduce Electromagnetic Interference (EMI).
Switching Controller (LNK625DG):This IC incorporates a 725V power MOSFET and a control state machine.It switches the primary winding of the transformer (T1) on and off at a high frequency (around 100kHz).
Energy Transfer (Flyback Transformer T1):When the internal MOSFET is on, energy is stored in the transformer's magnetic field.When the MOSFET is off, the polarity reverses, and energy is transferred to the secondary winding.
Output Rectification and Filtering:The secondary voltage is rectified by the SB380 Schottky diode (D6).Capacitors C7, C8 and inductor L2 filter the output to provide smooth 12V DC with low ripple.
Regulation and Feedback:The LNK625DG uses primary-side regulation, which eliminates the need for an optocoupler.It senses the output voltage via the feedback (FB) pin, connected to a resistor divider (R3 and R4).

Key Features
Optocoupler-less Design: Simplifies the circuit by eliminating secondary-side control circuitry.
Protection: Includes auto-restart for output short circuits, open-loop faults, and hysteretic thermal shutdown to prevent overheating.
Efficiency: The high switching frequency allows for a much smaller transformer compared to traditional linear power supplies.