ERICSSON type switching power supply circuit principle analysis - Power Circuit - Circuit Diagram

The circuit diagram for the mapping is provided in the attached image. The power supply employs a self-excited oscillation circuit, where the transformer couples the buck output. Once the mains power is activated, the 220V AC is converted into approximately 260V DC high voltage through the bridge rectifier formed by D1 to D4 and the subsequent filtering by C1. This high voltage is then delivered to the load L1 and the collector of the high-voltage switching transistor Q via resistors R3 and R5 (the collector voltage is regulated by a voltage stabilizer and protected by D5). When Q is triggered, the current generates a pulsed magnetic field through the primary winding L1 of the transformer T. This pulsed magnetic field induces a voltage of less than 9.5V in L3, which is rectified by D8 and filtered by C5 to produce an approximately 8V DC output.

The other part of the circuit is connected to the negative feedback voltage via L2. This negative feedback voltage is applied to the base of Q through capacitors C2, resistors R6, R4, and R5, causing Q to turn off. With the high voltage DC supplied by R3 and R5, the pulsed current is once again generated by L3, initiating another cycle of electromagnetic induction. This process causes the negative feedback current to follow its original path, turning Q off again. The circuit alternates continuously, allowing it to oscillate indefinitely while L3 consistently outputs DC power.

When this switching power supply is used to power a 6V recorder, the output circuit must be equipped with a 10Ω/8W wire-wound resistor and a 1500μF/16V electrolytic capacitor in series to form a filter before delivering the power. This ensures stable and clean power delivery to the device.