A20112 Power Supply Schematic May 2026

Title

A20112 Power Supply Schematic — Detailed Design, Analysis, and Implementation

Common Repair Issues

Even without a full schematic, most A20112 failures follow predictable patterns: a20112 power supply schematic

  1. Blown Fuse: Usually caused by a shorted Bridge Rectifier or a shorted MOSFET. Do not just replace the fuse; find the short first.
  2. Bulging Capacitors: The electrolytic capacitors in the output stage often dry out over time. If the tops are domed rather than flat, they need replacing.
  3. Cold Solder Joints: Due to heat cycles, the joints on the transformer pins and high-wattage resistors often crack. A quick reflow with a soldering iron can sometimes bring a dead unit back to life.

3.1 Netlist of Key Connections

AC Input Section:

  • AC Live → F1 → L1 pin1
  • L1 pin3 → CX1 → DB1 pin1
  • AC Neutral → L1 pin2
  • L1 pin4 → DB1 pin3
  • DB1 pin2 (+) → C1 (+) → T1 primary pin1
  • DB1 pin4 (-) → GND Primary

Primary Side Control:

  • T1 primary pin2 → Q1 Drain
  • Q1 Source → Rsense (0.33Ω) → Primary GND
  • Q1 Gate → Rg (22Ω) → U1 (OUT pin)
  • U1 (VCC) → D4 cathode (+) → C4 (+) → R5 end (R5 start → C1+)
  • U1 (CS) → Rsense hot side
  • U1 (FB) → Optocoupler transistor emitter

Secondary Side:

  • T1 secondary pin3 → D5 anode
  • D5 cathode → C8 (+) → L2 → Output (+12V)
  • Output GND → T1 secondary pin4 → Secondary GND

Feedback Circuit:

  • Output (+12V) → R12 (10k) → TL431 Ref
  • R13 (2.5k) → TL431 Ref to GND
  • TL431 Cathode → Optocoupler LED cathode
  • Optocoupler LED anode → Resistor (1k) → Output (+12V)
  • Optocoupler transistor → U1 FB pin to GND

Section 1: Overview of the A20112 Power Supply