: Uses a transistor to "chop" the DC into high-frequency AC for efficient transformation .
When designing or repairing a power supply with the A20112 , consider the following: ZCD Pin Resistor ( RZCDcap R sub cap Z cap C cap D end-sub
The voltage divider on the output node acts as the feedback loop, connected to the FB pin of the R2A20112 . This allows the IC to monitor the DC output voltage and maintain it at a constant level (e.g., Protection Mechanisms
Protects the output capacitor if the feedback loop is damaged. Over-Current Protection (OCP): Monitors the input current.
: Unlike proprietary power bricks, the A20112 is a bare-board or aluminum-cased switching mode power supply (SMPS) designed for integration into larger projects . It is prized for its 120W capacity , allowing it to handle high-power demands—like heating a 3D printer's bed or running multiple security cameras—without failing . a20112 power supply schematic
Where thermal balance on FETs and line noise reduction are critical. 4. Safety and Troubleshooting
Safely power the unit using an isolation transformer or a current-limited dim-bulb tester. Measure the unregulated DC voltage right after the bulk capacitors, then check the final regulated output at the terminal pins.
Legacy revisions might utilize heavy-duty 3-terminal regulators (LM317 for variable tracking, or 78XX/79XX series for fixed rails) wrapped in external current-boosting transistors. Stage 5: Output Filtering and Decoupling
Steps down the high-voltage AC from the grid to a lower, safer AC voltage. : Uses a transistor to "chop" the DC
"Aha," he said, touching the top of one capacitor. It was slightly bulged—a classic sign of age-related failure. When capacitors fail, they cannot smooth the signal, leading to high "ripple," which causes voltage regulators to fail or produce unstable power, crashing the system.
Specifically models like the HSP400-5S01.
Measure voltage across C4 (VCC pin of PWM IC). It should rise to 12–18V. If it stays below 10V, replace C4 and check R5 (startup resistor). If still low, the PWM IC may be shorted.
It shifts the phase by 180 degrees to improve ripple current on input/output capacitors. Protection Circuitry: The schematic typically includes: Over-Voltage Protection (OVP): Two modes (dynamic and static) for stability. Feedback Monitoring: Built-in detection for feedback loop opens or shorts. Soft Start: Over-Current Protection (OCP): Monitors the input current
| Symptom | Likely Failed Component | Schematic Area to Inspect | |--------|------------------------|----------------------------| | No output, no LED | Fuse, MOV, Bridge rectifier | AC input, DB1, C1 | | Output low or oscillating | TL431, optocoupler, output caps | Feedback loop, secondary filter | | PSU ticks / squeals | Rsense, PWM controller, auxiliary supply | CS pin circuit, VCC capacitor | | Output high (overvoltage) | Shorted optocoupler or TL431 | Feedback divider R12/R13 | | MOSFET shorted | Q1, Rsense, U1 | Primary switching, gate drive |
Insert a low-value sense resistor on the output return path and use an op-amp to feed back into the optocoupler. Refer to the schematic’s primary-side current sensing as a model.
As the magnetic field in the inductor completely collapses, these auxiliary windings generate a minor voltage drop signal.
This is the first section after the AC plug.