F4901 1.1a 24v Schematic ((better))

Based on your request for the F4901 1.1A 24V schematic , it is important to clarify that this designation most commonly refers to a specific fuse component

2. The Power Stage (MOSFETs)

1. Check the Input: Measure across C_IN. Is it 30V-48V? If 0V, trace back to the fuse or connector.
2. Check Startup Resistor: If the F4901 is getting hot but no output, the startup resistor may have drifted high. A cold IC usually means no power reaching the VCC pin.
3. Check the Diode: A shorted Schottky diode will trigger over-current protection (hiccup mode). A open diode will yield 0V.
4. Scope the SW pin: Do you see square waves? If yes, the IC is trying to switch. If the pin is flat, the IC is in UVLO (Under Voltage Lockout).

Part 5: Modifying the F4901 Schematic (Advanced)

Step 3: Energy Transfer (Flyback Action)

• Check: TL431 (U3) and optocoupler PC817.
• Fix: Disconnect the load. Measure voltage on the TL431 cathode. If it is pulled low (<2.5V), the feedback loop is broken. Replace U3 and U2.