Step 1 / 14
230 V mains input: from the socket to the bridge
This is every device's first stop. What is the voltage at the socket like, how does the bridge rectifier turn it one way, and why does the capacitor make 310 V? Follow it step by step on the diagram, then change the capacitor and load in the simulation below.
Tap the dashed parts for what they do, how to measure them and how they usually fail. Numbered points are scope measurements.
Phase 1/3: Positive half: D1 + D4
While the top line is positive, current flows through D1 to the + output, through the capacitor and load, and returns through D4. D2 and D3 are reverse-biased and don't conduct.
1. Mains (230 V AC)
230 V is the effective (RMS) value; the peak is 230 × 1.414 ≈ 325 V. It changes direction 50 times a second.
On the scope
🛠 Fault scenarios: pick a symptom and see what to measure, in order, on the schematic
🧪 Simulation: change the values, see the result
Change the rectifier type, the capacitor and the load power. The output voltage, ripple and diode current are calculated instantly.
Rectifier
Bulk capacitor
Load power
The ripple is reasonable: the SMPS runs comfortably.
⚠ Safety: This is mains voltage and it can kill. The bulk capacitor can stay above 300 V for minutes after unplugging: discharge it before touching. Use an isolation transformer or a series bulb when measuring.
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