Industrial electronics
Guess first
Add a freewheeling diode: what happens to Vdc?
Most students get this one wrong: guess before I explain.
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Lesson notes
Key points
- With an RL load, the inductor keeps current flowing past zero, so the output goes negative until the next SCR fires.
- The freewheeling diode clamps the load at zero, removing the negative part, so the average output voltage rises.
Definitions
- Freewheeling diode
- A diode across an inductive load that carries current when output reverses, clamping voltage near zero.
Takeaway: Freewheeling diode removes negative output and raises average Vdc.
Quick check: A controlled rectifier feeds an RL load. You add a freewheeling diode. What happens to average output voltage?
- It falls
- It stays the same
- It rises
A freewheeling diode removes negative output, so average Vdc goes up.
Negative regionClamped at zero
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