Industrial electronics
Explainer
Why Power Devices Are Switches, Not Amplifiers
A transistor half-on at 10 A can burn as much power as the load it feeds
Quick check · tap an answer to continue
Lesson notes
Explain why industrial electronics uses devices as switches, not amplifiers, and compare their losses
Key points
- Picture a 10 A load on a 100 V supply: half-on, the transistor drops 50 V and wastes 500 W as heat.
- Fully on, the same device drops only about 2 V, so conduction loss is just 2 V times 10 A, which is 20 W.
- An ideal switch has zero on-state voltage, zero off-state leakage, and changes state instantly, so it never dissipates power.
- Real switches lose energy each transition while voltage and current overlap, so switching loss grows with switching frequency.
Definitions
- Switching loss
- Energy lost during on/off transitions when voltage and current overlap
Takeaway: Fully on or fully off wastes little; in between wastes a lot.
Quick check: A power diode drops 1.5 V carrying 20 A. What is its conduction loss?
- 13.3 W
- 30 W
- 21.5 W
Conduction loss is V_on × I = 1.5 V × 20 A = 30 W.
power diodeconduction lossswitching lossLinear regionConduction lossIdeal switchSwitching loss
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