What Is Efficiency?
1 min read
Quick answer
Efficiency (η) is the ratio of a circuit's output power to its input power: η = Pout / Pin. It's usually expressed as a percentage and shows how well a system uses energy.
What Is Efficiency?
No circuit is 100% efficient; some of the incoming power is always lost. Efficiency tells you how small that loss is: 90% efficiency means 10% of the power is wasted.
Where Do the Losses Go?
Most losses turn into heat (Joule's law). That's why inefficient circuits run hotter and need more cooling.
Worked Example
If a regulator draws 10 W from the input and delivers 8 W to the output: η = 8 / 10 = 80%. The remaining 2 W is released as heat.
| Circuit | Typical efficiency |
|---|---|
| Linear regulator | Low (30–60%) |
| Switching regulator (SMPS) | High (85–95%) |
Common Mistakes
- Ignoring heat: low efficiency = lots of heat; cooling needs depend on efficiency.
- Measuring at one point: efficiency varies with load; full-load and light-load efficiency differ.
- Forgetting idle consumption: power spent even with no load lowers overall efficiency.
Frequently Asked Questions
Why can't efficiency be 100%?+
Because every component has resistance, switching and leakage losses, so some energy always goes to heat.
Which is more efficient, linear or switching?+
Switching (SMPS) is usually much more efficient; a linear regulator is simple but loses a lot as heat.
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