Topology comparison
| Topology | Typical η | Notes |
|---|---|---|
| Linear (LDO) | (V_out / V_in) × 0.95 | Dissipates difference as heat |
| Zener shunt | < 50% | Toy / reference — wastes energy |
| Charge pump | 70–85% | Discrete ratios (×2, ÷2) |
| Buck | 85–95% | Efficient step-down |
| Boost | 85–93% | Efficient step-up |
| Synchronous buck | 90–96% | Replaces diode with MOSFET |
| Flyback | 75–88% | Isolated; low-mid power |
| LLC resonant | 92–97% | Isolated high-efficiency |
Losses
| Conduction loss | I² · R in switches / inductor DCR |
|---|---|
| Switching loss | Depends on V × I overlap during transitions |
| Diode drop | V_f · I — use synchronous or Schottky |
| Core loss | Hysteresis + eddy currents in magnetics |
| Quiescent | IC operating current — matters at no-load |
| Copper / PCB | Trace resistance; significant at high current |
Load dependence
- Efficiency is usually peaked around 50–80% load.
- At very light load, switching and quiescent losses dominate — pulse-skipping mode helps.
- At heavy load, conduction (I²R) losses dominate.
- Report η at multiple loads (10%, 50%, 100%) — peak alone is misleading.
Rule of thumb
| LDO efficiency | = V_out / V_in (e.g. 3.3 V from 5 V ≈ 66%) |
|---|---|
| Switcher efficiency | > 90% across useful load range |
| Heat dissipation | P_diss = P_in · (1 − η) = P_out · (1/η − 1) |
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