Conduction losses
| MOSFET | P = I²_RMS · R_DS(on) |
|---|---|
| Diode | P = V_f · I_avg |
| BJT / IGBT | P = V_CE(sat) · I_avg |
| Wire / trace | P = I²_RMS · R_wire |
| Inductor DCR | P = I²_RMS · DCR |
Switching losses (MOSFET)
| Turn-on | E_on ≈ ½ V_DS · I · t_rise |
|---|---|
| Turn-off | E_off ≈ ½ V_DS · I · t_fall |
| Total P_sw | ≈ (E_on + E_off) · f_sw |
| Gate charge | P_gate = Q_g · V_gs · f_sw |
| Output capacitance | P = ½ C_oss · V² · f_sw |
Core losses (magnetics)
| Steinmetz | P_core ≈ K · f^a · B^b (K, a, b from datasheet) |
|---|---|
| Hysteresis | Scales with f and B^1.6–2.5 |
| Eddy currents | Scales with f² and B² — mitigated by lamination / ferrite |
Analysis checklist
- Calculate conduction loss at max I.
- Estimate switching loss using datasheet rise/fall times and gate charge.
- Add core loss from ferrite datasheet at your operating B and f.
- Include diode V_f · I for non-synchronous designs.
- Don't forget quiescent IC power.
- Sum → compute expected efficiency; check against thermal budget.
Was this article helpful?