Power Loss Guide

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.