Power Electronics — Cheat Sheet
Buck/boost/flyback duty, inductor ripple, switching & conduction loss, thermal.
Converter duty cycle
| Buck | D = V_out / (V_in · η) |
| Boost | D = 1 − (V_in · η) / V_out |
| Buck-boost | D = V_out / (V_out + V_in) |
| Flyback | D = V_out·N_p / (V_out·N_p + V_in·N_s) |
Ripple & sizing
| Inductor ripple (buck) | ΔI_L = V_out(1 − D) / (L · f_sw) |
| Inductor ripple (boost) | ΔI_L = V_in · D / (L · f_sw) |
| Output ripple (buck) | ΔV = ΔI_L / (8 · f_sw · C) |
| ESR ripple | ΔV_esr = ΔI_L · ESR |
| Rule of thumb | target ΔI_L ≈ 30% of I_out |
Losses
| Conduction (FET) | P = I_rms² · R_ds(on) |
| Switching | P = ½·V_ds·I_d·(t_r + t_f)·f_sw |
| Gate drive | P = Q_g · V_gs · f_sw |
| Diode | P = V_f · I_avg |
| Inductor DCR | P = I_rms² · DCR |
Thermal & protection
| Junction temp | T_j = T_a + P·(θ_jc + θ_cs + θ_sa) |
| Derate above | follow the datasheet SOA curve |
| Inrush | limit with NTC or soft-start |
| Snubber | RC across the switch to tame ringing |
Formula reference — verify against the governing standard. Not a substitute for engineering judgment.