H-Bridge MOSFET Selection

Select MOSFETs for an H-bridge driving a 24 V, 10 A continuous motor with 30 A peak inrush. Step 1 — Voltage rating (2× derating): V_DS ≥ 2 × 24 = 48 V → use 60 V rated MOSFETs Step 2 — Current rating (1.5× continuous + handle peak): I_D_cont ≥ 1.5 × 10 = 15 A continuous I_D_peak ≥ 30 A (for inrush) → Select a MOSFET rated 40 A continuous / 100 A peak Step 3 — Conduction loss per MOSFET at rated current: Assume R_DS(on) = 8 mΩ at 100 °C (e.g., IRFB3207) P_cond = I² × R_DS(on) = 10² × 0.008 = 0.8 W per FET Total for 4 FETs (2 conducting at any time): 2 × 0.8 = 1.6 W Step 4 — Gate driver requirement: Q_g = 70 nC (typical for this FET class) At 20 kHz PWM, gate drive power: P_g = Q_g × V_gs × f = 70e-9 × 12 × 20000 = 16.8 mW per FET → negligible Step 5 — Dead time requirement: t_dead > t_fall + margin = 50 ns + 20 ns = 70 ns minimum (set 100 ns) Result: 60 V / 40 A MOSFETs with R_DS(on) < 10 mΩ (e.g., IRFB3207, STP60NF06) are suitable. Add a dedicated gate driver IC (e.g., IR2104) with bootstrap high-side drive.