Three-phase inverter: three half-bridges
Six MOSFETs, gate driver, dead time, bootstrap and DC-link capacitor. The building blocks of a motor driver board.
Building blocks
| Block | Role |
|---|---|
| 6 MOSFETs (a high/low pair per phase) | Connect each phase to +Vdc or 0 |
| Three-phase gate driver | Turns MCU signals into gate voltages; drives the high side |
| Bootstrap diode + capacitor | Supply for the high-side gate |
| DC-link capacitor | Supplies the switching pulse current |
| Current sensing | Shunt + amplifier (1 to 3 channels) |
| Protection | Overcurrent comparator, overvoltage, overtemperature |
MCU side: advanced timers
TIM1/TIM8 on STM32 provide three complementary output pairs (CH1/CH1N …), hardware dead time and a fault input (BKIN). Connect the overcurrent comparator output to BKIN and the PWM turns off within nanoseconds, without going through software.
Setting the dead time
MOSFET turn-off delay + difference in driver propagation delay + margin. Usually 200 to 1000 ns. Too short gives shoot-through; too long distorts the output voltage and adds torque ripple at low speed.
3D labRun what you have read so far→DC-link capacitor
It carries a pulse of current at every switching event, so the ripple-current rating matters more than the capacitance. Use electrolytics together with MLCCs, and place them right next to the MOSFETs to keep the loop small.
Layout
Minimise the power loop (capacitor → high side → low side → capacitor) and keep the gate-drive loops short too. Take the current-sense signal with a Kelvin connection.