Five applied diode circuits — three-phase full-wave rectification (6-diode bridge + smoothing cap) AC→DC, switching/Schottky selection, a Zener voltage regulator (RS limits IZ), a Zener clamp that shaves peaks (uni-/bi-directional), and TVS protection that shunts ESD/surge to GND. Rectifiers/switching use forward conduction; Zener/TVS use reverse breakdown in a controlled way.
Three-phase full-wave rectify + smoothing
A 6-diode bridge rectifies three-phase AC (R/S/T) into DC. Diodes alone leave big ripple, so an output capacitor smooths it into clean DC.
This rectifier is the reverse of the 6-MOSFET three-phase inverter (DC→AC), and the smoothing cap is the same idea as the kickboard's 940 µF input electrolytic.
3-phase ACR·S·T
▷6-diode bridgefull-wave
Rippled DC
🔋Smoothing capclean DC
AC → 6 diodes → smoothing → clean DC
Zener regulator — clamp current with RS for steady V
Reverse-bias a Zener and it clamps at Vz, holding its voltage steady — but only while its current stays between IZmin and IZmax.
Size the series RS so current lands in that window; exceeding IZmax destroys the Zener, so RS current-limiting is mandatory.
RS=IZ+ILVin−VZ
VZ
Zener (clamp) voltage
IZ
Zener current (min–max)
IL
Load current
Size RS so IZmin < IZ < IZmax
Zener clamp — shave the peaks
Uni-directional (1 Zener) clamps the + peak at Vz; the − side turns on like an ordinary diode, limited to −0.7 V.
Bi-directional (two Zeners back-to-back) limits both polarities to ±(Vz+0.7 V) — one breaks down (Vz) while the series partner conducts forward (0.7 V).
Half-cycle
Uni (1 Zener)
Bi (2 back-to-back)
Positive (+)
clamp at Vz
+(Vz+0.7 V)
Negative (−)
−0.7 V (forward)
−(Vz+0.7 V)
Uni- vs bi-directional clamp output
TVS protection — idle, then shunt surge to GND
Place a TVS in parallel between the protected input (MCU) and GND. At normal voltage it's high-impedance and idle; on an ESD/surge over-voltage it conducts very fast, shunting the big current to GND to protect the MCU.
Use a bidirectional TVS to block both polarities; fit one by default on externally exposed inputs like connectors.
🔌Connector in
✅Normal → MCUTVS high-Z
⚡Surge → TVS → GNDabsorbs current
Pass when normal, absorb surge to GND
Pitfalls & gotchas
Three-phase rectify (6 diodes) ↔ three-phase inverter (6 MOSFETs) are an AC↔DC mirror — pair it with the upcoming MOSFET bridge and the whole inverter board comes into view. Exact RS sizing and load-variation handling stay to be filled from datasheets. For raw-transcript STT errors, check the correction table.