Body diodes simplify UPS & energy recovery circuits

Infineon IRF9540N IRLR8743

Peter Demchenko


This Design Idea illustrates a way to make use of MOSFETs’ parasitic body diodes in a power circuit that can be used in UPS and energy-recovery (e.g., regenerative braking) designs (Figure 1).

The circuit can work in two modes: as a bridge rectifier, or a PWM DC/AC inverter.
Figure 1. The circuit can work in two modes: as a bridge rectifier, or a PWM DC/AC inverter.

When the Mode input is high, the circuit acts as a bridge rectifier. The bridge consists of diodes D1, D2, and the body diodes of MOSFETs Q1 & Q2.

In this mode, Q1 & Q2 are off and Q3 is on, enabling DC output U1.

When Mode is low, the circuit performs as a PWM DC/AC inverter. Q1 & Q2 get PWM from the control block, while D1 & D2 together with Zener D3 eliminate overvoltage spikes on the MOSFETs. D1 & D2 should therefore be fast, low capacitance parts. Also, Q3 and hence the DC output are off.

Capacitor C1 together with the primary inductance of the transformer perform high-frequency filtering of the PWM waveform.

+Bat connects to battery circuitry, which could include a charge controller.

Materials on the topic

  1. Datasheet Infineon IRF9540N
  2. Datasheet Infineon IRLR8743
  3. Datasheet Won-Top Electronics SB1660


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