STEVAL-IHT008V1 Low standby loss front-end with inrush current limitation and insulated AC switch control

The STEVAL-IHT008V1 evaluation board limits the inrush current charging a DC bus capacitor so that it is compliant with the IEC 61000-3-3 standard. This inrush current is based on a soft-start procedure for the rectifier bridge achieved with a T1635T-8FP Triac added in series with the mains line, which is controlled by the STM8S103K3 microcontroller through progressive phase-control during the startup phase.

This solution drastically reduces standby losses as the DC bus can be totally disconnected from the AC mains when it is not required. The DC bus is easily turned off by turning off the series Triac, without needing an additional relay to open the circuit in standby.

Steady-state losses are also reduced because NTC resistors, traditionally used to limit inrush current, are not required; nor are the corresponding relays to bypass them.

This board also demonstrates that AC loads can be driven with an easy-design isolated solution using the same power supply for the whole system and some opto-transistors to control the ACST210-8FP, ACS108-8SN and Z0109MUF AC switches.