March 2016
DocID029048 Rev 1
1/37
www.st.com
UM2027
User manual
Inrush current limitation when charging a DC bus capacitor for
IEC 61000-3-3 compliance
Introduction
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 Triac added in series with the mains line, which is controlled 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 isolated easy-to-design solution by
using the same power supply as the whole system and some opto-transistors which control the AC
switches.
Figure 1: STEVAL-IHT008V1 evaluation board (top view)
