STNRG328S Digital Controller for STC/HSTC STMicroelectronics STNRG328S Digital Controller for STC/HSTC open-loop resonant converters is designed for power conversions. The device performs a power conversion from an input voltage in a typical range of 40V to 60V to an output voltage with a programmable conversion ratio from 2:1 to 10:1 with a fixed duty cycle and programmable frequency from 140kHz to 300kHz.