A CMOS DC/DC converter circuit, the ISDN Remote Power Controller (IRPC), especially designed for telecommunication environments, is described. The device is fully compatible to the CCITT power recommendations on the S-interface. The IRPC is an integrated pulse width modulator circuit, designed for fixed-frequency switching regulators with several additional ISDN-specific features. By this new circuit the realization of ISDN DC/DC converters with a minimum of passive external components is possible. The IRPC provides a stable DC-supply with minimum power consumption and very high conversion efficiency. The power controller is realized in a new High Voltage CMOS/SIPMOS technology and is packaged in a DIL22.