The UCC35701 from Unitrode Corp. (Merrimack, NH) is a new low-power voltage mode PWM controller that features an integrated oscillator and input voltage feedforward circuit to yield instantaneous rejection of input supply voltage changes. The controller is intended to enhance the overall system performance of isolated switching power supplies using primary side control, and is claimed to be especially well-suited for telecommunications applications, as well as industrial control and instrumentation applications.The UCC35701 features voltage mode control with input feed forward compensation to provide noise-free operation with fast and accurate response to input line voltage changes over a 4:1 range. The device operates over a 5:1 input range, and a programmable maximum volt-second clamp prevents transformer saturation. The device's high-frequency oscillator is usable up to 700kHz for high-density converters. Startup current is 130uA, and operating current is 0.75mA. A synchronization pin permits simplified synchronization to the main system or other power supplies.Protection features include overcurrent protection and a programmable soft start function. A fault counting function is also incorporated as a mechanism to ride through temporary load transients and changes. Available in a choice of DIL-14, SOIC-14, TSSOP-14 or LCC-20 packages, the UCC35701N is priced at $2.22 in quantities of 1,000.