Unitrode Corp. (Merrimack, NH) has introduced a new Primary Side PWM controller that is designed for cost-sensitive and space-contained dc/dc applications. The UCC3809 is built in BCDMOS technology for fast switching times and low power consumption, according to Unitrode.The UCC3809 is intended for systems where a secondary side error signal is already available. Using typical PWM controllers with an isolated optocoupler feedback, a '431 type' shunt regulator provides the error signal; and the error amplifier is usually programmed for unity gain. As a primary side controller, the UCC3809 does not include an on-board error amplifier, reducing the IC cost in most popular applications, according to Unitrode.The UCC3809 contains all other control and drive circuitry required for off-line and isolated dc/dc fixed frequency current mode switching power supplies. Features include a programmable, accurate maximum duty cycle clamp, high-frequency precision oscillator and under-voltage lockout featuring a startup current of less than 100uA. The UCC3809 also features a unique single feedback pin. It is a summing junction for the output voltage feedback information and the primary current for current sense input. Slope compensation can also be summed into this mode. In addition, the UCC3809 can be configured for voltage mode control by providing this input with a portion of the timing capacitor waveform instead of primary current. In this mode, voltage feed-forward can also be achieved by summing a fraction of the primary voltage into this pin. The UCC1809 is priced at $4.55 each in quantities of 1,000, the UCC2809 ranges from $1.17 to $1.33 and the UCC3809 ranges from $0.96 to $1.12.