The UCC28521 and UCC28528 combination PFC/PWM controllers provide complete control functionality for any off-line power system requiring compliance with the IEC1000-3-2 harmonic reduction requirements. By combining the control and drive signals for the PFC and the PWM stages into a single device, significant performance and cost benefits are gained.

Based on the UCC28511, the new devices employ an average current mode control architecture with input voltage feedforward. The major difference of the UCC28521/28 is the trailing-edge / trailing-edge (TEM/TEM) modulation scheme for the PFC/PWM stages. The UCC28528 differs from the UCC28521 as its PWM stage does not turn off with the falling bulk voltage. The UCC28528 PWM was designed for low power auxiliary supplies.

These devices offer performance advantages over earlier generation combination controllers. A key PWM feature is programmable maximum duty cycle. For the PFC stage, the devices feature an improved multiplier and the use of a transconductance amplifier for enhanced transient response.Read more