UC2849,UC3849,pdf(Secondary Si

The UC3849 family of average current-mode controllers accurately accomplishes secondary side average current mode control. The secondary-side output voltage is regulated by sensing the output voltage and differentially sensing the ac switching current. The sensed output voltage drives a voltage error amplifier. The ac switching current, monitored by a current sense resistor, drives a high bandwidth, low offset current sense amplifier. The outputs of the voltage error amplifier and current sense amplifier differentially drive a high bandwidth, integrating current error amplifier. The sawtooth waveform at the current error amplifier output is the amplified and inverted inductor current sensed through the resistor. This inductor current down-slope compared to the PWM ramp achieves slope compensation, which gives an accurate and inherent fast transient response to changes in load.