The UTC UC3854 provides all the functions necessary for active power factor-corrected pre-regulators. The controller achieves near unity power factor by shaping the AC input line current waveform to correspond to that of the AC input line voltage. Average current mode control maintains stable, low-distortion sinusoidal line current without the need for slope compensation, unlike peak current mode control.
Designed in UTC’s Bipolar process, the UTC UC3854 offers new features such as wide bandwidth, a low offset Current Amplifier, a faster responding and improved accuracy enable comparator, a VREF "good" comparator, UVLO threshold options (16/10V for offline, 10.5/10V for startup from an auxiliary 12V regulator), lower startup supply current, and an enhanced multiply/divide circuit. New features like the improved amplifier current-sinking capability, amplifier output clamps, and low offset VAC pin reduce the external component count while improving performance. Improved common mode input range of the Multiplier output/Current Amp input allows the designer greater flexibility in choosing a method for current sensing. Unlike its predecessor, the maximum multiplier output current is now clamped to a maximum of 2 * IAC at all times.
A 1% 7.5V reference, fixed frequency oscillator, PWM, Voltage Amplifier with soft-start, line voltage feedforward (V RMS squarer), input supply voltage clamp, and over-current comparator round out the list of features.
