illustrate

The UC3855A/B provides all the control functions required for high power, high frequency PFC boost converters. The average current mode control method allows ramp compensation without the need for stable, low-distortion AC line current programming. In addition, the UC3855 uses aggressive snub or zero voltage (zero voltage conversion technology) to greatly reduce recovery diode and MOSFET conduction losses, resulting in lower EMI emissions and higher efficiency. Boost converters with switching frequencies up to 500kHz are now monetized and require only an additional small MOSFET, diode and inductive resonance soft switch boost diode and switch. Average current sensing can be used in simple resistive parallel or with a current-sense transformer.

characteristic

• Near-boost PWM to control the unit power factor
• Fixed frequency average current mode controls line current distortion to a minimum
• Built-in active buffer (zero voltage) allows operation up to 500kHz, improving EMI and efficiency
• Inductive current synthesizers can be single-current transformers for improved efficiency and noise-tolerant current sensing
• Accurate analog multiplier band line compensation allows universal input voltage operation
• High bandwidth (5MHz), low offset current amplifier
• Overvoltage and overcurrent protection
• Two UVLO threshold options
• 150 &mirco; a starting power supply current typical
• 7.5V Reference Accuracy 1%