illustrate

The UC3855A/B provides all the control functions needed 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 cold drop or zero voltage (zero-voltage conversion technology) to greatly reduce the recovery diode and MOSFET conduction losses, resulting in lower EMI emissions and higher efficiency. Switching frequencies up to 500kHz for boost converters are now realized, requiring only an additional small MOSFET, diode and inductor resonance soft switching for boost diodes and switches. Average current sensing can be done using simple resistors in parallel or with a current-sensing transformer.

characteristic

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