LOW COST POWER-SAVING MODE PWM CONTROLLER FOR FLYBACK CONVERTERS

DESCRIPTION

The UTC UC3801 provides a CCM/valley switching mixed

mode operation for better efficiency performance. The operation

mode stays at CCM at heavy load, and switch to valley switching at

light load.

The UTC UC3801 is a high performance current mode PWM

controller ideally suited for low standby power. Low VCC startup

current make the power reliable on startup design and a large

value resistor could be used in the startup circuit to minimize the

standby power. At no load condition, the IC operates in

power-saving mode for lower standby power, decreasing frequency

for Higher conversion efficiency at light load condition.

The UTC UC3801 contains protection with automatic recovery

including OLP (over load protection), OCP (cycle-by-cycle current

limiting), and UVLO (VCC over voltage clamp and under voltage

lockout). It also provides the protections including OTP (over

temperature protection), BNO(AC Brown Out protection) , LNO(AC

Over voltage protection), OVP (VCC or DC output over voltage

protection) with automatic recovery. To protect the power

MOSFET, Gate-drive output is fixed up to 16V max.

The internal slope compensation improves system stability at

high PWM duty cycle output. Leading-edge blanking on current

sense input removes the signal glitch, which offering minima

external component count in the design. Excellent EMI

performance is achieved with UTC proprietary frequency hopping

technique (ZL201020615247.1) together with soft driver control.

Audio noise is eliminated due to switch frequency more than 20kHz

during operation.

UTC UC3801 is packaged by using tiny SOT-26 package. It has

such applications as: battery charger, power adaptor, set-top box

power supplies, ink jet printers, open-frame SMPS.

FEATURES

* Proprietary frequency hopping for Improved EMI performance

* Cycle-by-cycle current limiting

* CCM/Valley Switching Operation

* Fixed switch frequency 60~70kHz

* Dynamic peak current limiting for constant output power

* Built-in synchronized slope compensation

* Gate output voltage clamped at 16V

* Adjustable DC output OVP/UVP/OTP

* OLP/VCC OVP/OTP/BNO/LNO (automatic recovery)

* Internal Soft Start