LOW COST POWER-SAVING MODE PWM CONTROLLER FOR FLYBACK CONVERTERS

DESCRIPTION

The UTC UC3826 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 UC3826 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 UC3826 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 UC3826 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