LOW COST POWER-SAVING MODE PWM CONTROLLER FOR FLYBACK CONVERTERS

DESCRIPTION

The UTC UCQ3738 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 UCQ3738 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 UCQ3738 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), Programmable Propagation Delay Time ,

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.

 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

smart frequency hopping technique together with soft driver control.

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

during operation.

UTC UCQ3738 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 smart frequency hopping for Improved EMI and output Jittering ripple

* Cycle-by-cycle current limiting

* CCM/Valley Switching Operation

* Fixed switch frequency 60~70kHz

* Dynamic peak current limiting for constant output power

* Programmable Propagation Delay Time

* Gate output voltage clamped at 16V

* Adjustable DC output OVP/UVP

* Adjustable OTP (Over Temperature Protection) on CS Pin

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

* Internal Soft Start