UB3846

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

5 of 10

www.unisonic.com.tw

QW-R103-053.C

OPERATION DESCRIPTION

The UTC UC3846 devices integrate many useful designs into one controller for low-power switch-mode power

supplies. The following descriptions highlight some of the features of the UTC UB3846 series.

Start-up Current

The start-up current is only 22μA. Low start-up current allows a start-up resistor with a high resistance and a

low-wattage to supply the start-up power for the controller. For AC/DC adaptor with universal input range design, a 1

dissipation solution.

Power-Saving Mode Operation

The proprietary Power-Saving Mode function provides linearly decrease the switching frequency under light-load

conditions for higher efficiency. The feedback voltage, which is sampled from the voltage feedback loop, is taken as

the reference. Once the feedback voltage exceeds the threshold voltage, the switching frequency starts to decrease.

This Power-Saving Mode function dramatically reduces power consumption under light-load conditions. The

frequency control also eliminates the audio noise at any loading conditions.

Burst Mode Operation

At zero load condition, majority of the power dissipation in a switching mode power supply is from switching loss

on the MOSFET transistor, the core loss of the transformer and the loss on the snubber circuit. The magnitude of

power loss is in proportion to the number of switching events within a fixed period of time. Reducing switching events

leads to the reduction on the power loss and thus conserves the energy. The UTC UB3846 enter burst mode at

standby condition to minimize the switching loss and reduces the standby power consumption. The frequency control

also eliminates the audio noise at any loading conditions. Power supplies using the UTC UB3846 can easily meet

even the strictest regulations regarding standby power consumption.

Switch Frequency Set

operating. At no load or light load condition, most of the power dissipation in a switching mode power supply is from

switching loss on the MOSFET transistor, the core loss of the transformer and the loss on the subber circuit. The

magnitude of power loss is in proportion to the number of switching events within a fixed period of time. So lower

switch frequency at lower load, which more and more improve IC’s efficiency at light load. At from no load to light