US1651

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

4 of 7

www.unisonic.com.tw

QW-R129-005.a



OPERATION DESCRIPTION

The UTC US1651 is a primary control switch mode charger and adapter applications. It operates in primary-side

sensing and regulation. Opto-coupler and TL431 could be eliminated. Proprietary built-in CV and CC control can

achievegood CV/CC performance. The device integrates PWM controller to enhance the performance of

discontinuous conduction mode (DCM) flyback converters.

Startup Current and Start up Control

Operating Current

The Operating current of UTC US1651 is as low as 1mA. Good efficiency and very low standby power can be

achieved.

Soft Start Control

The UTC US1651 features an internal 4ms soft start to minimize the component electrical over-stress during

threshold gradually from nearly zero to normal setting of 0.82V. Every restart is a soft start.

Constant Voltage Operation

The UTC US1651 is designed to produce good CC/CV control characteristic as shown in the Fig. 1.

To support UTC US1651 proprietary CC/CV control, system needs to be designed in DCM mode for flyback

system. When INV is equivalent or larger than 1.25V, the system works in CV control, In CV operation, the output

voltage is sensed on the primary side and the sensed signal controls the duty cycle through a built-in error amplifier

(EA). Connected to a resistor divider from the primary side sensing winding, the inverting input of the Error Amplifier

(EA) is compared to an internal reference voltage of 1.25V to regulate the output voltage. The EA output is internally

connected to the PWM generator and controls the duty cycle.