UPSL102G-AF5-R datasheet(4/6 Pages) UTC

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UPSL102

Preliminary

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

4 of 6

www.unisonic.com.tw

QW-R125-028.c



OPERATION DESCRIPTION

The UTC UPSL102 is a cost effective PSR controller optimized for off-line LED lighting applications which can

achieve accurate LED current. It operates in primary side sensing and regulation, eliminating the need of

opto-coupler and TL431, which makes the solution simple, small and low cost. Proprietary built-in CC control

meeting accurate LED current.

Startup Current and Start up Control

Startup current of UTC UPSL102 is designed to be very low so that VDD can be charged up quickly. A large value

startup resistor can therefore be used to minimize the power loss in application.

Operating Current

The operating current of UTC UPSL102 is designed to be very low so that VDD could be charged up above UVLO

threshold and starts up quickly. Good efficiency and very low standby power is achieved with the low operating

current.

Adjustable CC point

In UTC UPSL102, the CC point can be externally adjusted by external current sense resistor RS at CS pin as

illustrated in typical application diagram. The larger RS is, the smaller CC point is, and vice versa.

Principle of CC Operation

To support the UTC UPSL102 proprietary CC control, system needs to be designed in DCM mode for flyback

system. For flyback operating in DCM, the output current Iout is given by

out

(1)

Where LP indicates the inductance of primary winding and IP is the peak current of primary winding.

Refer to the equation 1, the change of the primary winding inductance results in the change of the constant output

current. To compensate the change from variations of primary winding inductance, the switching frequency is locked

by an internal loop such that the switching frequency is

emag

(2)

Since TDemag is inversely proportional to the inductance, as a result, the product LP and fSW is constant, thus output

current will not change as primary winding inductance changes. Up to ±10% variation of the primary winding

inductance can be compensated.

The output LED current is

thoc

out

(3)

Where N is the ratio of transformer between primary side winding and secondary winding.

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