UPSL100

Preliminary

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

4 of 7

www.unisonic.com.tw

QW-R125-028.a



OPERATION DESCRIPTION

The UTC UPSL100 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 resistor can therefore be used to minimize the power loss in application.

Operating Current

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

current.

Adjustable CC point

Principle of CC Operation

To support the UTC UPSL100 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

2

P

SW

P

out

V

/

η

I

F

L

2

1

=

I

(1)

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

D

SW

T

2

1

=

F

(2)

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

S

thoc

out

R

V

N

4

1

=

I

(3)

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