UCL5811

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

5 of 5

www.unisonic.com.tw

QW-R125-060.a



FUNCTIONAL DESCRIPTION

Operating Description

The UTC UCL5811 is a primary side control offline LED controller that incorporates all the features for high

performance LED lighting. LED current can be accurately controlled with the real current control method form the

primary side information. Active Power Factor Correction (PFC) is included to eliminate the unwanted harmonic

noise injected onto the AC line.

Startup

of UTC UCL5811 are approximately 15V and 9V respectively. The 6V hysteresis voltage is implemented to prevent

shutdown from a voltage dip during start-up.

Quasi Resonance mode (QRM)

MOSFET turns off, the energy stored in the inductor forces the secondary side diode to be turn-on, and the current

of the inductor begins to decrease linearly from the peak value to zero. When the current decreases to zero, the

parasitic resonant of inductor and all the parasitic capacitance makes the power MOSFET drain-source voltage

decrease, this decreasing is also reflected on the auxiliary winding. The zero-current detector in FB pin generates

the turn on signal of the external MOSFET when the FB voltage is lower than 0.2V and ensures the MOSFET turn on

at a valley voltage.

As a result, there are virtually no primary switch turn-on losses and no secondary diode reverse-recover losses. It

ensures high efficiency and low EMI noise.

Active Power Factor Correction (APFC)

is constant basically because of very large loop compensation capacitance on COMP pin. According to following

equations.

OSC

2

on

m

avg

L

on

m

peak

L

T

1

T

L

*

2

t

Vpsin

I

T

L

t

Vpsin

I



















Real Current Regulator without Secondary Feedback

The proprietary real current control method allows the UTC UCL5811 to accurately control the secondary side

LED current from the primary side informatio. The output LED mean current can be calculated approximately as:

s

p

REF

CS

OUT

N

N

V

R

*

5

1

2

1

I









UTC assumes no responsibility for equipment failures that result from using products at values that

exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or

other parameters) listed in products specifications of any and all UTC products described or contained

herein. UTC products are not designed for use in life support appliances, devices or systems where

malfunction of these products can be reasonably expected to result in personal injury. Reproduction in

whole or in part is prohibited without the prior written consent of the copyright owner. The information

presented in this document does not form part of any quotation or contract, is believed to be accurate

and reliable and may be changed without notice.