1
dc1775afa
DEMO MANUAL DC1775A
DESCRIPTION
LT3799
TRIAC Dimmable Off-Line
Isolated LED Driver with PFC
Demonstration circuit 1775A is an off-line isolated fly-
back LED driver featuring the LT
®
3799. The demo board
provides a constant-current output of 0.5A over an LED
string voltage of 20V and 30V. It is optimized to operate
over a wide AC input voltage range (90VAC to 270VAC).
LED current typically stays within ±4% over the whole
input voltage range. The DC1775A provides a steep decline
in LED current with decreasing TRIAC dimming angle, to
achieve a wide TRIAC dimming range. It is designed to
comply with IEC 61000-3-2 Class C harmonics standard
and EN55015B conducted EMI standard.
The LT3799 controls an isolated flyback converter in
boundary mode. Its unique bleeder circuit makes the LED
driver compatible with TRIAC dimmers without additional
components. Its novel current sensing scheme delivers a
L, LT, LTC, LTM, μModule, Linear Technology and the Linear logo are registered trademarks of
Linear Technology Corporation. All other trademarks are the property of their respective owners.
PERFORMANCE SUMMARY
well-regulated output current to the secondary side without
using an opto-coupler. Open- and shorted-LED protection
ensures long-term reliability.
The LT3799 is available in a low profile, thermally-enhanced
16-lead MSOP package.
The LT3799 data sheet gives a complete description of
the part, operation and application information. The data
sheet must be read in conjunction with this quick start
guide for demo circuit 1775A.
Design files for this circuit board are available at
http://www.linear.com/demo
(T
A
= 25°C)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Input Range Line Frequency, 47Hz to 63Hz 90 120 270 VAC
Output Current V
IN
= 120VAC, V
LED
= 28V 0.5 A
Output Voltage 20 28 30 V
Open LED Voltage (Note 1) 34 V
Note 1: For applications with low LED string voltage, FB pin divider resistor
R6 and output clamp D3 can be adjusted to reduce the open voltage limit.
See Protection from Open LED and Shorted LED Faults section in the
LT3799 data sheet for details.
