Diodes ZXSC410/ZXSC420/ZXSC440 - Manual (Page 8)

ZXSC410/ZXSC420/ZXSC440
Document number: DS33618 Rev. 5 - 2
8 of 17
www.diodes.com
March 2013
© Diodes Incorporated
ZXSC410/ZXSC420/ZXSC440
Application Information
(cont.)
LED Driving
The ZXSC410/420/440 make simple low voltage boost LED drivers.
The resistor value is determined by the following:
LED
FB
LED
R
V
I

V
FB
GND
R
LED
Open-Circuit Protection
As a boost converter if the load (LED chain) should become open-circuit a Zener diode can be connected across the LED chain preventing over-
voltage and possible damage to the main switching transistor. The Zener diodes should be selected by ensuring its voltage rating is higher than
the combined forward voltage of the LED chain. Under open circuit conditions the current in the Zener diode defines the output current as:
Z
FB
Z
R
V
I 
The circuit example below give an open circuit output
current of 300µA.
V
FB
GND
R
LED
R
Z
1k?
ZD1
To
converter