Diodes ZXSC410/ZXSC420/ZXSC440 - Manual (Page 14)

ZXSC410/ZXSC420/ZXSC440
Document number: DS33618 Rev. 5 - 2
14 of 17
www.diodes.com
March 2013
© Diodes Incorporated
ZXSC410/ZXSC420/ZXSC440
Application Examples
(cont.)
High Current LED Photoflash
The input voltage is 3V with a maximum pulsed output current of 1A for 2ms.
Operation
In charging mode, SW1 is closed and SW2 is open the ZXSC410/420/440 is configured as a typical boost converter, charging capacitor C2 up
the regulated output voltage set by the ratio of R1 and R2. This is typically 16V. The peak current of the converter (current drawn from the
battery) is controlled by R3 plus R4, and is typically 280mA for this application. When C2 is charged to 16V the SW1 is opened and SW2 is
closed, converting the ZXSC400 to a step down converter to provide a 1A constant current for 2ms to the photoflash LED. During step down
operation, current flows from C2, through the photoflash LED, L1, U2 and is returned to C2 through R3. This means that the peak current is set
at a higher value than in charging mode, typically 1A. When the current reaches its peak value, U2 is switched off and current flows from L1
through the Schottky diode in U2, to the photoflash LED. This cyclic process is repeated until C2 is discharged.
ZXSC410
Q1
ZXTN
25012
EFH
C1
1µF
C3
1µF
C2
150µF
R3
22mΩ
R4
100mΩ R1
10k Ω
L1
12µH
U1 SW1
SW2
VBATT
D1 BAT54
V
CC
STDN
GND
V
DRIVE
I
SENSE
V
FB
Charging mode: SW1 closed, SW2 open
Discharging mode: SW1 open, SW2 closed