ZXSC410/ZXSC420/ZXSC440

Document number: DS33618 Rev. 6 - 2

14 of 17

www.diodes.com

August 2015

© Diodes Incorporated

ZXSC410/ZXSC420/ZXSC440

High-Current LED Photoflash

The input voltage is 3V with a maximum pulsed output current of 1A for 2ms.

Operation

In charging mode, with SW1 closed and SW2 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

22m

Ω

R4

100m

Ω

R1

10k

Ω

L1

12µH

U1

SW1

SW2

VBATT

D1 BAT54

STDN

GND

Charging mode:

SW1 closed,

SW2 open

Discharging mode:

SW1 open,

SW2 closed