Preliminary WS2801

3-Channel Constant Current

LED Driver With Programmable

PWM Output

10 / 15

WS-Preliminay-V0.3

http://www.world-semi.com

Fig8, Constant Voltage Driving with External Power Switches.

This driving mode is mainly used in high input voltage, high LED driving current (ILED>300mA). Its operating principle is using the

external power NPN switches to driving the LED lamps. The LED driving current can be adjusted by the external current limiting

resistor RL, RL can be derived by the following equation:

LED

CE

LED

DD

L

I

V

V

V

R

−

−

=

------------------------------------------------------------- (2)

The external NPN transistor operates in saturation region, VCE is the saturation voltage, and VCE=0.5~0.8V, the base resistor

RB=2~5K.

Constant Current Driving Mode with External Switches

This driving mode makes WS2801 can drive the cascading LED lamps with extreme low cost, at this mode, POL=’HIGH’ or

floating, see Fig10.

Fig9, Constant current drive with external switches