ZXLD1352 데이터 시트보기 (PDF) - Zetex => Diodes

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ZXLD1352

350mA LED driver with internal switch and enhanced PWM dimming range

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ZXLD1352

Dimming output current using PWM

When the ADJ pin is driven with a low frequency PWM signal (eg 100Hz), with a high level voltage

VADJ and a low level of zero, the output current will be switched on and off at the PWM frequency,

resulting in an average output current IOUTavg proportional to the PWM duty cycle. (See Figure 2

PWM Voltage

VADJ

0V

Ton

Toff

IOUTnom

Output Current

0

0.1/Rs

IOUTavg

Figure 2 Low frequency PWM operating waveforms

The average value of output current is given by:

IOUTavg = 0.1DPWM/RS [for DPWM >0 01]

PWM dimming is preferable to DC dimming if optimum LED 'whiteness' is required. It will also

provide the widest possible dimming range (approx. 1000:1) and higher efficiency at the expense

of greater output ripple.

Issue 1 - August 2008

20

© Diodes Incorporated 2008

www.zetex.com

www.diodes.com

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