LM3421 datasheet(8/24 Pages) NSC

Nome de Peças	LM3421

Descrição Electrónicos	N-Channel Controllers for Constant Current LED Drivers

PDF	24 Pages

Scroll/Zoom	100%

Fabricante Electrônico	NSC [National Semiconductor (TI)]

Página de início	http://www.national.com

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8 / 24 page

30kHz PWM Dimming

(95% Duty Cycle ON)

30067369

LED = 1A nominal, VIN = 12V, VLED(s) = 20V

Top trace: nDIM input, 2V/div, DC

Bottom trace: I

LED, 500mA/div, DC

T = 10µs/div

30kHz PWM Dimming

(10% Duty Cycle ON)

30067370

LED = 1A nominal, VIN = 12V, VLED(s) = 20V

Top trace: nDIM input, 2V/div, DC

Bottom trace: I

LED, 500mA/div, DC

T = 10µs/div

30kHz PWM Dimming

(5% Duty Cycle ON)

30067371

LED = 1A nominal, VIN = 12V, VLED(s) = 20V

Top trace: nDIM input, 2V/div, DC

Bottom trace: I

LED, 500mA/div, DC

T = 10µs/div

As shown in the Average LED Current vs. PWM DIM Duty Cycle curve the current

drops at very low duty cycle. This is due to the fact that the switcher is shut off

during the LED off time. At low duty cycle the choke does not have time to get

the current up to the control setpoint. This can be looked on as an advantage in

that it allows a wider PWM control range, albeit not linear under about 7.5% duty

cycle (this transition point can be set over a limited range by component value

selection).

LM3421 Folha de dados(PDF) 8 Page - National Semiconductor (TI)