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    LED Dimming using IRF540

    Hi All,
    I am using High Power LED for my project. To Dim the brightness of LEDs I have bought IRF450N(TO-220) Package.
    I am using 15V SMPS. 5 LED are connected in series. I gave +15V to one end of seriesly connected LEDs(say Anode). Cathode of Fifth LED is connected to Gate of IRF540N. Source is connected to Ground. For Gate I have used 1K resistor.. I am using PWM signals to generate ground pulsed to Swith ON LEDs.

    My problem is LEDs are glowing very Dull. Say 5% brigtness. But anyhow I can Dim the LEDs. What is the problem here? I have refered another one Board. There they have used 30V to SMPS and the have connected 10 LEDs in series..

    My doubt is about IRF540. In the datasheet they said VDSS =100V..I think there should be minimum voltage level for Drain(Above 20 I think).. Am I correct?

    •   Alt30th November 2015, 17:36

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    Re: LED Dimming using IRF540

    You bettter provide a schematics. Otherwise there should not be any gate current.
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    •   Alt30th November 2015, 18:03

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    Re: LED Dimming using IRF540

    A circuit diagram would avoid misunderstanding regarding to the depicted above, as for instance if you are using capacitors for softening the current pulses across the Leds.
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    •   Alt30th November 2015, 18:05

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    Re: LED Dimming using IRF540

    Reduce the 1k resistor to around 270 Ohm. That should give you near the 20mA you need through the LEDs for full brightness.



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    Re: LED Dimming using IRF540

    The LED color is what will dictate the value of the polarization resistance, once to the drop voltage accross terminals varies according to its color, decreasing from Blue to Red.
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