Re: High side driving N-channel Mosfet with PWM

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#1886

From: Mark
Date: Mon, 05 May 2008 13:54

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On May 5, 9:36 am, a7yvm109gf...@netzero.com wrote:
> On May 5, 7:24 am, "Phil in Melbourne" <reply@tonewsgroup> wrote:
>
> > So I would have thought that this would be a simple problem but the more
> > information I get the more I get confused......
>
> > I want to PWM a whole lot of LEDs. The current consumption of the bank of
> > LEDs is in the order of 15 Amps, at 12V.
>
> > For reasons I won't go into, my only option is to use a high side mosfet.
>
> > I have chosen an N-channel MOSFET (IRL3803) mainly because of its huge
> > current capability and very low on resistance of 7 milli ohms.
>
> > I am hoping to use PWM at a reasonably high frequency, say 20khz or higher,
> > and I want to use an efficient MOSFET driver IC that is designed for the
> > job.
>
> Why so high? If it's just for brightness control, you don't need that
> surely?

if you strobe LEDs too slow, then it causes a strobe effect if there
is any  movement... if you scan your eye past some LED rear car lights
you can get the strobe effect and it is very annoying... even if the
LED is not moving, your eye is always moving

I don't know how fast you need to pulse to avoid this but a few
hundred Hz is too slow.   5 kHz might be OK  I don't know...

At 5 kHz you might get audio interference so that is a good reason to
go to 20 kHz.

Mark

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From: Mark <makolber@yahoo.com>
Newsgroups: sci.electronics.design,aus.electronics
Subject: Re: High side driving N-channel Mosfet with PWM
Date: Mon, 5 May 2008 06:54:45 -0700 (PDT)
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