🚀 go-pugleaf

> 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.
> 
> I understand that to switch an N channel mosfet on the high side of the 
> supply line, I have to drive the gate with 10V **more** than the supply 
> voltage. This is correct yes?
> 
> This is where the question comes in. I am looking at the option of using the 
> IRS2001 to switch the high side fet. But looking at the datasheet, I am 
> confused. How can the  IRS2001 generate a voltage greater than VCC without 
> actually being connected to the high side voltage????? There is no talk of a 
> charge pump in the description and in any case it does not know what 
> potential the fet is connected to..
> 
> Maybe it is not suitable for my application as the IRS2001 seems to be used 
> for switch mode power supplies? I can't make sense of the first diagram on 
> the datasheet.
> 
> here is a link to the datasheet:
> 
> http://www.irf.com/product-info/datasheets/data/irs2001spbf.pdf
> 
> 
> 
> OK so if the above IC is not suitable, I have been looking at the MAX621.
> 
> http://datasheets.maxim-ic.com/en/ds/MAX620-MAX621.pdf
> 
> This one looks to be more straight forward. But I'm not sure how this IC 
> will go with 20Khz switching. There are many **low side** mosfet drivers 
> that are in the 2 to 7 amp range to ensure that the mosfets are hard on or 
> hard off within a few nS. This one doesn't look like it will do anywhere 
> near that switching current.
> 
> 
> Any other ideas for a high side N channel driver IC that packs a punch?
> 

You're going about this all wrong, no one makes a dimmable LED supply 
like this, the main reason being your excessive ripple current 
resulting in unnecessary heating and exponential reduction in LED 
lifetime. Another good reason for not doing it this way is to avoid the 
fairly huge current spikes resulting from what will be a hefty 
equivalent load capacitance producing enough EMI to be detected in 
another galaxy. And you want to go to all this trouble to produce a crap 
design because it's the only thing you understand. Do some background 
reading: http://powerelectronics.com/mag/710PET24.pdf and put more 
effort into your planning.