Chris, can you elaborate a bit on the advantage of c) configuration? Is it
to avoid any switching of the driver (by using the low pass filter) worth
the component count increment?


2007/6/7, Chris McSweeny <cpmcsweeny@gmail.com>:
>
> I'd recommend configuration c) - using a buck driver which has an external
> current control, and drive that by low pass filtering the PWM output of
> the
> PIC to give you a voltage to feed in.
>
> On 6/7/07, Ariel Rocholl <foros@arocholl.com> wrote:
> >
> > I think you meant diode opposite right? FET Drain-->ADiodeK--> +supply
> >
> > Nevertheless, your proposal is a good simple switching regulator, but I
> do
> > have already a buck DC-DC converter that theoretically can get about 85%
> > efficiency, so I just want to use it but connecting the FET driver
> > properly.
> >
> > Would you recommend configuration a) or b)?
> >
> >
> > 2007/6/6, Harold Hallikainen <harold@hallikainen.org>:
> > >
> > > Since you're using an LM317 as the current source, I'll assume your
> > supply
> > > voltage is higher than the LED voltage. So, how about this for a
> > circuit?
> > >
> > > +supply-->inductor-->LED-->FET Drain
> > >
> > > FET Source-->small current sense R-->ground
> > >
> > > FET Drain-->kDiodeA--> +supply
> > >
> > > Turn on the FET when the FET source current is below the LED current
> you
> > > want. Turn off the FET when the FET source current is above the
> current
> > > you want.
> > >
> > > Harold
> > >
> > > > Hi there,
> > > >
> > > > I am controlling a number of Luxeon LED with PWM using PIC12F family
> > > > capabilities.
> > > >
> > > > I've been using a simple LM317 constant current configuration and
> now
> > > > wanted
> > > > to move to a DC-DC circuit to reduce power loss.
> > > >
> > > > Now the 1st question: In my current LM317 setup, I am using a FET to
> > > > switch
> > > > the whole constant current circuit on/off as per PWM duty cycle, and
> I
> > > am
> > > > not sure that is the right way. I mean I have two options, right? I
> am
> > > > currently using option a) below
> > > >
> > > > a) PWM switches on/off the constant current circuit, or
> > > > b) PWM switches on/off the LOAD, having the constant current circuit
> > > > connected all the time.
> > > >
> > > > It was somehow easier to guarantee the LM317 is not having any
> option
> > to
> > > > work on the off side, but I wonder if a LM317 is designed to be
> > switched
> > > > at
> > > > 10KHZ in its input - probably not. So maybe is a more adequate
> > solution
> > > to
> > > > move to option b).
> > > >
> > > > Now the same question but for a DC-DC circuit (step down): I would
> > think
> > > > using option b) is again more natural, but I may need to protect the
> > FET
> > > > with a diode.
> > > >
> > > > Thanks in advance
> > > > --
> > > > Ariel Rocholl
> > > > Madrid, Spain
> > > > --
> > > > http://www.piclist.com PIC/SX FAQ & list archive
> > > > View/change your membership options at
> > > > http://mailman.mit.edu/mailman/listinfo/piclist
> > > >
> > >
> > >
> > > --
> > > FCC Rules Updated Daily at http://www.hallikainen.com - Advertising
> > > opportunities available!
> > > --
> > > http://www.piclist.com PIC/SX FAQ & list archive
> > > View/change your membership options at
> > > http://mailman.mit.edu/mailman/listinfo/piclist
> > >
> >
> >
> >
> > --
> > Ariel Rocholl
> > Madrid, Spain
> > --
> > http://www.piclist.com PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
> >
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>



-- 
Ariel Rocholl
Madrid, Spain
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist