Dave
Had a quick look at your circuit & there seem to be a number of issues.
1. There is no positive supply for the FET gate. The collector of the
2N2222 needs to be taken to a positive rail.
2. Even then it won't work as the maximum voltage that could be delivered
would not be enough to turn the IRF540 on as the emitter voltage will be
about 0.6V less than the base voltage which is going to be the PIC power
Supply voltage more or less.
3. The resistor values shown are unrealistic.
4. Driving LEDs in parallel like this can work but you may get significant
brightness variation due to unequal current share.
5. The 100 ohm input resistor is not needed unless the input signal is
going open circuit. In any event 100ohms is too low. 10k would be adequate.
If you are limited to a 3.3V supply then you will need to use a bipolar
power transistor - I would suggest a darlington such as the TIP122.

e.g  - If you can read it (Use a monospaced font eg Courier)

But even with a darlington you may not have enough base current for a
3x385mA (or so) drive. Dependent on the PIC you are using you may be able
to drop the 330ohm resistor to 100 ohms (20mA out maximum ? ) to get more.
LED current can be adjusted by changing the 3.3ohm resistors in each LED
line. They are based on a 3.3V supply, a 1.5V LED drop, and a  0.5V
transistor drop .i.e. 1V across the resistors = 330mA  Actual values may
need adjustment.

If you can't get the LEDs to full brightness, the PIC may not be able to
supply enough drive current (I think some of the older ones are limited in
this regard) so in this event you would need to add another transistor. -
and complicate the circuit somewhat.

If you need to switch the LEDs quickly (e.g this is being used for infra
red transmission purposes, then, again, you may need a better circuit.

Richard P
____________________________________
  3.3V Supply            |     |    |
                         V     V    V  LEDs
                         -     -    -
                         |     |    |
                        3.3   3.3  3.3
                         |_____|____|
                              | C
                         B    |
---------- 330 ------------ TIP122
PIC Drive                     |
                              | E
                             GRND






>Alternatively put a gif up on a web site somewhere or send it to me direct
>& I'll have a quick look.

I've put the information up on the backend of my website
at  http://members.shaw.ca/gnat/led.htm
That has the schematic for the problem section and a image of the scope
signals.

>If you are using MOSFETS you will need more than 3.3V on the gate to turn
>them on properly. If you have only this voltage to play with you will need
>to change to a bipolar power transistor or arrange a higher voltage gate
>drive supply using a charge pump/aux supply or whatever. It would only
need
>a mA or so depending on switching rate.
>
>Richard

Ok I'll dig out my books and get on the net and start looking for a
bipolar. It does need
to be able to handle about 1.7A at a 20% duty cycle. I'm almost stuck on
having to deal with
3.3 as my main supply voltage as going up to 5 will do a number on the cost
of things.It could
be done but I'd rather shy away from doing that unless I have to.

I really appreciate any and all help on this. I haven't had to play with
transistors for quite a few years
so I'm out of touch with what works in the 3.3v regime and what won't.

Cheers

Dave

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