Beefing up an existing circuit - simple way to do this?

Hi all,

I have a low-volume project that has several digital outputs. These
outputs were designed to source 12V at up to an amp. They don't turn on
every often - perhaps 2 or 3 times a day, for 20 minutes at a time max.

The output circuit can be seen at http://alpage.ath.cx/transistors.gif
- it's about as simple as it gets. Q7 is just a BC338, and Q1 is either
a TIP32 or MJE2955.

Now I need to modify these outputs to supply up to 3 amps instead. Even
without crunching the numbers the MJE2955 gets far too hot at 2 amps,
let alone 3. Heatsinking isn't really an option since the design is in
an enclosed box in a fairly hot environment. The PCB itself can handle
the 3 amps, just not the transistor.

I know I could use a FET or something - but can anyone think of a
better solution that doesn't involve hacking up existing PCBs too much?
The magic bullet would be a PNP transistor in the same pinout that can
handle 3A without needing a heatsink and tons of base current.

The project is fairly low volume so labour is more of an issue then
parts cost. I have about 30 of these devices to upgrade.

I'm sure there is an elegant solution to this. Does anyone have any
ideas?

Thanks a ton,

Al

.

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