James Tu wrote...

> I tried the second method...using PWM from my microcontroller to control a
> MJE3055T.  12 V supply is connected to one lead of the bulb, the other
lead
> of the bulb is connected to the collector.  the drain is connected to GND.

The 3055's are huge TO-3 bipolar beasts; it's unlikely that a PIC pin could
drive the base hard enough to give you the current you need (1.67A), and if
you used a resistor between the PIC pin and the base as is normally done....

IMO, you'd be much better off using a power MOSFET, which is designed for
"on-off" switching. There are so-called "logic-level" MOSFETs that can be
completely driven from a 5V pin. For example, the FQP13N06L from Fairchild
can handle upto 60V, 13.5A and has a Rds of 0.11 ohm @ 10V. It's pretty
cheap too. Do use a clip-on heatsink, at least, because per your specs, it
should dissipate about 300 mW.

LM317 and chums are big no-nos; they are *linear* regulators, meaning they
dissipate the remainder of the power (source power - power supplied to
device) as heat.

Cheers,
Ishaan

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