On Sat, 01 Jan 2005 12:05:33 -0600, itoldyouiamnotiamnotgeorge
wrote in
:

Frank Gilliland wrote in
:

On Fri, 31 Dec 2004 15:26:39 -0600, itoldyouiamnotiamnotgeorge
wrote in
:

snip
Use a Pulse width modulator and some fet's


.....uh, I don't think so. Efficiency is far less important to me than
eliminating possible RFI or regulator failure. I have a lot of MJ11028
power Darlingtons and a pair of those should do the job just fine.



so why would a pwm and some fets on the outputs be any different. I have
never seen rfi or failure due to these components, and a good designer
would add filter caps to the circuit where needed.

PWM tl494 and some P channel fet's would work flawlessly.

http://focus.ti.com/docs/prod/folders/print/tl494.html


Why would I convert from a switching regulator to another switching
regulator? That doesn't make sense. I want linear regulation because
switching regulators generate square waves; i.e, noise. Also, FETs in
switching regulators aren't just FETs, they're MOSFETs, and I wouldn't
trust a MOSFET in any harsh environment, let alone under the hood of
my truck.

And BTW, nothing works "flawlessly", especially MOSFET's.


Or you could go with 1-tip36c which would be more than adequate you
wouldn't need 2 MJ11028's


First, a single MJ11028 can handle the same collector current as -two-
TIP36C's. Second, the hfe of the TIP36C is 25 compared to a minimum of
400 for the MJ11028, so the latter doesn't require a power transistor
to drive it. Third, the transistion frequency of the TIP36C is 3MHz,
meaning it can be prone to oscillation -especially- in any application
where surges or spikes can occur; Darlingtons barely work above audio
frequencies. And most important, I don't have a TIP36C but I -do- have
a stock of MJ11028's.