12 V regulator

[Steve.Flanagan at VerizonWireless.com]

I have a requirement for 12 V regulation (+/- 15% or a range of 10.2 to 13.8
volts).

My application is driving several 12V time delay relays (TDRs) and I am
building it to work in a drag car that can be powered with 12v + Alternator
or a 16V system.  Keep in mind that with the 16V system, the battery charger
can put over 18V's.

The TDRs pull as low as 1 ma each when in the off state, and as high as 200
ma each when the relay is triggered.   So lets just say my requirements for
a regulator are:

Input Voltage:  10v to 20v
Output Voltage: 12v (+/- 15%)
Output Current: 1mA to 500mA

I tried to use a 12V regulator purchased from Digikey just as a test and it
seems to crap out at the lower current levels (I don't have the part number
handy, its at home, and this was a project I was working on over a year ago,
something just stirred up my memory that I never was able to resolve this.
Originally I was not aware of the lower current levels, so the regulator I
purchased worked in the 100ma range, but not at lower (1ma) range.  

Could someone recommend a very reliable 12V regulator that I can use to meet
my needs.  

As a work around I built my own regulator with a 12 V zener, resistor and
2n2222 transistor that seems to work, however, I am concerned about the
reliability and heat issues with the 2n2222.

Thanks,

Steve F
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