Recommend a good cheap LDO 5V

Hi, Hammy. The 78L05 has a dropout voltage of 7.0V max, which should do fine. There's not much power left in a 9V battery when it gets down to 7.0V. But the problem will be when you switch over to the 12V supply. You'll be dissipating 0.7 watts at 100mA, which will mean the

78L05 will get far too hot. (12V - 5V) * 0.1A =3D 0.7W

Now, if you go with an LM341/LM78M05C, your dropout voltage will be

7.2V at 0.5A, and should be comparable to the 78L05 at 100mA output current. It's about $0.40 in single quantities from Mouser, and is forgiving on the output cap issue -- an 0.1uF ceramic should be fine.

Cheers Chris =2E

Thanks I wasnt sure when a 9V battery dies. I'll try your suggestion.

LM1117 is a cheap "mdo" regulator with a little lower dropout than a

317. It's happy with a 22 uF aluminum elec on its output.

Once the battery is down to 6 volts or so, it's dying fast, so using that last volt won't buy much more time.

John

Maxim/Dallas MAX603 came to mind immediately because I'd just been playing with one. It might not be able to compete with the (undoubtedly good) options others have already mentioned, especially in price, but I thought I'd throw it in.

PDIP/SOIC, modern protection circuitry, shutdown mode, samples, good information imo etc.

If cheap and easy is what you want, try the MIC29xx series from Micrel. They have a bunch of different styles and you can get them from Digi-Key. Might be a bit more than you want to pay, depending upon package, but they'll do the job.

Steve.

--
Steven D. Swift, novatech@eskimo.com, http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC.      P.O. Box 55997
206.301.8986, fax 206.363.4367  Seattle, Washington 98155 USA

Hi , you might want to check out the TS2950ct-5.0 ultra low dropout

5volt pos. regulator,from Taiwan Semiconductor. 150ma.,only needs 1uf, quiescent current only 80microamps,and works right down to 5.2volts input! regards all doug.(in U.K.)