>> I'm working on a PIC project where I need a cheap, small 5V 
>> regulator (50
>> to 100mA out) that is rated for automotive use (is able to deal 
>> with
>> voltage spikes, reverse voltage, etc.). Anyone have any favorites?

> The cheapest I know is 78L05 SO8 at 0.115$/pcs (0.095eur)
> The smallest may be Maxim's SOT23 regulators (10x more expensive).
> The cheapest and the smallest I did'nt found it

The 78xxx family are not "automotive rated" in the normal sense of the 
term.
While they can be used with an eg automotive 12V supply as input they 
would require protection against the normal nasties that occur in that 
environment. Some (only) of which include load dumps, polarity 
reversals, high energy spikes to "most interesting" voltage levels, 
... . Also temperature ratings for equipment to be used on the hot 
side of the firewall are challenging. Even in-cabin temperatures can 
be remarkably high if the equipment is required to operated when the 
car is parked and closed up. Temperatures can exceed the standard 
industrial and commercial temperature ranges in some areas. Down under 
the dashboard is less severe but can still be annoyingly hot.

The NatSemi LM29xx series (293X?) are specifically rated for 
automotive 12V input use and a look at their spec sheets will give a 
guide as to what specifications you need to meet if you use other 
devices.

Generally well specd devices are not low cost. Addition of a few cheap 
parts to an LM78xx device may well prove cheaper and as effective. I'd 
start with a series diode for reverse polarity protection and TWO 
series resistors with a zener diode clamp to ground after each 
resistor. Add a few caps and you have something which will survive 
most "events".  We did something similar in a -50V Telecom environment 
long ago. The two stages of zener clamping do wonders to eliminate 
transients which are almost unstoppable with a single stage.

Whether all the above still qualifies as "small" or even cheap depends 
on your application. 1 regulator, 2 resistors, 2 zeners, 1 diode, 2 
caps, ... .
The beautiful LM2936 would be easier, but its far from cheap.



        Russell

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist