On 5/1/07, Russell McMahon wrote: > >> 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. Agree. However the operating junction temperature range for 78L05 could be -40 to +125C and the max input voltage +30V. Will be cheapest and safe enough using a 78L05 with a zenner spike killer than a 20x expensive automotive supply. The power dissipation problem will be the same for any linear device automotive or not, some tricks will need for being used at rated current. ie: +14V-5V=9V 9V *100mA = 0.9VA > > 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. Because of the -50V to +60V input transient survival protection ? That can be solved on 7805 too. Vasile -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist