At 02:49 PM 3/14/2004 +0000, you wrote:


>         I've largely abandoned 7805 voltage regulators for my hobby
>stuff, especially for battery operation.  They waste too much
>current and require several volts of input headroom.  I now use
>the LP2951 low-dropout regulator from National Semiconductor; it
>draws only about a hundred microamps for itself (vs. several
>milliamps for a 7805), will regulate well with an input only a
>few hundred mV above the output, and it also has a handy ERR
>output which you can use as a PIC reset input.  You can set it to
>5 volts just by strapping a couple of pins together, or program
>it to a different voltage with a resistor voltage divider.  It
>comes in an 8-pin DIP.  IMO, it's the ideal hobby voltage
>regulator.

The LM2931 is kinda cool too, "load dump" (automotive transient)
and reverse polarity (eg. battery) protection built in (also mirror-image
insertion protection). Cheap like the LP2951. Iq is around
400uA typically, which < 1/10 that of a LM7805.

All these bipolar LDO regulators are fussy about output capacitors
compare the to the 78xxx regulators. They can't be too lousy *or*
too good ESR, and have to be in the right general range of
capacitance or you can get oscillation. They also tend to draw more
current as the output current goes up (roughly 10% of output current
gets wasted) because of the lousy characteristics of the lateral PNP
on-chip pass transistors.

Then you have the great new CMOS parts like this one:

http://cache.national.com/ds/LP/LP8345.pdf
Unfortunately, no reverse battery protection, and 10V maximum input. 8-(

I doubt we'll see another real jellybean part like the 78xx regulators
anytime soon, all the upsides seem to have downsides.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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