LDO 3.3v regulator?

G

Grogster

Senior Member
Hi all.
Currently using LM3940's fed from 7805's to get the 3.3v I need to power Xbee modules.
This works just fine when the unit in question is fed from a plug-pack, but on batteries, it is killing batteries pretty quick, what with the 3940's 16mA standby current, coupled to the 7805's 5mA standby current.

Does anyone here recommend any other 3.3v regulator?
Low Drop Out(LDO) would be preferred, as you can use them with a smaller input voltage over the 78 series regulators etc.

I would be happy enough to buy them in from overseas if that is required, provided they fit the bill.

Looking for regulator with very low standby current, but able to pass up to 500mA or so at 3.3v
 
M

moxhamj

New Member
http://www.national.com/mpf/LP/LP2950.html 0.38V drop and 0.075ma standby.

But, I see you need high current too and these are only 100mA.

There are the simple switchers http://www.national.com/mpf/LM/LM2575.html

I use lots of these as they can do 1 amp, don't need a heatsink and accept a wide range of input voltages. They have a 5mA quiescent current according to the spec sheet.

If you know when you are going to transmit, you could use a LP2950 to run a picaxe, and then have the picaxe switch a dual transistor network to switch on power to a 7805 briefly while you transmit.
 
W

westaust55

Moderator
LDO 3.3v 500mA regulator

The TS2937 is a 500mA 3.3V output LDO type voltage regulator available in a TO-220 package. Input can be up to 26V.
 
G

Grogster

Senior Member
Thanks very much, guys - looking both at the one Natalie linked to(LM1117) and also still checking out the LP2950.

Would it be conceivable for lowest standby current design, to use the LP2950 with a pass-transistor to increase it's current ability a'la the MJ2955 across the 7805 to increase it's current ability above 1A type of idea...

Have all the datasheets and am printing them all now, so I can do a little research.

Thanks for posting, people, and further comments still welcome. :)
 
G

Grogster

Senior Member
A little more info for you all.
Using the LP2951, which I can get here in NZ(along with the LP2950), I can build a regulator programmed for 3.3 volts, with additional pass transistor giving up to 300mA or more.

See page 15 of the LP2950 datasheet to see what I mean.

This device(the 2951) is an 8-pin DIL package, but I don't really see that as a major problem.

Also still looking very closely at the LM1117 just for it's simplicity, but looking harder at the LP2951 purely for the smallest standby current concept, even though the 1117's 5mA standby is perfectly respectible.
 
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