a 5volt regulator cost 5mha in current?

Nick · Guest

I got an LM340T5 5v regulator. I have been working on getting the voltage down anyway I got it down to about 6 mha and couldnt find out where the rest was comming from. So I disconnected everything and it seems like the voltage regulator is costing 5mha, does this sound correct?

Nick

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Look at the spec for quiescent current on page 3 of the data sheet.
It says 6 ma is the max value (at room temperature), so 5 ma sounds
normal. http://cache.national.com/ds/LM/LM340.pdf
There are better regulators. Look at the websites for National, T.I.,
and also Seiko Instruments. (Seiko has really low quiescent current).

http://www.national.com/catalog/AnalogRegulators.html
http://focus.ti.com/analog/docs/analogprodhome.tsp?familyId=400&templateId=2
http://speed.sii.co.jp/pub/compo/ic/en/param_chrt.jsp?recordID=22

Will Reeve · Joined: 30 Oct 2003 Posts: 209 Location: Norfolk, England

Don't rule out the 'new' switch mode regulators, the later ones don't need the inductors, just a couple of caps, quiescent current measured in low uA range.

Will

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

Will,

I'm looking for something like that but this is the first time I hear of switch mode regulators without inductors. Can you give a few examples of type numbers?

Will Reeve · Joined: 30 Oct 2003 Posts: 209 Location: Norfolk, England

The only inductroless one I've used in a product is a MAX1759, a battery project which needed to run in the wild for a year without human contact! Its 100mA max giving 3.3V from 1.6 to 5.5V input, 1uA shutdown Mode, 50uA Quiescent current. I ran it off a single lithium (non rechargeable) cell, worked very well.

I will be searching the Farnell catalogue later this week to find one for another handheld device I am designing to run from 4AA batteries.

Keep well,

Will

rwyoung · Joined: 12 Nov 2003 Posts: 563 Location: Lawrence, KS USA

davidpk · Joined: 29 Apr 2004 Posts: 13 Location: Opelika, AL

I looked at the MAX1759 part and it would be really good for loads of less than 20mA. Li-ion cells would be great since their voltage doesn't drop to below 3.6V until they are nearly dead.

The drawback would be the package. It's a big step to go from a TO-220 to a uMAX package. It's a little harder to put on a breadboard! You'll need a circuit board.

Will Reeve · Joined: 30 Oct 2003 Posts: 209 Location: Norfolk, England

Indeed, I went straight to PCB for that design, http://www.pcbtrain.co.uk will do a couple of board for 40quid. Takes 10 days but if you get it right (or nearly right!) saves you a lot of time and you have the PCB laid out at then end of it :-)

Will

Will Reeve · Joined: 30 Oct 2003 Posts: 209 Location: Norfolk, England

In fact I swapped to the MAX682 because of the uMAX packaging of the MAX1759! I should read me notes better :-) I am now going to use the MAX682 again in the new design as it worked very well. It's still in a bloody small package but at least you can solder it by hand if you are careful. I remember getting a sample of the uMAX package and I could hardly see the gaps between the pins and decided to change to one a little bigger!

Keep well all,

Will