SparkFun Forums

[transcendentnb2]

I have a project I'm doing in which I need to regulate a 7.2v or so battery pack down to 5v that powers a router board. Sure, there's 5v regulators everywhere, but this sucker draws up to 2A!

So, my question to everyone here is: What is a good solution to get a 5v 2A power regulator? I know the LM7805 can do 1.5A, but I don't want to max that out.

Any advice would be great. Sooner the better too! (Gotta demo the project Dec 8th).

Oh, that reminds me... I'm planning on using 2 7.2v NiCd battery packs in parallel to get the current. If anyone has any other advice, it's more than welcome! It's gotta be light weight too...

EDIT:
Update on batteries... found this: http://www.onlybatteries.com/showitem.a ... D=13176.11

3A max discharge, and it comes with 2 of them.

The LM317's and M7805s seem to be able to handle a bit over 2A, but... if anyone can recommend anything better, I'm still all ears.

[propellanttech]

I just did a search on Digikey....and found this. It is a 220 package with three pins. LDO.....can handle 3 amps.

http://www.digikey.com/scripts/DkSearch ... 27&Site=US

Don't forget a heatsink.....that much power will make the regulator heat up quick.

Hope this helps

James L

[leon_heller]

I'd use a switching regulator. The Simple Switchers from Nat Semi are easy to use.

Leon

[propellanttech]

The problem with a switching regulator......when the batteries start going dead...the regulator stops working above 5 volts.

The LDO will go below the 5 volt theshold.

James L

[Philba]

there are smps IC that can do buck/boost. The real problem here is that a linear will waste a lot of the battery power. An LDO will have a period of fairly high efficiency when the input is is near the output voltage. The fairly flat discharge curve of Li-Ions means that most of the time it will be in the 7V range.

The LTC1871 is an example though I don't care for the amount of ripple it has. National LM3488 might be a bit better.

[SOI_Sentinel]

Oh gosh, use a switcher design!

Each LION battery cell (you have two, so double my numbers for that pack) is 3.7V nominal actually. Peak is 4.2V. Near dead is 3V. If you go below that (and depending on maker, TO that), you may experience the "small handheld incindary device" effect. You'll have a fireball before you fall outside of LDO regulation, so you'll just be wasting power.

[ohararp]

That battery pack is the biggest ripoff ever! Total parts might cost $15 from www.allbattery.com or www.batteryspace.com . You will not need an ldo since the series pack will be dead at 6V.

[transcendentnb2]

I think we're just going to go with a linear regulator. It's a senior design project and it really only has to work for about half an hour. The router we will be powering (WL500-G) was measured to just draw about 1.3A. Yes, it's not the best design, but this is a very very small part of the overall project. The hardware is for pure demonstration purposes... our real goal was a communication protocol.

Anyway, that place isn't a ripoff. It's $18 for a comparable battery pack on those other places (one isn't even functional), and this setup comes with 2, plus a charger.

[transcendentnb2]

Update: We're going with a switching regulator. 4watts is just way too much power to be losing. The L-ions work great.

Since our project is funded, we really didn't care much about the price and ended up ordering this: http://www.roboticsconnection.com/catal ... 422263.htm

Yea, wiring up our own would be much cheaper, but I'm guessing the large cost to this package is the PCB.

That brings up another issue that should possibly be addressed elsewhere, but the breadboard power supply that sparkfun sells here comes with a 1N4004 diode. According to the datasheet, that thing should only be taking 1A max continual current. Perhaps a more robust rectifier should come with the kit?

[reklipz]

That brings up another issue that should possibly be addressed elsewhere, but the breadboard power supply that sparkfun sells here comes with a 1N4004 diode. According to the datasheet, that thing should only be taking 1A max continual current. Perhaps a more robust rectifier should come with the kit?

The datasheet is rated in AC current at 60Hz. The diode is rated for peaks of a max of 30A.

Im not sure if the rating in AC would apply to DC current as well, although beefing it up to something like a 1N5391 or similar might not hurt.

[transcendentnb2]

The average forward rectified current, according to the datasheet's I've found at datasheetcatalog.com, give it a max of 1.0A. The 30A is a "non-repetitive peak forward surge". Usually the 3A+ rectifiers won't drop as much voltage at high currents as well.

But I doubt many people will be using 1A on a breadboard anyway, heh.