1.5 v to 3v and 5v? Really confused.

[kevj]

To expand on my previous post, I'm trying to put a very small battery into a very small application and it seems I'm finding frustration everywhere I turn. The application will require about 30mA of continual current. It's a radio based application where the transmitter requires 3v and the receiver requires 5v. Suffice to say I'm far enough along that it's too late to change radio hardware. I'd planned to run some CR cells but realized they would be way over drawn for current. This now means I need to pack another source of power into (hopefully) the same space.

I can move stuff around the board and fit a single AAA - so let's say I have 1.5v and need to make my hardware run on that.

I've spent literally the last 12 hours straight looking for the simple solution. I've dug all over the MAXIM site as well as others that make various step-up and boost components. Trouble is I don't understand a word of what I'm reading. I really just need to put 1.5 in one side and get 3 out the other, along with a very specific schematic on what to hook up to what. I've never used inductors before but I'm willing to learn what I need to.

I'm finding two major complications to doing this in a simple way:

1. Size - everything I'm finding is in micro-sized packages. This product will be run in very low quantites and must be hand soldered - running it through an oven for SMT is out. It's got to be through hole or very large SMT. I've found very limited products that advertise they'll work in an 8-DIP package (which I'd much prefer for ease of working). Those I am finding appear to have a short life left as various places are marking them as "soon to be non-stocking item".

2. I can't understand the suggested application schematic snippits in the data sheets. Apparently I can invert voltage with many of these - I don't want that - just a very simple step-up. Also, I'm having trouble finding the right inductors called for - most I'm finding are again 2mm SMT cubes - I'd like something I can at least pick up. And finally, as this is a radio based product, I'm a bit concerned about the amount of noise (both radio EMI and power line glitching) that appear to be associated with these sort of solutions.

3. The two or three solutions I have found are spec for voltage just out of my range - a part that requires 2v supply, not 1.5. Very frustrating.

EDIT:
The best solutoin I've found is using a 7660 to "double" the voltage - here's the datasheet for the one from microchip. See page 6 of this ds, left column "Positive Votage Doubling" - is this as simple as it looks? Could I just run the output of one of these into the input of the other then get approximately 1.5v x 2 (3v) x 2 = 6v (minus diode losses).... ???? I could probably use this solution if it really is this easy but it's like there must be a nasty trade-off or something in this solution. If this does work, can I get a suggestion on what sized caps to use for c1 and c2 in the schematics? Anyone know if these 7660's come in a double on one chip?
Here's the ds: http://ww1.microchip.com/downloads/e...Doc/21469a.pdf



Can someone please point me to an exact part number that may work? I'm sure Maxim carries what I need, but there's just too many products to understand. Also, is there a schematic someplace that shows very specifically exactly how to wire the circuit? I can read lines and match values of resistors and caps.

Thanks so much - I've always felt I had a good handle on basic DC stuff but after today, I feel like a total newbie again. Any help is very much appreciated at this point.

[mvs_sarma]

Check whether the Receiver will not work at 3V, ?
if so the problem is simplified and you can have three cells at 1.5 each and have a LM1117-3.3 as a regulator for both Tx and Rx

[kevj]

Thank you Sarma-

Unfortunately the receiver will only run down to 4v, I've already called the manufacturer to verify this.

And again, I don't have room for 3 cells - I've only got room for 1 cell and not a bit more. I wish it was as easy as just adding a couple more cells.

[T.Jackson]

The TC7662B looks good. Might try one out one of these days. No inductors to wind yippee!

[Acetronics2]

Hi, Kevj

I have some R/C designs that need 5v from 4 NiCd cells ...

so, I've used the MAX 879 ( converter/regulator ) ... was fine, but out of production now .


Now, I Use a MAX 630 Upconverter ... 641 if you need more power, and a LM2940 LDO ...

Inductors are Std ones ... no soucy !!!

Alain

[BobP]

Hi,

Have you thought of using a Lithium battery? We use a 'AA' size but there may be a 'AAA'.

Good bit is they are 3.4 volts and have a very good capacity. Bad points, price and disposal....

Bob

[ronsimpson]

The MAX856 and 858 come in 8-dip. The Max 856/858 has a pin to select 3 or 5 volts out. Cannot be much simpler. Vin 0.8 to 3 volts and 3.3 or 5 out.