Let's Make Robots!

5v voltage regulation.

Is there a simple thingy that I can hook up to any voltage higher than 5V (within reasonable range) and always get 5volt out?

As I'm starting this project I'm using a 6V battery pack, but I believe I'll be switching to a 7,2V as soon as fundings allow it. And I do have an old 14,4V battery drill that might become a donor in the future. I can always remake the voltage regulator part as the project moves along, but it would be awesome if any of you knew of the ultimate solution for lazy people like myself who only picks up the soldering iron when it can't be fixed with tape or a lot of tape...

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Does anyone know if I can piggyback a couple or more 7805s? I see mention of it in the thread. I have a handful of them and need 5v from a 12v lipo.

I have heard mention that straight doubling-up of linear regulators is a no no because they can start some kind of oscillation, causing one to eventually blow. Instead use a transistor or mosfet on the output to get more current.

I did as you suggested. A pair of TIP42s did the job. Thanks ezekiel!

Here's something I found earlier about regulators connected in parallel:
"And finally, you can run several 7805s in parallel. The easiest way to do it is to make the inputs a common connection and the grounds a common connection. But don't connect the outputs directly together. The 7805 don't all regulate at exactly the same voltage and the one that regulates at the highest voltage will do all the work while the others loaf along and you'll don't have solved anything. Instead, put a small-value (e.g., 0.47 ohm, 1-watt) resistor in series with each output and THEN connect the other ends of those resistors in common as your final output. That small value of resistance will allow each regulator to work independently of the others and the current will be shared by all of the regulators fairly equally. The down side of this fix is that it makes the regulation a little bit "softer" (i.e., a higher internal resistance for the supply), but in most cases, won't be much of a problem." (Original post: http://www.electro-tech-online.com/general-electronics-chat/7449-multiple-regulators-parallel.html#post35998)


Hey! Thanks Nuumio!  I'll dig out some resistors and try that. I was thinking I might need to build something with TIP42s or a pair of MOSFETS. A resistor for each output leg is much easier. Thanks again!


I finally used a pair of TIP42 PNP transistors in a darlington pair and controlled their output with the 7805. I have been able to put 4 DC motors on it (6v motors) and drive them for 15 or so minutes. The transistors get pretty warm but the 7805 stays cool. Heatsinks will help dissipate the heat and so I think I have a working power supply. I think it's putting out about 2.5 amps.

I'm not sure. Are you trying to piggyback them to provide more current?

Also, dropping all the way down from 12v to 5v is a bit inefficient. Another approach is a DC-DC converter like this one:


have a look at these


They are 2 Watt regulated DC-DC converters in a small 5 pin SIL body. They are 66% efficient so there's obviosly some heatloss, but there seem to be no problem piggybacking them to double or tripple the 400mA they deliver.

-and the vendor claims they don't need caps...!

Yes, I'm trying to get more current. I know I can buy a DC-DC converter for $20-25 but I have a bunch of parts here I'd rather try to use. The datasheet showed a pretty simple circuit to let TIP42s do the heavy lifting while the 7805 is used to control the output voltage. I have a bunch of TIP42s as well. Of course, I could always just go to using two battery packs; one for the logic and motors and one for the video. But where's the fun in that? :-/



These are great little devices and 400mA is more than enough for your processor and sensors (run your motors directly from the batteries).

The only problem is how much and where from?
I can get something similar from a local shop but it is very expensive in comparison to an LM2940. It is cheaper for me to buy a DC-DC converter that plugs into the cigarette lighter and remove it from it's casing. Then I can get 1A or more.

This is why I built my own DC-DC converter.