Topic: CHB power requirements

I'm working out a few robotics projects with my CHB and it's infocast brothers.  I'm having some problems with power supplies.  The CHB (and Infocast) need 5 volts @ 1 amp.  Normally I would try 6 AA NiMH cells and a 7805 voltage regulator.  The typical 7805 can do 1 amp.  That should do it, but what happens is that the CHB and the Infocasts rarely make it past logging on to my wifi before they brown out.

I'm not sure why this is happening.   The power requirements on paper come to less than 1 amp, but clearly it is more.  Any ideas on what is happening so that I can design a better power supply?

Re: CHB power requirements

From the 7805 datasheet, "The input voltage must remain typically 2.0V above the output voltage even during the low point on the input ripple voltage."   A typical NiMH AA produces 1.15-1.2V @ 1A, or 6.9-7.2V with six batteries; this leaves very little wiggle room before the voltage starts dropping to the point that the CHB gets unhappy.

You may want to look into a low-dropout regulator like the LM2940 -- with a dropout of only 0.5V, that gives you nearly 1.5V of wiggle room, so the batteries should pretty much be dead as doornails before the CHB starts to hiccup.  Don't forget to adequately heatsink the 2940!  Since you'll be running it near its max spec, proper heatsinking will increase its efficiency and longevity smile

Re: CHB power requirements

Oh, for reference, Jameco has the LM2940 in a TO-220 through-hole package, or TO-263 SMT package if that floats your boat.

(Yes, I love Jameco, and will happily toot their horn -- as an amateur electronics hobbyist, I have been well served by Jameco and they've specifically made changes to their shipping policy to better accommodate hobbyists, which is alright by me!)

To be fair:

Mouser in TO-220 and TO-263
Newark in TO-220 and TO-263
Digikey in TO-220 and TO-263

It seems Jameco's the cheapest for through-hole TO-220, but Newark wins for the SMT TO-263.  Don't forget to compare with shipping charges though!