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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I found'em in a Norwegian electronics shop. They cost roughly US$18 (dont know how much that is in Auzzy-dollars), but Norway is a high cost country, so it should be possible to get'em cheaper somewhere in the world.
Why not use the 7805? They are so easy to hook up and they have an output of up to 1A.

The 7805 needs a minimum of 7 volts to operation correctly. Your motors will pull the battery voltge (7.2) down below that.

You want a LDO (Low Drop Out) regulator, like the 2950 that only nees 0.6 volt headroom.

I've had a hard time getting hold of the 2950, so I've been playing a bit with the KA378R05 from Fairchild. "Dropout voltage of KA378R05 is below 0.5V in full rated current(3A)" Got a few of them as free samples a while back. If they're still sampling them, get some, they seem to work well so far.

I should make a component page for em too.

I'm still experiencing problems with the search function on LMR, but I found fritsl's praise for the 7805 regulator here.

And after reading through almast everything you've written i found a piece about a DIY Voltage regulator.

 Is that the one you're talking about?

Why cant I just du what fritsl did? Do I need the caps?

You mention DC-DC-converters, The only ones I find at pololu only boost the voltage UP, not down...

 

Frit's configuration will work in some cases but even the datasheet for the 7805 regulator will recommend caps. Depending on your power source and the demands upon it with motors and other heavy loads you should have a couple of capacitors on the input and output. The circuits I have drawn in my tutorial are general purpose and will suit most robots on this site. In some cases additional capacitances will be needed for heavy loads and noisy motors, servos etc.

There are DC-DC converter kits and circuits out there. I have done a quick tutorial on the MC34063A here.

You can get a switching regulator like this if you have the money but the only real advantage over a standard 3 pin regulator is that it is more efficient when generating 5V from voltages higher than 7.2V and won't need a heat sink.

There is no lazy cheap solution. There are expensive lazy solutions and cheaper solutions requiring some degree of hard work and soldering.

 

According to the 7805 datasheet you are supposed to use a .33uF across the input and a .1uF across the output. Would non polarised ceramics work or do they have to be electrolytic? I need to add a couple but I dont have any electrolytic that size but probably have a few hundred ceramic.

If you can make up those values with ceramics then they will be better.

Ceramics are actually better because of their low ESR but only come in small values because of their design. Monolithic capacitors are basically a heap of ceramics sandwiched together to create larger values. Electrolytics give you larger capacities in a relatively small package but have some limitations.

Will esr really be a major factor for for something like this?

Low ESR is important for noise suppression. Everything in a robot generates noise, servos, motors, relays, processor and even some sensors. If you don't have some low ESR caps in your power supply then your robot can behave unreliably.

One robot of mine refused to be programed because I was in a hurry and forgot to add a 0.1uF across the supply. It was running on batteries and no motors were running. It was due to the processors own internally generated noise causing it to reset.

This is why most regulated power supplies have both large value electrolytics and small value polyester or ceramic capacitors in parallel. While the electrolytic filters low frequency ripple the polyester and or ceramics short out the high frequency noise.