Voltage Regulators: Do I Need A Capacitor For Can I Get Away With Just The Regul

 
#1

im going to wire up my servos and I need my regulators ready. here's the regulator I have.

7807 Voltage Regulator 6-Volt 1-Amp TO-220

can I just use it as is or do I have to add a capacitor.

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#2

The datasheet should have the manufacturers recommended schematic. I've not seen one yet that doesn't have capacitors on it, so I would say so.

I covered the reason why capacitors are needed in another topic the other week, I'll see if I can find it (to save me typing it all out again).


Edit:

The capacitor on the input side supplies current when there's a sudden drain.

The capacitor on the output side has two purposes;
1. It supplies current at the regulated voltage when there's a sudden demand while the regulator attempts to compensate
2. It may be required for proper regulator operation. The datasheet for the regulator will indicate the minimum capacitance required.

In general follow the manufacturer's recommendations. If your circuit does not have large current spikes, you can go with the minimum output capacitor size recommended by the manufacturer.

Taken from this topic on page 3, post #22

It was your topic Smile

#3

@rich what size capacitor do I need for 7.2 volts? does radio shack have them? also how to wire it?

#4

Check the datasheet, the manufacturer will have specified the minimum recommended capacitors to use.

The datasheet will also have a schematic.

Any good stockist should have them. I can't vouch for radioshack as we don't have them over here in the UK.

#5

Digi-key, Mouser, and even amazon.com and ebay are good resources for ordering capacitors.

#6

@aameralis I still have less than a years experience in robotics, electronics and engineering (or robotics in general) so I find myself reviewing a lot of basic tutorials just so I can remember how to read some data sheets and schematics. I read the forums very often so I know you're very smart and helpful so, I think if you spend some time taking Rich's advice you'll have all the info you need. I've noticed Rich has gone from handing out answers to helping and encouraging people to learn how to do "it". Which in my opinion is far more valuable. The EZ=Community is awesome.

#7

That's mainly due to lack of time (although I have always been trying to aim more towards the learning angle and less of the spoon feeding.

@aameralis, the bigger the better really. In basic terms, the caps store the charge so the bigger the caps (the more microfarads it is) the more it can hold and the less likely you are that you'll have problems when there are surges. The voltage you use doesn't really make much difference, provided the cap is rated for the correct voltage.

I'd assume most are the same so you'll want a minimum of 0.33uF on the input and 0.1uF on the output but check the datasheet of whoever manufacturer yours to be on the safe side.

Just one thing though. Those are 1A regulators. If you are still using the HD servos that may not be enough current. MG995s can draw in excess of 2A under a load. Have you checked the stall current of the servos you are using?

#8

Also FYI to readers of this thread, the 7807 is a 7 volt regulator.

#9

@robodoc where did you see on the data sheet it was 7 volts? I thought the last two numbers 78xx were voltage code not literally the voltage of that regulator.

#10

no doc is correct, they are 7volt.