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# newbie newbie newbie

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#### Bentov

##### New Member
Hello all, I've been reading through some of the posts here, and I think I am just missing something. I'm just getting into eletronics again after blowing the circut breakers in my house when I was 10 trying to make an electromagnet plugged into the wall(I'm now 30, yes I was traumatized) So this is my question, I don't want to use batteries for everything, so I bought a power supply from radio shack 12VDC/1.75A. If I am just making simple circuts with say a 555 and some LEDs, what amount of resistence should I use. I tried to use Ohm's law, assuming 5vdc, but something isn't right. Could someone please point me to a link, or give me a simple explanation, I would be forever in your debt.

Thanks,
Bentov

That is a good tutorial, I made sure to bookmark it, but I think he's looking for answers on how to power it.

IMHO, the easiest way to power it would be from a computers power supply, since it puts out +5v, among other voltages. The 5v comes from all the red wires. If you have an old/broken computer then it would be worth it to get a power supply, they're quite handy.

But I'm going to guess you don't have such a supply and try to give you another method. I would use a voltage regulator. To find one suitable for your circuit, go to digikey.com, search for voltage regulator. Several links will probably pop up, choose voltage regulator. You will then be presented with several filters to narrow your search. Choose an output voltage of 5v and a packaging type of tube. This should give you several voltage regulators that will work. Click on some and read the datasheets, those will tell you how to use them.

He already has a 12V/1.75A power supply and can use it to power 555 directly without any resistor.

Oh, I didn't realize it would run at 12 volts

Oh well, if you ever need to run anything at 5 volts, thats how ya can do it Bentov.

kinjalgp said:
He already has a 12V/1.75A power supply and can use it to power 555 directly without any resistor.

I guess I was just a little worried becuase everything I read was always delt with currents in the milliamp range, not over 1 full amp. I just didn't want to fry anything.

Thanks to you both for your help.

Bentov

I guess I was just a little worried becuase everything I read was always delt with currents in the milliamp range, not over 1 full amp. I just didn't want to fry anything.

Although the supply is rated at 1.75 amps, it won't force 1.75 amps through your circuit. The current rating means your supply can produce up to 1.75 amps. Any circuit you attach to the supply will only draw what it needs from the supply.

Thats true. Your circuit will only draw that amount current which it requires to operate and this current depends on internal impedance of 555. So you don't have to put any current limiting resistor in its supply pins. Directly connect it to your 12V supply. You can operate 555 right from 3V to 16V.

I understand now, and was able to use the power supply last night. I really appreciate the help I have gotten from all of you. You've helped create a monster :twisted:

Bentov

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