Basic Resistor Training

this-is-me · Post by **this-is-me** » Sun Mar 27, 2005 8:24 pm

I am wondering what resistor to get if I want 5v out of a 12v power source. I know absolutely nothing about resistors, so I need to know exactly what to ask for in, say, Radio Shack.

HK-47 · Post by **HK-47** » Sun Mar 27, 2005 8:31 pm

http://en.wikipedia.org/?title=Resistor
Nice info page on resistors.
Also, to know how to get 5v out of 12v you have to know the current draw of whatever it is. An easy way to figure this out is to use the formula: R = (Vs - Vf)/I
R is the value of the resistor, Vs is the supply voltage, Vf is the foward voltage, and I is the desired current. So in this aplication the formula would be R = (12-5)/"current draw". You could also use a calculator like this one: http://www.bit-tech.net/article/68/

this-is-me · Post by **this-is-me** » Sun Mar 27, 2005 8:35 pm

Since I can't edit my own post anymore (thanks a lot ben) I will post a picture of what I think it should look like and someone tell me if this will work OK.

this-is-me · Post by **this-is-me** » Sun Mar 27, 2005 8:37 pm

HK-47, I am not at all familiar with all the things you have mentioned. I don't know the draw of the item I need the 5v out of. Do you have any ideas on how to help me out? I need baby steps for now.

HK-47 · Post by **HK-47** » Sun Mar 27, 2005 8:38 pm

What are you trying to power?

this-is-me · Post by **this-is-me** » Sun Mar 27, 2005 8:41 pm

I am converting a DVD player to 12v. I have a dvd player that plugs directly into a wall socket. I opened the unit and found that it is a power converter that supplies 12v and 5v to the dvd player tray and controller board. I want to completely remove the power supply and be able to power the whole box from a cigarette lighter adapter.

MajorLag · Post by **MajorLag** » Sun Mar 27, 2005 8:42 pm

Wouldn't you use a 7805 in this case?

HK-47 · Post by **HK-47** » Sun Mar 27, 2005 8:44 pm

A model number for the player would help.

this-is-me · Post by **this-is-me** » Sun Mar 27, 2005 8:45 pm

It's a cyberhome ch-dvd 300.

this-is-me · Post by **this-is-me** » Sun Mar 27, 2005 8:57 pm

This should help:

JackFrost22 · Post by **JackFrost22** » Sun Mar 27, 2005 8:58 pm

Hey I made a dvdp out of one of those. I took it apart shortly there after. I used a dc-dc coverter

this-is-me · Post by **this-is-me** » Sun Mar 27, 2005 8:59 pm

Will a resistor work? I am trying for as easy a setup as possible.

JackFrost22 · Post by **JackFrost22** » Sun Mar 27, 2005 9:01 pm

it will overheat in the long wrong and this is actually more complicated than soemthing like a 7805

this-is-me · Post by **this-is-me** » Sun Mar 27, 2005 9:02 pm

What will overheat? Also, isn't a 7805 a resistor?

JackFrost22 · Post by **JackFrost22** » Sun Mar 27, 2005 9:03 pm

no a 7805 is a regulator he resistor can melt or short out