dropping resistor value

Thread Starter

Gompers

Joined Feb 21, 2007
18
Newbie here Name's Ed. Trying to find the right dropping resistor value
to convert a plug in DC power supply of 5.0 volts @1.0amps to 3.0 (DC)volts to power a miniature Am/Fm radio that eats up batteries.
Thanx in advance Ed.
 

beenthere

Joined Apr 20, 2004
15,819
It's hard to come up with a good value for a dropping resistor, as the value is only good for one load value. Just grab 4 diodes, like 1N914's, and tie then all in series. They will drop about 2.8 volts and make a better source for your radio.
 

Ron H

Joined Apr 14, 2005
7,063
It's hard to come up with a good value for a dropping resistor, as the value is only good for one load value. Just grab 4 diodes, like 1N914's, and tie then all in series. They will drop about 2.8 volts and make a better source for your radio.
He only needs to drop 2 volts. Three diodes should do it.
 

Thread Starter

Gompers

Joined Feb 21, 2007
18
Been and Ron thanx again used four silicon diodes and VOILA! works fine

Next, I want to try to convert a similar plug-in to a lower voltage for use as battery eliminator for my Coolpix camera. Never thoughtof using diodes as resistors? Might make a decade box for quick voltage drop search??Cheers, Ed.
 

beenthere

Joined Apr 20, 2004
15,819
They are not really dropping resistors. They require a certain energy to be expended to push electrons across the P-N barrier. That's about .7 volts for silicon, and about .2 volts for germanium.

They come in handy for wall wart voltage droppers.
 
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