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Reduce 5 volts to 3 volts, suggestions?

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yanger

New Member
I'm really new to this as well.. i'm trying to light up a 2 AAA LED christmas light and to replace it, i found an old unused 110VAC to 5VDC cell phone adapter...replacing the receptacles on the base of the tree, was simple, and when i turned it on, it worked! about 40 minutes later, the LED popped, assuming 5 volts was too much for it to handle... reading up on it. i could use ohm's law to get a resistor that could reduce it to 3v (at the cost of heating up).. is that conventional? or would it be probably better to just find a 3VDC adapter?
 

#12

New Member
This demonstrates the importance of telling us what you are trying to do in the first place. All of the previous solutions will not work because an LED is not a voltage driven device. An LED uses current to make light and the voltage drop is not caused by a resistance.

What you do is find out the current you need for the LED, subtract the voltage it needs from the available voltage and divide the excess voltage by the current. That will tell you the resistance to put in series with the LED so that it will use the proper amount of current.

5v-3v = 2v
2v/.02 amps = 100 ohms
P=IE
Power of the resistor = .02 times 2
power = .04 watts.
any cheap 1/2 watt resistor will do the job.
That is assuming you use 20 milliamps for the LED.
 

shokjok

Member
If you enter "low dropout voltage regulators" into a search engine, you will find 3.3V fixed regulators from Linfinity and other makers. If you can find a source for those part numbers, your power requirements will be easier to meet and implement in your design.
 

David Deak

New Member
I am new electronics. I built a very simple 9 volts (battery) power supply to 5 volts using a 7805 voltage regulator. How do I to reduce the 5 volts to 3 volts, suggestions?
Put a 2 volt Zener diode between the ground pin on the 7805 and ground.
 

crutschow

Well-Known Member
Most Helpful Member
David, you are replying to a nearly 3 year old thread.
Why do many newbies to these sites troll for old threads to respond to? :confused:
It's a mystery.
 

JimB

Super Moderator
Most Helpful Member
David, you are replying to a nearly 3 year old thread.

Crutters old chap, the thread is actually nearer nine years old!
What makes it worse is that the "latest information" is just plain wrong.

JimB
 
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