# Reduce 5 volts to 3 volts, suggestions?

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by prprog, Dec 19, 2006.

1. ### yangerNew Member

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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?

2. ### #12New Member

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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.

3. ### vedangkNew Member

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how I will convert 5 volt to 3 of mobile charger
and battery supply to electric supply

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5. ### shokjokMember

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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.

6. ### David DeakNew Member

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Put a 2 volt Zener diode between the ground pin on the 7805 and ground.

7. ### Les JonesWell-Known Member

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David, That will give an output of 7 volts.
Les.

8. ### crutschowWell-Known MemberMost Helpful Member

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Why do many newbies to these sites troll for old threads to respond to?
It's a mystery.

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Cheers,
tv

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