# Changing 3 volt LED

Discussion in 'Electronic Repair' started by Neil Purtnoy, Sep 30, 2004.

1. ### Neil PurtnoyGuest

What size resistor should I use to change a 3 volt LED to a 5 volt LED?

2. ### Sam GoldwasserGuest

If you mean an LED that has a voltage drop of 3 V or 5 V:
Need to know the present resistor and input voltage, or the current (I).
If the current is known, you need to decrease the resistor by an amount
equal to 2/I.

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3. ### Neil PurtnoyGuest

The input power going to the LED is 5 volts from computer power supply, the
LED is 3 volts,(there never was a resistor connected) someone told me to
change the 3 volt to 5 you have to add a resistor)so if I use it that way,
won`t the 5 volt power burn out the 3 volt LED? "Sam Goldwasser"

4. ### Neil PurtnoyGuest

The input power going to the LED is 5 volts from computer power supply, the
LED is 3 volts,(there never was a resistor connected) someone told me to
change the 3 volt to 5 you have to add a resistor)so if I use it that way,
won`t the 5 volt power burn out the 3 volt LED? "Sam Goldwasser"

5. ### Sam GoldwasserGuest

Maybe, you need an additional resistor but without knowing the exact
current, can't give an exact resistor. Assuming 10 mA, use a 200 ohm
resistor. 10 mA is safe for most LEDs.

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| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

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6. ### NSMGuest

|
| > The input power going to the LED is 5 volts from computer power supply,
the
| > LED is 3 volts,(there never was a resistor connected) someone told me to
| > change the 3 volt to 5 you have to add a resistor)so if I use it that
way,
| > won`t the 5 volt power burn out the 3 volt LED? "Sam Goldwasser"
|
| Maybe, you need an additional resistor but without knowing the exact
| current, can't give an exact resistor. Assuming 10 mA, use a 200 ohm
| resistor. 10 mA is safe for most LEDs.

220 ohm is probably the nearest standard value. 1/4 watt will be fine as a
rating. If it's too dim, go to 180 or even 150 ohm. The LED probably has a
built in resistor.

N