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

"Neil Purtnoy" writes:

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

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.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header is ignored.
To contact me, please use the feedback form on the S.E.R FAQ Web sites.

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"
wrote in message
...
"Neil Purtnoy" writes:

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

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.

--- sam | Sci.Electronics.Repair FAQ Mirror:
http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ:
http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites:
http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the
excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header is
ignored.
To contact me, please use the feedback form on the S.E.R FAQ Web sites.

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"
wrote in message
...
"Neil Purtnoy" writes:

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

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.

--- sam | Sci.Electronics.Repair FAQ Mirror:
http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ:
http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites:
http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the
excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header is
ignored.
To contact me, please use the feedback form on the S.E.R FAQ Web sites.

"Neil Purtnoy" writes:

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.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header is ignored.
To contact me, please use the feedback form on the S.E.R FAQ Web sites.

"Neil Purtnoy" writes:

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

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.

"Sam Goldwasser" wrote in message
...
| "Neil Purtnoy" writes:
|
| 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