How do I connect a resistor?

Question

I need to run a laser diode at 4.5 volts and 35-45 mA. I have some resistors to use. What wires to I connect them to and which resistors should I use?

Example answer: Solder x wire to resistor and other end of resistor to x wire...

My power supply is 3 AAA batteries=4.5 volts.

When you say, "In series" what do you mean?
Otherwise do I just wire a resistor somewhere on the red wire?(Or black ground wire?)

Answer 1

Do you know the forward voltage of your laser diode?

If the forward voltage is V,

Then the resistor needed is:

R = (4.5 - V)/(0.045)

For example if the forward voltage is 3.1 volts,

R = (4.5 - 3.1)/(0.045)

R = 31.1 ohms.

Put the resistor in series with the diode.

Answer 2

If your supply voltage is 6v or more, you don't need a voltage divider, just a resistor to drop the voltage. For example, if your supply voltage is 9v, you need 4.5v across the resistor at, say, 40ma. Using Ohm's Law, E=IR, the resistance needs to be 112.5 ohms. The resistor will dissipate (4.5v x .04A) 0.18 watts, so a standard half watt resistor would do fine. The closest standard resistor values would be 100 ohms and 120 ohms. Try the 120 first and see if it provides adequate current for the particular diode you have. If not, try the 100. Be sure to observe correct polarity! The resistor is in series with the diode, so your connection could be B+ to resistor to +terminal of diode; B- to -terminal of diode.

Update: I now see from your additional info that your power supply is 4.5 volts. At what voltage is the diode specified to operate? If it's anywhere near a standard diode forward junction voltage of 0.6 volts, the 100 ohms should do fine. With key details like this omitted, any circuit design is likely to fail. Sounds like you need to get someone involved who knows what they are doing.

Answer 3

Your question about the meaning of connecting circuit devices in series gives you away. You are not ready to be waving a soldering iron around.

You need to take a course in basic electrical circuits before you handle any of the components. You could go to Radio Shack and ask for a basic electricity and electronics learning module. Sit down with that and go through the booklet and do all the experiments.

Alternatively, you might find some courses on line. Try an internet search on "basic electric circuits."

Have fun.

Answer 4

Whats your power supply? take two 1k ohm resitors and soldier them in series, with each leg connect to a 9 volt battery. This will give you a voltage divider for 4.5 volts, then tap the center voltage divider with the laser diode in and a potentiameter with a value of 1k. Adjust the pot as nessasary for your amps

Answer 5

You typically solder a resistor to a circuit card. You could also get a solderless "breadboard" and bend the leads of the resisitor 90 degrees and place them into the breadboard.