The LEDs need DC 5V and 20mA. I have a power supply with 5V DC and 850mA. How do I wire the LEDs in parallel? I tried once with no resistors but all the LEDs went out or blew within 2 minutes?
2006-10-18 05:49:37 · 4 answers · asked by Cyle 1 in Consumer Electronics ➔ Other - Electronics
Tie all the LED's cathodes (-) together, then to ground.
Then, the anode (+) from each LED needs to have 250 ohm resistor in series, then tie each resistor to a common 5V 'rail'.
The 250 ohm resistor will limit the current to each LED to 20 mA (5 volts/ 0.020 amps = 250 ohms.) You could use a slightly higher resistor to provide a longer life, but it will reduce the LED light output.
Good luck.
2006-10-18 06:03:39 · answer #1 · answered by Tom-SJ 6 · 4⤊ 0⤋
Aahh, the old "figured I didn't need all those expensive resistors" syndrome. An event that is of far more common occurrence than most people will let on. Like the other two said, but don't worry about the exact value. As long as it is between 250 and 500 it will work. In this case I would figure to error on the higher side, as most inexpensive 'wall-cube' type adapters are not regulated, and it is not uncommon to measure 8 or 12volts unloaded.
2006-10-18 16:51:01 · answer #2 · answered by Aurthor D 4 · 0⤊ 0⤋
Tom-SJ is right, use a separate series resistor to limit the current to each LED. The only thing I will mention is that 250 ohms is not a standard value. You should be just fine using either 240 ohm or 270 ohm resistors which are standard values.
2006-10-18 12:57:39 · answer #3 · answered by Anonymous · 1⤊ 0⤋
you're able to do the present limiting with one resistor yet you will could desire to calculate its resistance fee and power score based on the characteristics of the LEDs. confident, you may desire to have an in-line fuse on your circuit.
2016-10-19 22:48:41 · answer #4 · answered by mchellon 4 · 0⤊ 0⤋