Is a resistor required for a LED (Light Emitting Diode)?
Dave is totally correct if you use a power supply with the correct (exact) required voltage.
I have a large stock of many different types of LED’s from 3.MM (.118" Dia.) to 5.MM (.196" Dia.) from the standard round head LED’s, to the flat top LED’s, in many different colors. These LED’s operate in many different V-DC power supply that ranges from 1.8V-DC → 3.2V-DC mostly determined by the size of the LED.
LED’s of the same exact type and size, will also have a Different V-DC power supply determined by the Color of the LED used.
Also each different manufacture will also have a different V-DC power supply determined by the Color of the LED.
LED’s operate at very low limited V-DC power supply ranges and also require correct polarity connections.
Hello Guy’s thanks for the info on led’s but I do not paln to use any. I like the look of a bulb better. I should be done getting my lights in parallel this weekend. I will be able to only hook up 45 for now waiting on lamp shades. Then back to the power supply. Thanks Frank
Nice find Mark. I’ve been saying that forever but now you found a site that backs up what I’ve always known (probably actually learned exactly what they say there 30 years ago but have forgotten the exact math)…
There is exactly ONE case when no limiting resistor is needed - when you have a constant CURRENT power supply. Of course that’s a lot more complex than just a resistor. For example, I can set my lab power supply to 15ma and set the voltage to anything it can do and hook an LED directly to the terminals. Even if I set the voltage to 30 volts, the LED will be fine because the constant current mode will allow no more than the 15ma I set it to. There are constant current LED drive ICs you can use that accept a wide input voltage range but will only allow the LED a proper current. Again, more complex than just using a resistor. The drive ICs are great when you want to run the LED right to the limit without any chance of going over. When sizing a resistor, if you size it for half or less of the LED’s maximum current, even a relatively large voltage swing won;t cause the currrent limit to be exceeded - example is typical use of a 1K resistor for white LEDs on DCC. For mose, that reults in a nominal 9ma to the LED. Most white LEDs are good for 20-25ma. So even if the voltage to the rails should increase to say 20V, the LED would still get less than 20ma. It’s always good to leave a safety margin in any design.
While I agree that you should always use a resistor with LEDs if you don’t have a current regulated power supply, that doesn’t necessarily mean every LED needs a resistor. If your voltage is more than twice the LED voltage you can run LEDs in series off of one resistor.
Hello I have lights. RRMel helped me offline get the right stuff and helped me set it up and explained how things worked so I could understand. So now my lights run off a 20amp power supply with a DC-DC converter I have more power then I need but thats ok. Here is a photo of part of the light’s the rest are to spred out and wont showup. I have these brighter for the photo. Thanks for all the help
