All Questions
Tagged with current-limiting led
60
questions
42
votes
2
answers
22k
views
Correct formula for LED current-limiting resistor?
I'm trying to work out what value resistor to use in a LED circuit. The equation I'd use to do this is:
$$ R = \frac{V_{cc} - V_f}{I_f} $$
Seems logical, and makes complete sense. The answers to the ...
- 1,092
10
votes
4
answers
11k
views
Why is LED lighting up despite Supply voltage < Forward voltage
I have an LED which has specified Typical forward voltage of 3.5V and Maximum forward voltage 3.9V.
I applied 3.3V across it with a 300 Ohm resistor in series. Why did it light up?
I am wondering if ...
- 4,942
7
votes
2
answers
701
views
Current limiting resistors
I notice that in Ben Eater's project for the 74 series logic chip computer, which my son and I are building, sometimes he uses current limiting resistors on LEDs on the pins of some chips, and on ...
- 193
5
votes
3
answers
2k
views
Do I need a current limiting resistor when powering an LED below its forward voltage?
I've reviewed the questions:
Why can you use an LED below voltage?
Is a current-limiting resistor required for LEDs if the forward voltage and supply voltage are equal?
But combining them begs ...
- 34.3k
5
votes
5
answers
878
views
Dynamically dimming individual LEDs in a lighting system [duplicate]
I'm planning to build an aquarium lightning system with individually controllable LED's, I don't have much experience with electronics except from the irregular tinkering, but I'm a programmer and I ...
- 158
4
votes
5
answers
10k
views
How to limit current to LEDs
I have understood that this is a bad way to do it:
Since some LED can draw more current than others.
So lets say I would power some high powered LEDs, like say 10 x 3W LED with a DC forward voltage ...
- 697
4
votes
1
answer
7k
views
Need help calculating resistor values for IR LED Driver
I'm wiring an IR LED driver for an Arduino project I'm prototyping.
The Arduino will be run at 5V, and I'm planning on using it's 5V output to drive the transistor that runs the LED
The circuit I've ...
- 1,418
3
votes
2
answers
773
views
What's the difference of placing multiple resistors and one resistor for limiting the current of LEDs?
I'm looking at a diagram and wondering if I could use just one resistor to limit the current of the LEDs instead of multiple resistors so that the cathodes are all connected to the same resistor.
JL
- 51
3
votes
3
answers
2k
views
Current limiting from a USB supply
I am designing a device which must power a number of RGB LEDs. I am currently looking at WS2812 "NeoPixel" style LEDs, which have a max current draw of 60mA each. I would like to have a large number ...
- 133
3
votes
1
answer
768
views
Why are these LED current limiting resistors so big?
I'm looking at the charging circuit for a lithium ion battery that was made by Adafruit. Here's an excerpt:
If there's a 5V rail from the USB port and a 470 Ohms resistor, is that limiting the ...
- 626
3
votes
2
answers
601
views
LED fairy lights with series capacitor?
I've opened up the battery box of a string of fairy lights (like pictured at bottom) and found a resistor, plus what looks like a capacitor in series with the lights. Is this really a capacitor? If so,...
- 255
3
votes
2
answers
102
views
Boosting load current of voltage regulator
I'm trying to connect little 3v LEDs to a motorcycle's alternator and i want to regulate the voltage of it to 3 volts so the LEDs don't burn up
the alternator gives off 2.5 volts and over with 3 amps ...
2
votes
3
answers
889
views
Diode drop vs open drain output tolerance
I have an LED Driver IC that states a 5.5 V tolerant open drain output. It's Absolute Maximum section indicates 6.5 V with a note saying "The input negative-voltage and output voltage ratings may ...
- 73.2k
2
votes
2
answers
113
views
TPS2553 Current limiting for RGB LEDs
I'm building a keyboard which will use SK6803 mini-e LEDs (ws2812 driver). I'm using a Pi Pico and as such the USB limit for current draw is ~500mA. I'm looking to limit the current draw from the LEDs ...
- 31
1
vote
4
answers
1k
views
Why my hex inverter chips (all three of them) are not producing a HIGH output with low input?
I wont say I am great at reading datasheets, but I noticed that for 74LS06 chip, Ioh is 0.25 mA and Iol is 40mA. Does that mean it can light-up an LED when its output is low but not when its output is ...
- 120