Single resistor for a common anode or common cathode RGB LED? | Basic Electronics
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- čas přidán 30. 07. 2024
- Maybe it hasn't happened to everyone but it has happened to many of us. The first time we have an array of components or an RGB LED that share an anode or cathode and we think, "Hey, I'm only going to need one resistor on the cathode side instead of putting a resistor on each leg of the other side, right?" Wrong! We briefly show why the forward voltage of LEDs or other components makes this a bad idea. We also have a related written tutorial on CircuitBread that can clarify any questions that may remain after watching the video - www.circuitbread.com/tutorial...
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Table of Contents:
0:00 Introduction
0:18 Example of an RGB LED sharing a single resistor
0:55 Single LED circuit and how it operates
1:25 Two LED circuit with one resistor and how it operates
2:23 Why you'll see some current flowing even with different forward voltages
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I think you just explained why my curcuit wasnt working properly. Thanks!
Glad it helped!
Good stuff!
If I could make a suggestion, I would suggest using a marker or similar writing item to make thicker lines that show up better on camera.
I like the two camera set up; very professional looking video!
Thanks! Yeah, when we were reviewing the footage, we thought the same thing. I've been debating between using a small whiteboard with a dry erase (not sure how bad reflections will be) versus just using a sharpie on paper. Next time we get setup, we'll probably just have both on standby and see how it works out.
In LEDs with 3 LEDs of different forward voltage effectively in parallel, like the color changing LEDs, they are designed to be driven from a constant current source, not a constant voltage source, though 3.5-4v is usually safe, but the intensity will be all over the place without a constant current souce.
Yep, constant current sources as the best way to drive an LED for sure! But if the LEDs are in parallel, even a constant current source will be unable to balance the colors properly.
Why can´t I enlight all 3 colours at once in a 4 pin RGB diode with each 510R on 12V, but on 5V it works?
It should - as long as you're not overdriving your LEDs. If you're not changing your resistors when changing between the two voltages, then the 12V is probably damaging the LEDs. Particularly the red LED that has the lowest forward voltage.
i have a question rather. could we simulate capacitors and inductors base on electromics component
Hi Hamadou! I don't understand what you mean - simulate them in LTSpice?
@@CircuitBread i mean obtaining their behaviours while using electronic componenrs such as op amp
It might be in hardware or software or just logic how to do it
@@hamadouousmanou7307 hi! I'm not sure for capacitors but in audio applications op-amps are used to simulate the behavior of an inductor. They are usually used in graphic equalizers. This reference design from Texas Instruments will surely help you :) www.ti.com/lit/an/slyt134/slyt134.pdf
At time 2.00: why does it mean that dropping 2v across the left LED means dropping 2v across the right LED? I know they're in parallel and voltage is the same in that situation but why must it be that the smaller LED path determines the voltage for the larger LED too? Fundamentally: why is most of the current drawn by the 2v LED? I've done a bunch of breadboard tests with this and see it is the case but can you show the formula for that. I know the formula for total resistance of parallel circuits and so forth but this question eludes me. Why does that "smaller forward voltage" LED draw nearly the entire current? (As I've seen here on my desk that it does, too). Thank you!
These are great questions and basically exactly why did the video, because we remember being confused about this as well. I honestly think the best way to understand this would be to watch our video on how to solve circuits with diodes in them (czcams.com/video/sDWWGhuRqFs/video.html), particularly the non-ideal diode example. But in this particular case, the higher forward voltage LED isn't reverse-biased, it just isn't forward biased *enough* to really conduct. And since it isn't forward biased enough to conduct, you can just treat it essentially as an open-circuit, so it's not going to be conducting much, if anything. After watching the diode video, come on back and see if this makes more sense!
@@CircuitBread the link of video above is gone. I guess the video is czcams.com/video/sDWWGhuRqFs/video.html
Thanks! I'm not sure why that link stopped working, I just double-checked and it's the "official" share link provided by CZcams. Weird. Either way - your link works, so thanks again!
The link isn't working because the closing brace slipped into it.
How to connect a LED strip (say of 30 or more LEDs) to ARDUINO to control the color? Thank you!
Great video! Not that you play for my team most likely, but you're very handsome. Also, has anyone told you kinda look like the actor JR Bourne. A younger JR Bonurne. :)
Ha! Thanks, I could use a pick-me-up every once in awhile because all I see are the crows feet and the rapidly encroaching white hairs. And my youngest daughter grabbing my belly and yelling "Chub chub chub!" all the time doesn't help 😂 I had to look up JR Bourne and I wouldn't mind looking like him at all - or being able to grow a beard like his. I appreciate it!
My application is a traffic signal. Common anode. But only one LED is sequenced at a time, so only one resistor would work in the common anode. This video did not really apply to my situation.
What if we are using both blue leds?
Hi Samuel! Then you'll probably be able to get away with it, but there is sometimes a little bit of variation between LEDs of the same color or even from the same production line. But unless your application is extremely demanding and precise or needs to be robust, you'll probably be fine.