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32 votes

Where is the LED in this light bulb?

This is how a typical LED filament looks like when magnified and somewhat simplified: Image credit It is still "Chip-on-board" (COB), the difference is that the "board" is made as ...
fraxinus's user avatar
  • 9,194
31 votes
Accepted

Why is a LED with no resistor not a dead short?

When we call the LED a certain voltage, that's a simplification, or lie-to-children. Actually, you can look up the real current/voltage curve. If you have a specific LED in mind you can look at its ...
user253751's user avatar
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29 votes

4 parallel LED's connected on a breadboard

The most serious problem is that you have the LEDs connected directly across the input power, bypassing the resistor. There is also a more subtle issue with matching of Vf as Andy has described, but ...
Spehro Pefhany's user avatar
28 votes

The LED is dead... Why?

The infrared LED died from too much current. Excess current overheated its internal structure. Be aware of a caution on the data sheet: Note: Don’t drive at rated current more than 5s without heat ...
glen_geek's user avatar
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26 votes
Accepted

Where is the LED in this light bulb?

The LEDs are hiding in the filaments. Surface mount LEDs can now be made very small. Each filament in this style of lamp has a long string of surface mount blue or violet LEDs wired in series. The ...
Simon B's user avatar
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21 votes
Accepted

Dimming LEDs with MOSFET circuit causes low voltage devices to fail

Your isolated MOSFET driver has a rise/fall time of 50ns with 3nF load: From the gate charge plot of IRF840 and the driver's maximum output current it should switch in about 30ns. This is adequate ...
bobflux's user avatar
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19 votes
Accepted

Mini LED or diode that can turn on with 220 V

That is not a LED. That is a neon indicator lamp.
Justme's user avatar
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18 votes

LED circuit seems to defy Ohm's law. Of course it’s something else

To get 20mA with a 3.11V drop is 155 ohms just like you calculated. But you did not add in the fact that from the 3.11V, there is already a 2.8V drop over the LED like you measured, so that leaves ...
Justme's user avatar
  • 149k
18 votes
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LED Fails to illuminate, what am I not seeing in my configuration(s)?

Classic beginner's breadboard mistake. Figure 1. We somehow expect the green connections to be zero ohms while the red one is an open-circuit! All five sockets in a row are the one terminal strip. ...
Transistor's user avatar
  • 176k
17 votes

The LED is dead... Why?

LED is dead because you connected about 1.6V 700mA LED directly to a 3.99V battery. There was nothing except resistance of the wires and other conductors to limit the current so likely multiple amps ...
Justme's user avatar
  • 149k
14 votes
Accepted

4 parallel LED's connected on a breadboard

The problem is that the LED's are burning and i can't understand why. Any help is welcome One LED will have a slightly lower forward voltage than the others so... Initially, the LED with the slightly ...
Andy aka's user avatar
  • 458k
13 votes

What is the purpose of the second transistor?

When the current through R2000 becomes large enough so that the voltage drop over R2000 reaches the base-to-emitter voltage of Q2000 (about 0.6 V), then Q2000 activates and allows current to flow into ...
CL.'s user avatar
  • 19.3k
13 votes

What circuit for LED grow light?

All in parallel would be a lot worse. From a constant voltage source (PWM or not) would be worse again. Series diodes all have the same current flowing through them and differences will tend to ...
Spehro Pefhany's user avatar
12 votes

Low Percentage PWM LED Brightness (Equation?)

I'll try to give a helpful answer instead of telling you that this is a question of human perception and very difficult to answer correctly. Gamma correction is exactly what you need and want. ...
radioflash's user avatar
11 votes

The LED is dead... Why?

Your LED is dead because you misread the spec: This means the DC forward voltage at 700mA is: Maximum 2V This information is important to design the driver. Say you use a constant current buck LED ...
bobflux's user avatar
  • 77.6k
11 votes

Control two LEDs with only one PIC output

The bottom LED in the right hand circuit is upside-down. If you correct this this, then the right hand circuit is the correct approach. Drawing the left-hand design in the two conditions, output low (...
Simon Fitch's user avatar
  • 35.2k
11 votes

Do modern LED lights use thermal vias?

Aluminium PCBs are quite popular, especially for applications where the total LED quantity and/or power is high (e.g. COBs). Aluminium is used as the substrate, and the PCB tracks are isolated from it....
Rohat Kılıç's user avatar
11 votes
Accepted

Diode in reverse lights up LED

Schottky diodes have a lot of reverse leakage, and modern LEDs can emit visible light without much current. 1N5817 has more reverse leakage than 1N5819 (but also less forward voltage when conducting). ...
Spehro Pefhany's user avatar
10 votes

How can I make an LED strobe light for a turntable to replace a glimm light?

Honestly, the analogue way with diodes and using the AC frequency is a much better way to do this. The digital way here is just to explain the original example given in the question, or if you want ...
jonathanjo's user avatar
10 votes

How can I get similar brightness out of individually driven LEDs?

An LEDs brightness is mostly dependent on current, and their junction voltages can vary from batch to batch or even device to device, so to get consistent brightness from LEDs (of the same model) you ...
GodJihyo's user avatar
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10 votes

How to estimate LED lifetime?

Operated within ratings, the LEDs are unlikely to fail catastrophically i.e. stop emitting altogether. However, due to degradation of the crystalline structure, and possible delamination between the ...
elchambro's user avatar
  • 926
10 votes

LED Fails to illuminate, what am I not seeing in my configuration(s)?

My students often made this mistake. So I forced myself to make this image of a similar board with drawn connecting lines. Also, I removed (with great difficulty) the adhesive pad from the underside ...
Circuit fantasist's user avatar
10 votes
Accepted

What resistors for a 4 LED Arduino/breadboard project?

For most modern LEDs, 15mA or 20mA is way more than you need, and close to the maximum that can be driven directly from the Atmel/Microchip MCU chip you are using. Consequences of using too low a ...
Spehro Pefhany's user avatar
10 votes

Dimming LEDs with MOSFET circuit causes low voltage devices to fail

You're not getting much, if any, benefit from optoisolating the drive signal when both grounds are tied together. Look carefully at the path the LED currents take back to the power supply and make ...
Spehro Pefhany's user avatar
9 votes

Why is a LED with no resistor not a dead short?

An LED can be reasonably modeled with a couple ordinary silicon diodes and a series resistor. And the Arduino GPIO high output can be simulated by a resistor to Vdd, such that it will draw perhaps 60 ...
PStechPaul's user avatar
  • 7,425
9 votes

Diode in reverse lights up LED

So after all there's nothing wrong with my circuit and the led draws very little current. Since it might be useful to other beginners, I got an idea, instead of a simulation, i measured it with my ...
Reicken Back's user avatar
8 votes

Where is the LED in this light bulb?

Just like the LED devices you know are a semiconductor device (the actual light-emitting diode) embedded in a light-conducting plastic: The LED devices actually are the yellow elements. They are a ...
Marcus Müller's user avatar
8 votes

What is the maximum number of times an RGB LED could be made to flicker between RGB repeatedly in a second with currently available technology?

Also, at what rate would the flickering significantly impact the lifespan of the LED ?? I'm not aware of flickering having any influence on LED lifetime. What is the maximum number of times an RGB ...
Marcus Müller's user avatar
8 votes
Accepted

LTspice showing wrong voltage

A few quick points: Do use the LTspice help. If you access it using the menu, there is an option for searching and you can use "diode" or just "d" in the search, then look down ...
periblepsis's user avatar
  • 9,075
8 votes

How to estimate LED lifetime?

If you read your LED data sheet correctly you'll see that it contains this: - And, if you search the Cree site you'll find this document: - And, if you read that document they give you a life-test ...
Andy aka's user avatar
  • 458k

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