How to Turn an LED On

Below are my Super Patrons with support to the extreme!

Sam Lutfi
J4yC33

By: Mehdi Sadaghdar

[ElectroBOOM]

Hi All! Around 6:40, although my first LED was dead from the first capacitor experiment, the second LED was not dead! As some of you pointed out, I totally forgot about the fact that the LED, forcing the current one way through the capacitor only, charges the capacitor to the main voltage peak (hence the one quick blink) and after that because the capacitor is charged, the voltage across the LED doesn't go positive and so it won't turn on any more. The solution would be to discharge the capacitor, say by placing a reverse diode across the LED to discharge the capacitor in the negative cycle. The reverse diode could also be an LED, which means in both cycles you would have an LED on causing less flicker, which is nice!

[ChaosPootato]

Damn, when Mehdi is worried about his circuit's safety, you know it's serious shit

[ronaldschild]

I like Mehdi's style here. He demonstrates even with a university education and experience under his belt, an engineer still must build the circuit in real-life and see what happens.

[steveklassen]

I think this is one of my favourite videos. I could not stop laughing every time Mehdi changed up the whiteboard overlay. First he was in front, then his head was overlayed, then he was behind the whiteboard, then he was in front and tiny. So good. Mehdi has such a great eye for comedy. Like the latity song. Gold Jerry, Gold.

[mikethor]

As soon as he mentioned using a capacitor instead of a resistor, I knew there was going to be an explosion.

[pyrob]

Thanks to you, Mehdi, I have finally reached a level where I can predict most of your BOOMs instead of being surprised by them. Thanks for all the teaching and entertainment that carries me through university!

[limacharlie]

This video is great. The fact that it goes through theoretically "correct" ways to drive an LED, and the reasons for why there are better ways, which follows the learning curve so well. Bravo

[kellingc]

I remember studing this stuff for my Amateur Extra Radio exam. Amazing how much I retained, but still love seeing your practical demonstrations. Thank you for posting these.

[ardag]

I'm so happy to have learned about the relationship between event horizons and LEDs. Now I will be able to say "I already know all about LEDs, come on..." in the next video!

[tuskiomisham]

Hey Electroboom. Could you do a video on what transistor is a good pick for various applications? (driving a motor, logic level shifting, HF radio, UHF radio, sound amplification, signal filtering, etc)? There are SO MANY different transistor technologies out there, and I don't know what to pick for which application!

[nixdorfbrazil]

Love you dude! I was graduated as Electronic technician some 30 years ago. And it's nice that most of my knowledge is still valid today. Than I started an Electrical Engineering university course, but I feel in temptation with Computer Sciences, and I didn't mess up much with electronics all this time. You bring so much fun memories. Thank you very much for your work. 😂

[funguy]

14:57
He's invented the most stressful lightbulb ever

[jimsvideos]

Given enough current, pretty much _every_ component is light emitting.

[simon]

when you turn on an LED is pretty normal,

but when the LED turns on you .... thats a different story.

[foogod]

I honestly did not expect a video called "How to Turn an LED On" to finish up by actually teaching us how to make a full-on switching power supply (including the principles involved). That was really impressive (and cool).

[chillmonkey]

Chuck Norris once hired an electrician and taught him how to survive being shocked thousands of times.

[treybarnes]

Now that we have had LEDs taught Mehdi style, it would be cool to see a zener diode video. It would be funny to see you illustrate an over voltage protection system using a zener diode after you have already destroyed a bunch of LEDs.

[biboKralle]

7:02 That‘s something we don’t hear Mehdi say very often! :D :D

[junkerzn]

For a simple LED its just a DC source like an I/O port, the LED, and a resistor. But in commercial designs, driving an LED efficiently as well as controlling the brightness actually takes a bit of work. There are two methods.

The most common method is to use a current-controlled driver chip, usually set to near the LED's rated current (e.g. 20mA), and you then control the brightness with a PWM. The PWM is sometimes built-into the driver chip and controlled via I2C, but it is just as easy to use a little PIC microcontroller to handle the PWM. The PWM typically runs at 40KHz and has 256 brightness levels (base clock is thus around 10MHz). LED driver chips allow you to set a fixed current with a resistor and you use something like a PIC microcontroller to control it. However, there is a 'minimum' brightness when using this method because LED driver chips can't actually turn on and off quickly enough to handle PWM settings below around 100uS.

The driver chips work best for LED strings. We don't use inductors... Actually, we try to avoid using inductors at all because they vibrate and they are expensive components compared to other components on the board. They are EXTREMELY efficient. We try to arrange the voltage drop across the string such that the voltage is close to zero at the bottom of the string. The driver chip then basically connects the bottom to ground (current controlled), so the losses through the driver chip are extremely low. e.g. if you have a 20V series string of LEDs you make your power supply something like 21V and thus the driver chip's internal FETs only has to dissipate 1V, yielding an efficiency of 95%.

The second method is to servo the current with a FET/op-amp circuit for brightness and use a simple fixed PWM to limit power consumption. Again at around 40KHz. This is more difficult to get right because the FETs linear range is really sensitive to voltage (hence why it has to be a servo), but it works. It isn't as efficient because the FET eats the difference, but it allows the PWM to have a wide pulse width without being too bright, which is important for certain transmitter/detector applications.

Then finally, one might ask why use a 40Khz PWM instead of, say, 60Hz from a half bridge? Well... because the human eye can easily see the flicker at 60Hz, but won't see any flickering at 40KHz.

[caseyleirer]

First time catching a new upload after discovering your videos. I really appreciate your channel, and your incredible teaching. I ordered a Tesla coil kit yesterday (: