Led as amplifier - Page 1
Forum section: electronics / beginners

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 15, 2021, 08:48:03 pm
content: You guys think you could use the voltage drop of an LED to be a switch/amplifier?

author: TimFox
author_rank: Super Contributor
timestamp: November 15, 2021, 09:02:19 pm
content: No. Certainly not as an amplifier. It's a diode.(You can look up "parametric amplifier" for an exotic circuit that has some advantages at high frequency, using the variation with voltage in the capacitance of a two-terminal diode as the active principle.)

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 15, 2021, 09:04:03 pm
content: But it seems like you could to me.If you put a 1.5 v signal through + to -, this wont be able to travel through the led, because of the voltage drop.then if you send a 2v signal, low amperage, then both will travel through, even the 1.5v signal (which would be more potential amps), which is the one being switched by the 2v signal.

author: TimFox
author_rank: Super Contributor
timestamp: November 15, 2021, 09:05:48 pm
content: You seem to be saying that an LED forward biased with 1.5 V will not conduct, but it will conduct at 3.5 V. How is that useful? 3.5 V applied directly to an LED will probably kill it.And how could that be an amplifier?

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 15, 2021, 09:08:01 pm
content: You could increase the voltage drop to 20v with 10 in a row? It would be a little delicate tho indeed, but transistors are also delicate to use when they are small ones.

author: TimFox
author_rank: Super Contributor
timestamp: November 15, 2021, 09:13:32 pm
content: You seem to be talking about a switch, not an amplifier.A device, such as a Zener diode, can be biased to less than its breakdown voltage, and then a bit more voltage causes it to conduct. That is not a useful switch, and certainly not an amplifier.If you look at diodes in RF switches and balanced modulators, a large reverse biasvoltagereduces the junction capacitance to not pass high frequencies, and a forward-biasingcurrentallows the high frequencies (at voltage levels below the switching voltage) to go through. Is that what you are discussing?Looking at your update while I was writing this, you seem to think that the 2 V on top of the higher voltage will conduct less current. But the two voltage sources are in series, and therefore will conduct the same current.

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 15, 2021, 09:19:41 pm
content: Its possible to send out timed pulses of charge, if you put out four times the pulses at 1v, it actually counts as more amps than the 2v, even tho its less voltage, its more amps.

author: TimFox
author_rank: Super Contributor
timestamp: November 15, 2021, 09:24:28 pm
content: This statement is not clear.

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 15, 2021, 09:26:09 pm
content: *salute* yes sir... I understand, Jeeves fetch my bags Im outa here...

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 15, 2021, 10:33:34 pm
content: Well, I guess the moral of the story would have been low voltage spark gaps can actually be LEDs.... but it didnt work...

author: TimFox
author_rank: Super Contributor
timestamp: November 15, 2021, 10:36:48 pm
content: As you wish.

author: David Hess
author_rank: Super Contributor
timestamp: November 16, 2021, 05:39:58 pm
content: Any diode can be used as a switch. This is common where high bandwidth and isolation are required. Transistors can be used the same way with emitter switching. For instance oscilloscope channel switches use diode or transistor emitter switching to hundreds of MHz or even into the GHz range.Quote from: TimFox on November 15, 2021, 09:02:19 pmDiodes which display negative differential resistance can be used as amplifiers, but LEDs do not.

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 16, 2021, 06:19:45 pm
content: So theres funny ways to use transistors once u'r starting to get good. cool.

author: TimFox
author_rank: Super Contributor
timestamp: November 16, 2021, 06:41:33 pm
content: Yes: switching with transistors is a mature technology.