Powering 2.2v LEDs from 5v - Page 1
Forum section: electronics / beginners

author: redgear
author_rank: Frequent Contributor
timestamp: September 02, 2020, 11:06:27 am
content: I have a 5v powersupply and 3 2.2v LEDs with 20mA If.Can I use a 50 ohm resistor and power the LEDs using 5v?Reducing 5v to 2.2v at 60mA, so 5-2.2 = 2.8. 2.8/0.06 gives 50 ohms.

author: mikerj
author_rank: Super Contributor
timestamp: September 02, 2020, 11:10:51 am
content: Preferably use one resistor per LED of (5-2.2)/0.02 = 140 (150 Ohms nearest preferred value) to get equal current sharing. If you connect LEDs in parallel with no resistors the small variations in their forward voltage causes unequal currents, often with noticeable brightness variation.

author: ledtester
author_rank: Super Contributor
timestamp: September 02, 2020, 11:15:54 am
content: With just one resistor the LEDs won't share the current equally each being slightly different.Do the math for three resistors - one for each LED, i.e. R = (5-2.2)/0.02 = 140 ohms.Also check the resulting brightness... 20 mA is an awful lot of current to put through a modern LED. They might be bright enough with just 5 mA.

author: tunk
author_rank: Super Contributor
timestamp: September 02, 2020, 11:26:28 am
content: What's the maximum current for the LEDs? If it's20mA, then one/two of them may be driven too hard.Alternatively, you could use one LED + 140 ohm,and two LEDs in series plus a 40 ohm resistor.

author: Psi
author_rank: Super Contributor
timestamp: September 02, 2020, 11:40:46 am
content: Quote from: ledtester on September 02, 2020, 11:15:54 amI wouldn't say it's an awful lot of current.20mA is the standard LED current for almost all generic led's, except maybe tiny SMT ones.But with modern LEDs it can be a little too bright from a user perspective.

author: langwadt
author_rank: Super Contributor
timestamp: September 02, 2020, 11:49:55 am
content: Quote from: Psi on September 02, 2020, 11:40:46 am20mA is some leftover rule from the 80's, today a mA is usually plenty

author: SmokedComponent
author_rank: Regular Contributor
timestamp: September 02, 2020, 12:01:12 pm
content: Quote from: Psi on September 02, 2020, 11:40:46 am20mA is way too much for any modern LEDs with newer chemicals.Recently, I ordered a bunch of 3mm THT LEDs in four different colors, diffused, specifically chosing them by highest luminosity.I was blown away (quite literally, covering my eyes) just how bright they are and how little current they need (~ 1mA or *less*) for signalling purposes.It is possible to light a LED just by touching one terminal and hooking the other on a switchmode power supply, with mains leakage current alone. If I then touch the earth ground with other hand, LED becomes almost bright enough for signalling.

author: Peabody
author_rank: Super Contributor
timestamp: September 02, 2020, 02:52:16 pm
content: Even 7-segment displays are now really efficient. I recently used two Vishay digits in a project, and found that with multiplexing I got a very stable, readable "88" diplayed with total average current of 4mA at 3.3V.

author: redgear
author_rank: Frequent Contributor
timestamp: September 02, 2020, 02:56:00 pm
content: Quote from: mikerj on September 02, 2020, 11:10:51 amQuote from: mikerj on September 02, 2020, 11:10:51 amQuote from: ledtester on September 02, 2020, 11:15:54 amQuote from: tunk on September 02, 2020, 11:26:28 amQuote from: Psi on September 02, 2020, 11:40:46 amQuote from: langwadt on September 02, 2020, 11:49:55 amQuote from: SmokedComponent on September 02, 2020, 12:01:12 pmQuote from: Peabody on September 02, 2020, 02:52:16 pmThank you everyone, I will place separate resistors for each LED. Thedatasheettest conditions were at 20mA. Idk if it will be too bright, may be I should try for myself.