Led project need help with powering it. - Page 1
Forum section: electronics / beginners

author: arrowfan
author_rank: Newbie
timestamp: May 04, 2018, 05:00:34 pm
content: Hello eevbloggers! First postI am doing a project with a 3d printed model of tracer's gun from the game overwatch.inside this gun i have quite limited space to work with but i would like to fit 16 Led and preferable use 2 AAA batteries. (could fit more batteries but not without dissasemblying the gun). Alternatively a small rechargeable 3.7v 400+mah li-ionthe LEDs i have are 3mm standard blue ones. random ones from china so no specs.im trying to minimize usage of resistors.also looking to buy a switching dc boost converter to get a higher voltage to maybe put the LEDs in series+paralell?i found the LM2621 a possible candidate but i am a newbie at electronics so it may be no good? or any suggestions for through hole ic?if possible i would also like to put in a microcontroller or arduino or mp3player chip w/ tiny speaker. but lets not get too carried away, leds are most importantthanks in advance! also english is not my first language.

author: sokoloff
author_rank: Super Contributor
timestamp: May 04, 2018, 05:14:33 pm
content: Blue LEDs will run OK directly on ~3V from a battery. Their illumination from LED to LED won't necessarily be uniform, but you can run them straight off 3V-3.2V (2 dry cells) no problem.You might try that first (put each LED in parallel with each other across two dry cell batteries connected in series), depending on what exactly your goals are with the project.And edit: your English is excellent. No need to apologize there at all!

author: arrowfan
author_rank: Newbie
timestamp: May 04, 2018, 05:45:26 pm
content: it would be for decoration mostly, but with the availability to pick it up and use as prop/toy.perhaps with a pulsing/ brightnes mode with variyng pwm.and of course i would want to keep the batteries alive for as long as possible.mayby put in a slide swith to be able to drive the leds from a phone charger while it is a decoration and switch to battery mode when detached.but this is all speculation and wishes, i dont know how much is possible with just batteries therefore i was looking at switching converters.maybe i should just follow kiss (Keep it simple stupid)

author: arrowfan
author_rank: Newbie
timestamp: May 04, 2018, 06:57:22 pm
content: if we look at the efficiency graph of this ichttps://datasheets.maximintegrated.com/en/ds/MAX608.pdf.could i theoritcally have 2 led in series and 8 of those in paralell. should be like <20 ma * 8 <= 160 ma current at 6v or something right? then this ic would be overqualified?

author: sokoloff
author_rank: Super Contributor
timestamp: May 04, 2018, 07:17:56 pm
content: For driving LEDs, you want constant current, not constant voltage, in order to get safe and consistent brightness.Look into LED driver ICs if you're going to use an IC. Probably 30mA for a "1 Watt" blue LED is in the ballpark.Some LED drivers can also take a PWM modulation input.

author: arrowfan
author_rank: Newbie
timestamp: May 05, 2018, 11:29:56 am
content: i found this 1-2cell led driver ltc3490.http://www.analog.com/media/en/technical-documentation/data-sheets/3490fa.pdf.in the example on page 1 they are using one high current led. But is it possible to use many low current led in parallel instead without the leds burning up?

author: Nitrousoxide
author_rank: Regular Contributor
timestamp: May 05, 2018, 11:36:08 am
content: Quote from: arrowfan on May 05, 2018, 11:29:56 amTheoretically, you could. But keep in mind that all LED's are not identical, and thus one will draw more current than the others.It is good practice to use constant current drivers (there are many IC's out there) with a combined parallel and series connection.Since you're not using a large amount of LED's, or need to address them separately (or RGB). You could get away with a transistor based switching solution for PWM.

author: sokoloff
author_rank: Super Contributor
timestamp: May 05, 2018, 12:51:51 pm
content: Quote from: arrowfan on May 05, 2018, 11:29:56 amCurrent is the same inserialconnected LEDs and shared acrossparallelconnected LEDs. (Voltage is the same for parallel LEDs, where current is what matters.)If using a constant current driver of sufficient voltage capability, it can light a string of series connected LEDs (all with same current and therefore “same”[-ish] brightness)