Boost LED driver - Page 1
Forum section: electronics / projects

author: Cloud
author_rank: Regular Contributor
timestamp: February 15, 2015, 11:46:06 am
content: Hello,I am looking for a boost led driver, for a LED with U=3.15-3.4V, I=0.2-0.3A. And I want to power it from a AA battery (preferably rechargeable). What would you recommend?

author: Paul Price
author_rank: Super Contributor
timestamp: February 15, 2015, 03:18:47 pm
content: C B lo

author: bktemp
author_rank: Super Contributor
timestamp: February 15, 2015, 03:37:34 pm
content: MCP1643 is the LED driver version with constant current output.

author: SeanB
author_rank: Super Contributor
timestamp: February 15, 2015, 03:43:03 pm
content: You get 3 pin boost converters specially made for this. All you need is the small SO device, an inductor, an input decoupling capacitor and connect the diode across the output. works well for a torch off a single AA cell.I bought a few $2 torches with the whole circuit and a 5mm LED inside, just to take the LED module out, fix the poor assembly ( they wire the led incorrectly on about 1 in 2) and use them as incandescent lamp replacements. Same light, brighter colour temperature but about 1/4 the current draw. On an emergency lamp it now lasts 4 hours instead of 30 minutes.

author: Cloud
author_rank: Regular Contributor
timestamp: February 18, 2015, 09:23:41 pm
content: I ordered MCP 1623 and 1643s and will report when I get them

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 19, 2015, 08:29:05 am
content: ?If you don't need fancy control, a single transistor will do the job.Tim

author: Whales
author_rank: Super Contributor
timestamp: February 19, 2015, 09:10:14 am
content: I've just spent the last few weeks getting a 34063 to boost 12V to ~32V peak and run as a constant-current source. I blewso many ICsuntil I had the over voltage protection circuit going, and even now it has faults. I did learn much more than if I bought some better parts howeverT3sl4co1l: is that a joule thief?

author: Cloud
author_rank: Regular Contributor
timestamp: February 20, 2015, 12:05:53 pm
content: I was thinking about joule thief, but i don't think there will be enough space, since I want to make a compact and reliable flash light

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 20, 2015, 03:21:31 pm
content: Well, that one has a capacity a bit larger than your spec, so if that's too big, you're going to have a problem no matter how you cut it. You will always need the same basic circuit, whether driven by a single transistor or a fancy IC.Tim

author: DmitryL
author_rank: Regular Contributor
timestamp: February 20, 2015, 03:32:29 pm
content: Quote from: Cloud on February 15, 2015, 11:46:06 amLTC3490, I used them, nice ones.On the other hand, you may try doing a parametric search on a sites like Farnell, Digikey etc., you may find a bunch of drivers that suit you.

author: bktemp
author_rank: Super Contributor
timestamp: February 20, 2015, 03:39:09 pm
content: Quote from: T3sl4co1l on February 20, 2015, 03:21:31 pmThe main advantage of a special IC over the simple joule thief circuit is the synchronous rectification: If you drive a single white LED you are losing either 0.5V on a rectifier diode (~15% loss), or the LED gets pulsed by a high current (>100mA to get 20mA avarage. Both reduces the efficiency substantially. Another advantage of the ic: The output current is regulated. The brightness will stay constant when the battery discharges until the ic can not deliver enough current when the voltage goes below around 0.7V.I have build similar 1 transistor led drivers many years ago and they are still used occasionally, but today I prefer the MCP1643 or similar ics, because you can achieve better performance.

author: paulie
author_rank: Frequent Contributor
timestamp: February 22, 2015, 04:43:53 am
content: Quote from: joeqsmith on February 22, 2015, 03:49:31 amI suspect it will take more than a "couple" 9v to supply "a few amps".

author: dave_j_fan
author_rank: Regular Contributor
timestamp: February 22, 2015, 07:30:02 am
content: Quote from: joeqsmith on February 22, 2015, 03:49:31 amvery nice .. from text i suspect joeqsmith=daveJones himself

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 22, 2015, 07:32:45 am
content: Hmm, you'd be able to run that a little while from a couple or more LiIon cells, but 9Vs aren't gonna cut it for power or energy capacity. You're probably not getting much more light out of the poor boy than mine!On the upside, a flashlight using one of those at ratings is probably a little *too* aggressive, anyway.Tim