LED driver to run off 4.8V

Thread Starter

ian field

Joined Oct 27, 2012
6,539
I think Dennis was way too polite. You came here and asked if anyone had favorite circuit to solve your problem. You failed to provide many of the requested details. It appears to me that you already had a solution and were just here hoping that people would see how "smart" you are.

Thanks for wasting all our time.
Some people have a remarkable knack for appearing to be polite while being extremely aggravating. His suggestions were pointedly contrary to what I asked - and some of them were just plain wrong. I asked if anyone had a favourite circuit they were willing to share and he launched into a tirade of irrelevant detail that was pretty much opposite to anything useful - I did pretty well to remain polite as long as I did!

Actually I can't decide whether he's a troll or seriously dense.

After a lot of searching, I found a circuit that will do, its not of my own making, but looking at it I wondered why I didn't think of that - its in an ebook published for novices - so I'll let you draw your own conclusions from the fact no one here could suggest anything relevant.
 

Thread Starter

ian field

Joined Oct 27, 2012
6,539
You may be wasting your time with a buck converter. If the LED is 3.4 volts and the diode in the converter is .6, the current sense voltage .3 and maybe .5 for a FET and inductor it's a wash.
With a lot of searching I found this:-


http://www.talkingelectronics.com/projects/30 LED Projects/30 LED Projects.html

Listed in the contents is; 1Watt LED. This looks just the ticket - I'm not sure if its a buck or what it is, but it seems to have a fair bit in common with the hysteretic mode of operation.

Usually I like to study and compare several designs before deciding which one I like best, but I think the one in that ebook might be hard to beat. Still; its a good illustration of the type of thing I'm after.
 

ronv

Joined Nov 12, 2008
3,770
With a lot of searching I found this:-


http://www.talkingelectronics.com/projects/30 LED Projects/30 LED Projects.html

Listed in the contents is; 1Watt LED. This looks just the ticket - I'm not sure if its a buck or what it is, but it seems to have a fair bit in common with the hysteretic mode of operation.

Usually I like to study and compare several designs before deciding which one I like best, but I think the one in that ebook might be hard to beat. Still; its a good illustration of the type of thing I'm after.
Hmm, I don't get their claimed 85% when I simulate it. :eek:
But anyway here are 3 ways.
1- Resistor and LED - 249 mw LED 410 mw from battery - 60% - 26 hours
2- Talking elect. - 255 mw LED 395 mw from battery - 65% - 27 hours
3- Little buck - 270mw LED 355mw from battery 76% - 30 hours
 

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Thread Starter

ian field

Joined Oct 27, 2012
6,539
Wow... Just wow..

pot.kettle.black.
Not sure where you got that from - I'm notorious for telling it like it is.

It took considerable restraint on my part to not tell 324 to walk away with jerky movements after his first couple of replies.

He comes across looking like butter wouldn't melt in his mouth, but there's something decidedly pernicious about the way he acts dumb to foist suggestions that any fool can see aren't what was requested.
 

Thread Starter

ian field

Joined Oct 27, 2012
6,539
Hmm, I don't get their claimed 85% when I simulate it. :eek:
But anyway here are 3 ways.
1- Resistor and LED - 249 mw LED 410 mw from battery - 60% - 26 hours
2- Talking elect. - 255 mw LED 395 mw from battery - 65% - 27 hours
3- Little buck - 270mw LED 355mw from battery 76% - 30 hours
Thanks.

My build leaves out the diodes in the bias chain that cause it to shut off as voltage falls.

The (allegedly) low self discharge Ni-Mh cells I bought from Lidl seem very variable in performance, but some improve with deep aggressive cycling. Recently I took a couple of cells fresh out the charger for my Nikon camera - they just about charged the flash, then the camera shut down with low battery warning. Things have improved by when the cycle lamp puts on the low battery red LED, I leave it on overnight and swap fresh batteries in the next morning.

The one I assembled last night has been left running to get some idea how long 4x AA last, it doesn't have the same LED load as in the bicycle lamp and I can see the possibility of a tweak that might make it run a bit longer.

Putting that circuit together was a breeze - the nasty bit will be hacking the PCB in the lamp. If possible I'd like to keep the circuitry that latches on/off from a simple push button, the low battery warning LED would be nice too.
 

Thread Starter

ian field

Joined Oct 27, 2012
6,539
Hmm, I don't get their claimed 85% when I simulate it. :eek:
But anyway here are 3 ways.
1- Resistor and LED - 249 mw LED 410 mw from battery - 60% - 26 hours
2- Talking elect. - 255 mw LED 395 mw from battery - 65% - 27 hours
3- Little buck - 270mw LED 355mw from battery 76% - 30 hours
Whatever I finally chose doesn't have to be perfect. The original bicycle light uses a linear type dropper that may actually be no more than a resistor.

It gives me about 2 or 3 journeys with good brightness before I notice it starting to dim - its getting noticeably harder to see by the time the warning LED comes on. To charge cycle the cells I leave it on over night from that point, by morning its still producing light but wouldn't be useable.

Probably most switching types would give more consistent light for more of the discharge curve.

Its only recently that a second bought lamp failed, so I've only just got into properly pulling one apart and finding out the things I need to know. The one from the 30 LED projects is probably the simplest route to where I want to go.
 

ScottWang

Joined Aug 23, 2012
6,831
You are a helper here, I think you don't want to meet anyone say to you as you said to dl324, although he can't provide you the right answer, at least he push your thread to keeping on the upper line, he just tried to help you, you don't have to said those words to him, when you trying to help someone but you can't provide the right answer, please thinking deeper, do you hope you want the TS to say something bad to you?

Please be nice to anyone here, you are here to sharing your EE knowledge and learning something you don't know, you are not come here to creating the enemy and making trouble for other members and the forum, so please stop to say any bad words to anyone, our best wish, thank you ... :)
 

Thread Starter

ian field

Joined Oct 27, 2012
6,539
You are a helper here, I think you don't want to meet anyone say to you as you said to dl324, although he can't provide you the right answer, at least he push your thread to keeping on the upper line, he just tried to help you, you don't have to said those words to him, when you trying to help someone but you can't provide the right answer, please thinking deeper, do you hope you want the TS to say something bad to you?

Please be nice to anyone here, you are here to sharing your EE knowledge and learning something you don't know, you are not come here to creating the enemy and making trouble for other members and the forum, so please stop to say any bad words to anyone, our best wish, thank you ... :)
Sometimes some people just irritate me too much - as I've said elsewhere; I'm notorious for telling it the way it is.

While I try to be patient with people who become annoying, my powers of restraint ran out on that occasion.
 

ScottWang

Joined Aug 23, 2012
6,831
Sometimes some people just irritate me too much - as I've said elsewhere; I'm notorious for telling it the way it is.

While I try to be patient with people who become annoying, my powers of restraint ran out on that occasion.
You should learn to love the member who trying to help you, not to hate them, otherwise the members will keep away from you.
 

ScottWang

Joined Aug 23, 2012
6,831
There's help and there's 'help'.
If someone provided the info is not match what you want then you just say thanks, it's easy, t-h-a-n-k-s, why you get angry for, it will hurt yourself and other members who trying to help you or reading the posts, thinking in positive way will give you the positive energy, thinking in negative way will give you the negative energy, that will really hurt yourself, an EE man should be thinking in positive way to find out the methods to solve the problem ... :)
 

Thread Starter

ian field

Joined Oct 27, 2012
6,539
If someone provided the info is not match what you want then you just say thanks, it's easy, t-h-a-n-k-s, why you get angry for, it will hurt yourself and other members who trying to help you or reading the posts, thinking in positive way will give you the positive energy, thinking in negative way will give you the negative energy, that will really hurt yourself, an EE man should be thinking in positive way to find out the methods to solve the problem ... :)
That rarely happens.

Its when someone continually repeats the wrong suggestion and goes on to get ever further in the opposite direction to what was asked for.

That's a good example of what can wear out my patience.
 
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