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TIP127 current calculation....

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Hi again,

Ok so you've got to handle 2.5 amps now we know the full current load, which says a lot about this project.

If i sounded like i was a little against using a Darlington for this project before then let me update that to state that now i can see that it is definitely time for the Darlington to go. That particular device can drop as much as 4 volts and at 2.5 amps that means we'd have to get rid of 10 watts of heating power! That is far too much for such a simple project like this in this day and age. If you listen closely, you'll hear the cries of a MOSFET coming into play here <chuckle>.

You can a get high current logic level MOSFET that would handle this on/off chore in a heartbeat with very little power loss. Of course that shifts the burden of current limit to the current limiting resistor(s), but that's really where we want it anyway. That way we can use a separate resistor for each LED string and that means less power per resistor too. And the logic level MOSFET (N channel) means we can drive it with the uC pin or with a cheap tiny two transistor driver and get good results with a frequency that isnt too high (if we also want to use PWM). It's easier to go with low frequency anyway when using a uC for PWM.

So the best solution is probably to use an N channel MOSFET logic level transistor and try driving it from the uC pin itself and dont go over about maybe 5kHz if you decide to PWM it. Use separate resistors for each LED string and i think you will find this to work exceptionally well. Choose a nice high current MOSFET for low dissipation there. If the MOSFET gets hot driving from the uC pin alone then use a two transistor driver (two small transistors, schematic to follow).
 

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MrAl...

Gas - Petrol
Hood - Bonnet
Fender - Wing
Eraser - Rubber
Fag - Cigarrette
Flashlight - Torch

All part of the vast semantic differential spanning the Atlantic Ocen.
 
Hi Jim,

Yes, but didnt the "torch" analogy come in fairly recently as compared to the rest?

Here's the two transistor driver again for reference as i did not get it into the original post right away:
 

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MrAl

The thing which you guys in the USA refer to as a "flashlight", in the UK it has always been referred to as a "torch", at least during my 64 years on this planet.

Similarly a device used by a welder* would also be referred to as a torch.
Both oxy-acetylene and MIG.

JimB
(Derailing the thread, but I cannot help it, AG made me do it!)
 
Here is similar oval led **broken link removed**
As I suspected, when the ambient air is air-conditioned so it is 25 degrees C, the maximum allowed continuous current is 50mA but they recommend 10mA to 30mA. The maximum allowed peak current is 200mA for extremely short duration not very often.
The spec's are at only 20mA.

Cree is a trusted name-brand, your LEDs might be cheap copies that melt above 30mA.
 
MrAl

The thing which you guys in the USA refer to as a "flashlight", in the UK it has always been referred to as a "torch", at least during my 64 years on this planet.

Similarly a device used by a welder* would also be referred to as a torch.
Both oxy-acetylene and MIG.

JimB
(Derailing the thread, but I cannot help it, AG made me do it!)

Hi Jim,

Oh ok well that is very interesting. I wasnt sure about other places but here i only recently heard it being called a torch so it's new to this country i think, maybe in the past 10 to 15 years (time approximate) when LED's started to become popular. So it is interesting that you guys have been calling it this all along maybe since the introduction of the flashlight itself. Maybe it was then when they carried over the lighting aspect of it and didnt worry about the heating aspect of it.

I used to hate history but now i really like hearing about this kind of history and the way the language followed it so thanks much for informing me about this. This tells me it is not only for flashlight enthusiasts in the USA (who i believe only adopted this recently as noted) but for other people in other countries who must have been using this for a very long time.

When i look the word up i see definitions mostly talking about flame torches made from one form of wood or other combustible material, and i also see the "Chiefly British" definition as "Flashlight".
 
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Ronnie Biggs just left us, but when he and his mates pulled off the great train robbery all those years ago, they camped out in a house. According to the court case, they got sprung because of some evidence the fuzz found in the house. Some of the gang wanted to TORCH the house to get rid of evidence, but they didnt do it, but IF they had TORCHED the house, they may have never been convicted.
Ronnie of course escaped and finished up in this city, Melbourne, from where he fled to Rio.
Dont worry about derailing this thread Jim; it was defunct at about post 30. When it is asked for LED data and what is presented is here is; 'some cree data which is something like what I got(I think)', then we can assume that OP's attention to detail is somewhat lacking, so why worry.
 
I doubt that genuine CREE LEDs are available in India. He said in post #60, "Similar to these CREE LEDs".

I bought a bag of cheap blue LEDs made in India. Half worked and the other half even looked like they won't work so there was obviously NO Quality Control.
 
Hi,

Hasnt it been now established that the maximum output current (for all LED's) would be 2.5 amps?

Correct this if it is wrong, thanks.
 
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