Hello,
I'm using a tv-b-gone sketch that send out tv codes through a universal 5mm IR led, and instead using that led I'd like to use a large one and drive it at 1 or 1,4 amp with a NPN transistor.
Is this the right way ? If yes, how can I calculate the resistor ?
Thanks !
Is this the right way ?
No.
For such a large current you will need a constant current driver. Google for schematics.
Trying to blind everyone nearby?
No, that is not the way. Use a current-controlled driver to keep the LED from going into an overcurrent runaway situation.
Example:
Sounds like a job for a CAT4101...
CAT4101 underpowered for the stated current:
"The CAT4101 is a constant?current sink driving a string of
high?brightness LEDs up to 1 A with very low dropout of 0.5 V at full
load"
OP said "1 or 1.4A" and the subject is "Power 1A led", CAT4101 can satisfy that specification.
Diagram show 1400mA tho and CAT4101 will not meet that.
BD9207FPS with 1.5A capability will meet 1400mA.
CAT4101 is less pricey and needs fewer components, so if 1A is enough, it'd be the way to go.
Still not sure why so much IR is needed. Need some shades on when that puppy is fired up!
Note that that much IR can damage your vision with out you knowing because you can't see it.
Thanks for answers, I don't understand yet the need for a constant current driver.
Sure the IR danger is an issue :~ need to think about that and reduce the power.
The main purpose of the thing is to turn off a TV from far distance. The ir led blink fast, around 44khz for 3 sec.
I though even if the led sometimes draw 500mA or 1,5A for that short time the thing will work, the led handle more than that. Well thinking about danger may-be I'll only drive it at 300mA, it should be enough.
But is the constant current driver necessary or just the proper way ? Why wouldn't it work with the bare transistor ?
Thanks for your reading and help !
Why wouldn't it work with the bare transistor ?
Because there is nothing to limit the current. Read this about why you need to limit the current:-
http://www.thebox.myzen.co.uk/Tutorial/LEDs.html
But with over 100mA then a resistor is not sufficent and you have to go with constant current because the forward voltage drop of the LED changes a lot with temperature ans with LED age.
for that short time the thing will work, the led handle more than that.
You might know what this wonder diode is but you have not seen it fit to tell anyone what part number we are using so it is hard to say if you are right or not.
The ir led blink fast, around 44khz for 3 sec.
Bit of an over simplification and anyway most remotes work at 38KHz