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Temperature independent constant current with fast transient response to PWM ?

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Ian.M:
Coarse set the current by changing the sense resistor R2.  There's currently 12R and 1.8V across it so try 27R for nominally 66.6mA.  Fine trim the current to 70mA using the potential divider (+/-0.1V there is approx +/-5% ILED).  Uncomment the .op and fine temperature sweep and comment out the .tran and coarse temperature sweep to let you assess the effect of R5.  Hint: it helps to manually add a trace 150mA or whatever your desired LED current is to make it easier to see how close to the target it is.  It may well not even need changing.  In real life, you'd ball-park it in the sim, then set up a resistor substitution box to let you change R5 with the unit in a freezer, at room temperature and in a hot-box, so you could test several values without having to heat and cool the board each time.  Changing R5 also changes the current a bit, so once you've found the value that's most stable across the desired temperature range you'll need to tweak the divider to bring it back on target.

Heisen:
Finally, I got it. Works so good.
Thanks once again.

Jay_Diddy_B:
Hi,

What is the accuracy required here?

There is variation in light output from LED to LED even at the same current (even with binning).

There is variation in light output with the junction temperature of the LED.

A constant current with temperature may not be required or desired if you want to maintain constant LED brightness.

Regards,
Jay_Diddy_B

max_torque:
Why do you actually need the LED current to be "square"?  What is the purpose of the LED array (in what you say is an automotive environment)?  If it is a "visual" array, ie it will be seen by the human eye, then you very much need to account for the response of the human eye to "brightness" which is both highly non linear but also acts as a low pass filter (our eyes effectively integrate photons).

So given that you'll need to tune "apparent brightness" to "duty cycle" why do you care what the profile of the current looks like?


(obvs if this is some form of LED array for data transmission, reflectometry, or similar then yes, you may well care about the exact current profile)

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