Whats a simple analog method to light leds when current thru a load is at predetermined value?

This is for a strip of leds each lighting in 500uA increments with at least 8 leds which goes from 500uA to 4mA. The issue is the load isn't a constant value.

 

Comparators, a lot of them for 8 LEDs, and a current sense resistor. I'd consider an LM3914.

 

why not just use analog amp-meter

 

Comparators, a lot of them for 8 LEDs, and a current sense resistor. I'd consider an LM3914.

Does each comparator needs a current sense resistor?

 

they can share same current sense resistor but will need another voltage divider for each of them (unique setpoint), or ladder network

 

why not just use analog amp-meter

Its going to be faster and more accurate than an analog meter with more than 8 leds, which can be 1206 or smaller.

 

LM3914 ?

https://www.ti.com/lit/ds/symlink/lm3914.pdf




Just ignore the top two comparators if you want to stay with 8 LEDs.

Resistor that senses current for load should be low side sensing, calculate
off the ref value LM3914 has for the 500 uA resolution. Eg. the Vref/10 trip
level for first 500 uA in load.

(Vref/10) /.0005 = 1.28 / .0005 = 2560 ohms

If thats too high for load compliance issues scale it back and add an OpAmp
to gain up the input to the LM3914.

What is the accuracy you want in the system ?

Note this approach has all leds on when full scale, do you only want
one led on at a time ?

If so accuracy and solution fits a UP much better, low end, one that can also
do differential sensing of Rsense to get rid of any common mode problems.
Arduino with an IA or PSOC (has diff A/D input, Vref much more accurate).
The Arduino can be programmed in Block Language if you do not know C.
Kids are using Block language to program robots.

Some threads/post on block languages -

https://forum.allaboutcircuits.com/...ess-on-off-dual-function.130963/#post-1423271 Post #9 and beyond

https://forum.allaboutcircuits.com/...when-using-photoresistor.162364/#post-1423149 Post # 11 and beyond

https://forum.allaboutcircuits.com/...ntroller-dev-board.160538/page-3#post-1402777


Regards, Dana.

 

why not just use analog amp-meter

Probably it doesn't cool enough ...

 

Does each comparator needs a current sense resistor?

No. Since you appear to be driving the load with a current source, you just need to select a current sense resistor value that's appropriate for the available headroom. If you can tolerate at least 1.5V of drop from the sense resistor, using LM3914 is straightforward. If you can't, you'll need to amplify the voltage drop.