Linear led driver - 4 channels

[onsovik]

Hi all,
I would like to ask you for help or ideas how to make a LINEAR LED DRIVER with 4 channels. I have prepared the circuit with MAX16823 IC which has 3 output channels and it works fine. (I have 8 LEDs in total, 3 LEDs per channel (3+3+2), current is 140mAmps). There is a problem when the solution must be changed to 4 channels driver because of input voltage test. The circuit has to work from 9V so the solution with MAX IC is out of date. (VF of LED is 3,4V and based on disscusion 3 LEDs per channel I ca not use). I tried to find another IC but without any succes. I was thinking about the solution with transistors + LM317 but I dont know how to do it in right.

Reguirements:
-4 channnels
-one IC only like mentioned MAX circuit or transistor solution
-linear driver
-input voltage 9-17V and 140mA
-if one channel has error, remaining channels can not work (The MAX circuit has a LEDGOOD pin to inform about the channels status - this point was fine)

I will be very gratefull of some advice or circuit proposal.

 

[KlausST]

Hi
I'm confused.
3 LEDs in series need 10.2 V. Independent of channel count.

It can not work wit 3 channels also, as long as there us no voltage boost circuit.

Specify the input voltage range to be 12 ...17V and you can use 3 LEDs in series.


Klaus

 

[onsovik]

Hi
I'm confused.
3 LEDs in series need 10.2 V. Independent of channel count.

It can not work wit 3 channels also, as long as there us no voltage boost circuit.

Specify the input voltage range to be 12 ...17V and you can use 3 LEDs in series.


Klaus

Yes, you are right. I did not mention that circuit works fine from 11V, so I had to change the configuration to 4 channels and this one of the reasons why I can not use verified circuit.

 

[BradtheRad]

It sounds as though you want to control 4 lines, independently, from 3 pins?

You could send binary 00, 01, 10, 11. That is 4 possibilities. Then assemble a bunch of logic gates to decode these data. You'll have 4 independent outputs. This is a 1-of-4 detector.

Hmmm, I'm wrong. You do not have independent control. Only one led can be on at any one time.

You need a 1-of-16 detector, to handle all combinations. This would require 4 input wires.

However you want to do it from fewer wires. I think the solution is to turn on a timed power source to an led, and have it stay on for, say 2 seconds. Rotate an 'On' pulse to each led in turn (only the led's you want to be on), once per second. This method will require only 2 control wires.

 

[kam1787]

.................. There is a problem when the solution must be changed to 4 channels driver because of input voltage test. The circuit has to work from 9V so the solution with MAX IC is out of date

I do not understand. Specification sheet says the IC works with supply voltages up to 40V. Min is 5.5V

https://datasheets.maximintegrated.com/en/ds/MAX16823.pdf
https://www.maximintegrated.com/en/products/power/led-drivers/MAX16823.html

 

[onsovik]

It sounds as though you want to control 4 lines, independently, from 3 pins?

You could send binary 00, 01, 10, 11. That is 4 possibilities. Then assemble a bunch of logic gates to decode these data. You'll have 4 independent outputs. This is a 1-of-4 detector.

Hmmm, I'm wrong. You do not have independent control. Only one led can be on at any one time.

You need a 1-of-16 detector, to handle all combinations. This would require 4 input wires.

However you want to do it from fewer wires. I think the solution is to turn on a timed power source to an led, and have it stay on for, say 2 seconds. Rotate an 'On' pulse to each led in turn (only the led's you want to be on), once per second. This method will require only 2 control wires.

Thanks for answer, but I have only 2 input wires (power,GND). I can not use any other wires like diagnostics. What the circuit has to do is switch off all the LEDs when one channel is wrong.

- - - Updated - - -

I do not understand. Specification sheet says the IC works with supply voltages up to 40V. Min is 5.5V

https://datasheets.maximintegrated.com/en/ds/MAX16823.pdf
https://www.maximintegrated.com/en/products/power/led-drivers/MAX16823.html

Yes, but the MAX16823 is designed for 3 channels and I have 8 LEDs which I wrote at the beginning. If the input voltage will be set to 9V I am not able to run the circuit properly. There will be 3LEDs in series (3x3,4V) and this value is more than 9V and I do not calculate with the losses on power transistor etc. 4channel IC dos not exist only solutions with 8channels.

 

[onsovik]

I do not understand. Specification sheet says the IC works with supply voltages up to 40V. Min is 5.5V

https://datasheets.maximintegrated.com/en/ds/MAX16823.pdf
https://www.maximintegrated.com/en/products/power/led-drivers/MAX16823.html

Yes, but the MAX16823 is designed for 3 channels and I have 8 LEDs which I wrote at the beginning. If the input voltage will be set to 9V I am not able to run the circuit properly. There will be 3LEDs in series (3x3,4V) and this value is more than 9V and I do not calculate with the losses on power transistor etc. 4channel IC dos not exist only solutions with 8channels.