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I would like to drive a lot of LEDs with the same current, so I decided to use a current regulator.

I am not sure which circuit is better for uniform current in all branches.

Should I use two separate R resistors or one common R/2 resistor?

As an example, I would have 4 current regulators with 12 leds together.

enter image description here

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  • \$\begingroup\$ What's the min and max forward voltage of your LED and how closely do you need the currents to match each other? \$\endgroup\$
    – winny
    Sep 23 '21 at 14:43
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    \$\begingroup\$ I think those resistors need to be separate, but you could almost certainly share the pair of reference diodes connected to the base of the transistors. The resistor from the diodes to ground would probably need to be decreased proportionally to the number of transistors sharing it. \$\endgroup\$
    – brhans
    Sep 23 '21 at 15:22
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    \$\begingroup\$ I started a simulation for you to simplify your circuit but I need to address the elephant in the room first. How come you need to run several strings in parallel? Why can't you just string all LEDs in series and use one boost converter? \$\endgroup\$
    – winny
    Sep 23 '21 at 16:47
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    \$\begingroup\$ @DanielŠebík The modern way is to use some boutique IC, as winny suggests, for a boost design that adjusts voltage on the basis of a measured current through the LEDs. But you can see a horse-and-carriage way here using BJTs. The current mirror complexity shown there is required as it is possible that one or more LED strings are broken or disconnected and in that case the mirror BJT for that string would otherwise upset the other mirror strings. \$\endgroup\$
    – jonk
    Sep 23 '21 at 18:27
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    \$\begingroup\$ That "switch LEDs on and off at frequency about 20kHz (25us on, 25us off" is vital information to be edited into the original question. \$\endgroup\$
    – winny
    Sep 24 '21 at 9:17

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