LED driver for control panel

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OK, another question that I should be able to answer on my own, but I'm not finding what I need. I'm building a control panel and want LED back lights for the switches. There are about 40 switches, and two modes of operation that I want to handle (white or blue) with a "shift" key. LEDs will probably be tiny surface mount devices so around the 4ma current range. Now here seems to be one of the biggest problems, I'm only using 5 volt supply power which seems to mean that I can't put several LEDs in series with each other and have the proper output.

I want to stay away from putting a pile of resistors into this design but if this is the only way, I'll consider it. Size is a little bit of an issue but I should be able to squeeze in an 0603 resistor for each LED in use and I can just use a transitor to turn the power for each back on or off with the shift key.

Also I do not have a data connection to control the driver chip, so it needs an on/off (enable) function. The back lights are simply all white on or all blue on (shift).

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You could run 2 whites and an R in series from 12V, and 2 blues and an R in series from 12V, and have one mosfet to turn on 40 20ma pairs of whites, and another mosfet to turn on 40 20ms pairs of blues. 800ma for whites or blues.

Imagecraft compiler user

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Trying to avoid building a 5 volt power supply but it is looking like I may need to run things on 12v. There is an ON-Semi controller that will do 4 channels and 3 LEDs in series on each channel at 12v and accepts an EN/PWM input which would let me control dimming. Thing is I'm starting to get into feature bloat.

Since these are 4ma LEDs (tiny 0603 size), I should be able to switch them on and off with relatively small components so I am kind of thinking about just going with a passive design even though it is wasteful. I should be able to switch them on and off fast enough to accomplish dimming and can probably do it with a simple 555 timer circuit with a user set pot for the control.

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Ah yes.. 555 strikes again

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The more math and thinking about this the more likely that I'll just use a 555, transistor or mosfet, and a pile of resistors for each LED so I can use the 5 volt supply.

Now the need to decide if I run a single PWM circuit for both colors or if I make two PWM to allow each color to be tuned individually.

Yes I know, another "primitive" circuit on a forum dedicated to microcontrollers, but this is part of the same project that the flip flop will go into and I don't have control over the processors used (yet).