[sdiy] Switching leds on a constant current source

Rutger Vlek rutgervlek at gmail.com
Sun May 31 20:24:07 CEST 2015


Hi guys,

I'm working on a LED driver that switches between 16 different LEDs with a 4067 analog switch. As I'm using a mix of different LED colors I'd like to stabilize the current thru the LEDs and the current draw from the supply by using a constant current source. From Douglas Self's small signal design book I obtained a nice certain, and I'm trying to fit the 4067. However I've been wondering if this switch will defeat part of the purpose of using a constant current source, as switching disturbs the path for the current to flow ( some 4067 data sheets  guarantee it's break-before-make action, while others don't). I've tried making a parallel path to the switch, so the current can flow somewhere when the switch is not closed to connect any LED, but this didn't work out too well (the resistance of this parallel path should be high enough for the LED path to draw most current away from it's when the switch allows the LED to light. On the other hand, a high resistance changes the load on the current source too much. Bleh!).

Any advice?

Rutger

ps. Sorry if this message arrives twice on the list. I had sent it a couple of days ago, and didn't see it occur on the list, nor any replies to it. So resending it to be sure....


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