SMD LED Constant Current Driver Project.

Hi All,

My first post here.

I'm trying to build a 20mAh-30mAh constant current driver for SMD LED's for my Micro RC Helicopters. I found these SMD 10mA chips from Infineon...the info says they're easily used in parallel to increase current. I tried stacking them and the current didn't increase.

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What am I missing?

Here's a little video of the little scale RC Helicopter projects I'm working on.

YouTube - CB100 MD500E CHP Build Log Stage 11: Flying the Finished Project

Any help would be greatly appreciated.

Regards,
John

What's wrong with just using a resistor?.

But if you want to use the chip, just add an external resistor to set the current, as shown in the page you posted.

You don't "stack" them to increase the current, you put the outputs in parallel.

But just use an external resistor (Rext) to increase the current as Nigel suggested.

Hi guys,
I'm an architect and building contractor by trade, I'm pretty ignorant regarding electronic schematics. Thanks for your help.

Nigel Goodwin said:

What's wrong with just using a resistor?.

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Nigel,
These little helicopters are very weight sensitive. My gaol is to build a complete 8 LED light set weighing 2 grams or less, a resistor for each LED would just weigh too much.

crutschow said:

You don't "stack" them to increase the current, you put the outputs in parallel.

But just use an external resistor (Rext) to increase the current as Nigel suggested.

Click to expand...

Carl,
I think I'm getting a better understanding of how these chips work.

Thanks again to you both for your help, it is greatly appreciated.

I hope to have time tomorrow to experiment based on my newly gained knowledge, I'll post my results.

Regards,
John

Hammer said:

My gaol is to build a complete 8 LED light set weighing 2 grams or less, a resistor for each LED would just weigh too much.

Click to expand...

You can buy small surface mount resistors that weigh virtually nothing, much less than the weight of the LEDs or the IC.

Just use a surface-mount components to make this circuit. Connect the 4k7 to positive rail for continual output:
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I have SMD resistors I can barely see! My 0402 resistors weighs only 0.0010 grams - surely this isn't too heavy?

Even a big 1206 thick film SMD resistor is only 0.016 grams!

Simpler Cct added to #6