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Re: PCB Milling - Illumination disk and Limit Switch boards

Posted: Mon Aug 12, 2013 7:55 pm
by veng1
I agree: Why the cap?

It is not the best protection for LEDs. They are current operated devices and the resistor tends to protect against that. Instantaneously they will stand huge positive current spikes essentially to the limit of the bond wires. If you are worried about very high voltage spikes a Transorb or even a Zener after the resistor is better protection.

I'd be more concerned about negative going spikes around an inductive load and LEDs are not well suited to that kind of punishment. A free-wheeling diode, i.e., parallel between Vcc and ground would be a good idea or a bidirectional Transorb. That is the best of both worlds and will allow PWM in the future.

On the other hand, many white LEDs today have an internal reverse Zener for human body model ESD protection.