Why is GND always switched for LED's?

[mth5044]

Stupid question, but is there any reason that it is always the ground on the cathode of an LED that is being switched when it comes to bypass indication? When you have a grounded input on the switch, it makes sense because the GND connection is already present, but is there some other reason? Does breaking the + supply cause popping?

Danke.

[R.G.]

It isn't always ground that's switched. I've used the anode side switching many times.

However, switching to ground is convenient. I suspect that's why it's used so often. Well, actually, I suspect that it's switched to ground so often because that's what someone sees in a schematic somewhere and that's what they do. But convenience is probably where it started, long ago.

It's worth noting that it doesn't make any difference to the rest of the circuit whether you interrupt the anode or cathode side if you're switching something in series with the LED. External currents and voltages are the same.

[acromarty]

It may go back to driving LEDs from TTL logic outptus.
TTL chips could sink much more current into a low output than they could source from a high output, so it was more convenient to connect the logic output as an active-low sink directly to the LED cathode. Driving the anode of an LED high needed an extra buffer to get the required current.

[ORK]

The ground is not switched at all; the LED is switched! Fun aside: the important thing with switching the LED to ground is the fact that you can use a simple mono grounded jack/cable for remote switching! Current limited even.

[mth5044]

Nice info, thanks!