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Indicator LEDs and final tests

The PSU project is so close to finishing now I can almost smell it! (solder fumes or magic smoke?) I have learned so much along the way and as usual one of my favourite quotes bubbles up to the surface of my mind:

“There is no such thing as a problem without a gift for you in its hands. You seek problems because you need their gifts.”

Richard Bach (Illusions)

One of the remaining challenges I set myself is to provide an indicator LED for when one of the regulator circuits is live. So for instance if the 5V circuit is live, I'd like a visual indicator.

After a few trials, I used a simulator to narrow down the components required, centering on the BS170 mosfet. The reason I chose a mosfet and not my old favourite the SS8050 BJT is that a mosfet gate is triggered by voltage whereas a BJT base responds to current. 

So theoretically, as soon as the transistor gate senses voltage in the circuit above it's threshold voltage, it should let current flow to the LED.

The gate threshold voltage for the BS170 is typically around 2 volts and as I'm not asking for any voltage below 3.3V then it should be fine to trigger the LED in the circuit as shown.

After wiring up the components as shown in the diagram above, I was able to turn on the regulator and see the indicator LED, even under load.

Choices for the LED resistors are centred around Ohms Law and, using 10mA as a benchmark, should be as per the following spreadsheet snapshot:

After all the testing the concept seems quite sound, so now the final stretch of this <long> project is to box the whole shebang in a 3D printed housing, throw the switch and stand back!