Function of this diode....image included

[xwarp]

I'm drawing a blank on the function of the diode, but I'm going to guess it's suppose to help turn the transistor off?

 

So the open end of R3 has a either a low input, or, +5 via a pullup. VDD is +24 vdc

When the circuit it "on", it provides +24 vdc from VDD through the collector to another circuit.

Help me remember what I've forgotten, or, what I never knew.....lol

Thanks!

[GromBeestje]

What kind of load is this circuit supposed to drive?
If it is some inductive load, it might be a flyback diode.  If you remove the power from an inductive load it will generate a voltage in the opposite direction. A flyback diode will allow that surge to be dissipated. Otherwise it will blow up your transistor.

[Nusa]

Generally it's there to protect the transistor from feedback. In some transistors, it's integrated in the transistor package.

[graybeard]

If the base-collector junction becomes forward biased by a difference in the collector voltage and vid the diode will turn on preferentially since it has no external series resistance and prevent and significant current flow in the base-collector junction.  However since the entire circuit is not show it may be there for other reasons.

[xwarp]

I unfortunately do not have the schematic for the circuit this output supplies.

The input of the circuit that the VDD output goes to begins with several resistors. I believe to be essentially voltage dividers, so essentially a resistive load.