For a school assignment, where I had to control a DC Motor, were no diode's available for the flowback circuit. I looked up online how to use a transistor as diode, which then subsequently burned out.
Some details.
PSU is 12V
While the transistor burned, the motor was running
The circuit was functional in the tinkercad circuit simulator
The transistors are both of type BC337
Please see diagram below for the circuit
If any one could help me in troubleshooting this issue, it would be greatly appreciated.
OK, the lesson on using a transistor as a diode - don't!
Just go get a pack of 1N4004s (or equivalent number).
Why does it not work? Well, the base-emitter junction has a breakdown voltage of around 6 to 8 V. Minimum specified as 5.0 V for a BC337. And - it is breaking down if you connect it to 12 V.
Transistors may be used as a diode in such configuration. For example it is (used to be) used in temperature sensing circuits. I am not sure what are advantages over normal diode, maybe only easier implementation inside an IC.
Maybe you could use collector base junction as the flyback diode, leaving the emitter open. But ofc real diode is better solution.
If you know how a diode is made, you will know that it is 2/3 of a BJT transistor. It is a PN junction, where a BJT adds a third doping. That is why they are called bi-polar (think two diodes that share a common doping). I think that is what your instructor may be trying to reinforce, but I wouldn't do this outside of a classroom exercise. At any rate, your NPN transistor should be placed in the circuit with the P-junction tied to the positive, i.e. the base, and the N-junction tied to the negative, i.e. the emitter. The collector is left open.
The base-emitter junction has a very low breakdown voltage reverse biased, a few volts - this is the easiest
way to fry a transistor - basically never reverse bias the base-emitter junction.
The base-collector junction can handle voltage, but is very low current, so don't use that either.
Don't use a transistor as a free-wheel diode, use a diode as a free-wheel diode...