One transistor square wave amplifier: why doesn't it work?
Your circuit is wrong. You did this:
- So the transistor and the resistor needs to be interchanged
- you need a additional resistor to limit base current
Try it like this:
PS: the calculations are simplified and not 100% correct. but good enough to transport the principle
You are doing high-side switching when you should be doing low-side switching.
Think about what voltage you want the emitter of the transistor to be. Now, think about your base voltage in comparison to this voltage. As you can see, you will have a hard time forcing current into the base-emitter junction if the base is 12 V and the emitter is nearly 100 V!
Now swap your load and transistor and see how this changes. With the emitter at ground and the base at 12 V, it should be much easier to activate this transistor. Keep in mind, you will need a resistor to limit base current in this configuration.
Always remember you need current flowing through the base for a transistor (BJT anyway) to work. That current has to go somewhere, and if the collector and emitter are both over 12 V, there is no way a 12 V signal at the base is going to be able to go anywhere.
You have built an emitter follower, and that is how they work. Switch the load to collector side, which seems to be what you want.