Hi there!
I'm very new to electronics but I have been trying to build a transistor based amplifier to amplify a signal.
I've attached an image of my circuit
, which I designed in LTSpice.
It has a power rail of 55V and an input signal of 0.64 V peak-peak, giving a gain of around 50
.
I've built this circuit on a circuit board, however I can't seem to get it working with a 55V power rail. Whenever I increase the voltage above 35V the current draw becomes too large (it starts running away to upwards of 800 mA!), which is a much larger current draw than I'm expecting based on the models (500mA).
.
I'm using high power transistors, NPN: TIP 3055 and PNP: TIP 2955, which have a max base current of 7A and a max collector current of 15A. They get very hot when I turn the circuit on (I am using heat sinks) and once the current starts to run away above 35V the power supply shuts the circuit down (due to inbuilt safety feature).
I can't understand why this circuit isn't working at the full 55V power rail and why it is drawing such a large current? Is anyone able to explain this to me and suggest a way I could get the circuit working?
If you have any other ways I could get an amplifier working with a gain of over 50 with an input voltage of 0.64V that would also be appreciated!
Many thanks!
Olivia