Electronic – LTSpice Simulation – How to design pulldown with voltage supply

ltspicesimulation

I am trying to simulate a circuit which should pull the supply down.
circuit snippet

Problem here is, that the supply is a not current limited and the whole voltage is dropping accross the 0.1Ohm RC of Q4 and the voltage doesn't go down.

Is there a voltage component which behaves like the way I want to? Or what is the right way to simulate a pull down behaviour?

What I want to do, is shorten the supply with the GND when the transistor is in saturation.

Edit 1:
For the comments and Arisers answer:
After your input I saw that it would be better to name the question: How to design a non ideal voltage source and limit its current.

Best Answer

You have to put some amount of resistance in series with your voltage source. The simulator is giving you an "ideal" source, while any physical source will have some nonzero amount of source resistance.

You can also add a hard current limiter made from a current source and an ideal diode:

schematic

simulate this circuit – Schematic created using CircuitLab

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