a testing sorce for this circuit..

https://i48.tinypic.com/2je2omq.jpg

i need to find thevenin representation for this circuit
i found that [latex]V_{th}=I_3*7[/latex]
all the sources are dependant so we need to connect a testing source of 1 volt and see what current comes out

but here i have step function
so it could be 0 or 1 depending on the time

i dont know how to do it here
and there are inductive components

which represents differential equations and stuff which has nothing to do with finding the current that flow threw it)

Well, maybe the best way to obtain the answer is with superposition of each dependent source (yeah, this is possible) and then obtain the final answer adding the individual solutions.

Since there are dependant and independant sources present within the circuit, the best approach would be not to apply a 1 volt test source.

Instead you should open circuit the terminals of the network and solve for the voltage, Voc. Then you should short circuit the terminals and calculate the current that flows, Isc.

The thevenin resistance is defined as Voc/Isc.

I think this approach should be possible. Now solving for these values could be a pain, involving inductors etc.

Linear superposition, as previously stated, could be a viable option.

The option Boron gave is an alternative to obtain the thevenin resistance, but it should only be used when there are independent sources. In this case adding a voltage source is the correct form to obtain the answer you want. By the way, the circuit you are solving is a BJT transistor with a lot of components. Hope this helps.