# how to find equations for current of circuit with transistors?

using Ohm's law, i need to find the current for $$I_C , I_B$$ in terms of: $$V_B, V_C, V_{DC1},V_{DC2}$$ for the following ciruit. my solution is: $$V_{DC2}+{I_B}{R_B}={I_C}{R_C}+{V_{DC1}}+{V_E}$$ But this seems to be wrong. why? Thank you

• You're overthinking this. Notice that $I_C$ is the same as the current through one of the resistors. And you can write Ohm's law for this resistor in terms of two of the voltages you are given. Same thing for $I_B$. – The Photon Apr 28 '16 at 2:19
• You need the DC current gain of the transistor. – soosai steven Apr 28 '16 at 2:20
• @soosaisteven, no he doesn't, if he's allowed to take the node voltages as given. – The Photon Apr 28 '16 at 2:21
• @The Photon Do you mean that i can simply make $$I_B=V_B/R_B,,I_C=V_C/R_C$$? Thank you for your response – Hasnain Ali Apr 28 '16 at 2:26
• No, $V_C$ is the voltage between the collector node and ground, and the resistor is not connected between those two nodes. – The Photon Apr 28 '16 at 2:27

You can get $I_C$ very simply as
$$I_C = \frac{V_{DC1}-V_C}{R_C}$$
You can get the current for $I_B$ by a very similar statement of Ohm's law for $R_B$. I'll let you do that part yourself.
In the real world, of course, this has nothing to do with how you'd find $I_C$ in a real circuit, so just give your instructor the answer he wants but don't imagine you're learning much from it.