# From where is this thevenin equation derived?

The equation is:

$I_{in} = \frac{V_{th} - V_{in}} { R_{th}}$

This equation is from a one-port network.

Variables:

I = input current

Vth = thevenin voltage

Vin = input voltage

Rth = thevenin resistance

• Where is the schematic? Jun 15 '17 at 23:50
• @dirac question edited.
– 21rw
Jun 15 '17 at 23:55
• You added a single line, without a schematic. What did you miss about "where is the schematic"? Jun 16 '17 at 0:10
• @Jashazun I'm sorry. Reedited the question.
– 21rw
Jun 16 '17 at 0:14

Regardless of what is connected to the port, if the input voltage is $V_{in}$, then you can see the voltage across the thevenin equivalent resistor is $V_{in}-V_{th}$, so the input current can be obtained from Ohm's law as
$$\frac{V_{in}-V_{th}}{R_{th}}.$$