I tried this. According to Ohms Law R=V/I. Firsty, i put on input 8.4V (on 75u inductor) and the input current was 6.3A meaning that resistance is 1.33 Ohms. When i put as input 6V the current was 9A meaning that resistance is 0.66. So i think that something is wrong.Ohm's Law establishes a relationship between three quantities. If we know the values for two of them, the third one is determined.
I would like to calculate the resistance of the whole circuit. According to this method and changing load from 4 to 3 Ohms resistance was calculated to 0.12 Ohms that seems strange.You change the value of the load slightly and observe the change in voltage.
The equivalent output resistance is then the change in voltage divided by the change in output current.
Yes, but in both cases that i considered to perform crutschow's calculation, my circuit transforms the input voltage to standard 12V output. So i mean the circuit is on same operating range.Your circuit is not a resistor. For example, with 0.1 volts in no current is drawn so the resistance appears to be infinite. You need to choose part of the operating range over which you perform crutschow’s calculation in post #7 to find the circuit’s dynamic resistance.
You're going about this ALL wrong.I tried this. According to Ohms Law R=V/I. Firsty, i put on input 8.4V (on 75u inductor) and the input current was 6.3A meaning that resistance is 1.33 Ohms. When i put as input 6V the current was 9A meaning that resistance is 0.66. So i think that something is wrong.
The circuit has effectively been linearized about an operating point, and the TS asked for an "equivalent" resistance, which seems like a reasonable request. He is just having some difficulty with the volume of data being thrown at him.Resistance only has meaning for a linear load. Or over a very narrow, specified range.
If you want to know what resistor would load the power source as much as this circuit, It is as simple as knowing the efficiency and the output power. That tells you the total power drawn. Then with the power supply voltage, calculate the current draw. Resistance is the ratio of voltage to current.
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by Jake Hertz
by Jake Hertz