EXPERIMENT NO. 10
1. To verify the Thevenin’s theorem through an experiment. 2. To find the Thevenin’s resistance RTH by various methods and compare values.
Resistors, DMM, breadboard, DC power supply, and connecting wires.
Thevenin theorem states that any linear two-terminal circuit can be replaced by an equivalent circuit consisting of a voltage source VTH in series with a resistance RTH where
* VTH is the open-circuit voltage at the terminals, and
* RTH is the equivalent resistance seen thru the terminals provided that all the independent sources are turned off.
Determining the output voltage Vab in open-circuit condition (no load resistor meaning infinite resistance). This is known as the Thevenin voltage VTH. * i.e. VTH = Vab = VOC (open-circuit voltage)
There are different methods to find value of RTH as described below.
1. Method A:
(By measuring ISC – short-circuit current)
Short the points ‘a’ and ‘b’, then measure the short-circuit current Isc using an ammeter. Calculator RTH as follows
RTH = VTH/ ISC
(By measuring the equivalent resistance)
Remove all sources from the circuit, i.e. replace all voltage sources with a short-circuit and current sources with an open-circuit. Then with the help of a multimeter find the resistance between the points ‘a’ and ‘b’, denoted by Req.
RTH = Req
(By applying known voltage and measuring source current).
We can also find RTH by applying a known voltage to the circuit between points ‘a’ and ‘b’, then measuring the current from the voltage source. Suppose 1 Vdc is applied as the test voltage then,
RTH = Vtest / I
4. Method 4:
(By inserting two different resistors and measuring current) There is another method to find the value of RTH, by inserting two different loads between points ‘a’ and ‘b’ i.e....