# Determining Thevenin Equiv. Circuit & R Load for Max Power Transfer

• airkapp
In summary: Additionally, the resistor is in series with the current source, so its contribution to the current is also 0 (again due to the current source's disablement). So, the only thing that affects Rt and Vt is the value of RLOAD. Since RLOAD is the only thing that affects Rt and Vt, you can ignore the value of R1 when inputting the values into multisim.
airkapp
I'm trying to determine the Thevenin equivalent circuit for the attached circuit. Also, the value of the load resistance R load for maximum power transfer. I'm not to sure how exactly the Thevenin theorem operates but I simply added my resistor in series and parallel (where appropriate). I suppose that gave me "R equivalence" which equaled 15 ohms. Not sure if that is correct after shorting out the voltages and open the currents (zeroing out). Can someone help figure the "load resistance for max. power transfer?" I'm attaching the diagram here.

thanks,
air

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The Thevenin resistance is easy to find, you disable the current (turn it into an open circuit) and voltage sources (turn it into a short circuit), and then find the equivalent resistance across RLOAD (removing the resistor RLOAD itself of course). So you get Rt = R2 // R3 = (20^-1 + 45^-1)^-1 = 13.85 ohm.

To find the Thevenin voltage, one way is to find the open circuit voltage across where RLOAD (again RLOAD itself is removed), by using superposition. The voltage across RLOAD due to the current source only is 0 (the disabled voltage source provides a path directly to ground). The across RLOAD due to the voltage source is 20/65 * 6 V = 1.85V (by voltage division).

The value of RLOAD for maximum power transfer equal to the Thevenin resistance, which is 13.85 ohms.

s_a said:
The Thevenin resistance is easy to find, you disable the current (turn it into an open circuit) and voltage sources (turn it into a short circuit), and then find the equivalent resistance across RLOAD (removing the resistor RLOAD itself of course). So you get Rt = R2 // R3 = (20^-1 + 45^-1)^-1 = 13.85 ohm.

To find the Thevenin voltage, one way is to find the open circuit voltage across where RLOAD (again RLOAD itself is removed), by using superposition. The voltage across RLOAD due to the current source only is 0 (the disabled voltage source provides a path directly to ground). The across RLOAD due to the voltage source is 20/65 * 6 V = 1.85V (by voltage division).

The value of RLOAD for maximum power transfer equal to the Thevenin resistance, which is 13.85 ohms.

okay, I understand what you did, but I do not understand why you ignored the R1 value? Also, do you know how to input RLOAD into multisim?

thanks,
Air

airkapp said:
okay, I understand what you did, but I do not understand why you ignored the R1 value? Also, do you know how to input RLOAD into multisim?

thanks,
Air

When you open the current source, no current flows through R1, so it can be dismissed from the calculations of Rt and Vt.

## 1. What is the Thevenin equivalent circuit?

The Thevenin equivalent circuit is a simplified representation of a complex circuit, consisting of a single voltage source and a single equivalent resistance. It is used to analyze the behavior of a more complex circuit without having to consider all of its individual components.

## 2. How is the Thevenin equivalent circuit determined?

The Thevenin equivalent circuit is determined by finding the open circuit voltage (Voc) and the equivalent resistance (Req) of a circuit at two terminals. Voc is the voltage measured across the terminals when there is no load connected, and Req is the equivalent resistance seen from the terminals when all independent sources are turned off.

## 3. What is the purpose of determining the Thevenin equivalent circuit?

The Thevenin equivalent circuit is used to simplify complex circuits and make it easier to analyze their behavior. It is also useful for finding the maximum power transfer to a load, as the Thevenin resistance can be adjusted to match the load resistance for maximum power transfer.

## 4. How do you calculate the Thevenin resistance?

The Thevenin resistance is equal to the equivalent resistance seen from the terminals when all independent sources are turned off. This can be calculated by removing all independent sources from the circuit and using techniques such as series and parallel resistances to simplify the circuit and find the equivalent resistance.

## 5. What is the maximum power transfer theorem?

The maximum power transfer theorem states that maximum power will be transferred from a source to a load when the resistance of the load is equal to the resistance of the source. In other words, when the load resistance is equal to the Thevenin resistance, the maximum amount of power will be transferred from the source to the load.

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