Articles for the ‘Thevenin's Theorem’ Category

The Common-Collector Amplifier Input and Output Resistance – The Proof

Monday, October 12th, 2009

Summary:

In this article I will show a method to deduce the input and output resistance of the common collector amplifier. The common-collector amplifier is a well known circuit (see Figure 1). It is mostly used as a buffer due to its high input resistance, small output resistance and unity gain buffer. The equations derived in this article are symbolic, as is the derivation of any other formula in this website. Still, even if the resistances’ values are not numeric, the equations are intuitive enough to show the high input low output resistance property of the amplifier.

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Categories: Analog Design, Thevenin's Theorem, Transistor Circuits

Derive the Transfer Function of the Common Collector Amplifier with Thevenin’s Theorem

Sunday, October 4th, 2009

Summary:

How to Apply Thevenin’s Theorem for Solving Circuits with Dependent Sources.

Besides its use to simplify and calculate currents in electrical circuits, Thevenin’s Theorem is also a great tool that we can use to derive transfer functions. This article will illustrate how to derive the small signal transfer function of the Common-Collector Amplifier with bipolar junction transistors (BJTs).

The circuit is shown in Figure 1. It is also called a repeater, so we expect that the calculated transfer function to be close to unity gain.

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Categories: Analog Design, Thevenin's Theorem, Transistor Circuits

How to Apply Norton’s Theorem. Solving Circuits with Independent Sources

Sunday, September 27th, 2009

Summary:

Norton’s Theorem is a powerful tool for solving electrical circuits. Like Thevenin’s Theorem, it simplifies the circuit one needs to study and dramatically reduces potential calculation errors.

Norton’s Theorem states that networks with voltage and current sources, as well as resistors are electrically equivalent to one single current source and one single resistor in parallel with the source. The theorem is valid for AC circuits, where instead of resistors there may be reactive components. Since this theorem sounds very much like Thevenin’s Theorem, one can only imagine that Norton’s current source is equivalent with Thevenin’s voltage source. Indeed, they are equivalent as we will see further.

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Categories: Analog Design, Thevenin's Theorem

How to Apply Thevenin’s Theorem – Part 2. Nested Thevenin Sources Method

Monday, September 14th, 2009

Summary:

What are Nested Thevenin Sources? I came up with this name recently, while talking to an engineer about a design problem. I just said it, and I liked it. I then went and searched on Internet to see if anybody else used the term Nested Thevenin Sources before. I did not find it so, here it is. Let’s talk about it.

I borrowed the term from “nested loops” in the programming world. The main idea is that you can use a method to accomplish a task inside another method of the same kind, hence the word nested. As we saw in How to Apply Thevenin’s Theorem – Part 1, Thevenin’s Theorem is widely used to simplify the solving of a complex circuit.

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How to Apply Thevenin’s Theorem – Part 1, Solving Circuits with Independent Sources

Monday, September 7th, 2009

Summary:

Thevenin’s Theorem makes it easy to study complex networks by simplifying the circuit to be studied. It states that networks with voltage and current sources, as well as resistors are electrically equivalent to one single voltage source and one single resistor in series with the source. The theorem is valid for AC circuits, where instead of resistors there may be reactive components…

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Categories: Analog Design, Thevenin's Theorem