- #1

DragonPetter

- 830

- 1

I am going through some notes on a very simple BJT circuit setup as a voltage follower. It is simply an NPN with its collector connected to a voltage source, its base connected to a signal, and its emitter connected to a load resistor to ground.

A schematic is attached.

Now he setup a list of equations for this circuit:

1. [itex]i_{b} = \frac{V_{b}-V_{e}}{h_{ie}}[/itex]

2. [itex]i_{c} = h_{fe}i_{b}[/itex]

3. [itex]i_{e} = i_{c} + i_{b}[/itex]

4. [itex]V_{e} = i_{e}R_{L}[/itex]

I am familiar with equations 2-4. I am not so sure about equation 1. I am not familiar with the term [itex]h_{ie}[/itex] nor the relationship.

I can infer that the [itex]h_{ie}[/itex] term must have units of ohms, so it is different from the beta gain term I am used to seeing.

Can anyone explain what this term is and where the relationship comes from?

A schematic is attached.

Now he setup a list of equations for this circuit:

1. [itex]i_{b} = \frac{V_{b}-V_{e}}{h_{ie}}[/itex]

2. [itex]i_{c} = h_{fe}i_{b}[/itex]

3. [itex]i_{e} = i_{c} + i_{b}[/itex]

4. [itex]V_{e} = i_{e}R_{L}[/itex]

I am familiar with equations 2-4. I am not so sure about equation 1. I am not familiar with the term [itex]h_{ie}[/itex] nor the relationship.

I can infer that the [itex]h_{ie}[/itex] term must have units of ohms, so it is different from the beta gain term I am used to seeing.

Can anyone explain what this term is and where the relationship comes from?