What is meant by the input impedance of a voltage source?

In summary, the conversation discusses the concept of input impedance in relation to voltage sources and an example problem involving designing a circuit with certain specifications. The input impedance is the impedance 'seen' by the voltage source and is not a property of the source itself. The input impedance of both voltage sources in the example problem should be ≥ 100kΩ, and the use of an ideal op-amp as an integrator is suggested.
  • #1
Zarquon
20
0
I am familiar with the concept of the internal resistance of a voltage source, but what is meant by the input impedance?
 
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  • #3
Simon Bridge said:
Have you tried looking up the term?
Can you describe where the regular definitions online lose you?

http://en.wikipedia.org/wiki/Input_impedance

OK, maybe I get it now.. The input impedance of a voltage source is the impedance 'seen' by that source? So it's not a property of the source itself?

In that case I am still confused about this problem I'm supposed to solve (this should maybe go in the homework section, though):

"A circuit has input voltage V1 and V2. Design the circuit so that the output voltage is V0 = 10∫V1dt -5V2.
The input impedance of both voltage sources should be ≥ 100kΩ. Assume ideal op amp."

So if my understanding is correct, then I'm not sure what is being asked for here?
 
  • #4
A voltage source does not have an "input impedance", since it does not have "inputs".
I think I've seen the term used in the context of a voltage source before but am havig trouble finding an example besides yours.

A circuit has input voltage V1 and V2. Design the circuit so that the output voltage is V0 = 10∫V1dt -5V2.
The input impedance of both voltage sources should be ≥ 100kΩ. Assume ideal op amp.
... you appear to be asked to design a circuit using an op-amp - the circuit in question has two voltage sources in it - which should have some information about frequency and phase as well and amplitude (voltage) if only implied (i.e. perhaps they are variable DC sources?)

When you draw your circuit diagram, the voltage sources should probably be drawn as ideal sources in series with an ideal impedance. Consider: why do the impedances need to be ≥ 100kΩ? What is special about that? How does it impact on the design of the circuit?

Have you had some lessons about op-amp circuits?
Notice that the op-amp has to integrate the first source - do you know how to use the op-amp as an integrator?
 
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  • #5
I agree for the most part. I think the problem is probably referring to the input impedances as seen by the voltage sources. Think of the voltage sources as signal sources that would be loaded down by anything less that 100K ohms. They should probably still be modeled simply as ideal voltage sources.
 
  • #6
OK, thanks, I get it now. What threw me off whas the fact that I can't decide what the input impedances are, since these will depend on the load; but of course I can make sure that they are greater than 100 kΩ regardless of load.
 

Related to What is meant by the input impedance of a voltage source?

1. What is an input impedance?

Input impedance refers to the overall resistance presented by a circuit or device to the flow of electrical current when a voltage source is connected to its input. It is measured in ohms and is an important factor in determining the performance of a circuit.

2. Why is input impedance important?

Input impedance is important because it affects the voltage and current that can be delivered by a voltage source to a circuit. It also determines the amount of power that is transferred from the source to the circuit, and can impact the accuracy and stability of the circuit's output.

3. How is input impedance calculated?

Input impedance is calculated by dividing the voltage at the input of a circuit by the current flowing through it. It can also be calculated using Ohm's law, which states that impedance is equal to the voltage divided by the current.

4. What factors can affect the input impedance of a voltage source?

The input impedance of a voltage source can be affected by the type of circuit or device it is connected to, the frequency of the input signal, and the amount of internal resistance in the source itself. Other factors such as temperature and environmental conditions can also impact input impedance.

5. How does input impedance differ from output impedance?

Input impedance refers to the resistance presented to a voltage source, while output impedance refers to the resistance presented to a load by a voltage source. Input impedance is measured at the input of a circuit, while output impedance is measured at the output. Input impedance is also typically higher than output impedance.

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