Loading of Series vs. Parallel tank circuits

[Jdo300]

Hi All,

I have a few questions about resonant circuits when they are loaded. Let’s say that we have a simple series LC circuit and a simple parallel LC circuit driven by a function generator at frequency X. If there is one coil that is inductively coupled to the coil of each circuit and a load of X ohms is placed on each coil, how will the two circuits respond to the load?

From what I understand so far when I series LC circuit is driven at resonance, the source sees it as a dead short (plus whatever resistance there is) and the parallel circuit will not let as much power from the source through at resonance (please correct me if I got something mixed up here). But what happens in the case that the inductive load is placed on each circuit when they are driven at resonance? (assuming that they are not knocked out of resonance by the load).

Thanks,
Jason O

 

[SGT]

Hi All,

I have a few questions about resonant circuits when they are loaded. Let’s say that we have a simple series LC circuit and a simple parallel LC circuit driven by a function generator at frequency X. If there is one coil that is inductively coupled to the coil of each circuit and a load of X ohms is placed on each coil, how will the two circuits respond to the load?

From what I understand so far when I series LC circuit is driven at resonance, the source sees it as a dead short (plus whatever resistance there is) and the parallel circuit will not let as much power from the source through at resonance (please correct me if I got something mixed up here). But what happens in the case that the inductive load is placed on each circuit when they are driven at resonance? (assuming that they are not knocked out of resonance by the load).

Thanks,
Jason O

In a series resonant circuit, you put the load in series with L and C. At resonance the LC behave as a short and the source sees only the resistive load.
Ina parallel circuit, the load is in parallel with L and C. At resonance the LC behaves as an open circuit and again the source sees only the resistive load.
If you use an inductive load coupled with the primary inductance this will alter the resonant frequency, but the circuit will still behave in the same manner.

 

[ravenprp]

Hi Jason,

When a load is placed on a resonant circuit, it will affect the behavior of the circuit in different ways depending on whether it is a series or parallel tank circuit. Let's break down the two scenarios:

1. Series LC circuit: When a load is placed on a series LC circuit, it will decrease the Q factor of the circuit. This means that the circuit will have a wider bandwidth and will not be as sharply resonant as before. The source will still see the circuit as a dead short, but the power transfer will be reduced due to the lower Q factor. This can be seen as a decrease in the amplitude of the current through the circuit.

2. Parallel LC circuit: In a parallel LC circuit, the load will have a larger impact on the resonant frequency. It will shift the resonance frequency slightly, but it will also decrease the Q factor of the circuit. This means that the circuit will be less selective and will allow a wider range of frequencies to pass through. The source will not see the circuit as a dead short, but the power transfer will still be reduced due to the lower Q factor.

In both cases, the load will have a dampening effect on the resonant circuit, reducing its efficiency. However, the specific impact on the circuit will depend on whether it is a series or parallel tank circuit.

I hope this helps clarify things for you. Let me know if you have any further questions.