How Does a Capacitor Introduce Phase Delay in a Circuit?

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Discussion Overview

The discussion revolves around the concept of phase delay introduced by capacitors in electrical circuits, particularly in the context of simulations using LTSpice. Participants explore how to measure this phase delay and the implications of different types of waveforms on the analysis.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about measuring the phase delay between input voltage and output current in a simulated circuit.
  • Another participant asserts that currents in a series circuit are always in phase, prompting a discussion on the implications of this rule for the circuit in question.
  • A participant questions which signals are being referred to when discussing "delay," emphasizing the need for clarity in definitions.
  • It is suggested that sine waves are more appropriate for analyzing phase delay due to their single frequency nature, as opposed to square waves which contain multiple frequencies.
  • A participant notes that the transient analysis used in the simulation may not be suitable for observing frequency domain characteristics and suggests exploring a different SPICE analysis mode.
  • There is a discussion about how a square wave interacts with a capacitor, with one participant explaining that it charges immediately upon application of the first pulse, while subsequent pulses alternate between charging and discharging the capacitor.
  • Another participant points out that the term "phase delay" is better referred to as "phase lag" and critiques the formulation of the original question regarding phase delay.

Areas of Agreement / Disagreement

Participants express differing views on the appropriate methods for analyzing phase delay, the definitions of terms used, and the suitability of different waveforms for this analysis. No consensus is reached on the best approach or the formulation of the initial question.

Contextual Notes

Participants highlight the importance of specifying conditions, such as the input waveform, for phase delay analysis to be meaningful. There is also an acknowledgment that the term "phase delay" may not be accurately used in the context presented.

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TL;DR
Understanding the phase delay
I simulated the below circuit to capture the phase delay between input voltage and output current in LTSpice
1689755433868.png

How do i measure the phase delay introduced due to capacitor?
1689755562602.png
 

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The rule is that currents in a series circuit are ALWAYS in phase. So I'll ask you what can you conclude from that rule and the circuit you have drawn.
 
When you are using the term "delay" - which signals do you have in mind? Such a delay is the delay between two signals (voltage and/or current) resp. the corresponding phases of these signals,
When you remember your own definitions, you will know what you have to measure/simulate.
 
This would normally be done with sine waves, not square waves. This is because the phase delay depends on the signal frequency. A pulse waveform contains many frequencies. It still can have a phase shift, but it's complicated. So sine waves, which are a single frequency, often swept through a range to make a frequency response (Bode) plot, is what most EEs use.

In any case, you need to specify the conditions, like the input waveform, for phase delay to make sense.
 
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PhysicsTest said:
TL;DR Summary: Understanding the phase delay

I simulated the below circuit to capture the phase delay between input voltage and output current in LTSpice
It looks like you are using a Transient Analysis -- that is not the type of analysis that you should use to see the Frequency Domain characteristics of a circuit. Have a look at this article, and let us know what a better SPICE analysis mode would be... :smile:

https://techweb.rohm.com/know-how/simulation/7916/
 
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I am analyzing the circuit and will come up with the exact problem i am facing.
 
PhysicsTest said:
I am analyzing the circuit and will come up with the exact problem i am facing.

A square wave will charge a capacitor up as soon as it is applied because it is similar to direct current.

Are you wanting to test the time constant, tau, as it is charging?
 
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osilmag said:
A square wave will charge a capacitor up as soon as it is applied
More accurately, a square wave will start to charge up a capacitor with the initial application of the first pulse. Subsequent pulses alternately start to discharge it and recharge it... (see the OP's transient SPICE simulation):

1690549470447.png
 
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Ok
 
  • #10
As has been noted the term phase delay (better called phase lag) is defined as the response to a particular frequency sine wave. So your question is not well formulated. Please try again.
 
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