YAGEO Group
Webinar Date: September 26, 2024
Basics of RLC Circuits: Looking Deeper than Idealistic Conditions
This post covers Key Takeaways and Frequently Asked Questions from the Yageo Basics of RLC Circuits: Looking Deeper than Idealistic Conditions webinar regarding addressing the nuances when applying RLC circuit principles to real world components such as important component specifications and technologies, parasitic effects of resistors, capacitors, and inductors, designing parasitic effects into a model and how to select components to minimize unwanted component limitations. Whether you’re a seasoned professional or a curious newcomer, you’ll find plenty of valuable information watching the webinar. Links to the Webinar, Resources, and Related Content are provided within the post. A copy of the PowerPoint presentation will be provided for customers that register to watch the recorded webinar. All Snippets and Content Compliments of Yageo.
Key Takeaways
- An RLC circuit consists of a resistor, inductor, & capacitor
- Applications include variable tuned circuits, filters, & oscillators
- The actual capacitor model consists of a series circuit including ideal capacitance, Equivalent Series Resistance (ESR), & Equivalent Series Inductance (ESL)
- The actual resistor model consists of a series circuit of ideal resistance and parasitic inductance with a parasitic capacitance in parallel
- The actual inductor model consists of a parallel circuit including Equivalent Parallel Capacitance (EPC), Equivalent Parallel Resistance (EPR), & parallel inductance, all in parallel to a series circuit Equivalent Series Resistor (ESR)
- Rated capacitance decreases from an increase in DC bias voltage (inversely proportional)
Frequently Asked Questions
Can you explain what an RLC circuit is?
- An RLC circuit is an electrical circuit made up of a Resistor (R), an Inductor (L), and a Capacitor (C). These components control the flow of current and energy in the circuit, often used in tuning circuits to select certain frequencies or output filters.
What does resonance mean in an RLC circuit?
- Resonance in an RLC circuit happens when the inductor and capacitor balance each other at a certain frequency, called the resonant frequency. At this frequency, the circuit allows maximum current to flow.
What is resonance in an RLC circuit?
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Resonance occurs in an RLC circuit when the inductive reactance (XL) and capacitive reactance (XC) cancel each other out at a specific frequency, called the resonant frequency (f₀). At this point, the circuit’s impedance is purely resistive, and the current reaches its maximum value in a series RLC circuit. The resonant frequency is given by the formula:
f0= \frac{1}{2\pi\sqrt{LC}}
What are the types of damping in an RLC circuit?
- Damping refers to how the circuit’s oscillations decrease over time. There are three types:
- Overdamped: No oscillations, slow return to normal.
- Critically damped: Fast return to normal without oscillating.
- Underdamped: The circuit oscillates before settling down.
What is the Q factor in an RLC circuit?
- The Q factor measures how sharp or focused the resonance is in an RLC circuit. A higher Q means the circuit is more selective, allowing a narrow range of frequencies to pass.
How does the quality factor (Q factor) affect an RLC circuit?
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The Q factor is a measure of how underdamped an RLC circuit is, and it affects the sharpness of the resonance peak. A higher Q factor means a narrower and sharper resonance peak, indicating less energy loss and higher selectivity. It is calculated as:
Q= \frac{1}{R} \sqrt{\frac{L}{C}}
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In high-Q circuits, energy dissipates more slowly, and the circuit is more selective to a narrow frequency range.
How does impedance change with frequency in a series RLC circuit?
- Impedance (the total resistance to current flow) changes like this:
- At low frequencies, the capacitor causes high impedance.
- At the resonant frequency, impedance is lowest, allowing more current to flow.
- At high frequencies, the inductor increases the impedance.
How does impedance behave in a series RLC circuit at different frequencies?
- In a series RLC circuit:
- At low frequencies, the capacitive reactance (XC) dominates, making the impedance high.
- At the resonant frequency, the inductive and capacitive reactances cancel each other out, leaving only the resistive impedance, which is minimal.
- At high frequencies, the inductive reactance (XL) dominates, increasing the total impedance.
When to use thin film thick film or metal film in our application. Please suggest some appropriate examples related to each.
- Thin film typically is used for high precision application if you need low noise, sensitive analog circuits, high performance device such as medical or military applications. Thick film is more of a general purpose or consumer market resistor which is great for cost effective solutions or higher power capabilities.
Are values related to the DC bias effect given in capacitor datasheets?
- You typically will not find that on the datasheet which is why we have our K-Sim simulation tool to see what the DC bias effect is for your particular situation.
Please discuss the differences in reliability and stability between mylar, ceramic, and electrolytic capacitors.
- The mylar capacitor is probably the best you can buy but it is also the most expensive for applications where you need high reliability, stability, and long-term applications. Mylar are also typically larger which may be an issue. Ceramic capacitors can have very good stability depending on which class you are using whether it will be class 1, class 2, class 3 dielectrics. Electrolytic capacitors are generally suited for higher storage capacitance and lower frequency applications for more general applications such as power smoothing applications.
Do COG capacitors maintain stable ESR as well as capacitance over their rated temperature range?
- They do, and that’s actually the big thing with why COG capacitors are so great in many applications. They also typically have a very high resonant frequency which is very important in high frequency applications and are very stable over their whole temperature range.
What about generated stray fields and are toroidal inductors better?
- Toroid’s generally have less stray magnetic fields, but it may depend on the application. A metal power inductor however may be a better choice if for use in a smaller compact design.
For a resistor as it will heat up due to I2R loss, how can I estimate the surface temperature of the resistor. I know there are temperature derating curves that tell me how much power the resistor can handle over temperature, but I just can’t know how much the resistor is heating up.
- Typically, on the datasheet there will be a value system a resistor dissipation factor and a thermal resistance. I don’t have the equation at the top of my head, but it should be in the datasheet regarding delta and thermal resistance.
How do you deal with capacitor resonant frequency in your low-pass filter design. In another words what adjustments do you make to your design to counter the effects of the resonant frequency?
- The biggest thing you can do is to choose the right capacitor. Choose a capacitor that has a very high self-resonant frequency to send unwanted signals to ground. You can also play around with putting multiple capacitors in parallel with different values which can help spread out a little bit what that resonant frequency will be like for your application.
Is there a way to integrate the K-Sim tool to interact with LT Spice or similar. It would be good to be able to run a spice analysis with all these factors.
- You can download the LT Spice model from K-Sim and just integrate it into LT Spice and just use that as your example.
We stock both class 1 and class 2 ceramic materials, COG, NPO, is which class?
- These are class 1 dielectrics, typically the X7R X5R these are considered class 2 dielectrics and then the Y5V are class 3 dielectric. If you need something that is class 1, typically use COG, NPO, and we also have another one U2J.
What is the Q factor in an RLC circuit?
- Higher Q means that your circuit is a little bit more selective on allowing a narrower frequency range that can actually pass through the RLC circuit.
What is the realistic calculation of capacitor lifetime under normal room temperature 80–90-degree Fahrenheit operating. Is there a simulator for it?
- Using our K-Sim tool, you can put in variables like this to see how it will perform.
Should ripple be consideration for a capacitor selection when the voltage source is a battery?
- Probably not so much for batteries since the battery will take the bulk of it since it acts like a giant capacitor, but I don’t know the exact application of this.
Can you speak to the earlier simulation with a modified capacitance based on various applied parameters were used but had not appeared all the ESL and ESR were factored into the simulation.
- The ESL in comparison to the overall inductance that we had was so low that it didn’t really have an effect in that situation, same with ESR it is so low it doesn’t really affect this particular example. For some applications you may need to consider those values, this was only an example. If you have different examples that are not ceramic, then you may deal with much higher ESRs which can potentially cause issues for your application. There are some situations where ESR and ESL will have a much bigger impact than that example.
We can download Kemet.s2p S-Parameter models where Yageo seems to have .stp models only, what is S1P, how can we find .s2p for the Yageo capacitors?
- Please reach out to us, we can provide them if we have them as they may not be readily available online and not all products are going to have that, but we can possibly generate it for you.
For a published DC bias curve for a particular capacitor can you provide some guidance as to the unit-to-unit variation that would be considered normal?
- I would suggest having to simulate it. I wouldn’t recommend unit to unit comparison as it really depends on all the little details on what the mixture exactly is and how the components are put together there are so many factors so I would simulate the product on K-Sim.
Why is rule of thumb for the voltage rating for a capacitor twice what the desired voltage is?
- This probably comes mainly from the fact that the DC bias effect hasn’t been a very well-known thing to everybody, and a lot of time a circuit may experience voltage spikes. It is more of a general engineering rule of thumb that has been out there but I’m not sure who actually created this rule.
Regarding K-Sim, with factors like lifetime analysis somehow be done with spice simulation as an example.
- I don’t know if we can do that, again the data points that you have are all real data that we have selected over time so I don’t know how we can do collaboration with that, but we can definitely investigate.
Does K-Sim use frequency dependent models such as ESR vs. frequency for instance or fixed like LT Spice?
- Right now, they are fixed depending on what you put in when you download the Spice model that frequency range will be fixed for that particular area. With frequency independent models, it has a very big challenge as models are very elaborate however we haven’t given up on this but right now they are frequency dependent.
Aging analysis, based on if the circuit is in-use and turned off?
- When you look at the simulation tool, they have profiles in there that you can use such as when it’s on or off at certain percentages.
In regard to board repair, I know the most reliable method of testing capacitors from the circuit to get a true ESR but are there time saving methods that you use in practice, so you don’t have to recap the entire board if it is not necessary?
- No unfortunately that is the only way there is no other method. You must remove it from the board.
Why are temperature coefficiencies for resistors for example a thick film resistor with ±100ppm always documented with the symmetrical ± tolerance. I am confident that this bowtie tolerance is not realistic. Such a resistor will never have anything close to -100ppm temperature coefficient. Why are the tolerances not represented more accurately?
- They are actually fairly accurate the big thing is you are looking for a temperature range such as -55 to 150C. once you start measuring your resistance in a negative temperature range you may have a negative effect on your PPM and that’s per degree C. in the lower range you can have a temperature drift that gives you less resistance but when you go up in temperature you actually have the positive temperature drift so it’s not 100% sure what it’s going to be in which area and which resistor but they all have a curve that is depending on negative and positive temperatures. So, you will see negative ppm is actually going to be true so really just looking at negative levels that’s when you see a lot of times a -100ppm / C.
Can you recommend a capacitor type for 250C ambient?
- You’re going to be limited to ceramic as most other technologies aren’t going to be able to handle that. Tantalum caps can go in that range but typically this is going to be limited to MLCCs. We offer MLCCs up to 260C where tantalum can go up to 230C, but you are talking about heavy power derating on those high temp tantalum caps where the ceramics can handle that.
Webinar Links and Resources
Webinar Registration Link:
DigiKey Webinar Center:
DigiKey TechForum Webinar Posts:
Supplier Center:
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Additional Resources:
- All Content
- Yageo Kemet Capacitor Simulation
- Thin-Film Automotive Resistors - RP Series
- Thin-Film Chip Resistors
- 01005 Miniature MLCCs
- MPEV Series Power Inductors
- Organic Polymer Capacitors (KO-CAP®) deliver long life and stable performance
- C0G Capacitors with KONNEKT™ Technology
- Y2/X1 Film EMI Suppression Capacitors - R41D Series
- Composite Core Inductors - PA2241/PA2242/PA2243/PA2244 Series
- Mini-Molded Power Inductors - ADCC/BDCC Series
- High-Current Molded Power Inductors - BMxx Series
- DigiKey Calculators - Low Pass/High Pass Filter Calculator
- Discover the Unexpected Frequency Response of Wire Wound Resistors
- Thin-Film Automotive Resistors - RP Series
- Thin-Film Chip Resistors
- 01005 Miniature MLCCs
- MPEV Series Power Inductors
- Organic Polymer Capacitors (KO-CAP®) deliver long life and stable performance
- C0G Capacitors with KONNEKT™ Technology
- Y2/X1 Film EMI Suppression Capacitors - R41D Series
- Composite Core Inductors - PA2241/PA2242/PA2243/PA2244 Series
- Mini-Molded Power Inductors - ADCC/BDCC Series
- High-Current Molded Power Inductors - BMxx Series
- Yageo Supplier Center
- DigiKey TechForum
- DigiKey Calculators - Low Pass/High Pass Filter Calculator
- Discover the Unexpected Frequency Response of Wire Wound Resistors
K-SIM
Example Webinar Slides
-Much more in-depth slides and a copy of the PowerPoint presentation will be provided for customers that register to watch the recorded webinar.
