How does one know ESR and ESL value a capacitor should have when choosing one? - Page 1
Forum section: electronics / beginners

author: matrixofdynamism
author_rank: Regular Contributor
timestamp: September 13, 2023, 01:17:52 am
content: ESR and ESL are properties of capacitors. They are always there. The ESL matters at higher frequencies perhaps but the ESR matters at lower frequencies as well, I assume down to DC (since its called ESR). Also, capacitors have leakage current.What is puzzling for my mind is that once I know what capacitance value I should have, how do I know what value for ESR, ESL and other non-ideal characteristics I need to check in the datasheet?Lets put some constraints. I am talking about electrolyitc, tantalum and ceramic capcitors. I am referring to use of capacitors with switched mode and linear power supplies, amplifier design (coupling and decoupling), power supply decoupling and filter design.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 13, 2023, 02:10:20 am
content: Not DC but AC. Temperature rise kills the life. Data sheets for the controller ICs should have what you need.For decoupling, you normally want a flat impedance. I made a video going over using a cheap VNA to measure the impedance and calculate capacitor values to improve it. Video has a few demonstrations of it.

author: jwet
author_rank: Frequent Contributor
timestamp: September 13, 2023, 04:19:42 am
content: For switching or even linear supplies, the data sheet will give you at least limits if these parameters are important. Some circuits, especially low drop out regulators, and buck converters that operate at high duty cycles place a lot of constraints on the ESR/ESL of the output cap. It creates a pole and source of instability similar to driving a capacitive load with an op-amp. ESR is the main effect, ESL is usually secondary but can create some really gnarly stability issues.In most cases, ESR and ESL are second order effects and can be ignored if not expressly mentioned in the data sheet. You can simulate (add small R's or L's to the cap branch in SPICE) or do calculations that take into account these parameters. Ohms law, V=iR prevails as well as Ldi/dt- the latter is also a complex term- ie reactive. Problems arise when you have large ripple currents going into caps (buck converters) and high frequency, high current signals that come into caps like bypass applications. The most demanding apps are generally high frequency switching power supplies operating in continuous conduction mode. Any ESR in the caps (input or output) will produce ripple when large charge or discharge currents are handled. ESL has similar effects that also increases ripple but adds reactive out of phase components that can affect stability. This kind of stuff is what separate the amateurs from the pros in power supply design. Read data sheets carefully, be careful with layout- minimize loop areas in such circuits and avoid electrolytics in general.

author: matrixofdynamism
author_rank: Regular Contributor
timestamp: September 18, 2023, 10:38:44 pm
content: Lets say I am going to create some sort of filter using capacitors. It could be LPF or HPF, could be with or without op-amp, it could be a pi-filter that also uses an inductor. In these cases there is no data sheet giving guidance. So, how does a person know in this case what value of ESR or ESL is acceptable or required? After all in these cases we need to be as close as possible to the ideal capacitor isn't it?

author: tggzzz
author_rank: Super Contributor
timestamp: September 18, 2023, 10:55:33 pm
content: Quote from: matrixofdynamism on September 18, 2023, 10:38:44 pmFirst you define your problem, your solution, and the allowable imperfections in your solution.Then you create a simplified model of your solution, one that can be analysed and/or simulated.Then you use your analysis to guide your simulations.(Analysis gains understanding of the key important features and how they interact. Simulation gains understanding of detailed behaviour that is too complicated for analysis.)The key points are to define problems that can be analysed and implemented. Your question above is too vague to implement. What can be put in your model will depend on the information available, plus skill. Skill requires dedicated thinking to gain understanding, plus experience. That isn't easy

author: soldar
author_rank: Super Contributor
timestamp: September 19, 2023, 07:32:14 am
content: Quote from: matrixofdynamism on September 18, 2023, 10:38:44 pmYou determine the ripple current that will go through the capacitor and with the ESR determine the power that will be converted to heat.The datasheets will also tell you the max allowable ripple current.You have lots of experience and learned from previous designs and failures.

author: CaptDon
author_rank: Super Contributor
timestamp: September 19, 2023, 01:40:54 pm
content: In most cases the capacitor will be better than what your specs require. If your audio filter network consists of 3.3K resistors what difference would 5 ohms of ESR really make? If the capacitor is a grid coupling capacitor and the grid resistor is 47K then a coupling capacitor with a leakage of 100M or higher would be fine. One case where ESR is important is switch mode supplies or current carrying situations like a voltage doubler or speaker coupling capacitor. In these cases the ESR must be a tiny fraction of the load impedance. Audiophools make all kinds of claims about the 'sound' of certain styles of capacitors in the audio chain. When we are talking about 20Hz to 20KHz a capacitor would have to be a real piece of shit to noticeably color the audio!! In R.F. work it is important to pay attention to the 'self inductance' of capacitors which varies wildly with style/make and the capacitor could become self resonant and even look like an open circuit a certain frequencies!! When working with tube circuits under repair I sometimes will test older capacitors with their 'worst case' anticipated voltage applied and look for leakage currents that are stable in the single digit microamp range and I may even test them at elevated temperatures typically found around vacuum tube circuits.

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: September 20, 2023, 12:21:13 am
content: I think the OP's question got lost somewhere, and I have the same one, all the datasheets I've read (and I've read over 100), out there just specify the ESR or dissipation, from which you can compute the ESR. How does one know the ESL?

author: soldar
author_rank: Super Contributor
timestamp: September 20, 2023, 08:32:55 am
content: Quote from: ballsystemlord on September 20, 2023, 12:21:13 amESL is not something so simple you can condense in a single number. It probably depends on frequency and other factors.Once you get into parameters that are so specific the only real way is to build prototypes and measure how they perform.The abstract world of numbers and papers can only approximate so much and then you need to start dealing with the real world.

author: Psi
author_rank: Super Contributor
timestamp: September 20, 2023, 09:05:58 am
content: The datasheet should make it clear if you need low ESL caps. Or at least when it's critical for correct operation to spec.I had a Maxim analog reluctance sensor IC that made a point of saying you need 3 caps in parallel as close as possible to the IC, 1uF 100nF and 10nF and they must all be low ESL. So that's what I did, oddball 0508 and 0306 sized caps (reverse). but meh, it worked and I never had any problems with the circuit, so I can't complain.I actually needed two chips so I had 6 of those caps all next to each other.Could probably have gotten away with them sharing 3 caps each, but meh. best to do what the DS suggests.

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: September 20, 2023, 09:26:51 am
content: In the user manual for the Peak ESR meter, it gives typical values to expect.https://www.peakelec.co.uk/acatalog/esr70-capacitor-esr-meter.htmlFor RF filters, also consider the Q value of the inductors and capacitors. The Elsie program has very high default values for Q, which produce “perfect” filter plots, you need to put lower values into the settings, try Q values of 200 to 500. The filters measure very close to predicted, an excellent program and free.http://tonnesoftware.com/elsie.htmlSJ

author: cathykai
author_rank: Newbie
timestamp: July 10, 2025, 07:25:30 am
content: 1. Determine your circuit’s operating frequency and ripple current.2. Check capacitor datasheets for ESR and ESL values at that frequency.3. For high-frequency or switching circuits, choose capacitors with low ESR and ESL.4. When unsure, pick the lowest ESR and ESL within your size and voltage needs—more detailed info is always better.