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I'm trying to make a Marx Generator with a fast rise time (~5 ns). One analysis of the generator's design shows that the largest factor inhibiting the rise time of the generator is the inductance of the capacitors.

My question is: Is there a general design or type of capacitor with low equivalent series inductance (ESL)? General answers are good to have, but a thought towards high-voltage applications would be especially appreciated.

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  • \$\begingroup\$ Most ceramic capacitors have very low ESL and ESR, partially due to their (usually) small size but also because of their construction (lots of very short plates in parallel, not rolled like electrolytics). Failing that, many polypropylene capacitors tend to have pretty low ESL/ESR, especially the ones used for big IGBT snubbers. \$\endgroup\$
    – Sam
    Commented Feb 9, 2017 at 8:22

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X2Y capacitors are available from various manufacturers, the MLC structure has three plates, and two of them can be paralleled which cuts back on the ESL (kind of like two inductors in parallel).

The Layout will also affect your application as vias and a few nH of inductance. A spice simulation might help find out how much inductance the circuit can tolerate by adding board and component parasitics.

The voltage rating can be increased with the capacitors in a series configuration if needed but the inductance also increases. A parallel\serial configuration might be solve both problems.

Regular Capacitor parasitics look like this:

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Thanks for the schematic! It definitely helps with understanding what to look for. I checked Digikey; they largest rating they have for this type of capacitor is 100V, which would unfortunately require a lot of them to be stacked. \$\endgroup\$ Commented Feb 8, 2017 at 22:24
  • \$\begingroup\$ How will person get the parasitic values to be used in the simulation? \$\endgroup\$
    – quantum231
    Commented Jun 22, 2023 at 17:53
  • \$\begingroup\$ You can pull them off of an impedance graph or sometimes they are listed in the datasheet. For simmilar packages the ESL can be estimated because its the metal in the pins/pads that give you most of the ESL parameter. \$\endgroup\$
    – Voltage Spike
    Commented Jun 22, 2023 at 17:56

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