Author Topic: DC blocking capacitor value  (Read 560 times)

Offline John123

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DC blocking capacitor value
« on: December 18, 2019, 06:44:23 AM »
You know those film capacitors people put in series with the tesla coils and gate drive transformer primary, how do they decide the value? Is it just a case of capacitive reactance or is there something else going on?

I've seen some people use 100nF all the way up to 10uF for tesla coils, how do they choose? I've got a little half-bridge running a CRT flyback transformer at 40khz and at first I used 1uF, but saw some improvement to the gate drive waveforms when I added an extra 1uF in parallel.

Offline Mads Barnkob

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Re: DC blocking capacitor value
« Reply #1 on: December 18, 2019, 09:00:16 AM »
DC blocking capacitors should behave like a dead short at the resonant frequency of the Tesla coil or inverter. So anything below 2 Ω reactance should be considered to work.

It is pretty simple to calculate the capacitance needed, I wrote down all the calculations for it here: http://kaizerpowerelectronics.dk/tesla-coils/sstc-design-guide/ you can also find some other good design tips for building a SSTC.

The reason why you see all kinds of different capacitances that work, is that they will do the job of blocking the DC, but with more or less losses in the blocking capacitor.
http://www.kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics

Offline John123

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Re: DC blocking capacitor value
« Reply #2 on: December 18, 2019, 10:20:13 AM »
DC blocking capacitors should behave like a dead short at the resonant frequency of the Tesla coil or inverter. So anything below 2 Ω reactance should be considered to work.

It is pretty simple to calculate the capacitance needed, I wrote down all the calculations for it here: http://kaizerpowerelectronics.dk/tesla-coils/sstc-design-guide/ you can also find some other good design tips for building a SSTC.

The reason why you see all kinds of different capacitances that work, is that they will do the job of blocking the DC, but with more or less losses in the blocking capacitor.

Ah thanks! Are they even needed in series with the primary coil in a half bridge configuration where the rail splitting capacitors already block DC, I have seen them in ATX power supplies which use this topology which I find confusing.

Offline nick

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Re: DC blocking capacitor value
« Reply #3 on: December 18, 2019, 04:26:59 PM »
DC blocking capacitors should behave like a dead short at the resonant frequency of the Tesla coil or inverter. So anything below 2 Ω reactance should be considered to work.

It is pretty simple to calculate the capacitance needed, I wrote down all the calculations for it here: http://kaizerpowerelectronics.dk/tesla-coils/sstc-design-guide/ you can also find some other good design tips for building a SSTC.

The reason why you see all kinds of different capacitances that work, is that they will do the job of blocking the DC, but with more or less losses in the blocking capacitor.

Ah thanks! Are they even needed in series with the primary coil in a half bridge configuration where the rail splitting capacitors already block DC, I have seen them in ATX power supplies which use this topology which I find confusing.

Yeah but that's on the other side of the GDT right?

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Re: DC blocking capacitor value
« Reply #3 on: December 18, 2019, 04:26:59 PM »

 


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