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I am in process of designing a power supply for heating a filament in an electron gun. The AC heating current has to float on top of DC high voltage acceleration voltage. The following circuit seems to work (at least simulated..) such that I get about 2 A of current onto the filament. Yet I have seen circuits that includes a capacitor C1 in series with the AC source. Is this capacitor necessary in real world application and if so, then why?

thanks!

enter image description here

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  • \$\begingroup\$ This requires that your supply can be floated to -5000V. Often that isn't possible so other techniques need to be used to allow a grounded supply to be use. \$\endgroup\$
    – Kevin White
    Commented Oct 3, 2020 at 20:24
  • \$\begingroup\$ R6 seems very large compared to R3 \$\endgroup\$
    – Jasen Слава Україні
    Commented Oct 4, 2020 at 3:15
  • \$\begingroup\$ Mass spectrometer? \$\endgroup\$
    – Andy aka
    Commented Oct 4, 2020 at 9:39
  • \$\begingroup\$ Thanks for your comments and answers. This supply comes to SEM and R3 represents the filament here. All values here are still vague. I am usig an isolation transformer with a shield/screen between the windings. It should be enough for 5kv, but i will check this first of course. The transformer does not have a center tap on the secondary. will then skip the capacitor, which is good... \$\endgroup\$
    – Don I
    Commented Oct 4, 2020 at 22:03

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no in the real world the capacitor is not needed.

micowave ovens use a circuit where the DC source is directly connected to the AC source,

instead of feeding the DC to a resistive divider I'd look at feeding it to a centre tap on the AC transformer's secondary.

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