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I have 2 series zener diodes like these in the schematic.

Their capacitance is C=225pF

How do I calculate their equivalent capacitance so I can calculate my time constant?

Is it 225pF || 225pF or just C1+C2?

  • 3
    \$\begingroup\$ 1/((1/C1)+(1/C2)) = Ctot \$\endgroup\$ – winny Jan 8 '18 at 19:03

Diode capacitance often rated at some DC voltage such as 0V which decreases reverse bias.

If it were two fixed caps of equal value the answer you should know for 2 series caps is 1/2 of C as @winny said

Cs = 1/((1/C1)+(1/C2))

If they were parallel then Cp=C1+C2


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