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Will a capacitor actually help to lessen the effects of ESD? Because, with rise time of about 1 ns, the frequency of the ESD signal will be well above the self-resonance frequency of the capacitor and it won’t act as a capacitor. Maybe it won’t actually help to reduce the transients.

Please share any insights on this topic to help me better understand.

Blair Fonville
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ChandanN
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  • A capacitor *can* help to improve ESD protection. It depends on the value and properties of the capacitor and the **schematic** of the complete circuit (protection and circuit you're trying to protect). I can use a capacitor such that it does **nothing** for ESD. I can also use a capacitor such that it improves the ESD robustness. Include your schematic! Also try to find out **how** a capacitor would help. What mechanism is behind the fact that it will help (or not). – Bimpelrekkie Feb 15 '19 at 11:09
  • I went into quite some detail on ESD protection that *includes* the use of capacitors: https://electronics.stackexchange.com/questions/203500/esd-protection-for-opamp-inputs-and-outputs/208891#208891 – Peter Smith Feb 15 '19 at 11:17
  • Keep in mind that there is no such thing as "**the** frequency of the ESD signal". The energy is spread over a range of frequencies, some much lower than the resonant frequency of a capacitor. Don't oversimplify the problem. – Elliot Alderson Feb 15 '19 at 13:45

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Yes, it probably does. An ESD pulse has very high voltage, still very low charge. If your finger+body would be represented as capacitor, it would be about 100pF, charged to (for example) 8kV.

\$ Q_{body} = C_{body}*V_{body} = 100pF * 8kV = 800nC \$

When discharging to a 100nF capacitor the voltage becomes:

\$ V = Q_{body} / (C_{body} + 100nF) = 800nC / 100.1 nF = 8V\$

I still would recommend also adding a resistor, it functions as RC filter as well then.

PS. the human body capacitance (HBC) is traditionally chosen as 100 pF

Huisman
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