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I am making a voltage divider with four 1M 1206 thick-film resistors and a single 2.7k resistor. The input to this voltage divider will be mains line and neutral.

I want to measure the voltage at line with respect to neutral, with the nominal voltage being 240 V +/- 1%.

I also want to protect this circuit against lightning surges. For that purpose, I am using four resistors in series to deal with high voltages, something like this circuit:

enter image description here

I can't decide which type of resistors I should use. Should it be general-purpose resistors, high-voltage resistors or anti-surge resistors?

I have seen similar units fail in the field due to lighting surges, with the burning of resistors and PCB traces in that section.

  • Would adding MOVs at input be useful also?
  • Does the PCB layout matter much in this section?
  • Any other protection device that I should consider?
  • How should I select rating of my high-voltage/anti-surge resistors to protect against lightning?
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    \$\begingroup\$ ”Would adding MOVs at input be useful also?” If you have any source impedance, then yes. ”Also, does the PCB layout matters much in this section?” Certainly. You need to provide sufficient creepage and clearance. \$\endgroup\$
    – winny
    Jul 29 at 18:41
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    \$\begingroup\$ What lightning standard do you need to meet? Mind that HV chip resistors may require potting to achieve their maximum ratings. \$\endgroup\$ Jul 29 at 18:45
  • \$\begingroup\$ PCB layout always matters, but especially when dealing with high voltage events like lightning strikes. \$\endgroup\$
    – Hearth
    Jul 29 at 20:41
  • \$\begingroup\$ I like to add a small R/C filter with 100 ohm and 1nF, X qualified, to eat very short high voltage spikes before they jump right across the resistor chain. This chain also is a capacitive divider with some pF and 100 pF parallel to the 2.7 kohm can suppress the feedthrough. \$\endgroup\$
    – Jens
    Jul 30 at 0:33
  • \$\begingroup\$ @jens Can you elaborate your comment with a schematic? \$\endgroup\$ Jul 30 at 2:33

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