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We are designing an industrial control board. The input voltage of the board is +12V, ground and -12V. Our previous design does not include any power protection and now I want to add over voltage and ESD protection, as well as voltage polarity protection.

Previous design enter image description here

New design enter image description here Schottky diodes are added to prevent reverse voltage. Zener diodes are to prevent ESD, voltage transients and over voltages.

My questions

  • Could I have comments on the design?
  • Can this set up secure the system from all kinds of wrong voltage inputs?
  • What shall be the clamping voltage of the zener diode? Shall it be around +15V?
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  • \$\begingroup\$ If you apply reverse voltage then schottky won't conduct, but zener will and then burn. For ESD you could use a bidirectional tranzorb diode instead of zener. \$\endgroup\$ – Marko Buršič Nov 7 '15 at 13:38
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It won't work because D1 and D2 are always reverse biased - try swapping them around.

Can this set up secure the system from all kinds of wrong voltage inputs?

No, of course not but you could help matters by fusing the lines so that the zener diodes are protected from an overcurrent. You could also think about using crowbar methods to prevent zeners from overheating on marginal over-voltages. Crowbar circuit: -

enter image description here

What shall be the clamping voltage of the zener diode? Shall it be around +15V?

This depends entirely on what voltages your control board can permanently survive.

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  • \$\begingroup\$ sorry for confuse caused, p101 is the source. \$\endgroup\$ – richieqianle Nov 7 '15 at 13:26
  • \$\begingroup\$ OK that clears up the diode polarity issue! \$\endgroup\$ – Andy aka Nov 7 '15 at 13:32
  • \$\begingroup\$ After re-reading, thanks for the crowbar! \$\endgroup\$ – richieqianle Nov 9 '15 at 1:06

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