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I read that the Raspberry Pi 4 uses a uni-directional TVS as over-voltage protection on USB power.

I also read some AC PSUs use a bi-directional TVS as over-voltage protection.

My circuit is powered by +5 V / -5 V (DC, 2-rail)

Can I use a bi-directional TVS as over-voltage protection?

As in this picture:

Edit

Add my design after consult with @PCBCrew Engineer

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2 Answers 2

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It is not a good idea.

Let's assume the following situation:

  • V+ rated as +5V
  • V- rated as -5V
  • TVS diode rated as 12V.

If 24V is applied on V+ input, Instead of holding V- at the given range, The V1 will be left as 24V, and V- will be drawn up to +12V.

Thus, over-voltage on V+ will affect to V-, or vice versa.

TVS diodes should be used on each terminal. Also, it's better to use with resetable fuse together. Because at strong over-voltage, TVS diode will be blown out soon with heat.

enter image description here

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  • \$\begingroup\$ I get it now! Resetable fuse likes good choice. Thanks! \$\endgroup\$
    – curlywei
    Commented Feb 7, 2023 at 9:45
  • \$\begingroup\$ You're welcome. \$\endgroup\$
    – PCBCrew Engineer
    Commented Feb 7, 2023 at 9:48
  • \$\begingroup\$ I've update my design after consult with you. My inputs are DC power, so I think uni-direction TVS diode seems to be enough. \$\endgroup\$
    – curlywei
    Commented Feb 7, 2023 at 10:49
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In your case, for sure I think you need to use a bidirectional TVS, because if you use a unidirectional diode you will not be protecting one of the lines, so for your application, I think the bidirectional TVS is the best choice... But take into account that the voltage across your TVS is 10V, so you should choose a 10V TVS because you are connecting it between -5V and +5V instead of from -5V to GND and +5 to GND

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  • \$\begingroup\$ Thank you mentioning my design error. As @PCBCrew mentioned, splitting +5V/GND and -5V/GND to connect TVS diode seems to be a good choice, or select resetable fuse. \$\endgroup\$
    – curlywei
    Commented Feb 7, 2023 at 9:49

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