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For the following circuit I need a TVS. Ideally it should be a bidirectional TVS like SMBJ400CA. But since I only have access to its unidirectional version (SMBJ400A), considering the half wave nature of the circuit which blocks the current in the opposite direction, is it possible to use the unidirectional TVS instead?

my circuit

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    \$\begingroup\$ Please don't update your question to request updates to answers that were for the original question. Also your diodes now prevent AC from driving AC loads. What are you after? \$\endgroup\$ Commented Oct 7 at 11:03
  • \$\begingroup\$ @Justme, as you can see in the first diagram of my question, and explicitly mentioned in first lines of the question, the circuit has a half wave nature and there is no problem with not being able to use full sine wave. \$\endgroup\$ Commented Oct 7 at 11:19
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    \$\begingroup\$ @AKTanara - Hi, You extended the question by adding a different schematic, after already receiving answers. That "moving the goalposts" was flagged by other site members as it breaks the SE approach, where people answer a specific question. It can make answers to the original version of the question look poor/wrong, as they are not expected to respond to what you added later. You can research on Meta Stack Exchange why "chameleon questions" (as they have been termed) cause problems. Therefore I reverted the question to the state when it was originally answered. Please avoid changing answered questions. \$\endgroup\$ Commented Oct 7 at 12:40

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Just use two back-to-back unidirectional TVS diodes like this: -

enter image description here

You can't use a single unidirectional TVS diode across an AC main supply because it conducts current in one direction and will blow the fuse in a fraction of a second.

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I say no, you have an AC mains and an unidirectional TVS will be conducting when the voltage change directions. You could make a bidirectional TVS, by setting two unidirectional together in series.

If it is placed after the diode, it will block the ESD some will escape from the parasitic capacitance, but it is advisable to have the TVS as close to the entry point as possible so the current is not taken another route in your circuit.

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  • \$\begingroup\$ Thanks, So if I put it after the diode it wont be perfect but it gets most of the job done? \$\endgroup\$ Commented Oct 7 at 9:14
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    \$\begingroup\$ I will not recommend doing that. \$\endgroup\$ Commented Oct 7 at 9:51
  • \$\begingroup\$ After the diode should be fine. In both cases TVS2 will be one diode away from the input, and directly attached to ground. \$\endgroup\$ Commented Oct 7 at 21:22

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