I only have bidirectional TVS diodes at hand, can I use one of those instead of D1 (unidirectional) in the diagram?
\$\begingroup\$
\$\endgroup\$
1
-
\$\begingroup\$ Did it work for you? I'm also working on this same product and I currently only have bidirectional diodes on hand. \$\endgroup\$– lemonpledgeCommented Mar 13, 2023 at 18:21
Add a comment
|
3 Answers
\$\begingroup\$
\$\endgroup\$
4
Yes.
BUT: If your circuit is "hot-plugged", connected to a long cable, or connected to a poor powersupply; negative transients may occur. In your current setup the unidirectional TVS diode protects against those. If you replace with a bidirectional those transients may destroy C1, U1 or both.
If you are prototyping, testing, and just want to use what you have at hand then I would say that a bidirectional is fine, as long as you understand that it adds a bit of risk.
-
\$\begingroup\$ Thank you for your answer! It seems like I still don't understand TVS diodes very well. Could you explain how come this is the case? If anything, I'd have guessed the reverse would be true - as in, when there's only a unidirectional diode, current can passe from the ground back into the circuit, but if it's bidirectional, both sides are protected. \$\endgroup\$– aanonymCommented Feb 13, 2021 at 12:27
-
\$\begingroup\$ TVS are really simply beefed up zeners, the tech behind is the same. They are simply optimized for transients instead that for linear work. If you put 2 zeners back to back you mostly have a bidirectional TVS. \$\endgroup\$ Commented Feb 13, 2021 at 13:48
-
\$\begingroup\$ @Andyaka why is it incorrect? I'm running into this situation with the exact same product. It's the only thing I have on hand until the new diodes get delivered. \$\endgroup\$ Commented Mar 13, 2023 at 18:21
-
\$\begingroup\$ OK, a unidirectional TVS will protect in reverse no problem; in other words it isn't an open circuit in reverse and will protect against any negative voltage magnitude greater than about 1 volt. In other words there is no risk if you can use a unidirectional TVS diode. \$\endgroup\$– Andy akaCommented Mar 13, 2023 at 19:03
\$\begingroup\$
\$\endgroup\$
3
if you can rely on C1 to provide sufficient reverse polarity protection that could work.
if not add a diode in parallel with your double-ended TVS. with thwe parallel diode it will be electrically very similar to the original TVS.
answered Feb 13, 2021 at 10:20
-
\$\begingroup\$ Thank you for your answer! I'm just starting out with electronics, could you perhaps explain your reasoning behind this? \$\endgroup\$– aanonymCommented Feb 13, 2021 at 10:40
-
1\$\begingroup\$ What? And What? C1 does not add any reverse protection. Nether does adding a paralell diode to the TVS. \$\endgroup\$– ArcatusCommented Feb 13, 2021 at 11:58
-
\$\begingroup\$ C1 is likely to start conducting at some low voltage reverse polarity. without datasheets, or knowing how long it supposed to survive for I can't say if that will be enough. \$\endgroup\$ Commented Feb 13, 2021 at 20:23
\$\begingroup\$
\$\endgroup\$
Yes. Put a rectifier diode in parallel with it for protection against negative inputs.
The MIC29302 (unusually) is capable of withstanding at least momentary negative inputs, absolute maximum -20V to +60V.
If there is no way anything outside of that range could possibly be applied to the input then the TVS does nothing (except protect C1 against negative voltage in excess of about -1~-2V which a simple diode, in series (blocking) or parallel (shunting) will or may do respectively).
If C1 is a typical aluminum electrolytic capacitor it can easily withstand a volt or two of reverse potential.
answered Feb 13, 2021 at 21:15