Selecting TVS diode - Page 1
Forum section: electronics / beginners

author: derGoldstein
author_rank: Regular Contributor
timestamp: June 05, 2017, 09:02:41 pm
content: I'm sure this is a question that's asked frequently, so I googled as many documents as I could before asking and actually came out with more questions than I started with (I'll link the documents below).I'll start with where in the circuit I think it's needed and why: I have a 12V DC input to the circuit with multiple possible connectors. The "default" is a 5.5mm barrel connector, but there will likely be other ways to hook up to it, possibly an XT60 connector or even screw terminals.The "loose wire" scenario is likely -- I can't know for certain which end of the wire will be connected first, so I could grab a cable that's been gathering static with nowhere to unload it and plugging it into the circuit. The first component in the circuit is a reverse-mounted N-channel MOSFET to prevent reverse-polarity connections, so the gate of that MOSFET could be fried by an ESD, which is what I'm trying to prevent with a TVS diode.My first question would be -- is the scenario that I'm trying to prevent (the MOSFET's gate getting zapped) something that a TVS diode would solve, or should I be doing something else?Additional questions:If I'm only trying to prevent ESDs, what kind of wattage am I looking for? How do I estimate the wattage of a potential ESD?Is there any reason not to get a bidirectional TVS?Are TVS diodes also the part to use if I'm trying to prevent small voltage spikes (noise from the power supply), or should I be looking for a different solution in that case?Here are the documents I've been looking at:http://www.completepowerelectronics.com/tvs-diode-selection-tutorial/https://www.ttieurope.com/docs/IO/15325/TTI_TVS_Diodes_Selector_Guide.pdfhttp://www.powerelectronics.com/regulators/selecting-protection-devices-tvs-diodes-vs-metal-oxide-varistorshttps://www.microsemi.com/document-portal/doc_view/14650-how-to-select-a-transient-voltage-suppressor

author: Tomorokoshi
author_rank: Super Contributor
timestamp: June 05, 2017, 09:18:57 pm
content: Littelfuse also has some documents:http://www.littelfuse.com/technical-resources.aspxDo you already have reverse polarity protection? This is one reason to use a unidirectional instead of bidirectional.How sensitive is the rest of the circuitry to overvoltage? With a nominal 12 V circuit, is it damaged at 13 V or is it fine to 24 V? Keep in mind that TVS diodes are rather loosely defined until they are conducting significant currents.How well regulated is your plug-in supply? Is it switcher at 12.00 V or a linear at 16.5 V open circuit? This will determine the reverse standoff voltage.Can you afford a small series resistance between the input connector and the clamping diode? That would help with charged, high-capacitance supplies arcing when connected.For instance:Zener:https://www.digikey.com/products/en?keywords=1N5350BRLGOSCT-ND%20TVS:https://www.digikey.com/products/en?keywords=%205KP12ALFCT-ND%20

author: nour
author_rank: Frequent Contributor
timestamp: June 05, 2017, 11:22:36 pm
content: There is a dedicated solutions for ESD protection available in a monolithic package take this for examplehttp://www.st.com/en/protection-devices/esda5v3sc5.htmlI don't know if this one suitable for your situation or not but you can search for something similar to fit your needs.