Surge protection design and calculations - Page 1
Forum section: electronics / projects

author: MattM
author_rank: Contributor
timestamp: January 05, 2023, 08:34:24 pm
content: Dear All,I’m designing surge protection for a device (DUT). The DUT should withstand 4 kV (1.2/50 µs) voltage surge and 2 kA (8/20 µs) current surge.Please, see the attached pictures as well. Questions are at the end of the explanation.GDT25-09 - 500V impulse sparkover voltage rating (considering the more pessimistic 1 kV/µs spec).SMAJ12CA – 25.9V max. clamping voltage at max peak pulse current Ipp of 100.5A (8/20 µs spec)R is 1218 CRCW-HP e3 pulse proof resistor.However, the peak power that the resistor will see during the surge is significantly higher thanit's rating. Considered adding another stage with R and MOV between GDT and TVS but the peakpulse power is still above the resistor rating (checked also surge resistors other than CRCW-HP e3).Any design advice from someone who has already designed protection circuitry?EDIT/UPDATE:- possibility of using an inductor instead of the R1 is being investigated- GDT in a DC circuit may not self-extinguish after the surge event has passed

author: trobbins
author_rank: Frequent Contributor
timestamp: January 05, 2023, 10:28:22 pm
content: Have you done a sim using the standard surge generation circuits?

author: f4eru
author_rank: Super Contributor
timestamp: January 05, 2023, 10:43:27 pm
content: what will happen if you replace the resistor by an inductor (ttake care not to saturate it)?

author: jonpaul
author_rank: Super Contributor
timestamp: January 06, 2023, 01:11:07 am
content: gas tube has no current limitSMD TAZ and R incapable of required power, voltage creep, strike.What's the compliance or regulation on the power bus. eg Avaition D0-160, IEC 60004-1 level 3 etc?j

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 06, 2023, 05:28:03 am
content: What is the application? 2 ohm differential surge is quite unusual to require on SELV supplies.Tim

author: MattM
author_rank: Contributor
timestamp: January 06, 2023, 02:15:02 pm
content: @f4eru, how would you go about choosing such inductor?

author: MattM
author_rank: Contributor
timestamp: January 06, 2023, 02:44:33 pm
content: Quote from: T3sl4co1l on January 06, 2023, 05:28:03 amSensor system in a harsh environment. Unless I'm mistaken, even with a 12 or 42 ohm couplingthere will be current of ~100A flowing when the voltage at the GDT raises to ~500V. Still stressingthe R1.

author: jonpaul
author_rank: Super Contributor
timestamp: January 06, 2023, 03:18:15 pm
content: "harsh environment"Can you be more specific, land, sea, air?military, insustrial, consumerbus is on vehicle, welder, heavy motor control...etc?Safety related function?Jon

author: MattM
author_rank: Contributor
timestamp: January 06, 2023, 03:47:03 pm
content: Quote from: jonpaul on January 06, 2023, 03:18:15 pmHi Jon, I can, industrial, land and possibly sea. Can you elaborate as to why is this important?I know that there might be different requirements, however, I specified that theDUT should withstand 4 kV (1.2/50 µs) voltage surge and 2 kA (8/20 µs)(IEC 61000-4-5 level/class 4).

author: jonpaul
author_rank: Super Contributor
timestamp: January 06, 2023, 04:20:17 pm
content: Matt: Unclear in your posts if you need transient protection eg lightning or bus inductive load, or the much longer and higher energy alternator load dump, that affects any vehicle electronics powered by a battery charged by a generator or alternator.These are related but very different issues.So, in decades of consulting, I had many designs for power line conditioners, broadcast, medical, aviation equipment requiring transient and surge protection and compliance.The easy alternator load dump high energy surge (~ 60..120V, many Joules) is handled with large area TAZ designed for the application.In 1980s..1990s we used the axial Motorola MR2525, MR2535 diodes, several in series if needed.Sea faring equip may be subject to compliance for gas vapor safety eg fire ignition due to an arc or spark into a gasoline vapor .A fishing boat will have different requirements than a Naval cruiser or submarine.IEC 610004-5 LEV 4 is very well known, AFIK, normally a gas gap is NOT used.We used filters, series inductors, and low inductance shunt C, and ferrite CM and DM mode chokes in combinat with a properly selected Transient Absorbing Zener.We generally avoid the high C, short life MOVs which are also a fire hazard, and the gas gaps.the components we used were TH and not SMD.See the many papers and app notes, from manufacturers and IEEE, etc. as well as the excellent books on transient and surge protection.Hope you find this note useful!Bon ChanceJon

author: MattM
author_rank: Contributor
timestamp: January 06, 2023, 04:46:05 pm
content: Sure, Jon! Merci!

author: f4eru
author_rank: Super Contributor
timestamp: January 06, 2023, 10:16:25 pm
content: basically, I would:- calulate the approx inductance so not to get overcurrent on te TVS with the 500V GDT output during the pulse time.- choose the inductor for it's DC perf.- experimentally check with the relevant impulse at hand that it does not get into saturation during the impulse and firing of the GDT.

author: MattM
author_rank: Contributor
timestamp: January 07, 2023, 10:26:03 am
content: Thank you f4eru!

author: MattM
author_rank: Contributor
timestamp: January 07, 2023, 10:34:53 am
content: @jonpaul, transient protection. Transients due to power systems switching and possibly ligthning (induced surge).Passing level 4 test is the current requirement. Intrinsic safety is currently not required which led me to the useof the GDT.

author: niconiconi
author_rank: Frequent Contributor
timestamp: January 12, 2023, 04:07:44 pm
content: Quote from: MattM on January 05, 2023, 08:34:24 pmThrough-hole resistors, including wire-wound, carbon composition (not carbon film), and ceramic composition resistors would have a much greater surge energy withstand capabilities than a small 1218 SMD part. It's entirely possible for a 3 W part to absorb a 30000 W surge, as long as the energy is low enough. Consider them if circumstance allows.From your description, it seems that you have an assembly or size constraint, so their huge size is probably not acceptable to you... Still, perhaps it would be useful in the future. Just my recent experience from designing a IEC 61000-4-2 Level 2 surge generator.

author: jonpaul
author_rank: Super Contributor
timestamp: January 13, 2023, 11:33:41 am
content: Rebonjiur MattM:RE SMD vs TH, most SMD parts are lacking in power diss and creep/strike voltage ratings.Most protection desgins we have seen are dealing with V, I and transient powers that are better met with TH parts.Assy houses are fine with mixed TH/SMP designs.Suggest not to be limited in your thoughts by SMD only layouts and parts.RE series L for protection:V= L *di/dt is the basic formulaInductor energy stored is 1/2 LIexp2.Stock inductors (see Coilcraft, Renco, Pulse Eng) have full specs for design.RE Transient protection IEC 61000-4-5 level/class 4It was not intended for LV battery or vehicles but mains at various environments eg industrial buildings.We used in both these mains apps as well as our 28V avionics PSU bus these in order from the power source:Input EMI /CM/DM choke, series L or R, Transient Absorbing Zener, or MR2535.In the device we added Schottky catch diodes to protect sensitif TX/RX PHY and opamps/comparators.In our 1989 medical xenon illuminator designs we needed all of the above and more to stop CPU reset and crash upon lamp ignition by 35 kV series injection Tesla coil fast rise pulse.Hope this is useful in your design.Jon

author: jonpaul
author_rank: Super Contributor
timestamp: January 14, 2023, 02:36:55 pm
content: Matt, Will find some old designs schema.The book I mentioned , Electrical transients in Power systems 1st Editionby Allan Greenwood is a great reference for the theory, methods and practice.It is one of the best, the old 1st ed is fine and $25 at Amazon (no digital version!)(2ond ed $237!)https://www.amazon.com/gp/product/047132650X/ref=ox_sc_saved_image_1?smid=&psc=1The author was professional EE expert in electric transients at General Electric, T&D div.Thus the book is written for power system engineers, not power supply designers.But a lot of great info that applies to all transients generation and surpression, eg lightning, inductive etc.Jon