Need chip to handle surges at power supply input? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: December 27, 2022, 03:01:22 am
content: Hi,We are doing a Full Bridge, 10-36vin, 32vout, 300wout, 125kHz.The input will see surges to MIL-STD-1275E and also DEF STAN 61-005 Part 6.The LTC4364 is the beefiest of all offTheShelf surge protectors, but isn't capable of handling these standards' surges. Do you know of any that do, or are we looking at a home brew circuit only?LTC4364https://www.analog.com/media/en/technical-documentation/data-sheets/ltc4364-1-4364-2.pdfMIL-STD-1275Ehttp://everyspec.com/MIL-STD/MIL-STD-1100-1299/MIL-STD-1275E_45886/DEF STAN 61-005 Part 6https://global.ihs.com/doc_detail.cfm?document_name=DEF%20STAN%2061%2D5%3A%20PART%206&item_s_key=00517937

author: David Hess
author_rank: Super Contributor
timestamp: December 27, 2022, 06:34:31 am
content: Long ago when I had to meet that standard, or a very similar one, I used a source follower in front of the regulator to increase the input voltage capability. In that case I could tolerate the increased voltage drop since I was dropping the voltage anyway, but the same idea could be used with a charge pump to provide drive to the gate allowing essentially zero voltage drop. Then if the input voltage rises, even quickly, the source follower will maintain the same output voltage. If the voltage rises too high, over-voltage detection should cut the gate drive off shutting off the power MOSFET and preventing it from being destroyed. Surge capability is then only limited by the voltage rating of the power MOSFET.The control circuits for this draw very little current, making them easy to protect, perhaps with the same lower current circuit that I used.

author: Faringdon
author_rank: Super Contributor
timestamp: December 27, 2022, 12:14:50 pm
content: Thanks, having that follower sounds good....the surges here are up to 250V, and so it means, AYK, that the source follower has 30A flowing through it, with a drop of some 250-36V flowing through it....for the duration of the surge.......which is long, but the exact duration doesnt seem clear from the standard.DEF STAN 61-005 part 6 we dont even have, you have to pay for it.I am just wondering if we should add a boost converter at the front end...boost up to 100Vin...and then simply switch out the input surge if it goes above 100V....then the Boosters output cap can serve the innput current for the duration of the transient.?

author: David Hess
author_rank: Super Contributor
timestamp: December 27, 2022, 01:11:16 pm
content: When I did it the requirement was that there be no damage to the device, and it had to resume normal operation after the surge.A 300 watt boost converter is not a trivial addition, and does not inherently disconnect from the input but instead passes the surge on, requiring even more complexity. SEPIC converters are sometimes used because they provide DC isolation from input to output, but are questionable at 300 watts.Even if you use a switching topology that can handle high voltage surges at the input, I would still want to current limit and disconnect before the input capacitor. But what would be wrong with sometimes like a forward converter but with the input switches rated for much higher voltage so that it can just stop switching during the surge?

author: Faringdon
author_rank: Super Contributor
timestamp: December 27, 2022, 02:24:57 pm
content: QuoteThanks, yes, you are right, but if the surge is up to 100v, and the output of the booster is 100v normally, then who cares if the surge gets through?....its just the normal input voltage to the follow-on full bridge SMPS....we would just put a bypass diode to bypass the boost inductor when the surge happened.But you are right, a 300W boost is not trivial, and in fact, i think it would need to be two dual_cascaded_boosters in parallel........since 10v to 100v boost at 300W/2 will need a cascaded booster.....then two in parallel due to the 34A of input current that you get when vin is just 10V.So i think a custom linear regulator with a fast response will be required.....its going to be a real chunker of a solution though.The thing i like about front end boosters , especially paralelled and interleave switched, is that they really reduce the diff mode input filter inductor requirement.

author: jonpaul
author_rank: Super Contributor
timestamp: December 27, 2022, 04:20:25 pm
content: MR2535 Alt load dump TAZ fine for automotive or 28V bus avionics use several in series if higher clampj

author: Faringdon
author_rank: Super Contributor
timestamp: December 27, 2022, 04:45:46 pm
content: ...So, As you know, certain 28V automotive bus systems are saidd to suffer surges of "100V for 50ms". MIL STD 1275E tells that equipment connected to the 28V bus must keep delivering max load power throughout this surge. (ie, not just simply switch the surge out from its inputs)Page 3 of this below, tells what causes the surge voltage of "100V for 50ms" on the 28V bus of certain automotive systems...ti.com surge protector App Note:https://www.ti.com/lit/ug/tidudg1/tidudg1.pdf?ts=1672143896460&ref_url=https%253A%252F%252Fwww.electro-tech-online.com%252F..it says that these such surges "occur during motor events, such as the main turret turning, which is then seen by any accessory that is connected to the 28-V bus."...Do you agree that this just doesnt sound right? Admittedly the current drawn from the 28V bus to turn the turret would be high. ..Then when the turret stopped turning, the energy in the stray inductance of the 28V bus would need somewhere to go....but surely it would simply go into the input capacitor bank of the turret motor, and thence not cause any overvoltage at all?.......If the input capacitor bank gets dried out (eg with age, wear-out, etc), and becomes less in capacitance, then the stray L energy would still need somewhere to go, and so would surely charge up that input capacitor bank to more than 100V....in which case , any item on the 28V bus, that was in accordance with MIL STD 1275E, (ie, protected up to 100V surge) would fail anyway?As such, would it not be better to simply switch out the surge, rather than try and port the device running current through an enormous, step-down, linear regulator, during the surge? Switching out the surge would result in non-service of the load for approx 100ms or so, but at least it could resume operation after that......i mean, you could always make the device go into "power throughput limited operation" mode during the surge aswell, so that if it happened to be on light load at the time of the surge, then the Vout woudlnt drop out at all anyway.And in any case, many devices have an input battery which would see them through a 100ms surge anyway.Isnt this standard ill thought out?..Also, its wrong to call it a "voltage surge"...since it is a surge caused by current flow in the stray inductance..when the turret stops turning, the voltage on the bus will rise to whatever voltage it rises to, in order to keep the broken stray inductive current flowing.Also, since the turret motor current is known, and so too is the stray inductance of the 28V Bus...then why not just put a proper surge arrestor on the 28V bus, to handle that?.....So, why put large , expensive ,"ride through" surge protection in every single device? In any case, if all the devices on the 28V bus are on light load when the surge happens, then without a surge arrestor, the bus voltage will rise to well over 100V anyway.....making MIL STD 1275E conformant devices unprotected.So surely you agree, that what is needed, is a proper surge protector on the 28V bus?.....and nothing more than simple "switch-out" surge protection in every device on the bus?Please do not fear giving away military secrets by respnding to this, virutally the entire Western Power Electronics and SMPS sector has been outsourced to outside of the West anyway.....leaving the West massively way behind in this respect, so you'll only be telling things that those outside the West already know far batter than the West anyway.

author: floobydust
author_rank: Super Contributor
timestamp: December 27, 2022, 05:36:14 pm
content: Local loads need local surge protection. Some motor loads have generator action due to mechanical inertia, they can dump regen energy into the B+ rail and kick it up, in addition to the cable/wiring inductance spike. If you "switch out" the surge source, sometimes the load is relying on the DC bus being there, to keep the electronics from seeing a gross, long-term high energy overvoltage.One product we usedLTC4364and it was a failure - inadequate reverse polarity voltage coverage, and the pass mosfet roasted during a transient as it was in linear mode to ride through. Calculate that power dissipation and it's very high. I would just switch off until the transient clears and ensure there is enough hold time downstream so things don't reboot.For 24V systems now I use a pair ofSM8A27but watch the clamp voltage at cold temperatures. You could look at that TVS family.

author: Faringdon
author_rank: Super Contributor
timestamp: December 27, 2022, 05:54:20 pm
content: QuoteThanks,This is correct, and thanks for telling what the actual problem is.....This is the problem which needs addressing.Basically, whats needed, is a big resistor , which simply gets switched across the Bus by say an IGBT, whenever the bus goes above X volts....and it switches out, when the bus voltage goes back below X volts (or add a little hysteresis there).Maybe they already do this, and the result is a maximum of 100v on the bus (??_)Supposing though, that i do choose to add "ride through surge protection", in other words, i build a (big!) circuit that can allow my device to still deliver 300W right through the surge......well, that would have the advantage that no processors would get reset by the vout dropout.....but then.....it doesnt take 300W to stop a processor from resetting....so surely, another way, would be to simply make the Device power supply go into power limited mode, such that it still delivers some power to the output (enough to stop the processor from dropping out)...but not the full 300w....because making a linear regulator to carry that amount of current ( and putting it in every device on the bus) seems like madness. Also, it would have to be maybe extremely big, because in the event of much turret changing of direction, then the linear_regulator_surge_protector would surely overheat...unless it were made enormous...which would surely be madness?

author: jonpaul
author_rank: Super Contributor
timestamp: December 27, 2022, 06:28:07 pm
content: read very old papers and articles on alternator load dump, a large die area TAZ like MOT MR2525, MR2535 is specifically rated for that service.The avionics bus spec is very well proovedj

author: Faringdon
author_rank: Super Contributor
timestamp: December 28, 2022, 01:24:28 pm
content: This App Note...https://www.ti.com/lit/ug/tidudg1/tidudg1.pdf?ts=1672143896460&ref_url=https%253A%252F%252Fwww.electro-tech-online.com%252F..details a front end linear regulator which clamps the input voltage to some 40V when a 100V surge occurs......this means about 200W being dissipated in the regulator for the duration of the surge.I just wondered how frequently these surges occurred in these vehicles?If it was one every second, then i expect that regulator would fry.Just now found out that our 300W converter, (10-36vin), must also keep supplying 300W throughout the attached load dump surge aswell...I believe you would agree that this needs us to boost up the input voltage to 175V, and beat the surge like that?.....So i believe we need a triple cascaded boost converter...and three of those in pllel, at the front end...then we beat the surge!.....we dont even see it...because our effective vin is now above the surge!

author: Faringdon
author_rank: Super Contributor
timestamp: December 29, 2022, 01:45:10 am
content: The attached shows a 300W SMPS (LTspice and pdf) with nominal vin of 10-36vdc, being protected from a 175VDC surge.Just uses a linear regulator. (voltage clamp)Do you think its OK?(though think will have to make 10 separate linear voltage clamps , each with a clamped maximum current, to prevent current hogging){EDIT....Image added as per Jon Paul..... END OF EDIT}

author: jonpaul
author_rank: Super Contributor
timestamp: December 29, 2022, 04:53:02 am
content: FTTS, if you can't post an image, I cannot bother with your pdfs or asc.Note that the avaition regulators specify the transient on a power bus, eg FAA in USA had DO-160, includes energy, voltages and model generator for 28 bus.Sure UK, EU regulations cover similar.Jon

author: Faringdon
author_rank: Super Contributor
timestamp: January 25, 2023, 12:01:41 am
content: The attached is the most pathetic thing you will ever see in the world of SMPS....its a Full Bridge for vin=10-36v, vout = 32v, pout = 300w.BUTThe input has surges to DEF STAN 61-005 which means Vin sometimes goes to 175vdc for 500ms and the converter must be able to provide 32v and 300w throughout this.So the three Surge Buck converters as shown are pretty well the only realistic way of handling the surge...but just look at the heaps of components!!!LTspice and jpeg as attached. Also, a waveform plot of Vin, Vin at FullBridge input, and Vout during the surge, when on full load.I think four pllel flybacks, with FETs capable of handling 350V, would be a better way? (ie, instead of three surge bucks and one Full Bridge)Would you agree?

author: jonpaul
author_rank: Super Contributor
timestamp: January 25, 2023, 10:19:47 am
content: As always FTTS, time to consider retiring?Essence of fine Engineering is the simplest solution.Bus>>transient protection (filter, TAZ)>>ONE STAGE converter, topologies capable of buck boost.We easily handled 750W in single stage double Foward.Back to the drawing board.j

author: Faringdon
author_rank: Super Contributor
timestamp: January 25, 2023, 06:47:50 pm
content: QuoteThanks, thats not possible for us, because there is no transient protection capable of quenching the 500ms surge which is at 175vdc.The system we are installing into does not have that.The only realistic way is to have a surge Buck converter at the front end.......or, use enough paralleled converters with the capability to handle the 175VDC input....in this case, say four paralleled flyback converters.

author: jonpaul
author_rank: Super Contributor
timestamp: January 25, 2023, 06:58:49 pm
content: FTTS .asmentioed before...Alternator load dump large die TVS for over 12/28V bus, we use several in series, old parts MR2525 MR2535https://www.vishay.com/docs/88490/tvs.pdfhttps://www.littelfuse.com/~/media/electronics/application_notes/littelfuse_tvs_diode_meet_automotive_load_dump_standard_application_note.pdf.pdf?la=enhttps://www.powerelectronictips.com/automotive-load-dump-tvs-a-unique-transient-voltage-suppression-application/Enjoy!Jon

author: Njk
author_rank: Frequent Contributor
timestamp: January 25, 2023, 07:48:02 pm
content: I've a stock of ST RBO40-40 devices (leftovers from old projects). Yes, they're approved, certified, etc, etc. But only for certain specific conditions. For instance, it requires 60s to cool down after each load dump pulse. It's assumed an overvoltage is just a rare accidental event. It may not be always the case (examples already provided). It may not be always possible to forecast (let's think outside a formal requirements). Assume you've to withstand 1 second of 100V frequently. A TVS diode will blow up. So the question how to handle the excessive voltage can make sense.I don't think it'll be a good idea to overcomplicate the design by a multi-stage conversion (as proposed). Complexity results in more real estate is occupied by multiple smart components, reducing the reliability. Perhaps it'll be better to substitute them all with a single dumb component, a huge serial resistor (inserted temporarily) that will dissipate the heat, helping the diode to clamp the pulse. Eventual thermal shutdown when overheat.

author: dmills
author_rank: Super Contributor
timestamp: January 27, 2023, 07:23:26 pm
content: My instinct here says hysteretic buck converter on the input of the power supply proper if you cannot design the power supply to run thru the high voltage surge.Most of the time you just hold the mosfet on, and nothing very interesting happens, but if the voltage at the output of the buck starts to rise excessively (whatever that means in your context) you turn the fet off and wait for the voltage to fall, it will sit there oscillating until the surge passes and things get back to normal.Control doings should be fairly simple, inductor will be a bit of a pain I expect, but having it hold the input to your main doings to 40V or so should work easily enough, and the nice bit is it doesn't try to dissipate a surge (Which if it is from a reasonably butch alternator load dump, you will likely fail at).

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 28, 2023, 05:17:42 am
content: I didn't see any mention of how much space is available, another possibility is to clamp the surge but dissipate most of the energy in something that's cheaper than semiconductors, for example a power resistor.

author: dmills
author_rank: Super Contributor
timestamp: January 28, 2023, 03:01:16 pm
content: The nasty thing about automotive load dump surges is that they can be from functionally near perfect voltage sources, there can be a LOT of current behind them, for hundreds of ms, so anything dissipative is potentially going to be handling a huge amount of energy.It can obviously be done (a lead acid battery makes a great sink for this sort of thing!), but absorbing it into a cap bank (Which is a cool way to handle transient as opposed to surge suppression) or resistor can get annoyingly large.It is something that you can design around, and doing so is not magic, mostly a case of pick the appropriate topology and ate components for worst case. There is a reason this stuff costs the MOD what it does, and the twenty year availability requirement is only part of it.

author: Njk
author_rank: Frequent Contributor
timestamp: January 28, 2023, 06:14:28 pm
content: So it depends on the overvoltage statistics and on desired perfection level.The dissipating solution may work as many cooling options are available, from heat pipes to liquid cooling. Provided there will be no overheating through this somewhere else, e.g. at the source side. While the active solution will have to switch back and forth smoothly and at random time. That can eventually result in something like on-line UPS with buffer energy storage.

author: Faringdon
author_rank: Super Contributor
timestamp: January 29, 2023, 12:24:39 am
content: Thanks,The attached appears to be THE way to implement this ugliest of all converters...the Surge Buck Converter.Needs the hi side supply to be added for the gate drives.The delay time on the high current sensing comparator is the key to the whole thing.....making it about 150ns in delay time sounds about right.Would you agree?(LTspice and jpeg attached)

author: dmills
author_rank: Super Contributor
timestamp: January 29, 2023, 12:41:32 am
content: That looks PAINFULLY complex to me, I was thinking in terms of putting the mosfet in the negative connection so removing the need for the boost supply, and ditching the current limit as being something the second stage would deal with.Then a jellybean comparator with a little positive feedback and a low side driver?Probably still need some kind of trivial supply to power the control doings, maybe a current source and zenner diode at a few mA or something?The output stage would of course need to be isolated, which yours isn't.Still feels like something that should be possible in a single stage converter, so this switched mode buck clamp thing feels like a bit of a bag on the side for poor design of the main supply doings?

author: Faringdon
author_rank: Super Contributor
timestamp: January 29, 2023, 06:31:45 pm
content: QuoteThanks, it is a bad situation all round...the converters normal vin is 10-36vdc, and its 300W. When vin is 12vdc, Iin is some 28A, and so whatever does the surge handling has to be able to port the 28A (33A when vin is 10v).So yes......the only other way we came up with was to ditch the surge buck and just make the main converter as 4 pllel'd flybacks, instead of the single full bridge....then each flyback could have NFETs etc, that could handle the 175vdc input.QuoteThansk, yes, i also tried that...but didnt like the isolated feedback then going on within the surge buckQuoteThanks, i have thought about that also, and still consider it now.........but the lack of limitation of current in the surge buck's fet put me off...as i thought it may then go pop in some cases.