Power device torture circuit aka horrible DC/DC? - Page 1
Forum section: electronics / projects

author: Amper
author_rank: Frequent Contributor
timestamp: July 04, 2022, 11:39:04 am
content: Hi!Im looking for a way to age powerdevices like igbt and mosfets by heat and also elecric load as close to the datasheet limits as possible, but not exceeding them.For logic transistors this is pretty straight forward, just heat them in an oven and drive them according to what you want through some sort of ohmic load.The big issue is larger devices in the order of a few hundred volts and a few amps. The load quickly exceeds several kW wich will have to run through the entire test of several weeks or even months, not really practical, also larger power resistors suffer from too much inductance, they will degrade the current waveform and cause too much overshoot already at a few kHz.To summarize: I want to cause a Current of a few A to be switched by an igbt at high voltage but with no unnessecary losses in the test circuit.An idea i have comes from motor test stands, having identical drivetrains connected by their DC-Links and mechanically, one running as alternator, one as motor, this way the power runs in circles, sort of like a real version of reactive power, only the thermal losses have to be supplied from outside of the loop.This may be realized by some sort of dcdc converter as well, skipping all the mechanics, just loading and unlaoding a transformer of some sort, maybe even just some inductor.What i could not figure out yet is the topology though, since im tryng to reach the opposite of the usual goal of zero voltage/ current switching. I have to switch the full current at full voltage both rising and falling.Is this even possible?How is this done in industriy or science?I hope someone can point me in the right direction

author: Someone
author_rank: Super Contributor
timestamp: July 04, 2022, 11:50:25 am
content: Its a thing:https://pacificpower.com/2021/01/regenerative-ac-dc-programmable-ac-power-sources/https://nhresearch.com/power-electronics-test-systems-and-instruments/ac-dc-regenerative-loads/ac-regenerative/https://www.keysight.com/au/en/products/dc-power-supplies/ate-system-power-supply/rp7900-series-regenerative-programmable-power-supplies-5kw-10kw.htmlhttps://www.chromaate.com/en/products_list/ac_power_sourceThe magic keyword you were missing is "regenerative source"

author: Amper
author_rank: Frequent Contributor
timestamp: July 04, 2022, 11:54:45 am
content: Mh, im not sure about that, in my experience, loads like this are pretty slow, certainly not sub us speed, thats limited already by the wiring and the inductance due to their phsysical size. Also the test circuit will have to be build fpr several DUT, a lot like 10 or 20 at once, all separately loaded so they will be strained equally.Im not looking into building a dcdc for inputting and loading a switch, i want the switch to be inside of the dcdc topology itself and switch at >20kHz.

author: mag_therm
author_rank: Frequent Contributor
timestamp: July 04, 2022, 12:41:24 pm
content: If you are or will be a user in quantity of a particular device, then I suggest to contact the applications engineering of the semiconductor manufacturer. It is not in the interest of either the equipment manufacturer or the semiconductor manufacture that a product gets out with improperly selected devices.It used to be that some devices were made in batches to meet equipment manufacturer spec, then given his local part number and not published in catalog.For example if the circuit required higher balance of commutation losses compared to on -state voltage, the magic stuff like doping and irradiation can be adjusted for a specific application.That is less common now with published parameters for circuit simulation and a wider range of catalog ratings.The test jigs you mention would be costly, usually the device will be tested in prototypes.Have a look at the simpler measurement /test circuits published in the datasheets.For example Rohm still does a traditional well detailed data sheet.

author: Amper
author_rank: Frequent Contributor
timestamp: July 04, 2022, 01:12:13 pm
content: Oh no, im not trying to do selection, the issue is, we distrust the manufacturers, youd be surprised how often datasheet values are not held and how often the parts degrade quickly. The aim is to select second source components and qualify/verify the manufacturers claims before using the devices in production.We already have several widely known manufacturers that ar not bought from because we know about process issues in their manufacturing facilities wich have lead to our products failing. Today, since nothing is available and the sources get sketchier and skechier, these tests become very important.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 04, 2022, 02:35:11 pm
content: A 2 switch bridge circuit similar to that's used to drive SR motors will do. Build a pair of those circuits and by alternating the switching, the ripple current through the input capacitors would be largely cancelled out.

author: Stray Electron
author_rank: Super Contributor
timestamp: July 04, 2022, 04:27:19 pm
content: The Elgar AC Power Sources are designed for (among other things) stress testing AC powered devices. The can provide over and under voltage, variable frequencies and other non-standard conditions. The Elgar 251 series is very popular and pretty easy to find. You can find manuals online and read them.

author: Marco
author_rank: Super Contributor
timestamp: July 04, 2022, 07:28:11 pm
content: Quote from: Amper on July 04, 2022, 11:39:04 amMake a two switch "converter", which is just driving an inductor. Overdimensioned top switch and flyback diodes, bottom switch is IGBT under test. Power goes straight back to rail after switches turn off.Should be an okay regenerative emulation of a hard switched half bridge.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 05, 2022, 12:37:38 am
content: The one difference is, you get inductive turn-off (ZVS?), and ZCS turn-on if duty cycle is low (DCM) (but can be hard switching by servoing inductor current in CCM). So, not quite the same as a forward converter (~square current), or resonant (~sine humps with modest reversal). Maybe that's good enough.There's also the two-pulse test, which is done with essentially a boost setup, with the bottom switch driven with one long on-pulse, then short off, short on, then off for a long time. If supplied from a low voltage (enough to account for inductor and switch V drop), this allows testing saturation and switching behavior, albeit at a low duty cycle. You of course need something to recycle the diode output (dump) side, if you want this to operate at much peak voltage and duty cycle. So, reduces to the buck/boost case, basically.Quote from: Amper on July 04, 2022, 11:54:45 amNot... sure how exactly you expected to use the thing there. You'd set up the power supply as you would anything else ever, and dump its load into the thing. Your supply's inductors and bypass caps already handle ~us and ~ms scale fluctuations. The load just soaks up the DC left over.Similarly, you could set up a combined buck and boost supply (or synchronous), basically a mirror image of one stage, so that the higher voltage is bucked to a lower voltage, boosted back up, feeding each other from a common rail; and one acts as an e.g. constant current sink, and the other as constant voltage source. Or vice versa, or any resistive characteristic inbetween those two extremes. Then a smaller main supply just provides enough current to "top up" the difference (losses). No need for grid-tie. Or, it is already, but to its own internal "grid" (DC link).Sometimes, this might not be very easy to arrange. Like, at my first design job, we tested induction heaters into water-cooled loads -- wasn't worth the effort to make a regenerative inductive load. That was a pretty wide application (in terms of frequency and power range) though. If your application is narrower focused, it might be easy enough to, say, set up a load of particular Fo, Q and just dump it into a rectifier and back into the same unit's supply rail. Which is what a resonant supply already is, so that's a fairly trivial case; but this already covers square-pulse and resonant converters of a number of types. Or also, for like a VFD, if it can be set to 0Hz, then the output (albeit from just one or two poles) is right there; if not, then again a rectifier, filter and possibly converter would do the job.Tim