Your experience with isolated igbt/mosfett drivers - Page 1
Forum section: electronics / projects

author: MarkoAnte
author_rank: Regular Contributor
timestamp: October 27, 2015, 08:53:31 am
content: Hi,I'm looking to build a costume high power igbt driver for my project.I have been looking around and I'm stuck between choosing TI isolated driver chip (eg. iso5851) or infineons isolated driver chip (eg. 1ED Family). Does anybody have any experience using them?Is one more reliable /better then the other - or it doesn't matter. I'm looking for isolation voltage grater then 1 KV for power around 10 KW and switching frequancys above the audio rage.Also I have been looking at examples for the dc-dc isolated converter. I have seen all - from simple flybacks, to complicated flybacks with snubbers, to ringing choke converters to half- bridge, full bridge and some resonant converters. It looks like every driver module I take apart has its own topology. Even IT in their application notes suggest push-pull or flyback (for the same power raiting mind you). Any experience on which topology is the most reliable. (Because of my duty cycle bootstrap capacitors are not ok).Best regards,MarkoUpdate: It appears that the IT parts, tho being better in voltage insulation, are practically unobtanium(delivery in 6 -4 months with 2000+ paces).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 27, 2015, 09:44:41 am
content: It's very common to "roll your own" for that power level, and up. Some good chips includehttp://www.digikey.com/product-detail/en/ACPL-339J-000E/516-3160-5-ND/4211132or just using high speed isolators (6N137, SFH6345, HCPL something or other, ADUM2101 type magnetic isolators, and so on) with a gate drive chip.I don't recommend building anything over about 3kW without desat protection or similar fault protection hardware. Wire it into a physical logic circuit, not a software interrupt. You will save many burned transistors with this protection!Tim

author: MarkoAnte
author_rank: Regular Contributor
timestamp: October 27, 2015, 10:17:10 am
content: Quote from: T3sl4co1l on October 27, 2015, 09:44:41 amI knowThat's why I'm looking at the IT or Infineon parts. But I have no way of testing them (lack of instruments and knowledge) other to build the entire thing up and see how good it does. What is the most common isolated dc-dc topology that is used in this application?Best regards,Marko

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 27, 2015, 07:48:01 pm
content: If you have a lack of instruments (oscilloscope, differential probes, current probes such as clip-on or Rogowski), I'm afraid you're looking at the wrong kind of project! If this is for an employer, make it perfectly clear that you are utterly unable to complete your task without these tools.The TI part seems like it would be fine, as long as you don't need much drive power or switching speed. I see there's a number of "1ED" parts, but I would think they're okay too.FWIW, I would never use a non-isolated HVIC (bootstrap) type driver for high power applications. Even if 1200V devices are available.DC-DC can also be "roll your own", including planar magnetics, custom or off-the-shelf transformers, or using ready-made modules. I would recommend reinforced insulation, whatever the method. RECOM 8kV modules are good: a bit more expensive than others, but they will be very reliable. Whatever the case, be sure the isolation barrier is well enough isolated.Tim

author: MarkoAnte
author_rank: Regular Contributor
timestamp: October 27, 2015, 08:41:09 pm
content: The IT parts, are new, are hard to get and the IT5500 is old (and easy to get) but is not 1kV working voltage. I think I will go whit the infineon part.I have, with the exception of the current probes, all those instruments. But they are probably not good enough(with my knowledge) to set up and test all the differences of the IT part and the Infineon part and to tell witch is better.Best regards,Marko

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 27, 2015, 11:01:03 pm
content: IT??

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 28, 2015, 12:36:25 am
content: I've designed a high frequency (t_r < 50ns), high power (Vin ~ 700VDC, 5kW per module) inverter, using magnetic couplers (the ADUM series). They're good for the slew rate (40kV/us) and isolation voltage (should be >50yr life at full operating voltage), and have good timing characteristics (10Mb+, low enough jitter, delay, skew, etc.).I wouldn't recommend the (cheaper, e.g. SI brand) variants, which don't claim DC stability or fail-safe (default levels) performance.Opto are good as well, but you're pushing into fiber optic territory when it comes to really high slew rates and tight timing. I have seen very few optos rated over 10kV/us slew. For IGBTs, they're just fine.Tim

author: eneuro
author_rank: Super Contributor
timestamp: October 28, 2015, 12:07:21 pm
content: Quote from: MarkoAnte on October 27, 2015, 08:53:31 amIt will probably depend on type on application where this driver will be usedIn 230VAC H-bridge project decided to test shared GDT isolated mosfets driver but it will be used for full wave DC-DC converter.This is only one stage of H-bridge (in final design there will be more mosfets in parallel ).Anyway, depending how critical high power igbt/mosfet application is I'd choose different drivers and protectionThis H-bridge willbe ued in some kind of research project, so I've decided use such strange driven GDT by... ZVS drover from 12V car starter battery

author: ElectronicTonic
author_rank: Contributor
timestamp: October 28, 2015, 03:04:53 pm
content: For my Double Resonant Solid State Tesla Coil, I used TI UCC27321 and UCC27322 mosfet drivers for the IGBT H-bridge, made of IXYS IXGN60N60C2D1 in SOT-227B mini-BLOC package. The drivers do not have isolated output, so I used a ferrite transformer between each driver and two mosfets to achieve a few hundred volts of isolation. For 1 kV or more, you'd just need some thicker wire insulation on transformer coils. The drivers worked well with no problem, although they did get a little warm to the touch since I ran them at 100 kHz. At one point, I blew up a couple IGBT's because I forgot to ground the bottom of the Tesla coil secondary. The driver ICs survived. I made a video showing what happened and how I fixed it:

author: Wolfram
author_rank: Frequent Contributor
timestamp: October 29, 2015, 08:08:58 am
content: Quote from: T3sl4co1l on October 28, 2015, 12:36:25 amWhat do you mean by DC stability and fail-safe performance? I checked the datasheet for the devices I've been using (Si8234) and they don't claim any minimum frequency or pulse width on the input. They also have an UVLO on the input side (as well as the output), which implies that the behavior is safe when the input side (or gate drive) supply fails.Edit:From the Si823x datasheet:Quote

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 29, 2015, 09:30:57 am
content: At least back when these things were introduced, ADI went to some length to describe their patented method -- DC stability and fail-safe are assured by the transmitter constantly pulsing, which reasserts whichever logic level it's supposed to be. In addition to pulsing on every input rising/falling edge. The "refresh" rate is something like 10us between pulses. They're also rated quite well for interference, so it should be a rare event indeed that the gate drive hiccups on its own (for whatever reason).If those parts are fail-safe with UVLO, they might be DC stable, too. I don't recall seeing the UVLO part before!Tim

author: mzzj
author_rank: Super Contributor
timestamp: October 29, 2015, 12:27:20 pm
content: Quote from: eneuro on October 28, 2015, 12:07:21 pmFor any beginners out there: This picture is probably wrong on so many levels that don't be tempted to copy the desing.

author: Richard Head
author_rank: Frequent Contributor
timestamp: October 29, 2015, 01:15:25 pm
content: The leakage inductance is a function of the geometry (amongst other things) between the primary and the secondary. Hence there will be massive leakage between the primary and secondary.Also, the four secondaries should be wound quadrafilar to reduce leakage between them. I've used wire wrap wire before but its breakdown voltage could be a limitation here. The primary-secondary leakage will erode the dead time with a higher possibility of shoot through.Also, the core is uncoated, which is tempting fate.The twisting of the leads is a good step though.

author: Wolfram
author_rank: Frequent Contributor
timestamp: October 29, 2015, 04:13:52 pm
content: Quote from: T3sl4co1l on October 29, 2015, 09:30:57 amThese use a similar method as well where an RF carrier is keyed by the gate drive signal, so they should be fail-safe in the same way as the AD parts. Both gate drive outputs for the dual versions are completely galvanically isolated from the input. This is unlike the classical high-side driver chips where everything is referenced to the same ground and the input transitions are transmitted to the high-side driver as pulses.I especially like the "PWM" input ones as they contain internal overlap protection and programmable deadtime generation, as well as UVLO on the input and both outputs. I've used them in several projects, and the only problems I've ever had were related to exceeding the dV/dt rating between the output and input side through a fault in my design. I've even had them survive IGBT failures while powered from mains (though without any significant bulk capacitance on the DC bus).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 29, 2015, 04:18:13 pm
content: The open design guarantees maximum inductance, not to mention the heatsink tabs are in the least useful places for cooling.Tim

author: nazardo
author_rank: Contributor
timestamp: October 29, 2015, 06:20:44 pm
content: Quote from: MarkoAnte on October 27, 2015, 08:53:31 am2SC0435T could fit your needs?

author: Siwastaja
author_rank: Super Contributor
timestamp: October 29, 2015, 06:36:28 pm
content: How about this:http://www.avagotech.com/products/optocouplers/industrial-plastic/isolated-gate-drive-optocouplers/highly-integrated-smart-gate-drives/acpl-337j-000eUsed the 2.5A version in a 1200V 150A IGBT 3-phase inverter; worked fine. Not a single blown transistor, and desat protection got thoroughly tested on field.

author: Richard Head
author_rank: Frequent Contributor
timestamp: October 30, 2015, 05:40:35 am
content: BlueskullI gave your question a bit more thought and in principle you should be able to distribute the primary between the secondaries as shown without seriously affecting the leakage. However, I have a suspicion in practice the leakage (P-S) will be higher than if they were all wound pentafilar. Luckily there's an easy way to measure the leakage so it's easy to test. I discovered years ago that as soon as you physically seperate two windings the leakage shoots up, even with a toroid. The best way is to twist all five wires together and then wind the transformer, like an RF balun.As far as the dead time is concerned, the leakage inductance smears (reduces dv/dt) the sharp edges during the turn on and off transitions so makes it possible both upper and lower devices could be on simultaneously.Uncoated cores place their dielectric strength entirely on the wire insulation. They also sometimes have sharp edges that can damage the insulation of the wires. If you can control those issues then there's no problem. They are admittedly far cheaper than coated cores. In fact, toroids are such a PITA for volume production that they are best avoided if possible. This goes for common mode chokes, CT's, gate drive and power transformers.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 30, 2015, 06:34:31 am
content: FYI, the leakage inductance of a transformer is defined by the space between wires. In conventional designs, the core has almost zero effect on leakage (less than 5% difference!).Windings on opposite legs of a core will struggle to transfer much power at all (at least, over any frequency range). Windings wound nearby (say, on top of each other in layers) work quite nicely, and twisted pairs work even better.More generally, the two conductors (primary and secondary) can be viewed as a parallel-wire transmission line. The leakage inductance is the inductance of that line. This makes pretty good sense for a winding made of twisted pair (a reasonable transmission line on its own), and makes rather less sense for windings that are distant (in separate layers, or hardly even coupled at all). But then, distant windings don't make much sense, either, because that maximizes leakage!Transmission lines have a more general property: the characteristic impedance, Zo. Almost always, when one is talking about stray inductance, or leakage, they're making the approximation that, for impedances below Zo, at low frequencies, the TL looks like an inductor. But it actually goes away and looks flat, into a matched impedance, and looks capacitive for higher impedances.So if you need absolutely the smallest leakage (regardless of capacitance), you must need an extremely low impedance. This can be done with any construction that yields a low impedance: wide parallel plates, alternating primary and secondary wires in a ribbon cable, any cable assembly with many wires alternating P/S, etc.For gate drive transformers (direct drive), both aspects (capacitance and inductance) are difficult to deal with. Inductance must be low, on par with the gate damping resistors, equivalent gate capacitance, and the driver's output capability. But isolation capacitance must also be low, to allow for line isolation and EMI purposes.Tim

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 30, 2015, 06:47:56 am
content: Yeah, and you'd expect -- if they are wound as twisted pairs -- that the transmission line impedance of each winding should be about 100 ohms, so that each gate is effectively driven through that length of 100 ohm transmission line. And the gate driver sees a total load of four in parallel, or 25 ohms.Tim

author: eneuro
author_rank: Super Contributor
timestamp: October 30, 2015, 07:04:42 pm
content: Quote from: blueskull on October 30, 2015, 05:53:07 amYep, this toroid core was not shown in high quality from both sides for the moment, to do not reveal all details and all tricks made there, but it looks like you've guessed very well my intentions and principles of this circuit designI wish, I didn't made more twisted ethernet wires pairs for each of four local a few turns transformers, but in this prototype I rather thinking on correct winding direction and polarity of secondary EMF, so my goal was to make those two gorups of coils for H-bridge gate driving in correct EMF polarity and at the same time I tried to provide higher short current for turning off two mosfets in H-bridge, to slow down turn on of another two mosfets, so that is why I thought, that grouping them on the same toroid and makeing all connections the same length (created some kind of symetry) with intentionally created magnetic flux leakage between those two goups of pri-sec coils (opposite coils are grouped together), I believe it should create slightly different gate charge/discharge current, hoping that push pull configuration is still fine to provide more turn off current than turn on in each of two groups of windingsEach one of four transformer pri-sec on single toroid core are twisted more than they are in factory in this cable, but we should twist them even more to get better results in GDTs.Random bead ferrite core was used there without any precise calculations, as I said only to try manage those four transformets secondary windigs direction and polarity, so yes from safety point of view such kind of toroid core and this wires insulation was not provided here ar any kind of reference design-it is rather research project, so unintentionally I see I've created small off topic there, but thanks for your thoughts and "brain storms" how it might workI will post in another thread how it works with connected ZVS driver which was real purpose of such tricky magnetic circuits design there.

author: mzzj
author_rank: Super Contributor
timestamp: November 01, 2015, 10:03:23 pm
content: Quote from: blueskull on October 29, 2015, 12:42:42 pmGate driver transformer looked horrible considering leakage inductance. My bad, didn't notice the multiple primary windings on the first time.Total construction still looks like very open with big inductance.