Re: Driver for IGBT? (-ve off and +ve on from CMOS)

Terry Given <my_name@xxxxxxxx> wrote:
>Glen Walpert wrote:
>> <ignoramus24489@xxxxxxxxxxxxxxxxxxxx> wrote:
>>>
>>>That said... How do you get to plot rare events such as my switchings,
>>>on the oscilloscope, so that I see voltage spikes.
>
>carefully. usually with a DSO, so you can catch the damned transient
>event that snots your IGBTs. I once spent 3hrs in the lab, blanket
>draped over me & the PM3394 scope in analogue mode, brightness cranked
>up, to catch a glimpse of something I suspected was there, but couldnt
>make the digital scope trigger on. I eventually saw one glitch, me & a
>buddy then reasoned out the cause in about 3 minutes flat, and had a fix
>running about 1/2 an hour later. metastability causing a race condition
>causing runt pulse causing very intermittent self-destruct. yay for ISP
>CPLDs.
>
>> Trigger on the gate drive for instance.
>>
>>>Also, would high voltage not endanger the oscilloscope itself?
>>
>> Perhaps, stay within its ratings using a voltage divider if necessary.
>>
>
>then, when it gets destroyed, replace the scope and get a few P5200 diff
>probes.

Good idea. I expect he can get away without them while testing with
his low power supply if he is careful, but at full power the same
transients that will destroy his IGBTs could easily fry his scope at
the same time. While he is looking for diff probes on eBay he might
want to keep an eye out for suitable current transformers as an
alternative to measuring currents with a shunt and a diff probe.

>>>>and wear safety glasses and a face shield at all times his equipment
>>>>is energized. Buying a few dozen spare IGBTs and gate drivers would
>>>>be a good idea too.
>>>
>>>haha
>>
>> Not joking, I have seen large plastic packages explode with the noise
>> of a shotgun blast and similar dispersal of small bits. How much do
>> you value your eyesight?
>
>1,000J will destroy many plastic packages. A Semikron rep once proudly
>announced their "rupture-proof" 1/2-bridge modules. So we bolted some to
>our 100kW prototype, and blew them up. The first one didnt rupture, but
>the drive leaped about 1' into the air. So we replaced the IGBT, and sat
>an anvil on top of a *** of nomex on top of the unit, and the module
>blew itself to tiny pieces. He was suitably embarassed, but bought us
>lunch so that was OK. IIRC it was only a kJ or so....

Well at least he should be well under a kJ. Although I previously
guessed that his inductor was on the order of 10 uH, that was a typo,
I meant 10 mH. I see that Hobart uses the classic 6 phase double-Y
connection with interphase transformer, so the SCRs fire 6 times per
cycle or every 2.8 ms, and if the inductor is sized to allow current
decay of 5 amps at 20 volts in 2.5 msec then the inductor would be 20
volts / 2000 volt/sec = 10 mH. They might easily have designed for
less ripple but probably not less than 1 amp, for a 50 mH reactor. So
with a short circuit current of say 400 amps he only has 20 joules to
dump somewhere unless I screwed up again :-).
.

Quantcast