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Re: [TCML] IGBT paralleling
With a 2,400 VDC IGBT, running it at a line doubled 220 VAC gives 2400 VDC -
616 VDC --- over 1,784 Volts of wasted headroom that needs to be filled,
hence the use of a power transformer to boost the AC input from 220 to
around 1700 VAC. The headroom I'm referring to is similar to your audio
reference only in this case wasting AC power headroom on a large IGBT that
should be driven at higher potential to maximize coil output.
This is, of course, all not relevant with standard medium size coils using
rectified line drive (such as CM300 circuits) or line rectified drive with a
voltage doubler circuit common with CM600 IGBTs.
D.C. Cox
On Sun, Jul 11, 2010 at 4:13 PM, Drake Schutt <drake89@xxxxxxxxx> wrote:
> Dc- what do you mean when you refer to headroom in this post? I'm used to
> the term only in music production referring to dB.
>
> Regards
> Drake
>
>
> On Jul 11, 2010, at 3:22 PM, DC Cox <resonance@xxxxxxxxxxxx> wrote:
>
> With CM300s or CM600s you can just double the 220 VAC line to get 642 VDC
>> for a good match.
>>
>> If running, perhaps, a CM2400, you want to go up to near 2,400 VDC on the
>> drive, so you end up using a 220/480 Volt 3 phase to get up to at or near
>> the 2,400 VDC rectified. This gives you better output because you go from
>> 642 VDC to 2400 VDC that is being switched into the primary inductor.
>>
>> Typically, with really large systems the only way to get from 220/440 VAC
>> to
>> produce the 2400 VDC drive max is to use a small 25 to 50 kVA xmfr
>> (surplus
>> pole units).
>>
>> Not a dual pole pig unit, just a 220/440 VAC 3 phase xmfr delivering
>> around
>> 1650 VAC before rectification.
>>
>> The main point with large DRSSTC type coils is efficiency --- eliminating
>> all those losses in the heat & UV light production in the spark gap, and
>> obtaining quicker dI/dt rates.
>>
>> As you pointed out small and medium size coils run just fine without using
>> any pole xmfrs. Usually above 15-18 ft long sparks the pole xmfr boost
>> helps out get to the higher potential of the larger IGBTs without wasting
>> a
>> lot of headroom.
>>
>> Dr. Resonance
>>
>>
>>
>>
>> On Sun, Jul 11, 2010 at 2:14 PM, Gary Lau <glau1024@xxxxxxxxx> wrote:
>>
>> I'm going to bare my ignorance here. I thought that the whole point of
>>> solid state TC's was that you don't need a multi-kilovolt power supply.
>>> Are
>>> pole pigs really used to power these? A _dual_ pig powered magnifier???
>>>
>>> Regards, Gary Lau
>>> MA, USA
>>>
>>> On Sun, Jul 11, 2010 at 12:16 PM, Scott Bogard <sdbogard@xxxxxxxxx>
>>> wrote:
>>>
>>> Hi John,
>>>> By chance is there a compiled list somewhere of "good IGBTs" that
>>>> are used and those that aren't. Anyway back to the original question,
>>>> is
>>>>
>>> it
>>>
>>>> possible to parallel them? Lets say for kicks I'm building a dual pig
>>>> powered 30kVa magnifier with a LTR cap (I'm clearly not, we are talking
>>>> theoretical here.) Clearly the peak currents will be beyond any
>>>>
>>> reasonably
>>>
>>>> priced IGBT, is it possible to parallel lesser current units to handle
>>>>
>>> the
>>>
>>>> load, and what would that entail? Thanks.
>>>>
>>>> Scott Bogard.
>>>>
>>>> On 7/10/2010 5:09 PM, John Forcina wrote:
>>>>
>>>> Those IGBT's seem far from ideal. The TO220 package is a very poor
>>>>>
>>>> choice
>>>
>>>> as far as thermal conductivity and the datasheet says it all 0.75C/W.
>>>>>
>>>> You
>>>
>>>> will not be able to remove enough heat from the surface of the IGBT die
>>>>> quick enough between current pulses and the device will fail. They do
>>>>>
>>>> not
>>>
>>>> have a internal anti-parallel diode so adding that externally will add
>>>>>
>>>> to
>>>
>>>> the final cost also. Not to mention doing that will add additional loop
>>>>> area and stray inductance between units. One more thing is the
>>>>>
>>>> switching
>>>
>>>> times are surprisingly slow for that small of a unit. td(OFF) 96ns.
>>>>>
>>>> It's
>>>
>>>> not that slow however it does seem slow for that small of a device. I
>>>>> have
>>>>> seen much better overall performance from larger IGBT's. My suggestion
>>>>>
>>>> is
>>>
>>>> to just spend more money and use IGBT's that have been used and proven
>>>>>
>>>> to
>>>
>>>> work in Tesla Coils time and time again. There must be some reason that
>>>>> we
>>>>> all use them ;)
>>>>>
>>>>> On Sat, Jul 10, 2010 at 4:38 PM, Scott Bogard<sdbogard@xxxxxxxxx>
>>>>>
>>>> wrote:
>>>
>>>>
>>>>> Interesting,
>>>>>
>>>>>> I am in the wee beginning stages of building my first SISG, and
>>>>>>
>>>>> as
>>>
>>>> such am in the market for IGBTs. I found these, which look very
>>>>>> inexpensive
>>>>>> and have decent ratings.
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>> http://www.newark.com/fairchild-semiconductor/hgtp12n60a4/single-igbt-600v-54a/dp/90B5642
>>>
>>>> My thinking is if heat is a problem or peak current, can I just
>>>>>>
>>>>> parallel
>>>
>>>> them? at $1.50 a pop it seems infinitely better than 1 $18 IGBT of
>>>>>> nearly
>>>>>> the same ratings... I didn't look at temperature or package
>>>>>>
>>>>> information
>>>
>>>> yet, so maybe there is a problem there.
>>>>>>
>>>>>> Scott Bogard.
>>>>>>
>>>>>>
>>>>>> On 7/10/2010 8:26 AM, McCauley, Daniel H wrote:
>>>>>>
>>>>>> Scott,
>>>>>>
>>>>>>>
>>>>>>> The electric ratings may be the same or similar, but you also have to
>>>>>>> compare the mechanical ratings - in particular the thermal ratings.
>>>>>>> This
>>>>>>> would be junction-to-case thermal impedances etc... The expensive
>>>>>>>
>>>>>> IGBTs
>>>
>>>> that are commonly used in DRSSTCs are usually ISOBLOC type packages
>>>>>>> which
>>>>>>> excellent thermal impedances. Compare this vs. a TO-247 package of
>>>>>>>
>>>>>> the
>>>
>>>> same
>>>>>>> die.
>>>>>>>
>>>>>>> And when comparing a TO-247 package to an ISOBLOC, keep in mind that
>>>>>>>
>>>>>> you
>>>
>>>> STILL NEED to add a thermal insulator between the TO-247 and heatsink,
>>>>>>> which
>>>>>>> just makes the thermal impedance even worse. The ISOBLOC (or
>>>>>>> SOT-227)
>>>>>>> doesn't require a thermal interface other a small smidgeon of thermal
>>>>>>> grease
>>>>>>> or a graphite pad.
>>>>>>>
>>>>>>> Dan
>>>>>>> http://www.easternvoltageresearch.com
>>>>>>> DRSSTC, SSTC, Flyback, Plasma Speaker Kits
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> -----Original Message-----
>>>>>>> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
>>>>>>> Behalf Of Scott Bogard
>>>>>>> Sent: Friday, July 09, 2010 9:52 PM
>>>>>>> To: Tesla Coil Mailing List
>>>>>>> Subject: EXTERNAL: [TCML] IGBT paralleling
>>>>>>>
>>>>>>> Greetings all,
>>>>>>> So, after a bit of researching I've noticed there are IGBTs on
>>>>>>> Newark with exactly the same ratings as some of the SSTC approved
>>>>>>>
>>>>>> IGBTs,
>>>
>>>> but
>>>>>>> at 1/10th the price. What makes these others so special that they
>>>>>>> are
>>>>>>> better, and if it is just a matter of peak current ratings, since
>>>>>>>
>>>>>> IGBTs
>>>
>>>> are
>>>>>>> gate driven, can we just parallel a few to get the required pulse
>>>>>>> current
>>>>>>> rating? I ask because I've not heard of anybody doing this, then
>>>>>>>
>>>>>> again
>>>
>>>> I've
>>>>>>> only begun to research SSTC a little bit ago. Just musing.
>>>>>>>
>>>>>>> Scott Bogard.
>>>>>>>
>>>>>>> _______________________________________________
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