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Registered Member #42796
Joined: Mon Jan 13 2014, 06:34PM
Location:
Posts: 195
I'm in the process of building a general purpose inverter with variable frequency and duty cycle based on TL494 but i'm not sure what max frequency and/or lowest ON time my IGBT's can suport. I have a 2MBI75UA-120 and 2MBI100TA-060 From datasheet the switching characteristics for each are the fallowing:
2MBI75UA-120
2MBI100TA-060
The large difference in Typical vs Max switching times confuses me When is recommended to use the Typical values and when is not?
Note that the design will be half bridge with adjustable frequency and duty cycle so no resonance and no ZCS.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
It all depends whether you are a hobbyist building one-off, and tuning it according to 'turn it up until the smoke comes out, then back off a bit', or a designer producing power inverters for cars transmissions that will sell by the 100,000, and *must not break down*.
Use typicals. If it gets hotter than you want, back off a bit.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Most surplus IGBTs you can find would have been used in motor drives, hard switching an inductive load at 5kHz. If you want to hard switch much faster than that, you will need to derate them. Probably no big deal as most domestic outlets won't allow for 75 or 100 amps of DC bus current.
In DRSSTCs we use them at something like 50 or 75kHz, but they only run in bursts for 5 or 10% of the time, so the average switching frequency is more like 5kHz.
Registered Member #42796
Joined: Mon Jan 13 2014, 06:34PM
Location:
Posts: 195
im not going to use them in a DRSSTC... so by hard switching them at a lower current than their rated current which values for the switching times should i use to calculate the minimum ON time and /or the maximum frequency Typical or Max?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I would ignore the switching times and use the rule of thumb that if you halved the current compared to what it can handle in a motor drive at 5kHz, you can double the switching frequency compared to 5kHz. And at 1/4 the current, 20kHz and so on.
This isn't exact because DC bus voltage also comes into the equation, but it should get you in the ballpark.
There is no minimum on-time as such. If you apply a gate pulse that's shorter than (Td(on)+Tr) then the device won't turn fully on. If you apply one shorter than Td(on) then it won't turn on at all. However, nothing bad will happen as the pulse is so short that no great energy will be dissipated inside the device.
Switching times generally increase with temperature and current, and manufacturing variations. The Max times are for the worst device that wouldn't be rejected in factory testing, at the highest temperature and current. Most of the devices will be closer to Typical most of the time, but in mass production you are supposed to do worst-case design with the Max values.
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IGBT max switching frequency
