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Registered Member #3964
Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332
hi All,
Wanted to ask what would be the highest frequency a CM300DY-24H can handle?? Cause I have a 200kHz drsstc, S.ward's UD1.3 driven, (no phase lead comp).. Planned to input power 500Watts (325VDC).
According to D.Sheet,
it has td(on) = 550ns tr = 180ns td(off) = 600ns tf = 350ns
Since my coil is 200khz, the time per cycle is 0.005sec I have totaled all the above time and reached about 1680nsec.. *in milliseconds.. 5ms per cycle and switching is 0.00168ms
I am thinking that all the delays etc are completely acceptable by the speed requirements,
Any comments about this will be highly appreciated.. THanks!
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
your switching cycle is 5us, not 5ms, and switching speed is 1.7ms... this will work very bad, maybe not even at all (IGBT death), especially with no delay compensation.
Registered Member #3964
Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332
how did you come up of that conclusion?? is there a computation for this? I mean what is the relation formula or rule of thumb here? It will be a great help if you can show it, thanks.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
Switching time at 200kHz is 5uS The IGBT can turn on and off in 1.68uS
Rule of thumb... Best practise... I got no idea, but would assume that a 200% rule ain't too bad to go by. Like if you want to look at a 25MHz signal, use a 50MHz scope. If you want to run a coil at 200kHz, use a IGBT suitable for atleast 400kHz. This is just guess work, careful study of each devices datasheet will tell you much more about losses vs. frequency etc.
Registered Member #3964
Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332
5us will mean 2.5us per half cycle, if there is 1.68 needed for 1 square cycle, it is still in the required speed, although not in the region of 50% margin,. hmmm.. not to mention the delay introduced by the driver itself could add more delay. The losses you are telling is the heat made by the switch isn't it? how do we look for that loss? Thanks..
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
look at it this way- if the igbt spends 1.7us turning on, then another 1.7us turning off, then its spending 60% of its time in the linear region where losses are huge. the rule of thumb i go by is: Fmax=1/((Ton+Toff+switching delays)*10)
Registered Member #3964
Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332
with the turning ON delay, it only requires 0.73us and not the whole 1.7us. okay.. so i think I'll try to find another IGBT =) .. thanks for the info guys!
btw, what brick can you recommend for my coil as such? 200khz
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
The delays are literally propagation delays; time from when the gate voltage hits zero to the time when the collector voltage starts rising. In hard-switched applications, they don't contribute towards losses. In a soft-switched circuit such as a DRSSTC, they contribute towards losses by causing the switching to deviate from ZCS, but the IGBT is not operating linearly during these delays.
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igbt speed
