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Registered Member #1879
Joined: Mon Dec 22 2008, 04:11AM
Location:
Posts: 40
I finalized the primary current feedback cirqutry and the current sense front end and I played with the coil at low voltage last night. It blew my mind to se over 120A peaks in the primary with only 20V range of the input voltage.
Unfourtunally I only have one live input on my scope and I dont own current probes so I cant measure what is going on as much as I would like to do. What I am curious over is how c101 vs C121 ns C122 comes into play. What is the currents going through them? My gut feel is that the current goes out of C121, through the IGBT and the tank into C122. How does C101 fit in to this? I cant imagine the electrolytic caps handle a few hundred amps. Are they ok with that or am I messed up in my thinking and the bult current really goes through C101?
An other question; To me it looks like the voltage over Q102 and Q101 at worst is the rail to rail voltage (+ the voltage drop over the free wheeling diode just before the other IGBT ignite)
Is there any part of the cycle where the Uce exceed this?
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
[quote] What I am curious over is how c101 vs C121 ns C122 comes into play. What is the currents going through them? My gut feel is that the current goes out of C121, through the IGBT and the tank into C122. How does C101 fit in to this? I cant imagine the electrolytic caps handle a few hundred amps. Are they ok with that or am I messed up in my thinking and the bult current really goes through C101? [/quote]
C121 and C122 are the energy storage capacitors for the DC bus. Almost 99.99% of the energy for each burst comes directly out of these capacitors. Current leaves C121 and returns through C122. They handle all the peak current.
C101 is used to control spikes as well as act as some local bypassing on the bridge.
wrote ...
An other question; To me it looks like the voltage over Q102 and Q101 at worst is the rail to rail voltage (+ the voltage drop over the free wheeling diode just before the other IGBT ignite)
Yes
wrote ...
Is there any part of the cycle where the Uce exceed this?
Depends on layout. If you have good layout (low inductance), you shouldn't see big Vce spikes, however, with a bad layout, you can get large ringing spikes when the IGBTs turn off etc...
Registered Member #1879
Joined: Mon Dec 22 2008, 04:11AM
Location:
Posts: 40
Thanks,
I can see why running CW is a bad idea
I recently purchased some EPCOS 1100uF caps for 63 v to filter the input into a motor drive driven by a fuel cell. It was not easy to find lightweight caps that could deal with 20kHz at about 30A and you guys punish them with hundreds of amps...... Power of duty cycling
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IKEA Mini Brute rising from the ashes, What voltage does the IGBT's see?
