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Registered Member #141
Joined: Sat Feb 11 2006, 01:14PM
Location: Southern California
Posts: 96
I have a few questions about cm600's and the megaBrute gate driver.
1. What is the maximum recommended frequency of the cm600? The max. current in DRSSTC use?
2. What happens if I exceed this frequency? Does it simply lose efficiency or does it reach a point where it won't switch any faster or does it explode?
3. Could I use a miniBrute resonant board to drive a halfbridge of cm600's (including the MegaBrute gate driver boards)?
4. Would I need to parallel the UCC gate drivers on the resonant board? Would any other modifications (to the resonant board) be necessary?
5. Would a gate drive transformer identical to the one used in the miniBrute work?
6. How is the value of R4 on the MegaBrute board determined?
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
wrote ...
3. Could I use a miniBrute resonant board to drive a halfbridge of cm600's (including the MegaBrute gate driver boards)?
Yes
wrote ...
4. Would I need to parallel the UCC gate drivers on the resonant board? Would any other modifications (to the resonant board) be necessary?
No, you're only using the output of the miniBrute driver board as a signal input to the CM600 driver board.
wrote ...
5. Would a gate drive transformer identical to the one used in the miniBrute work?
That one could possibly work, however, it can probably be much smaller. But you will need to evaluate performance before applying power to CM600. Remember, you're only passing signal, not high current.
wrote ...
6. How is the value of R4 on the MegaBrute board determined?
CM600 datasheet should provide all these details regarding series gate resistance selection, frequency of operation, etc...
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
You should use a dedicated CM600 high-side gate driver. I'm sure Steve has gotten his circuit to work with just FETs driving a gate transformer, but to ensure proper operation, a high-side driver is highly recommended.
Sure, maybe its a bit more work, but you're guaranteed to switch those CM600's every time. With a low-side driver, as Steve was doing, you are much more dependent on the transformer design being properly designed and tuned, which is also dependent on frequency of operation as well as duty cycle, pulsewidth, etc...
With a high-side driver, the transformer only passes a "signal", its not transferring power.
So use a high side driver for the CM600s. Its the safest and most reliable bet out there.
Banned on 3/17/2009. Registered Member #487
Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617
Safest and reliable? Hmm except when the power supply blows and all IGBT's turn on at once, lol. I think they both have their advantages and disadvantages. I might give both a try once I get to that point. Your drivers use the IXYS 18 amp fet drivers right?
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Tom540 wrote ...
Safest and reliable? Hmm except when the power supply blows and all IGBT's turn on at once, lol. I think they both have their advantages and disadvantages. I might give both a try once I get to that point. Your drivers use the IXYS 18 amp fet drivers right?
-Tom
Which power supply?
If you design your drivers right, loss of power supply will NOT affect the gate of the CM600. My particular drivers in fact use independent power supplies and also will not fail or latch up with loss of power. Steve's high-side drivers are work in a similar fashion i believe.
The IXYS gate drivers also have a undervoltage lock-out, so when Vcc falls below a particular threshold, the device no longer turns on.
Also, CM600s are used by the bazillions in industry from everything from high power motor drives to high power inverters on locomotives. In alll instances, they are driven by dedicated high-side supplies.
Banned on 3/17/2009. Registered Member #487
Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617
Dr. GigaVolt wrote ...
Tom540 wrote ...
Safest and reliable? Hmm except when the power supply blows and all IGBT's turn on at once, lol. I think they both have their advantages and disadvantages. I might give both a try once I get to that point. Your drivers use the IXYS 18 amp fet drivers right?
-Tom
Which power supply?
If you design your drivers right, loss of power supply will NOT affect the gate of the CM600. My particular drivers in fact use independent power supplies and also will not fail or latch up with loss of power. Steve's high-side drivers are work in a similar fashion i believe.
The IXYS gate drivers also have a undervoltage lock-out, so when Vcc falls below a particular threshold, the device no longer turns on.
Also, CM600s are used by the bazillions in industry from everything from high power motor drives to high power inverters on locomotives. In alll instances, they are driven by dedicated high-side supplies.
Trust me, there is a reason for it.
I thought Steve had a problem way back when his 120v fuse blew which was powering the gate drivers they latched on.Oh I completely agree with you on the industry. I've never seen them driven with a GDT alone but then again who drives them at 100KHz in the industry either? I'm not trying to argue just trying to get some more info behind why its done one way or another.
What I'm thinking is making a dedicated driver similar to yours and Steves using a dual gate driver chip 27425 and 2 n channel fets since that's what I have on hand. P channels are pretty scarce now.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
The thing is that the CM600s are a hefty load. If you drive from the low side, you need to drive power through a transformer which needs to pass loads of current at very high bandwidth (fast rise / fall times) which can be quite difficult. With a high-side driver, you're only sending a signal through the transformer (or optocoupler) and the power is all on the high side.
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MegaBrute CM600 gate driver
