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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567
Input is 240vac @50A. The dc to the inverter will be 750vdc
I think I have that book on a shelf somewhere. I'll have to dig it up.
While the slapped-together buck is working on my bench with a 11R load, there is some ringing on the gate. When I slapped together a 0.01uf cap and 15R resistor the ringing is all gone.
when I take the buck to my induction heater and try to get it to give it some power (I have not tried the snubber yet) it appears the gate is misfiring all over the place. this is why I want to try the snubber. I'm also waiting to get some powdered cores to make a common mode choke. I tried one with a ferrite core and it did reduce some of the switching spikes.
How do you get to 750v dc from 240ac? Buck converters can only lower the voltage, not raise it.
Also the 240v ac are offline, from the wall socket? At 50A that's still 12KW, you can't draw that from a wall socket. The most you can expect from a wall socket is 2-4KW.
And, you most definitely don't want a snubber on the igbt/mostfet gate. What is the gate driver that you use right now?
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
There is some confusion here.
The input to the dc source is 240vac/50A. The line is rated with 30A wire, but I can draw more power for a short time before the fuse goes. I usually don't do that; I turn off the device before I reach that point. This power goes to the voltage doubler.
Output from the voltage doubler is 750vdc (240vac x 2 x 1.4)
The snubber is connected across the common-emitter, but I had a scope across the gate-emitter.
The emitter on a igbt in a buck converter is floating/not at ground. The power supply feeding the buck needs to be isolated, or, the scope power supply needs to be isolated, if you want a reliable reading.
If both the scope and the buck are powered offline, connecting the ground clip of the scope to the emitter will make a short. This is also why you need the isolated gate drive.
If your scope has 2 channels and can do diferentials, connect a probe to the gate another to the emitter and display the difference, while leaving the ground clips of both of the probes unconnected.
If you are using a proper gate driver IC with short leads to the gate, I'm guessing the spikes on the gate are not really there and they are just a problem on the readings from the scope.
All that aside, buck converters are not meant to step down voltages from 750v. Why do you need such high voltage? What is the range of voltages and amperes you need on the out of the power supply/input of the induction heater?
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Daedronus wrote ...
The power supply feeding the buck needs to be isolated, or, the scope power supply needs to be isolated, if you want a reliable reading.
If both the scope and the buck are powered offline, connecting the ground clip of the scope to the emitter will make a short. This is also why you need the isolated gate drive.
If your scope has 2 channels and can do diferentials, connect a probe to the gate another to the emitter and display the difference, while leaving the ground clips of both of the probes unconnected.
If you are using a proper gate driver IC with short leads to the gate, I'm guessing the spikes on the gate are not really there and they are just a problem on the readings from the scope.
All that aside, buck converters are not meant to step down voltages from 750v. Why do you need such high voltage? What is the range of voltages and amperes you need on the out of the power supply/input of the induction heater?
The supply is isolated. I am using two channels and getting a differential. The gate driver is posted a few replies up using an isolated FOD3180. The large power is needed for the application. Here is an example of what this power is doing
I am able to achieve power control right now with a variac. I was hoping that a smps would allow me a cheaper solution to control power than a $500-$1000 variac.
What is a good solution for controling 10kw of power other than detuning the tank?
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Ok.
I had already tried the diode approach so time ago.
Understand, the device works in on a bench; it is when I connect it to my induction heater it goes crazy. Maybe the noise from my induction heater is setting off the buck's gate.
Right now I will just have to wait till I make another board with the shorter leads. Maybe the common mode choke will help.
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switching noise/spikes on buck converter
