I am also interested for something that makes negative off signal... If you find anything, let me know.
i
I am also interested for something that makes negative off signal... If you find anything, let me know.
iI'm not sure why you'd need to drive the gate negative. below the threshold voltage should be fine to turn it off (just like a Mosfet). if you insist on turning swingint it negative, you might look at a gate drive transformer that naturally swings negative (ac coupling the gate signal)
A discrete design wouldn't be to difficult to come up with.
I found this some where, I forget where, but its a novel approach. A MAX232, +/-10 volt swing.
Cheers
Those MAX232 chips have been around for a while, so they probably aren't too dangerous to depend on (although I've had my run-ins with Maxim and Dallas). However, getting them to drive an IGBT at 40kHz may not be possible, due to the large input capacitance, which may require lots of current to overcome quickly. They use a charge pump, which may not be able to supply the needed current.
There are dedicated IGBT driver chips available. There are also integrated H-Bridge chips that would work nicely. Using one of those is probably the simplest and safest course.
-- Regards, Bob Monsen
I would like to drive an IGBT from a microcontroller (CMOS). Is there a driver circuit that can outputs around +15v (on) and a -5v (off) for switching frequencies around 40Khz. I think -ve voltage supply is avaliable What is this type of circuit called?
Thanks Richard
I would never even *think* of Maxim or Dallas VaporWare.
Surprisingly it is called a gate driver circuit. IGBTs imply large power switching so that even though the switching frequency is a modest 40KHz, the driver is still required to switch the device through ON/OFF transitions quickly to reduce losses and component heating. Micrel at
MAX232s are multiple-sourced these days, so you're not stuck with Maxim, any more than you need fear the uA709A because you don't trust Fairchild. ;-)
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com
i really don't understand why you need that?, normally pulling the gate low will do how ever if you insist. simply provide a +15 volt source via a resistor sufficient enough to drive the gate in the on mode, use something like a simply NPN transistor to pull it low at the gate to shut the IGBT off, put the emitter to a - supply. since these Gates are H Z, the - source does not need to be much. using either a high freq OSC from something simple like a 555 or an output from the MC, you can generate - voltage via a Cap and diode et.. the base of the transistor will get switched from the MC signal line.
-- Real Programmers Do things like this. http://webpages.charter.net/jamie_5
Remember the early ones, that typically lasted about 3 months? They later changed the circuit, so that the high side output capacitor went to 5V instead of ground. Before that, it would latch up unpredicatbly, usually when you'd just delivered a lot to an important customer.
Paul Burke
For big IGBTs, some negative gate drive is an advantage.
There's a lot of capacitance.
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com
because negative gate bias can prevent dV/dt thru Cmiller from turning the darned thing back on again.
IR wrote a nice paper about 6-7 years ago, where they go through and show at what point -ve bias becomes necessary. its mandatory for man-sized IGBTs, but baby IGBTs can often do without.
Check out Fuji's gate driver:
Apparently, it makes negative reverse bias of -5V and has a built in opto coupler.
i[...]
Use an LT1081. They are easy to get. I think they are about as slow and weak as the MAX232 so it really isn't such a good idea.
-- -- kensmith@rahul.net forging knowledge
I trust Fairchild, but I'd fear a uA709, even if it was an "A" version!
-- Thanks, - Win
I am actually playing with IGBTs.
I have Toshiba-MG200Q2YS40 IGBT.
It does NOT turn off itself if I simply remove Gate/Emitter voltage.
I have to apply reverse voltage to turn it off. I actually tried it.
It would, possibly, switch itself off with a small resistor between gate and emitter, but it is just a hypothesis of mine.
i
I was going to say, "MC1488", but I looked it up and its output is limited to +- 10 mA, so I looked up the MAX232, and it's got the same output current limiting, +-10 mA. If that's enough to drive your IGBT into cutoff at the freq. that you need, I'd say pick whichever of those you can get your hands on. I've also seen it done with a couple of ordinary transistors - look for a "level shifter" circuit.
Good Luck! Rich
I just googled MAX232, and a TI data sheet came up.
Cheers! Rich
Gate charge is what you really mean...capacitance can be misleading because it ignores threshold voltage. After looking at that Fugi Electric line, it seems they require hundreds of ohms of gate series damping resistance- because of the bipolar current gain multiplying the lead inductance reflected into the gate circuit most likely- and this explains the negative bias requirement, as a lower impedance pulldown would shunt the Miller transient- at turn-off.
Terry, it is great that you participate in this thread and actually have experience with power switching. I am building a DC -> AC inverter for a TIG welder and seems like I can learn a lot from you.
This is a 200A constant current, 28 V welding current, 80 v open circuit voltage tig welder.I have aforementioned IGBTs.
Can you give a little schematic of how go give the gates negative bias during turn off. I definitely want to turn IGBTs off in the best possible way. I want the simplest solution.
Another question, would a resistor between gate and emitter solve ths issue? Or is that not the case?
thanks a lot for your time!
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