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IGBT Gate Driver Voltage Question

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Robert Francis

Fri Sept 23 2022, 07:37PM

Registered Member #2355 Joined: Thu Sept 10 2009, 09:12PM
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Posts: 71

I am building an inductor based marx generator. I originally was going to use a high voltage SF6 switch in place of an uncontrolled spark gap for the first stage. With a resistor based marx gen the pulsing was pretty consistent with just a spark gap on the first stage but with inductors it wasn't. I decided to use in place of a spark gap a high voltage switch for the first stage but using an arduino and optocoupler I was only able to get the pulse firing duration down to 350ms. So adding charging times wit wouldn't even pulse 2 times a second.

I decided to use some IGBTs in series in order to increase the pulses per second, hoping to reach around 10 per second with IGBT controlling the first stage and spark gaps in the rest.

I bought 30 IGBTs to control the first stage which sees a voltage of around 24kV.

The problem is I am confused about the IGBT's gate driver voltage listed in the PDF.

It says in the first table maximum rating of gate driver in continuous mode is +/- 20 volts.

In the second table it says characteristic values Min 4.0 / Max 6.5 volts.

Does this mean I should be controlling the IGBTs with a voltage between 4.0 - 6.5 on and 0 volts for off?

RoV IW3IPD

Sat Sept 24 2022, 09:22PM

Registered Member #64746 Joined: Sat Sept 08 2018, 09:22PM
Location: Italy
Posts: 27

use 12-15 V in the ON period and 0 V in OFF.
Pay attention: that IGBT doesn't have a reverse diode between CE, so you should probably add one externally (I say probably, because I don't know your circuit).

Robert Francis

Tue Sept 27 2022, 08:03PM

Registered Member #2355 Joined: Thu Sept 10 2009, 09:12PM
Location:
Posts: 71

Thank you. I have another issue. I cannot find female sockets for the wider than jumper pin IGBT pins. Normal pin spacing is 2.54mm but IGBTs are larger than that and the pins themselves are wider than normal jumper pins.

At first I tried to find 'IGBT stripboard' or 'IGBT perfboard'. I cannot find shit on Google or anywhere else for that matter for any of this. The 4th result on 1st page of duckduckgo was an amazon page for perfboard with not a sign of IGBT anywhere on the page. I cannot even find anything on female sockets 1.25mm in diameter that I could use to connect to an IGBT pin. Did search always suck this badly?

RoV IW3IPD

Wed Sept 28 2022, 07:33PM

Registered Member #64746 Joined: Sat Sept 08 2018, 09:22PM
Location: Italy
Posts: 27

You don't find socket adapters for TO247 because no one would use them! Those devices work with high current levels and need to be soldered to obtain a sufficiently low contact resistance.

Robert Francis

Thu Sept 29 2022, 10:16PM

Registered Member #2355 Joined: Thu Sept 10 2009, 09:12PM
Location:
Posts: 71

I think I made an error looking to use IGBTs in series. I figured since the marx gen I am building would pulse around 10 times a second and the capacitors on each stage are only 2000pF that current wouldn't be an issue.

I only looked at IGBTs because the SF6 relay I have seems to have such a slow switching time. Looking at the datasheet for it though it says operate time, max 15ms and release time, max 15ms, more than enough to pulse at 10hz. I have not been able to get mine to work using an arduino and optocoupler below 350ms for the discharge pulse to fire.

Not sure why my experience is so slow. I have 2 total and haven't had the chance to try the 2nd one instead to see if it works better.

I am using 2 double AA battery enclosures in series (8 batteries per enclosure) for a total of 24 volts connected directly to the 2 turret nodes to control the high voltage switch. Could the problem be too low of an amperage? I have 12volt tractor batteries I could use in series instead but I was afraid the current would fry the optocoupler.

RoV IW3IPD

Fri Sept 30 2022, 10:05PM

Registered Member #64746 Joined: Sat Sept 08 2018, 09:22PM
Location: Italy
Posts: 27

You should share the datasheet of the relay and your schematic, otherwise it's difficult to help. Just an idea: did you put a diode in antiparallel to the relay coil? If yes, it could be the cause of slow operation, because the diode recirculates the coil current and makes the relay opening phase very slow.

Robert Francis

Sat Oct 01 2022, 11:02PM

Registered Member #2355 Joined: Thu Sept 10 2009, 09:12PM
Location:
Posts: 71

Here is the datasheet.

It is the K61C841.

The Arduino's GND is connected to the optocoupler GND and pin 13 on the arduino is connected to PWM on the optocoupler. I just use a turn pin 13 high and low on the arduino, I don't use PWM.

Code:
void setup() {
// put your setup code here, to run once:
pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
// put your main code here, to run repeatedly:
digitalWrite(LED_BUILTIN, LOW); // turn the LED off by making the voltage LOW
delay(1500); // wait for one and a half seconds to make sure caps on marx are fully charged
digitalWrite(LED_BUILTIN, HIGH); // turn the LED on (HIGH is the voltage level)
delay(350); // was the lowest time that would work allowing the marx gen to fire
}

The AA battery cluster is connected to the Input Power (red to + black to -) and wires connected to the Output Load are connected directly to the 2 pins on either side of the hex connector. The wires coming off of the Output Load connect to the turrets using alligator clips. I used electrical tape to wrap around that metal hex thing in between the 2 turrets to ensure there are no shorts.

I would have tried to solder wires directly to the turrets but on a previous switch of the same model I stepped on the wire connected to one turret and the turret broke off and the switch then became unrepairable.

I don't have a schematic.

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