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Messages - ritaismyconscience

Pages: [1] 2
1

^ Feedback transformer (1:1023 for both)


^ 1:1023 current transformer + 10 ohm resistor (connects to scope)


^ Circuit design


^ A picture of the driver I'm using. It doesn't seem to have phase lead compensation. Is it possible to modify the circuit to add this?

2
I tested it at half bus voltage today (170V) and I got this:



There seems to be some switching spikes (1 div = 100A). Does this look normal?

3
Electronic Circuits / Re: Unusually long-lived electrolytic capacitor
« on: February 26, 2020, 06:08:05 AM »
Did you measure the ESR? Bad capacitors may look good to a multimeter but it might have too high internal resistance to be usable.

4
Thanks for all of your help, looks like my setup is working now

Here's what the waveforms look like on 25VAC (the bus voltage is double the AC voltage, so the bus voltage is 70V DC)



1 div = 20A current

This is my first time building one of these, so I might need more help in the future

5
Mads has said in other posts that -30V is fine for momentary undershoot, even though it's beyond the IGBT's specification limit.  I have no personal experience with such.

To avoid damaging your circuit, especially once bus voltage is applied, be careful about grounding sensitive nodes to your scope.  Even if the scope is floating (not connected to line ground), capacitance from the scope "ground" to the line power can be enough to disrupt circuit operation.  So, "ground" only low-impedance nodes that don't have intentional AC signals on them, such as the low-side emitters or high-side collectors (bus voltage - and + nodes), not gate signals or bridge outputs.  If you "ground" a floating scope to any high voltage such as + bus voltage, be careful not to shock yourself from the scope case!

I'm going to use a second current transformer to monitor the current and I'm going to stick a wire through the gate transformer to keep track of gate voltage. This way my scope is completely isolated from the voltage.

6


Looks like you were right, here's the waveform on the positive cycle.

Anyways, is -30V going to kill my IGBTs or should I not worry about it?

7
Looks like I must have connected the scope leads backwards then, because it probably caught the negative cycle. Anyways, would -30V across gate and emitter be enough to kill my IGBTs? It looks like my zener diode circuit I came up with was too slow to deal with the spike.

When you say "haven't tested it with voltage yet", are you saying that the IGBTs fried with no collector voltage, only gate drive?  That would be extraordinary.

Yes, but it's probably because I messed up the circuit in my first attempt. I've also used a hammer to reveal the die, and there aren't any burn marks.

8
My question to you is are you using one GDT?

I'm using 2 GDTs, one to drive each half of the fullbridge. Seems to work so far.

How are you getting your feedback signal?

Haven't tested it with voltage yet. However, using a 1:1023 feedback transformer should work.

Also, I fixed my driver and I saw this on my oscilloscope:



Does this look normal? For some reason the voltage spikes to 30V at the start

9
Haven't tested it with voltage yet, so it's probably not the controller's fault

10
I'll try replacing the TVS diodes and I'll try adding 24V Zener diodes.

Edit: I came up with this. Will this work?



Also, I looked at other people's schematic, and they used 5.1 ohm resistors on each gate instead of doing what I did. Does this matter?

11
Dual Resonant Solid State Tesla coils (DRSSTC) / GDT keeps on killing IGBTs
« on: February 21, 2020, 02:41:03 AM »
Hi,
I have a problem with my gate driver, as it randomly kills IGBTs. I've already had to replace 4 of them due to this problem.

Here's what my circuit looks like:



Here's a couple pictures of my setup:



The brown and green wires go to the GDTs



A picture of the waveform with 2 44nF capacitors simulating the gates of the 4 IGBTs being driven by the GDT:


(Scale: 10V/div & 2us/div)

The driver circuit is a chinese version which uses a CPLD, but the output stage uses the same parts as the UD 2.7 (It uses the FDD8424)
Here's a picture of it:





I think I might need to swap the TVS diodes for a lower voltage one. Anything else I need to change?

Edit: Unrelated question: I heard that you should use a fast diode instead of relying on the internal diode in the IGBT. Would using RURG8060 work, and would I need to put the diode on a heatsink? Thanks.

12
Transformer (Ferrite Core) / Re: Homemade HV transformer
« on: September 14, 2019, 06:35:32 PM »

13
I can also get these:
https://www.infineon.com/dgdl/Infineon-IKW75N60T-DS-v02_08-en.pdf?fileId=db3a304412b407950112b42890113e25

for about a third of the price. Seems like a better idea?

14
So I found a good deal for these transistors:
https://www.mouser.com/datasheet/2/240/ixys_ds99525cixgq24n30pbix5187-1547450.pdf

The main problem I see with using this in a Tesla coil is that it's only rated for 300V. However, it can handle quite a bit of current. Is there anything I should be aware of before buying?

15
Electronic Circuits / Re: Induction Heater schematic modification
« on: September 11, 2019, 07:48:43 AM »
Looks like there's a mistake with my circuit. Turning the pot changes the frequency instead of the phase shift. I also found out that the op amp was not needed.

This one should hopefully be correct:


16
I second using a flyback as your supply. You can easily find stuff like this on google:
https://rimstar.org/science_electronics_projects/high_voltage_power_supply_w_flyback_transformer_builtin_diodes.htm
If its too much power you can always add a resistor to the output.

You can also buy a ready made HV module for a few dollars off ebay that run off 3.7V lithium battery. (They advertise numbers like 400000V but are actually around 15-20kV. There is also a capacitor inside so you should probably use a HV resistor to limit the current)

17
Electronic Circuits / Re: Induction Heater schematic modification
« on: June 13, 2019, 07:51:18 AM »
Update: Improved layout so it would fit on my blank pcb:


I'll probably make the pcb tomorrow.

18
Capacitor Banks / Re: Bought huge capacitors
« on: June 12, 2019, 06:38:07 PM »
One of my other concerns is that my neighbors would get mad at me (it'll probably sound like an explosion)

19
Capacitor Banks / Bought huge capacitors
« on: June 12, 2019, 03:02:50 AM »
http://imgur.com/gallery/OcA4IgW

I bought these 15600uF 2800v for 50 dollars each and I was wondering what kind of project I should build with them. I probably won't be able to afford scrs and switching 100kj is likely not easy. Any ideas?

20
Electronic Circuits / Re: Induction Heater schematic modification
« on: June 06, 2019, 02:34:30 AM »
There are two terminals for driving the GDT. I will be using this to drive a full bridge of IGBTs on mains voltage. Also I assume that the frequency should change more as the metal melts. See pic below for more information



Edit: I found out that the PNP transistors are backwards. I also made a PCB of this schematic.



Since this is my first time making a PCB there might be a few mistakes I made.

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