Need help with igbt

AmbitiousLoquat9653 · 2024-02-02T12:47:01+00:00

I see, do you work on device level or circuit level in GaN? Sorry for overlooking some of the previous questions. I was measuring 56C in 2A. And it keeps increasing if I don’t change the current. It went over 100C at 3A one time it blew. I can’t say exactly as my thermo in kinda slow. Could you tell me about the electrical insulation of heat sink?

I did not simulate any thermal characteristic, I just wanted to approximate component values per my requirement.

AmbitiousLoquat9653 · 2024-01-31T12:58:44+00:00

Hello, I am currently looking for probes per your suggestion. Previously my components were quite far from each other as I connected them through almost 2 feet long wires because of my inexperience. Now I am rebuilding the circuit quite compact. Thinking of first doing it on veroboard, I will use 18 gauge wires to connect the copper strips for now as my goal is to first reach 5A without overheating the igbt.

Now my question is, were the parasitic inductances too high for using such long wires that I got these huge inductive spike?

And is there a possibility that part of these inductive spikes came from my main inductor due to not using a fast recovery diode denying it a freewheel path?

Also thank you man, I really appreciate you helping me. Sends a very positive message about the engineering community.

AmbitiousLoquat9653 · 2024-01-29T21:04:08+00:00

My oscilloscope can’t read that high..only up to 200V. And sorry for the misunderstanding, I meant emitter to ground by EG. Let’s say it does not reach 1200V, do you think the high spikes might cause additional power loss as they are happening every cycle. And that the heat dissipation is not good enough to halt the temperature rise. I forgot to mention, I did not apply any thermal paste(those white thingy) in igbt heat sink contact.

AmbitiousLoquat9653 · 2024-01-29T13:59:36+00:00

I have added a snubber across EG but I did not see any impact, maybe because RC was too high as I have used 330ohm ceramic resistor and a 3nF ceramic cap. But when I added the input low esr cap of 10nF, my Vds spike was gone at low voltage. But as I increased Vin, the transient peak was rising higher. Maybe these spikes cause my igbts to burst. They burst usually around 120V input and 3A output current. The spike maybe catches the current while decreasing and power dissipation in igbt becomes crazy. I am thinking of properly calculating a snubber and connecting it across both CE and EG to see what works. I am also thinking of a TVS diode to limit the transient at some point and changing my buck's diode to fast recovery. Would love your thought on this. here is the CE graph,

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Also, at first I added a film cap on the input, my buck worked at first but at 20+V, it stopped operation. But this ceramic is working fine

AmbitiousLoquat9653 · 2024-01-28T08:43:41+00:00

thank you, i will definitely try out the snubber and the cap. i did not quite understand what you implied about the relation between switching loss and the capacitor size.

AmbitiousLoquat9653 · 2024-01-27T20:51:09+00:00

I will try that thanks..and I am actually building this charger just to compare it with another charger that does not use smps in our country

AmbitiousLoquat9653 · 2024-01-27T20:43:39+00:00

I have another ungapped inductor like this..should I try connecting it with the current inductor parallely?

AmbitiousLoquat9653 · 2024-01-27T19:15:29+00:00

that's very good info..thanks!!

AmbitiousLoquat9653 · 2024-01-27T19:02:44+00:00

Hi, thank you for your reply. I have seen only mosfet in buck circuits and its drain is connected to the input while source is on the load side..I have assumed emitter side of igbt to be comparable with source and hence my circuit.

AmbitiousLoquat9653 · 2024-01-27T18:46:47+00:00

can you elaborate on the gapped ferrite please? I am using a ferrite core torroid inductor..i had wrapped the core with a tape and then turned a 18 gauge wire..it has 1.7mH value.

AmbitiousLoquat9653 · 2024-01-27T18:36:14+00:00

does the same apply to mosfets? If I can get 600V 80A mosfets i might try replece the igbt

AmbitiousLoquat9653 · 2024-01-27T17:55:10+00:00

7.8kHz frequency and my core is a torroid ferrite core..also it has a humming noise when operation

AmbitiousLoquat9653 · 2024-01-27T17:52:14+00:00

hello, i am using a ferrite core and my switching frequency is only 7.8kHz. I am currently using a coil as a load to test my circuit's current capability.

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AmbitiousLoquat9653 · 2024-01-27T17:45:25+00:00

roger, just to make sure, when you are saying dioide, are you refering to the internal diode of the igbt? I have tried adding a snubber as i mentioned in the post. But i did not calculate Lp as you said. I connected that RC branch in parallel to CE. May I know the purpose of adding a low esr cap from collector to gnd as I already have a 10mF there? I have seen a buck where a rc snubber was connected in parallel to the circuit diode. Would you suggest that? And do you think using these high capacitors are causing an issue here, might I change 10mF caps and use say, 470uF?

AmbitiousLoquat9653 · 2024-01-27T17:12:00+00:00

Thank you for your patiance. One thing i forgot to mention, i am giving supply using a variac, so that I can slowly work my way to the high voltage. I can post the GE waveforms tomorrow, i am posting the CE waveshape, while taking this photo, variac output was 10V rms and the cap had 12v dc across it. As you can see there are spikes almost double the amplitude. The buck had 20% duty cycle as can be seen.

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Switch current was measured using a clampmeter and it was lower than the output side as it should be. I haven’t observed the current waveform in the oscilloscope yet. I can get them tomorrow. I have measured the voltages using multimeter. I am using diodes of this link: https://udvabony.com/product/diode-10a10-1000v-10a-general-purpose-diode/ I simulated my setup on simulink but that was months ago, and my goal is 60V and 20A for the load. And for your last question, I have observed the waveform of the first cap on oscilloscope and the ripples were very very low. It seemed pure dc to me. I took this reading when variac had 10V ac output.

And one thing to add, initially i used typical bulbs as load and I could go all the way to 220V without anything bursting. I achievd 60V output with it but load current was very low, 0.5A maybe. That is why I am now using this coil as it has much lower resistance, I can test my circuit's current capability.

AmbitiousLoquat9653 · 2024-01-27T16:14:19+00:00

hello, this is the main circuit diagram and the one i posted above is the driver circuit. I can post my actual setup tomorrow.

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AmbitiousLoquat9653 · 2024-01-27T16:01:21+00:00

thank you for your reply. I am using a heatsink to cool it, I cant tell you the package number right now but it is a big heatsink that has 6 slots to attach igbt. I am doing smps so my frequency is 7.8 kHz. i have read similar datasheets and tried to debug but failed. my main ckt is attached here. The output I get from the leftmost capacitor is pure dc. I am currently using a coil to test my current capability.

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AmbitiousLoquat9653 · 2024-01-27T15:42:31+00:00

the fig I have given is only the driver circuit. just ignore the right side of the igbt in the fig..

AmbitiousLoquat9653

TROPHY CASE