Hi, I am working on Tesla coil. So I far I have destroyed over 15 MOSFETs (irf540n). I cant seem to figure out why. I tried adding hyperfast rectifier diode (30eth06) in parallel with mosfet. I have tried using different power supplies for logic and mosfet. I'm really frustrated with this and I can't seem to pinpoint the issue. The oscilloscope shows Tesla coil oscillating at 90kHz (1900 turns secondary, 3 turns primary). The antenna also works hit or miss. Sometimes I have to touch the antenna to make circuit work (I'm guessing charge gets accumulated on antenna). Please help me with the mosfet issue (that is my main issue).

 

Go back to basics. How much current flows if you short the transistor lead (simulating the on state)?

 

Go back to basics. How much current flows if you short the transistor lead (simulating the on state)?

Hi, my BJTs work fine. It's my mosfet burning out. They just die silently. I have current limited my power supply to 1.5A

 

Again how much current are you trying to use? Help me help you. Measure the current. Next step I'll try redrawing your schematic to see if we are on the same page.

 

Again how much current are you trying to use? Help me help you.

I'm sorry if I'm not understanding you question. For testing phase I have current limited the power supply to 1.5A @ 12v. I would assume that mosfet IRF540n would survive because it is listed for 100v and 23-33A. The current never usually goes above 900ma but the mosfet burns out the power supply automatically switches to over current protection mode. I checked the mosfet leads with multimeter and the are all shorted.

 

You are likely exceeding the safe operating area of the MOSFET (below).
You will need an oscilloscope to see if that's what's happening.

Note that the peak current is likely much higher than the 900mA average current from the power supply.
Try putting a small series resistor in series with the primary to limit the peak current to a few amps.

 

You are likely exceeding the safe operating area of the MOSFET (below).
You will need an oscilloscope to see if that's what's happening.

Note that the peak current is likely much higher than the 900mA average current from the power supply.
Try putting a small series resistor in series with the primary to limit the peak current to a few amps.

View attachment 322058

Hi, new mosfets are coming tomorrow. I will update you once they show up. I will try to learn more about safe operating area of mosfet and how to check it with oscilloscope. Thank you.

 

There are three electrical causes of active device failure, excess voltage breakdown, excess current burnout, or excess power overheating. Operating outside the given safe operating area will lead to at least one of these causes.
Have you monitored the temperature of these while operating? In addition, there may be too slow of a switch on time, so that there is excessive heating during the switching on interval. The switch-on drive may not be adequate. The gate drive signal may be the problem.

Of course, given that we only are shown a small part of the circuit, it might be from something we do not see.
How long to the MOSFETS last before they fail??? Seconds or minutes, or almost instantly??

 

In other words to the devices get hot?

 

Please help me with the mosfet issue (that is my main issue).

You have the back EMF diode in the wrong place. You should have it across the primary with the anode on the drain.

 

In other words to the devices get hot?

You might never know, depending on pulse rate & duty cycle they could vaporise internally long before the case got warm...

@Simranjit What is your pulse rate & duration

 

Feeling components with my index finger was a tried and true technique to see if a component was stressed or not. That is until you burn your finger and create a reverse image brand of the transistor on said finger. This happened to me several times.

 

You have the back EMF diode in the wrong place. You should have it across the primary with the anode on the drain.

Yup.

The drain will exceed Vds,max upon turn off.

 

Here is the promised drawing I did make some changes and some corrections just let me know if it helps.

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you really do not need base resistors for the transistor drivers, but it does protect against certain failure modes. The diode shown on Q3 is part of the transistor.

 

You have the back EMF diode in the wrong place. You should have it across the primary with the anode on the drain.

Yeah, I saw that right away too.

 

Here is the promised drawing I did make some changes and some corrections just let me know if it helps.

View attachment 322094​

you really do not need base resistors for the transistor drivers, but it does protect against certain failure modes. The diode shown on Q3 is part of the transistor.

I'm the last one to ask this question, but are Q1 & Q2 backwards? Q2 should be on top? No?

 

I'm the last one to ask this question, but are Q1 & Q2 backwards? Q2 should be on top? No?

Unless Vcc is negative the transistors are indeed reversed, at least in the drawing on post #14

 

Oops, You got me.

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