Referring to my previous post. I have successfully generated 500V. The problem I am facing an issue. MOSFET I am using for switching is FQB34N20LTM. The MOSFET is burning badly. The snap of drain pulse is attached below. I have attached a good heatsink having fins as well but temperature never stops. Previously I made the prototype using breadboard and my circuit was cool, now I have made the PCB and it is burning. Please suggest me what should I do? Thanks in advance.
Electronic – 500V generation, MOSFET Heating Problem
circuit-protectiondamping-factorheatsinkhigh voltageoverheat
Related Solutions
Making a 500V supply capable of a few uA is actually pretty trivial:
The transformer can be any generic 1:1 isolation transformer, the phone isolation transformers you can buy at radioshack work quite well.
However, this power supply is not capable of supplying any real power. It works great for a geiger-counter, but if you have a load smaller then ~\$50M\Omega\$, you will begin to overload it.
If I use the procedure I wrote at the beginning the temperature rise becomes
ΔT = P × θ = 30 × 62 = 1861°C
But this is insane. ... Do I need a heat-sink here?
You are neglecting to consider the heat capacity of the chip. This acts like a capacitor in the thermal equivalent circuit, connected between Tj and (some arbitrarily defined) ground, which prevents the chip from heating up instantaneously. Unfortunately you are unlikely to find good data on exactly what the value of this capacitor should be.
You can refer to the safe operating area curve for your MOSFET:
Based on this it's probably safest to keep your switching time below 10 ms, instead of close to 1 s as you have currently.
Best Answer
Try the following.
As it worked in lashup mode these may well help.
Add a say 10V zener gate to source close to FET.
Add maybe also a reverse biased small Schottky diode in same location.
Use a small resistor in gate drive. (3 - 10 Ohm range).
Zener clamps induced gate spikes via Millar capacitance from drain.
Schottky clamps negative 1/2 cycles of gate oscillations.
Drive R helps damp gate oscillations.
Report back.
What is the turns ratio?
FET must be rated >> [500 VDC / turns ratio]
FET data sheet here