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Good morning
30 seconds after power is applied during SMPS test
FET and IC are burned out
I do not think there's anything wrong with the circuit, so let me know which part is wrong.
But this is a high frequency, high current switching circuit.
It needs a carefully designed PCB layout. Extremely short traces, fast decoupling capacitors at any DC node..and they all need to be connected to a solid GND plane. Single GND traces have too high stray inductance. This causes ringing and high voltage overshot during switching.
These overshots are short in time, maybe only a couple of nanoseconds, but they hurt the semiconductor internal isolation barrier. Not immediately. Such circuits may run a couple of seconds ...or up to several month until the isolation barrier totalky brakes down.
The board you are using is not useful for such circuits. At least a two layer PCB is needed.
An experienced user may be able to modify your circuit...a capacitor here, a diode there, a resistor to reduce rise and fall times...and it may work reliably.
I recommend to read some design notes, application notes, datasheets of MOSFETs and their gate drivers. Usually they explain how to design an appropriate layout.
Hi Eonscom,
Since your mosfets are getting burned, then it is very clear that your mosfet is doing something more which can't be tolerated by it.
Obviously it is draining more current
Think for reason which creates this scenario
Since your IC has a built-in high side driver, you are using two N-channel mosfet instead of a P-channel mosfet to drive high side.
Imagine when both of your mosfet are turned on simultaneously.
Obviously then it is short circuit to ground right?
Since you are operating at high frequency it takes some time to burn fully, else it would happen within a couple of seconds.
So now the debugging.
Slightly reduce the operating frequency
Check for both mosfet gate drive overlap
A sufficient gap between turn on signals will do good and check for some dead time control in the IC datasheet, since it is not a pwm controller I guess, it will not be facilitated with that, but have a check.
Slightly improve the value of the gate resistor
Use a flyback diode with a small resistance in series across the mosfet gate resistor
This should do the job!!!!!
Congrats!!!!
I could understand how it pricks when a circuit promoted to be simple in online but not working for us.
Many people promote circuits without testing, and if the circuit is working for someone it is not mandatory for everyone who test the circuit will work in the same way
A good heat sink is also needed.
It's difficult to read the MOSFET numbers from the picture but it looks like 2SK2950. If it is, that device is completely unsuitable for this application, it has an RDSon of 23 Ohms!
I read 2SK2850, which has considerably lower Rdson. But we don't have a load specification, I'd say any NMOS with sufficient Vds rating can work in this circuit, with appropriate load. Similarly I can't determine from the given information if a heat sink is needed.
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