Hi,

I am strugling to understand why my mosfet keeps burning that I intended to use it as a load switch in some cases.

I use a p-channel mosfet (Q1) which internally includes an internal diode (D2), to invert the normal behaviour of a switch (S1):
- If the switch (S1) is open, the load of my schematic has power.
- If the switch (S1) is closed, the load of my schematic has no power.

I ordered 20 units of my circuit and 5 of them already got the mosfet in short, after replacing the mosfet everything works.

When does it burn?
- First time after giving power to the circuit
- When the switch (S1) is open (I dont know if this was a coincidence); this means when the load has power.

Im looking for ideas of why I could be having this issue.

Thanks

 

What is the load?

 

What are the values of the resistors? Why the cap from gate to ground?

 

The load is a 5VDC LDO that powers 2 60mA LEDs (total load is 120mA)

R1 is 1K
R2 is 100K
C2 is 1uF. I intended to use C2 as a debounce, to have a more steady power from the switch (S1)

Thanks

 

Most likely exceeding the Vgs voltage. Most mosfets are rated + or - 20 volts.
S1 appears normally open meaning the mosfet is activated when power is first applied, is that correct?
What part # mosfet are you using?

 

Most likely exceeding the Vgs voltage. Most mosfets are rated + or - 20 volts.
S1 appears normally open meaning the mosfet is activated when power is first applied, is that correct?
What part # mosfet are you using?

That is correct.
I am using AS6004
https://www.digikey.com/en/products/detail/anbon-semiconductor-int-l-limited/AS6004/19523667

 

Need to reduce the gate voltage. Try this circuit with C2 removed also.

 

R2 pulls the gate to ground, turning the FET on. Closing the switch turns the FET off. Is that what you want?

 

R2 pulls the gate to ground, turning the FET on. Closing the switch turns the FET off. Is that what you want?

That's correct, see post #6

 

As Goxeman has mentioned, you are exceeding the maximum gate to source ratings, if your supply is actually 24 volts.

 

As Goxeman has mentioned, you are exceeding the maximum gate to source ratings, if your supply is actually 24 volts.

You mean sghioto has mentioned.

 

Your Schematic would be easier to understand if You would
stick to the conventional "rules" of creating a Schematic.

A single Power-Rail should start at the top/left, and be extended to the right, and then down.
Ground is normally shown as the lowest line or point in the Schematic.
Inputs are normally on the left, and Outputs are normally on the right.

Sometimes, following these conventions are not practical in complex Schematics.

When You are creating a Schematic,
the "rules" simplify following the flow of Current,
and the operation of the Circuit,
it also helps to make reading of the Schematic easier for others.
.
.
.

 

Need to reduce the gate voltage. Try this circuit with C2 removed also.
View attachment 297892

Thanks for your proposal.
Also deleting the gate resistor?
Arent R1 and R2 acting as pull-up and pull-down at the same time?

 

As Goxeman has mentioned, you are exceeding the maximum gate to source ratings, if your supply is actually 24 volts.

I had to check more than twice to see it in the datahseet, I read over and over that gate to source was +-60V

Now that I found the issue I need to find the easiest way to fix it increasing the gate voltage.

I still don’t understand why it works in most cases when voltage is still 24V. In fact I tried my circuit many times at voltages of 30V where gate voltage is almost 30V and everything worked well

Thanks again

 

I had to check more than twice to see it in the datahseet, I read over and over that gate to source was +-60V

Now that I found the issue I need to find the easiest way to fix it increasing the gate voltage.

I still don’t understand why it works in most cases when voltage is still 24V. In fact I tried my circuit many times at voltages of 30V where gate voltage is almost 30V and everything worked well

Thanks again

Recheck your datasheet one more time... DRAIN to SOURCE = 60V max GATE to SOURCE = 20V max.

 

Arent R1 and R2 acting as pull-up and pull-down at the same time?

That would in effect act as a voltage divider making your gate either 24V or 12V depending on the switch open or closed.

 

Arent R1 and R2 acting as pull-up and pull-down at the same time?

Both acting as pull downs to turn the mosfet on but dividing the 24 volts appx in half to the gate.
12 volts across Vgs when ON and 0 volts when OFF

 

Both acting as pull downs to turn the mosfet on but dividing the 24 volts appx in half to the gate.

If I'm understanding things right when you close the switch it would bring the gate voltage to 24V then which would be over the gate limit right??

 

No because the voltage is measured from gate to source.

 

Nevermind what I had here... I noticed @sghioto had answered my question while I was thinking