Hi all,
I was testing some sot23 jfets and made an error, with the gate and drain tied together instead of gate and source. Unsurprisingly the jfet conducted enthusiastically and hit the 400ma current limit that I had set on the power supply. I then turned it off (within seconds).
My question is would this damage the parts? The supply was at 10v so the part was dissipating a lively 4W for a few seconds.
As a corollary, what is the continuous dissipation for a sot23 Bart? The intended purpose is as a complementary buffer at the front end of a F6 with somewhat lower PSU rails...
I was testing some sot23 jfets and made an error, with the gate and drain tied together instead of gate and source. Unsurprisingly the jfet conducted enthusiastically and hit the 400ma current limit that I had set on the power supply. I then turned it off (within seconds).
My question is would this damage the parts? The supply was at 10v so the part was dissipating a lively 4W for a few seconds.
As a corollary, what is the continuous dissipation for a sot23 Bart? The intended purpose is as a complementary buffer at the front end of a F6 with somewhat lower PSU rails...
Surprised at SOT23 JFets (not MosFets) passing 400 mA at all.
What was the supply voltage?
In any case they are inexpensive parts, jung them and get a new pair.
Why build anything with (highly) suspect compromised parts?
What was the supply voltage?
In any case they are inexpensive parts, jung them and get a new pair.
Why build anything with (highly) suspect compromised parts?
@jm yep agreed. I've maybe over thought it due to the time and faff of mounting them on adaptors. call that a bit of sunk cost fallacy. 🙂
Most of the little Jfets l play with, like 2SK170 / 2SJ74, are symmetric, and
you can switch Drain and Source and they work fine, even identically.
😎
you can switch Drain and Source and they work fine, even identically.
😎
Yes, totally true; but he put +10V on the gate AND the drain.
So it acted as a switch.
Even if the device survived the ordeal, would you still want to put it in a circuit, not knowing if it still lives for ever ?
How much risk you want to take for the rest of the circuit for < 1USD ?
Patrick
So it acted as a switch.
Even if the device survived the ordeal, would you still want to put it in a circuit, not knowing if it still lives for ever ?
How much risk you want to take for the rest of the circuit for < 1USD ?
Patrick
That's the best one yet.
I love it.
It doesn't get much better than that.
There is something about destructive testing and curiosity that never gets boring.
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old 10" TV speakers directly on AC line power are a blast (though not really educational....just fun).
Last time I had that kind of entertainment, Wayne and I were destruct
testing SIT-1's.
Pop!
There goes another $100.
😎
And every greedy diy-er on the pass labs part of this forum just flinched there. 🙂
My original question should probably have been rephrased as 'i did something dumb, but the microscopic part seems fine! It couldn't be surely?'
Maybe I'll just do it again without the current limiter on 😉
Maybe I'll just do it again without the current limiter on 😉
It is likely that it did not see the 10V when the limiter kicked in. So you
have a 400 mA current through a 400 mW part. If it was 1 volt Vds, then
maybe you were within limits, as there is no maximum Ids on the spec sheet.
(probably not)
😎
have a 400 mA current through a 400 mW part. If it was 1 volt Vds, then
maybe you were within limits, as there is no maximum Ids on the spec sheet.
(probably not)
😎
A small surface mount package will usually show a bulge on it's top surface when power rating is grossly exceeded.
A simple test with an Ohmmeter will tell the tale. From Drain to Source you should see a resistance somewhat close the the Rds(on) number from the data sheet. The Gate to Drain (or to Source) should show a diode like reading, low resistance one direction and very high with reverse polarity.
A simple test with an Ohmmeter will tell the tale. From Drain to Source you should see a resistance somewhat close the the Rds(on) number from the data sheet. The Gate to Drain (or to Source) should show a diode like reading, low resistance one direction and very high with reverse polarity.
Testing with a fake 7mA J74BL by treating it like an NJFET for 10V IDSS test with just 25mA PSU CC limit for a minute it did not blow up but after a little time the CV started to rise near 8V giving it about 200mW. After that its RDS permanently went from circa 20 Ohm to 618 Ohm and its IDSS down to 0.5mA. It ended up in the bin that it was going to anyway 😀
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