Re: QDX and QMX+ (soon at least) what is the max safe swr?
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Chris,
As I've stated many times before, NEVER exceed the absolute?maximum rating of a semiconductor as spec'd by the manufacturer. Doing so is asking for trouble, possibly short term, or maybe a gradual weakening of the device under stress until it fails long term. Furthermore, relying on a manufacturer?underrating their device is a bad idea. I've seen a few manufacturers underrate by as much as 20% but this is not at all typical across the semiconductor industry. You'll find that many devices have very little safety margin relative to their maximum ratings so my advice is to never exceed?the manufacturer's specs under any conditions.
As far as current-limiting to 100 uA or so during breakdown testing, I don't think it will save you from?permanent?damage but you can certainly try this on your first DUT and see what happens. If you see some odd behavior after the FET breaks down, you should consider it unreliable even if it seems to work when the voltage is lowered. I always consider breakdown voltage testing as destructive. If you test multiple devices, I'm not sure what the stats will look like unless you're willing to test hundreds of them. The same goes for any TN0110 testing you consider trying.
Your zener fix was one of a few that were discussed way back when. Hans added diode?pads to the schematic so he was OK with this workaround.?
How many BS170's are you planning to perform breakdown testing on?
Tony
On Tue, Sep 17, 2024 at 12:48?PM Chris KB1NLW via <chrisrey1= [email protected]> wrote: Thanks Tony;
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After I get the dissipation concluded I am thinking of measuring breakdown of my batch of BS170.? I think the QMX design is relying on the typical breakdown being significantly higher than the speck.? If I do this I should also check TN0110.
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I'm thinking of limiting current during breakdown to ~0.1ma (concerned about damage), any thoughts?
It does seem that Hans should be more concerned.
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I have three QMXs that have zeners across the BS170s.? Before I added the Zeners I had multiple failures, none since!
Of course I don't have them in my QMX+ so I could do these test.??
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