Electronics > Projects, Designs, and Technical Stuff
Testing N-JFET gate - source breakdown voltage (FAKE jfets!) (Successful finale)
David Hess:
The common practice is to limit the test voltage to 5 volts or lower until the device is known to prevent damage from things like base-emitter breakdown which is a destructive test.
SilverSolder:
I downloaded the user manual for the PEAK DCA55, it seems to also limit the test voltage to 5V, so it would probably struggle with this Jfet as well.
For the first time, I also downloaded and read (some of) the comprehensive documentation on the "cheapy" tester.
On paper, they are quite similar. A surprisingly massive amount of work has gone into the "cheapy". That said, the PEAK unit is cleaner and more professionally presented, wont short out against random pieces of metal on your bench (ask me how I know...). Carrying the cheapy testers around surplus electronics stores in a ziploc bag does also get a little old after a while. Still, they do a good job for what they are, even if they can't cope with PN4391 and similar devices.
edavid:
--- Quote from: SilverSolder on March 26, 2019, 08:08:39 pm ---On paper, they are quite similar. A surprisingly massive amount of work has gone into the "cheapy". That said, the PEAK unit is cleaner and more professionally presented, wont short out against random pieces of metal on your bench (ask me how I know...). Carrying the cheapy testers around surplus electronics stores in a ziploc bag does also get a little old after a while. Still, they do a good job for what they are, even if they can't cope with PN4391 and similar devices.
--- End quote ---
You can get a "Component Tester" in your choice of case, still for much less than a Peak tester:
https://www.aliexpress.com/item/Handheld-LCD-Digital-multimeter-Transistor-Tester-SMD-Resistance-Diode-Inductance-Capacitance-ESR-Meter/32962735947.html
https://www.aliexpress.com/item/Multi-purpose-Transistor-Tester-128-160-Diode-Thyristor-Capacitance-Resistor-Inductance-MOSFET-ESR-LCR-Meter-TFT/32812264664.html
https://www.aliexpress.com/item/Clear-Acrylic-Case-Shell-Housing-For-GM328-Transistor-Tester-Capacitance-ESR-Mega328/32779436939.html
You can also find cases for your existing testers, for a few dollars.
SilverSolder:
I was able to measure the gate-source breakdown voltage by using a current source to drive 1uA in reverse through the gate into the N channel and measuring the compliance voltage required to do that.
The pn4391 (manufacturer: Fairchild) junctions break down at 52V at room temperature.
The Fairchild data sheet says 30V, whereas the Central Semiconductor spec says 40V. Looks like the 40V number is safe for the Fairchild part too, based on the evidence so far.
For sure you are not stressing it by using it at the max rated voltage of 30V, which is what I really wanted to know in the first place.
Winner, winner, chicken dinner!
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