I was testing few types of transistors on my newly acquired peak atlas pro and came across some N-channel depletion mode JFETs marked 2n3819. When I analysed them on the device it indicated they are BJTs. Using my multimeter in diode mode, the voltage drop from centre pin (2) to other two (1,3) showed 0.693v for each pair and between 1 and 3 was OL. I understand that if they were real JFETs, the resistance between drain and source would be low, which is not the case for these transistor as they showed OL. Am I right to assume they are fake? NPN BJTs rebranded as 2n3819?

 

I do not think those tests have excluded it from being a JFET. The drain to source resistance may be "low" but not low enough to give you something other than OL in diode test mode.

Try measuring the resistance of the drain to source resistor using the multimeter resistance mode.

 

I measured them in resistance mode, same results, it showed OL.

 

The 2N3819 JFET is a BJT, with junctions from 2 to 1 and from 2 to 3. The two voltage readings are what one would expect. I don't know how your Peak analyser works, so don't know whether the OL reading indicates a good or bad FET. Was the gate connected to anything during the 1-to-3 measurement?

 

The OL reading of 1 and 3 was from multimeter. No, 2 wasn't attached . Peak atlas showed the parameter as hFE=286 at Ic=5mA, Vbe= 0.749v at IB=5Am etc.

 

Hi,

I am suffer from fake JFET recently, I bought mp102 and 2n3819 (TO92) from taobao and found that all of them are fake jfet, they just use npn bjt transistor+sand paper to make it, to identify this fake jfet is very easy, just plus in the transistor test holes on digital multi meter, you will see the beta hfe value, 300-500, to avoid paying money to fake maker, buy sot23 package jfet, like mmbf4391, cheap and good.