How to Test Transistors with a Multimeter - NPN, PNP, JFET
BJT - Bi-Polar Junction Transistors
NPN 2N3904 EBC
PNP 2N3906 EBC
Collecter is larger materal than Emitter, Emitter is heavely doped than Collect)
So Base to Emitter is slightler higher forward voltage (0.663) than Base to Collector 0.645)
J-FET 2N5457 Pins DSG
G => D S N-Channel
G <= D S P-Channel
Construction of N-Channel J-FET
One N type of Silicon going from Drain to Source and
Another P type of Silicon on the Gate
2 section of P type Materal connect to Gate
Test from Gate to Drain or Gate to Source
REverse Bias -ve on Gate; +ve on Source (OL open circuit)
REverse Bias -ve on Gate; +ve on Drain (OL open circuit)
Forward Bias +ve on Gate; -ve on Source (0.708 Silicon Diode Drop)
Forward Bias -ve on Gate; +ve on Drain (0.708 Silicon Diode Drop)
Go into Resistance and measure Drain to Source
If JFET is in Good Condition, you should measure a couple hundred of Ohms resistance
So you have P type on Gate and N Type on Drain to Source
It create a single PN Junction
If the FET channel is open
The FET Channel is open if Gate to Source is Zero Volts
Black lead on Drain (P-Materal)
Red Bridging Source and Gate (make it Zero Volts) and measure resistance = 138 ohms
If you are not touching the Gate, and try to measure resistancethe reading could be drifting all over the place, because the gate is floating
if you short the gate an source to open the channel, you'll get 138 ohms
Identify which pin is the Drain, Gate and Source
Pin
1 2 3
Gate Drain Source
Put MultiMeter in Diode Mode
+ve led to Drain and -ve led to Source Result there should be NO Connection (OL) between drain and source
-ve led to Source and touch the Gate with Positive Led RESULT there should be a connection when it is put back to Drain
Once you touch the Gate and Drain with your finger, RESULT there should be no connection between Drain and Source anymore
Ref: https://www.youtube.com/watch?v=2IkAPU9X33k
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