transistors and digital multimeters

[joajas]

measurement npn transistors with multimeter

Hi,

is there anyway we can check whether a transistor is NPN or PNP using a digital multimeter?

please advice, thank you.

 

[eltonjohn]

how to check the legs of transistor

To test for a BIPOLAR TRANSISTOR you don't need a SPECIAL HARDWARE is SIMPLE .. JUST ..FIRST see if the TRANSISTOR is OK .. You do that by locating the BASE .. you should be able to locate two FORWARD BIASED JUNCTIONS with any STANDARD TESTER .. IT won't matter if they are NPN or PNP .First try to identify a FORWARD BIAS JUNCTION
it should mesure on a resistance meter sround 500 Ohms .to 200 ohm for some particuliar transitors .. 100 or less means the JUNCTION is damaged
more 1000 ohms means .. The trasistor is also damaged ..
So once you identify a GOOD FORDWARD BIAS JUNCTION //I means you have a DIODE The red cable is teh CATHODE ,, the BLACK wire is the ANODE .. Well now a transistor can be assimilated to two DIODES..just for testing POURPOSES .. try find the other FORWARD BIASED DIODE

If the two anodes are in the same PIN the transistor is a NPN
if the two cathoddes are in the same pin the transistor is a PNP
I also good to mesure the inverse biased junction once the two diodes ones are Known .. They should mesure INFINITY . if the juctions are ok

Example let say we have an unknown trasnistor with legs 1 2 3 ..
we find that ther is a foward bias junction bewteen legs 3 -> 1
and legs 3 -> 2 . So is evident that the base is leg 3 .. Now if the Juctions become evident with RED tester cable in leg 3 then the transistor is a NPN
if the Forward bias junctions become evident wih the black wire at leg 3 now the transistor is PNP .. Just to be shure that the TRANSISTOR is in good condition CHECK with tester 1-> 3 and 2-> 3 junctions BOTH shoul mesure INFINITY .. then chances are the TRANSISTOR is OK
The base is pin 3

 

[Basil]

japanese trasnistor

Hi,

is there anyway we can check whether a transistor is NPN or PNP using a digital multimeter?

please advice, thank you.

1 - set your multimeter in Ohms (2KOhm scale is OK)
2 - look for a diode, put the common (negative) tip in the cathode and the Volt/Ohm (positive) tip in the anode. You should read some resistence value. If you read infinite (OL, over range) do invert tips (or change the diode!). Thanks to this test you now know the polarity of your multimeter. I asume the black tip is negative and the red tip is positive.
3 - in your unknow transistor look for a lead which has a few hundred Ohms measuring to the other two leads. This lead is BASE; the other two emisor and colector. If you have your red tip in the base your transistor is NPN.

Saliva HFE measurement

it's not a joke really, it works after a bit of trial.

So we have a NPN transistor. Asume one of the other two leads is colector and the remaining emiter. Put your positive (red) tip in the colector, theblack tip in the suposed emisor, lick your forefinger (or the finger you want) and feed the base from colector conecting both with your licked (conductive) finger. It's possible you have to change scale. Reverse emisor & colector and do repeat. The one who has mor gain is colector, otherwise you are using emisor as colector and it works but with a very low HFE.

The licked finger method is useful to see if a transistor gains. You will discover tha power transistors need more finger presure than low signal high gain ones.

 

[barrybear]

how to identify npn and pnp without multimeter

Most multimeters have a diode test function on them. Positive lead will turn the diode on ( you can read forward voltage drop ie .7 volt). The ohms range would not normaly have enough voltage/ current to turn the diode on.

I would not recomend testing diodes this way as often a junction can become noisy/ leaky and cause intermitent problems . Best way is with a dynamic component tester and an ossiloscope.

Barrybear

 

[serg1976]

trasnistor lead testing

Hi,

is there anyway we can check whether a transistor is NPN or PNP using a digital multimeter?

please advice, thank you.

Hi,
see my file transistor.doc