I got 0.6V drop between Emitter and Collector on 2SC1971 transistor!!??

[Willen]

It was diode test. All others test was fine but when I connected Black probe to Emitter and Red probe to Collector, multimeter is showing 0.6V (excatly 620mV) drop voltage at diode test mood. But there is no voltage drop if I changed the probes red to Emitter and black to Collector.

Base (red) to emitter (black) and Base (red) colllector (black) is showing 0.66V drop but not the other way arround, it's good. (Pinout of C1971 is 'BEC')

This is the transistor marked as 'Mitsubishi C1971'. I bought this new one from a shop. How can I explain it? Anybody, do have any practical experience?

 

[mvs sarma]

The test appears OK.
This test alone cant certify the device bought. We can only hope that it could be OK.

 

[Willen]

But all others transistors has '0' drop (shows no link) between EC or CE!!!

 

[MrAl]

Hello there Willen,

One explanation is that there could be high leakage current collector to base. High leakage or even a little leakage could turn the transistor on and that would give a low reading collector to emitter. This is just a guess though without being able to test it myself. But what you could do is bias it with a few resistors and see if it performs correctly.
Using a 9v battery perhaps and a 1k collector resistor and 10k to 1M resistor to bias the base, you could verify that the collector to emitter voltage goes up and down as you decrease and increase the base current. That will tell you much more than an ohm meter could tell you.

 

[Nigel Goodwin]

Why would you even test for such a thing?.

However, high power high frequency transistors often have reverse connected diodes internally - I don't know if it's specifically added, or if it's in some way part of the particular construction (rather like MOSFET's).

 

[Willen]

Why would you even test for such a thing?.

However, high power high frequency transistors often have reverse connected diodes internally - I don't know if it's specifically added, or if it's in some way part of the particular construction (rather like MOSFET's).

just to be sure- it is damaged or well in condition. But.....

 

[mvs sarma]

@willen
the test result you indicated on post#1 is OK. What is your doubt? Do you expect a diode across the collector and emitter in the reverse, like some FETs and power switching transistors? It may not be there in this transistor as it is RF power device.

 

[Willen]

@willen
the test result you indicated on post#1 is OK. What is your doubt? Do you expect a diode across the collector and emitter in the reverse, like some FETs and power switching transistors? It may not be there in this transistor as it is RF power device.

I have a cordless phone set which has C1971 as a final output transistor.

'Test OK' mean is the transistor fine? But why this transistor shows few hundred mV between Emitter to Collector but other transistors not? (may be internal reverse diode as Nigel Goodwin said?)

 

[mvs sarma]

if i again read post#1,
you said,
1. collector to emitter reverse is 0.62V (collector red)
2. same in normal (collector black) is nil.
1 and 2 indicate that there is a diode across collector and emitter in reverse direction.

3. emitter to base normal *base red) NIL and reverse is 0.66 it is OK

hence as per your test the device has a reverse diode protection.

try with a load of 50 ohms or 100 ohms on collector to 12V positive.
connect -ve to emitter
then apply a variable bias voltage using a pot and with a series resistor of at least 10 ohms to base.
from approx 200mV to 1V (NOT DIRECTLY)
you find collector current changing and there by voltage at collector wrt emitter.

once the test is showing amplification
you can believe it.
However please study the datasheet for 2SC1971 for the test circuit application
they don't use any base bias. at high power application,