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Transistor testing

Started by RobH March 4, 2020
I have some BC547 transistors which I want to use in a circuit, but 
according to this:

Hook the positive lead from the multimeter to the to the EMITTER (E) of 
the transistor. Hook the negative meter lead to the BASE (B) of the 
transistor. For an good NPN transistor, you should see “OL” (Over 
Limit). If you are testing PNP transistor, the meter should show a 
voltage drop between 0.45V and 0.9V.4 May 2017

None of the BC547's give the those readings, as I get 0.02V on a few of 
what I have, and not 0.45V.

Are mine no good and should I bin them. I have had them for a couple of 
years or so now, and only used 1 of them.
In article <hca5oiFtbctU1@mid.individual.net>, rob@despammer.com says...
> have some BC547 transistors which I want to use in a circuit, but > according to this: > > Hook the positive lead from the multimeter to the to the EMITTER (E) of > the transistor. Hook the negative meter lead to the BASE (B) of the > transistor. For an good NPN transistor, you should see ?OL? (Over > Limit). If you are testing PNP transistor, the meter should show a > voltage drop between 0.45V and 0.9V.4 May 2017 > > None of the BC547's give the those readings, as I get 0.02V on a few of > what I have, and not 0.45V. > >
If you are seeing .02 v it is as if the transistor is shorted. Try testing in both directions with the meter set as an ohm meter. I assume you are using a digital meter which usually will not have enough current/voltage to bias the transistor into conduction. It will probably show shorted or very near zero ohms in both directions. An analog meter will usually bias the transistor into conduction so it will show low resistance in one direction and if the leads are reversed , a high resistance. Seems that you are using the meter like a diode tester. That is fine. For any type of a a bipolar transistor put one lead on the base. Then put the other lead on the emitter, then the collector. It should show around .2 to .4 volts if the older germanium and .6 to .9 if silicon. Then reverse the leads and do the same . The meter should show an open circuit or OL . Then put the leads on the emitter and collector. They should show open OL on in both directions. A common transistor will test like 2 diodes in series or back to back with the base as the common connection point.
On 04/03/2020 19:22, Ralph Mowery wrote:
> In article <hca5oiFtbctU1@mid.individual.net>, rob@despammer.com says... >> have some BC547 transistors which I want to use in a circuit, but >> according to this: >> >> Hook the positive lead from the multimeter to the to the EMITTER (E) of >> the transistor. Hook the negative meter lead to the BASE (B) of the >> transistor. For an good NPN transistor, you should see ?OL? (Over >> Limit). If you are testing PNP transistor, the meter should show a >> voltage drop between 0.45V and 0.9V.4 May 2017 >> >> None of the BC547's give the those readings, as I get 0.02V on a few of >> what I have, and not 0.45V. >> >> > > If you are seeing .02 v it is as if the transistor is shorted. Try > testing in both directions with the meter set as an ohm meter. I assume > you are using a digital meter which usually will not have enough > current/voltage to bias the transistor into conduction. It will > probably show shorted or very near zero ohms in both directions. An > analog meter will usually bias the transistor into conduction so it will > show low resistance in one direction and if the leads are reversed , a > high resistance. > > Seems that you are using the meter like a diode tester. That is fine. > > For any type of a a bipolar transistor put one lead on the base. Then > put the other lead on the emitter, then the collector. It should show > around .2 to .4 volts if the older germanium and .6 to .9 if silicon. > Then reverse the leads and do the same . The meter should show an open > circuit or OL . Then put the leads on the emitter and collector. > They should show open OL on in both directions. > > A common transistor will test like 2 diodes in series or back to back > with the base as the common connection point. >
The meter I am using is an old Fluke77 digital from RS about 30 or 35 years ago, and I have tried x5 BC547 tansistors. Using the voltage selection, I get 0.0v with negative lead on the collector and positive on the Emitter, and swapping round I get 0.25v Using the Ohm selection, I get OL in both directions, and the same using the diode selection with the negative lead on the base of the transistor I don't have an analogue meter now. Thanks
On 2020-03-04 21:40, RobH wrote:

> The meter I am using is an old Fluke77 digital from RS about 30 or 35 > years ago, and I have tried x5 BC547 transistors. > Using the voltage selection, I get 0.0v with negative lead on the > collector and positive on the Emitter, and swapping round I get 0.25v > Using the Ohm selection, I get OL in both directions, and the same using > &#2013266080;the diode selection with the negative lead on the base of the transistor > > I don't have an analogue meter now. > > Thanks
Well, then your transistors look fine as far as you could test them. The voltage test is useless, a transistor does not generate a voltage. What you might see is the diode of the B-E (or C-B) rectifying noise from the environment. Useless as an indicator. The ohms range test is also useless, it normally test with 0.2V which is not enough to bias the diode and will give an OL reading in both directions. As you properly described. You _MUST_ use the diode testing range! The B-E test should be about 0.55V with + on B side, and OL in the other direction. Same for the B-C test: about 0.55V with + on B side and OL in the other direction. The C-E test should be OL in both directions. Regards, Arie
In article <hcai1iF1cqgU1@mid.individual.net>, rob@despammer.com says...
> > The meter I am using is an old Fluke77 digital from RS about 30 or 35 > years ago, and I have tried x5 BC547 tansistors. > Using the voltage selection, I get 0.0v with negative lead on the > collector and positive on the Emitter, and swapping round I get 0.25v > Using the Ohm selection, I get OL in both directions, and the same using > the diode selection with the negative lead on the base of the transistor > > >
I may have misunderstood what you said about using the voltage selection. The diode selectionis what I would have thought you were using. That puts a voltage on the probes, then reads how much voltage is dropped across the leads so to speak. The way I remember the first posting was 0.025 volts. It could have been a typo and you ment the 0.25 which sounds more reasonable. If you get a voltage (number showing up on the meter readout) with the leads in one direction and the OL in the other direction while in the other direction going base to emitter and then base to collector, and OL in both directions emitter to collector, the transistor is probably good. The main thing is not the total number,but a large difference in each direction with the exception of collector-emitter which should be very large resistance in both directions or OL in the diode poaition.
On 2020-03-04, RobH <rob@despammer.com> wrote:
> I have some BC547 transistors which I want to use in a circuit, but > according to this: > > Hook the positive lead from the multimeter to the to the EMITTER (E) of > the transistor. Hook the negative meter lead to the BASE (B) of the > transistor. For an good NPN transistor, you should see &ldquo;OL&rdquo; (Over > Limit). If you are testing PNP transistor, the meter should show a > voltage drop between 0.45V and 0.9V. 4 May 2017
> None of the BC547's give the those readings, as I get 0.02V on a few of > what I have, and not 0.45V.
You must put your meter in diode-test mode, (on the fluke 77 it looks like that's also continuity beeper mode) it should say OL with the leads unconnected and 0.00V with them toucheing eaco other. then do the above measurements.
> Are mine no good and should I bin them. I have had them for a couple of > years or so now, and only used 1 of them.
I'm guessing operator error, they should still be good after only a few years. -- Jasen.
On 05/03/2020 05:21, Jasen Betts wrote:
> On 2020-03-04, RobH <rob@despammer.com> wrote: >> I have some BC547 transistors which I want to use in a circuit, but >> according to this: >> >> Hook the positive lead from the multimeter to the to the EMITTER (E) of >> the transistor. Hook the negative meter lead to the BASE (B) of the >> transistor. For an good NPN transistor, you should see &ldquo;OL&rdquo; (Over >> Limit). If you are testing PNP transistor, the meter should show a >> voltage drop between 0.45V and 0.9V. 4 May 2017 > >> None of the BC547's give the those readings, as I get 0.02V on a few of >> what I have, and not 0.45V. > > You must put your meter in diode-test mode, (on the fluke 77 it looks > like that's also continuity beeper mode) it should say OL with the leads > unconnected and 0.00V with them toucheing eaco other. then do the above > measurements. > >> Are mine no good and should I bin them. I have had them for a couple of >> years or so now, and only used 1 of them. > > I'm guessing operator error, they should still be good after only a few > years. >
Putting the meter in diode-test mode,it reads OL when leads are unconnected and 0.00v when touching each other. Then connecting the positive to the Emitter and negative lead to the Base the meter beeps, then reads 0.666, the same reading when the positive is connected to the collector.
On Thursday, 5 March 2020 09:34:30 UTC, RobH  wrote:
> On 05/03/2020 05:21, Jasen Betts wrote: > > On 2020-03-04, RobH <rob@despammer.com> wrote: > >> I have some BC547 transistors which I want to use in a circuit, but > >> according to this: > >> > >> Hook the positive lead from the multimeter to the to the EMITTER (E) of > >> the transistor. Hook the negative meter lead to the BASE (B) of the > >> transistor. For an good NPN transistor, you should see &ldquo;OL&rdquo; (Over > >> Limit). If you are testing PNP transistor, the meter should show a > >> voltage drop between 0.45V and 0.9V. 4 May 2017 > > > >> None of the BC547's give the those readings, as I get 0.02V on a few of > >> what I have, and not 0.45V. > > > > You must put your meter in diode-test mode, (on the fluke 77 it looks > > like that's also continuity beeper mode) it should say OL with the leads > > unconnected and 0.00V with them toucheing eaco other. then do the above > > measurements. > > > >> Are mine no good and should I bin them. I have had them for a couple of > >> years or so now, and only used 1 of them. > > > > I'm guessing operator error, they should still be good after only a few > > years. > > > > > Putting the meter in diode-test mode,it reads OL when leads are > unconnected and 0.00v when touching each other. > Then connecting the positive to the Emitter and negative lead to the > Base the meter beeps, then reads 0.666, the same reading when the > positive is connected to the collector.
that means the tr is dropping 0.666v as each junction conducts. Black lead is +ve on diode test so you have an npn tr behaving normally. NT
On 05/03/2020 10:39, tabbypurr@gmail.com wrote:
> On Thursday, 5 March 2020 09:34:30 UTC, RobH wrote: >> On 05/03/2020 05:21, Jasen Betts wrote: >>> On 2020-03-04, RobH <rob@despammer.com> wrote: >>>> I have some BC547 transistors which I want to use in a circuit, but >>>> according to this: >>>> >>>> Hook the positive lead from the multimeter to the to the EMITTER (E) of >>>> the transistor. Hook the negative meter lead to the BASE (B) of the >>>> transistor. For an good NPN transistor, you should see &ldquo;OL&rdquo; (Over >>>> Limit). If you are testing PNP transistor, the meter should show a >>>> voltage drop between 0.45V and 0.9V. 4 May 2017 >>> >>>> None of the BC547's give the those readings, as I get 0.02V on a few of >>>> what I have, and not 0.45V. >>> >>> You must put your meter in diode-test mode, (on the fluke 77 it looks >>> like that's also continuity beeper mode) it should say OL with the leads >>> unconnected and 0.00V with them toucheing eaco other. then do the above >>> measurements. >>> >>>> Are mine no good and should I bin them. I have had them for a couple of >>>> years or so now, and only used 1 of them. >>> >>> I'm guessing operator error, they should still be good after only a few >>> years. >>> >> >> >> Putting the meter in diode-test mode,it reads OL when leads are >> unconnected and 0.00v when touching each other. >> Then connecting the positive to the Emitter and negative lead to the >> Base the meter beeps, then reads 0.666, the same reading when the >> positive is connected to the collector. > > that means the tr is dropping 0.666v as each junction conducts. Black lead is +ve on diode test so you have an npn tr behaving normally. > > > NT >
Thanks, and by accident I found that the transistor is working correctly. I have put together a IR circuit with transmiter led and and photo diode, using x2 transistors and a 555. I couldn't get to work until a wire from the ground rail of a breadboard touched a leg of a 220ohm resistor. Then, for some unknown reason, it works in reverse!!
On 05/03/2020 11:17, RobH wrote:
> On 05/03/2020 10:39, tabbypurr@gmail.com wrote: >> On Thursday, 5 March 2020 09:34:30 UTC, RobH&nbsp; wrote: >>> On 05/03/2020 05:21, Jasen Betts wrote: >>>> On 2020-03-04, RobH <rob@despammer.com> wrote: >>>>> I have some BC547 transistors which I want to use in a circuit, but >>>>> according to this: >>>>> >>>>> Hook the positive lead from the multimeter to the to the EMITTER >>>>> (E) of >>>>> the transistor. Hook the negative meter lead to the BASE (B) of the >>>>> transistor. For an good NPN transistor, you should see &ldquo;OL&rdquo; (Over >>>>> Limit). If you are testing PNP transistor, the meter should show a >>>>> voltage drop between 0.45V and 0.9V. 4 May 2017 >>>> >>>>> None of the BC547's give the those readings, as I get 0.02V on a >>>>> few of >>>>> what I have, and not 0.45V. >>>> >>>> You must put your meter in diode-test mode, (on the fluke 77 it looks >>>> like that's also continuity beeper mode) it should say OL with the >>>> leads >>>> unconnected and 0.00V with them toucheing eaco other. then do the above >>>> measurements. >>>> >>>>> Are mine no good and should I bin them. I have had them for a >>>>> couple of >>>>> years or so now, and only used 1 of them. >>>> >>>> I'm guessing operator error, they should still be good after only a few >>>> years. >>>> >>> >>> >>> Putting the meter in diode-test mode,it reads OL when leads are >>> unconnected and 0.00v when touching each other. >>> Then connecting the positive to the Emitter and negative lead to the >>> Base the meter beeps, then reads 0.666, the same reading when the >>> positive is connected to the collector. >> >> that means the tr is dropping 0.666v as each junction conducts. Black >> lead is +ve on diode test so you have an npn tr behaving normally. >> >> >> NT >> > > Thanks, and by accident I found that the transistor is working correctly. > I have put together a IR circuit with transmiter led and and photo > diode, using x2 transistors and a 555. I couldn't get to work until a > wire from the ground rail of a breadboard touched a leg of a 220ohm > resistor. Then, for some unknown reason, it works in reverse!! > >
Update: The circuit works correctly now, as I swapped another transistor, and put in the wrong way round, Doh!