testing diode?

[Dante]

I have some problems with diodes:1) if the diode is connect directly
(anode connect to + and catode connect to -) the current flows: but
the real toward is from catode to anode. is it wright? 2)if I want to
try diode with tester connecting + pole of tester with anode and -
pole of tester with catode does it display endless resistence or does
it display ended resistence? 3)the inside "battery" of a tester has
positive pole connected with "+" in the outside of tester or is it
connected with negative pole connected with "+" in the outside of a
tester? thank

 

[Dbowey]

Dante posted:

<< I have some problems with diodes:
1) if the diode is connect directly (anode connect to + and catode connect to
-) the current flows: but the real toward is from catode to anode. is it
wright?
Yes. That is the conventional view of current flow.

<< 2)if I want to try diode with tester connecting + pole of tester with anode
and - pole of tester with catode does it display endless resistence or does it
display ended resistence?
I'm sure, Endless resistance. This would appear wrong, but it is right,
because every resistance tester (Ohmmeter) I have ever used had the negative
voltage on the + pole and the positive voltage on the - pole of the meter.


<< 3)the inside "battery" of a tester has
positive pole connected with "+" in the outside of tester or is it connected
with negative pole connected with "+" in the outside of a
tester?
The latter.

Don

 

[Michael]

Dbowey wrote:

Dante posted:

I have some problems with diodes:
1) if the diode is connect directly (anode connect to + and catode connect to
-) the current flows: but the real toward is from catode to anode. is it
wright?


Yes. That is the conventional view of current flow.

2)if I want to try diode with tester connecting + pole of tester with anode
and - pole of tester with catode does it display endless resistence or does it
display ended resistence?


I'm sure, Endless resistance. This would appear wrong, but it is right,
because every resistance tester (Ohmmeter) I have ever used had the negative
voltage on the + pole and the positive voltage on the - pole of the meter.


3)the inside "battery" of a tester has
positive pole connected with "+" in the outside of tester or is it connected
with negative pole connected with "+" in the outside of a
tester?


The latter.

Don

FWIW, some analog multimeters (I have limited experience with digital
MM's) are wired such that + probe to a diode's CATHode causes current
flow, while other meters (the Simpson 269 for example) are wired the
other way 'round. In the Air Force I was supplied with a multimeter of
the former type - after I'd used a Simpson 269 for about five years -
which always gave me fits when I checked diodes.

 

[guy pastuzak]

"Dante" <dantez2003@libero.it> a écrit dans le message news:
5bd93c35.0502022323.542a0c@posting.google.com...

I have some problems with diodes:
2)if I want to
try diode with tester connecting + pole of tester with anode and -
pole of tester with catode does it display endless resistence or does
it display ended resistence? 3)the inside "battery" of a tester has
positive pole connected with "+" in the outside of tester or is it
connected with negative pole connected with "+" in the outside of a
tester? thank

The test will depend the MM used.

1- analog MM, usually with only ohm meter. The polarity of the plugs are
reversed, ie + is present on the "common" "-" plug, and - on the other. One way,
the measured resistance is endless, so the diode is equivalent to open circuit,
diode is off, in reversed bias. Other way, the indication will be dependant on
the RANGE of the ohm meter, and is meaningless. The diode "looks like" a
resistor but is not. However, a current flows.

2- DMM have a diode test, which is made of a constant current generator
connected to the plugs, with right polarity (+ on +, - on -), AND a volt meter
across the diode. So, we measure the forward (or reverse) voltage across the
diode. When in direct mode, the mesaure is typically .6V and this should be OK.
In reverse bias, the voltage should be maximum, and the result is usually
overflow, meaning that no current flows, the diode is off.

--
Guy Pastuzak

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