Diodes

>>8131934
Of course they have. Though it's not the same in forward- or reverse-biased configurations. Forward resistance is tiny, reverse is huge, until you reach the breakdown voltage.

>>8131934
I mean you could probably start by turning the multimeter to the resistance settings

File: 1N400X.png (59KB, 778x327px) Image search: [Google]

59KB, 778x327px

>>8131934
>diodes have resistance?
sort of

>>8131934
diodes have varying resistance, as a function of the voltage applied

File: image.jpg (1MB, 3264x2448px) Image search: [Google]

1MB, 3264x2448px

>>8131950
Hey wow that helps

you have the multimeter set to measure DC voltage at the moment

>>8132037
Kek

>>8132037
Now perhaps adjust the range to be more appropriate than megohms.

>>8131947 answers your question. High reverse resistance is the entire purpose of a diode. Forward resistance is unavoidable in the real world, but intended to be small.

>>8132093
>Now perhaps adjust the range to be more appropriate than megohms.
OP, you should use the "diode" setting.
The switch position that has the diode symbol?
Yeah, that one.
Here's why: even in forward bias, it still takes a certain amount of voltage to get a diode to conduct.
The other resistance settings don't push enough voltage to get a diode to conduct.
And even then, the numbers you get from the meter are useless.
Unlike a resistor, the diode doesn't have a fixed resistance.
Instead, it always drops a fixed voltage across the p-n junction, usually it's 0.6v for a silicon diode.

File: diode.png (40KB, 1000x1000px) Image search: [Google]

40KB, 1000x1000px

>>8131934
Yes, but it's nonlinear. You can use your multi meter to find the forward bias voltage drop across the diode, and the diode should have a rated reverse bias breakdown voltage.

>>8132109
Am the person you responded to, knew of the diode setting but thanks for the detailed explanation on the reasoning.

>>8131934
>Do diodes have resistance?
No, they are not linear components. They don't follow Ohm's law even approximately, so they can't be said to have a resistance.

That's not the same as have zero resistance, it's that the proper concept of a resistance, which is tied closely to Ohm's law, does not apply usefully to diodes.

File: img_0059.jpg (34KB, 500x360px) Image search: [Google]

34KB, 500x360px

Everything has resistance.
Fight the power.

>>8132130
No. It has resistance, but it has a non constant resistance. It is completely wrong to say that the concept of resistance does not apply to diodes.

>>8132109
That's what my first picture displays m8, just showing him that the multimeter measures resistance across a diode as infinite. I'm asking what the 590 means.

File: 1N400X_Vf.png (68KB, 891x680px) Image search: [Google]

68KB, 891x680px

>>8132508
>what the 590 means
590 mV forward voltage at some current. Touch it and watch the voltage decrease.
>>8132109
>always drops a fixed voltage
No, see diagrams posted. Vf depends on type, current and temperature.

>>8132597
>590 mV forward voltage at some current
>at some current
at what current?

>>8131934
They do have non linear resistance which means for every single DC point they exhibit a different resistance value. So depending on the DC condition of your multimeter you can see something very close to zero, infinity or if somehow it is biased around the region where diode is turning on you can see some value. Such is the nature of the DC resistance of a diode.

In linearized AC analysis, they just calculate the DC op point and then approximate the whole diode as resistor (or a combination of linear elements depending on how accurate you want it to be).

So the value you read as you show in your picture is basically meaningless. You need to measure the resistance in the region you are interested in and under the bias conditions you are interested in.

But in the end, diodes are not usually connected directly, and the current limiting resistor usually sets the equivalent series resistance in either case, so there's also that.

In ideal case depending on your bias point you should either see 0 or infinite.

Source: I liek diodes.

>>8132623
One additional thing is how you actually measure the resistance, Kelvin method would yield in accurate results, but you are not using that, and it is probable that your multimeter applies large enough variance that the readings are pretty meaningless anyway unless the diode is deeply biased in any of its operating regions (cut off breakdown or on)

>>8132623
>DC point they exhibit a different resistance value.
Addition: Resistance is the derivative of I-V curve, and diode has an exponential relation, which means its resistance also changes exponentially with the bias point.

Man I missed a lot of stuff and made mistakes. Sorry.

>>8132130
They are just non-linear resistances in circuits and systems.

Source: Linear and Non Linear Circuits, Leon O. Chua Chapter 2.1.2

>>8132620
>at what current?
Read the graph in >>8132597

>>8132620
>at what current?
The current the multimeter puts out at that voltage. My one (same crap type model) shows 2.6 V open loop voltage and 1.3 mA short circuit current suggesting an internal 2kΩ series resistance. So the forward current should be about 1 mA. You need a second meter to find that out.

File: 1N4148_Vf.png (86KB, 735x1017px) Image search: [Google]

86KB, 735x1017px

>>8132656
>Read the graph
Ends at 10 mA.
Semiconductors have large tolerances and diagrams only show the average values.
Pic has low current range but for a different diode.

>>8132620
Keep the meter in diode test mode but replace the diode with a variable 1kΩ resistor and adjust it to also display 590mV on the meter. Switch to the 2000Ω range and read the R value. 0.59V/R is the current you're looking for and R is the static (V/I) resistance of the diode at that current. I got 583mV for a 1N4148 diode at 26°C and 582Ω for the resistance.