My Free Online Simulator for Testing Diodes with Multimeter

GabrielVinicios

GabrielVinicios

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I don`t know if this is the correct place, but I will post it here.

My name is Gabriel Maganha, and I have a YouTube channel called GVensino, where I teach Electronics in Portuguese. Lately, I've been working on developing some simulators, and I'd like to share with you an online, free simulator for testing diodes with multimeters.

Here's the link: https://gvensino.com.br/sim/diodo

Feel free to use it—it's completely free. I hope you find it helpful, especially if you're a teacher or learning electronics.

Thank you and best regards!
 

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Nice job Gabriel. Welcome to participate.

I like to simulate imperfect discrete designs with added RLC in slow motion to demonstrate techniques of dynamic load testing for example instead of Bode Plots.
e.g. DCDC + 5 to -5V reg. We have a good number of retired experts in this group and many new comers.

e.g. in Falstad. https://tinyurl.com/27rzsown

Tony
EE since 1975.
 
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Hello Tony! That's wonderful! And Falstad is indeed impressive. I enjoy creating educational simulators.

I have other simulations that I am testing, and one of them is a significant project where students can program a PLC with interactive scenarios in Ladder. I will post it here when it is released.
 

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bug report The smaller Diode must have a higher average value, but both shown vary 550 +/- 60 mV roughly.

for example a TO-92 Vbe will average 630 mV

1742844964635.png
I wonder what the actual If current used in each meter.

It seems to change. The parts are random but the diode test current is normally < 1 mA where bulk resistance variations have less affect. I suspect you programmed based on experimental results.
e.g. 500 uA * 0.1 ohm = 50 uV

variation
Bulk resistance affects the result which is inversely proportional to Pd max rating.
--- Updated ---

FWIW

My Rule of Thumb is Rs of any forward diode is Rs= 0.5/Pmax rating +/-50% Ohms which I have verified from 10 mA diodes to 100A diodes.

I added + I*Rs to the AI generated facts
 
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Thank you! So, the resistance of the power diode should be a lower value, correct? Did you calculate a plausible value for it?
 

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Yes I corrected my images. But there is still an error in the readings.

My Fluke 75 for example reads 3 Meg on a small PN junction in a transistor C-E and 638 mV. This is normal even for an analog meter because of the very low constant current used to measure resistance. If it changes currents with full scale, it might be as high as 1mA for 10 Ohms full scale, but never for Diode test mode. This uses a current much less than 1 mA to save battery energy. Your reading of 0.617 Ohms is actually what I would expect if the meter used 10 to 30 mA in 100A industrial diode with a high ideality factor.

The Ohm reading is false. It is lower which might occur if you measured 490 mV/1mA or 490 V/1A It should be reading > 100 kOhm This should be the diode leakage resistance as Ohm reading use very low current.


--- Updated ---

For a standard 1 A diode , one should expect the resistance to meet specs at 25'C
e.g. 1N4005


For 1.999 full scale Ir max=10 uA this implies worst case 2/10e-6 or 200k or 2V/0.05 uA = 40 Meg typical
The Industrial diode rated for say 50 to 100A will be more like 10k to 100k resistance in DMM's and measure less than 500 mV in diode test mode due to the lack of bulk resistance voltage rise at 50 uA.
 
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Thanks for your observations! I've just updated the simulator. Refresh the page and test it now. I think now it is more realistic.

Thank you Tony!
 

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better but still too high and too much variation for a 1A diode in this case size since diode test barely illuminates a RED LED meaning much less than 1 mA and more likely <10 uA so that cannot exceed 500 mV unless it is a small TO-92 transistor diode junction which was 630 mV.

I tested two meters . Fluke 75 in diode test mode did not reach 1 uA on another Chinese 4 1/2 digit meter while visa versa diode test registered 10 uA.

Revised: Microcurrent fuse was NG on Chinese meter and Chinese meter Diode mode retested at 200 uA on Fluke 75 with 710 mV on Vbc on TO-92 so I estimate Fluke 75 at 100 uA.

So unless you know what your model provides in current and know what mV vs If is for a diode, it can be misleading.

But good enough to tell the junction is "probably" OK if open cct. in reverse.

If you test real diodes with a real meter, you can verify what I am saying.
--- Updated ---
Rev B Or see the typical Vf vs If for low currents
 
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You're right. What would be a rasonable value to the resistance of both diodes? Don`t have a diode here to test now.

About the voltage measure of Pluke, it is now corrected. Thank you!
 

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D.A.(Tony)Stewart said:
Fluke (not Pluke)

A 1A diode R typically may be 200k worst case min and up to 40 Meg typical
The Industrial diode rated for say 50 to 100A will be more like 10k to 100k resistance on a DMM
Click to expand...

Pluke is the name I gave in the simulator to avoid problems with the original brand, lol.

I've changed some factors in the simulator and now I think it's a little bit better.

Thank you for all your feedback, Tony!
 
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So far we have only talked about two generic parts of diodes when infact there are millions in Si, and Schottky types and many other materials like GaAs and Al In Ga As

But for Si Diodes all the variation in forward voltage, Vf is due to logarithmic current and then linear current x bulk resistance when in saturation. This depends on the area of the chip and process quality controls which is not Gaussian but skewed to the high side of nominal. Whereas resistance measurements done at much lower currents are more due to leakage effects with high resistance.

But now I am getting into the nitty gritty of diode performance beyond the intent of your exquisite DMM virtual clone.

For those who understand, there are many levels of accuracy in model simulations. But on log I vs linear V we see an asymptotic point above the exponential rise in current followed by the linear bulk resistance effects which affect the differences in diodes until you pass a few % of its rated steady current. The other interesting parameter is than bigger diodes also have bigger capacitance at 0V dc which always reduces with reverse voltage. This affects recovery time for applications when this matters. Although I have never had a DMM with a C position during my early R&D career, it would have been useful.
 
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