Electronics > Repair
Help identify glass encapsulated diodes
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Kim Christensen:
Looking at the schematic, it seems like they are some sort of constant current diode.
Example attached:
晓看风云:

--- Quote from: MathWizard on August 25, 2024, 08:46:20 pm ---So is there a problem with the circuit tho ? If you have a soldering iron and remove them, it should be easy to check if they are zeners, with a 9V battery and some resistor. A current 10mA should be enough to get a small zener fully conducting.

I didn't try the circuit, but for example say they drop 5.1V=Vz, with about 10mA=Iz. Then the resistor size would be R=(Vcc-Vz)/Iz

--- End quote ---
I have tried using a 10k resistor in series, limiting the current to 10ma and setting the power supply to 14v. It did not perform according to the script because it has a forward infinity and a reverse voltage drop of 0.6v. So obviously, when I tested using this method, the voltage between the two segments of the diode remained stable at around 0.6V.
晓看风云:

--- Quote from: Kim Christensen on August 25, 2024, 11:31:27 pm ---Looking at the schematic, it seems like they are some sort of constant current diode.
Example attached:

--- End quote ---
I searched and found it very difficult to purchase and the price is expensive. If it is really a current regulator, I would like to know if this type of current regulator would exhibit a forward infinity and a reverse voltage drop under normal circumstances? This is very important, at least I can know if they are normal now. Or are there any commonly used diodes to replace them?
fzabkar:
You could replace the diode with an n-channel JFET and series resistor.

https://en.wikipedia.org/wiki/Constant-current_diode
Kim Christensen:

--- Quote from: 晓看风云 on August 26, 2024, 02:29:18 am ---I searched and found it very difficult to purchase and the price is expensive.
--- End quote ---

I wouldn't replace them unless you know they are faulty. Besides, the ones I linked are just an example of the type of device that I think they might be.


--- Quote ---If it is really a current regulator, I would like to know if this type of current regulator would exhibit a forward infinity and a reverse voltage drop under normal circumstances? This is very important, at least I can know if they are normal now. Or are there any commonly used diodes to replace them?
--- End quote ---

You could try testing them in a circuit like depicted below. The 100 ohm resistor is just for safety to make sure you don't damage the diode or meter. Set the power supply's current limit to 10mA as well.
Slowly adjust the power supply voltage from zero to apx 15V and plot the current at 1V intervals. If it is a constant current diode, the current should hold fairly steady once the power supply voltage reaches 1-3V or so... I suspect the current will be around 1-4mA or so.
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