Electronics > Repair
Help identify glass encapsulated diodes
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晓看风云:

--- Quote from: fzabkar on August 26, 2024, 04:23:11 am ---You could replace the diode with an n-channel JFET and series resistor.

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

--- End quote ---
Okay, thank you for your suggestion! I will use it as a backup measure. After all, I don't know much, so if I act rashly, I'm worried that I might mess it up. I will first try to understand the model or quality of this electronic component.
晓看风云:

--- Quote from: Kim Christensen on August 26, 2024, 04:34:23 am ---
--- 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.

--- End quote ---
Okay, thank you for your suggestion! I will try to set up a testing environment and observe the results, and then provide feedback! (As for whether they have faults, I can only compare them with other things within my knowledge, such as voltage regulators and rectifiers: they all have the characteristics of forward voltage drop and reverse infinity.)
晓看风云:

--- Quote from: Kim Christensen on August 26, 2024, 04:34:23 am ---
--- 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.

--- End quote ---
Before using your testing method, I searched everywhere and found that the model should be CRD E-102 produced by SEMITEC in Japan, with a current of 1mA. After using your testing method, I further validated this result. When the voltage is 1V, my power supply displays 0.000A, and the current remains at 0.001A at any stage between 2-15V. I think this should indicate that it is a 1mA current limiting diode and is working completely normally! I am very glad that your answer has enabled me to reach the current level, and I will continue to try to find other possible faults! This instrument is Yokogawa CA100, which is a process calibrator. The other gears are very good, but the frequency gear cannot work properly. No information was found on the forum, so I had to face it myself! If there are any new developments in the future, I will publish a new repair post about the frequency of maintenance faults.
Kim Christensen:

--- Quote from: 晓看风云 on August 26, 2024, 06:41:23 am ---After using your testing method, I further validated this result. When the voltage is 1V, my power supply displays 0.000A, and the current remains at 0.001A at any stage between 2-15V. I think this should indicate that it is a 1mA current limiting diode and is working completely normally!
--- End quote ---

Though the current meter on your power supply doesn't have enough resolution, it appears to be working as expected. If both diodes check out the same, you can put them back in circuit if you haven't done so already.

Looking at your circuit again, it looks like the transistor circuit is a current buffer for the LT1007 Op-Amp. I assume the output load is connected at the junction of R19 & R22. If the circuit is operating properly, the voltage at R19 & R22 should follow the voltage at the output of LT1007 (pin 6), within a slight error, while connected to an appropriate load:

fzabkar:
I expect that the junction of R19 and R22 would be connected to pin #2 of the op-amp, possibly via a potential divider. The output would then follow the input at pin #3, scaled down by the divider.
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