ZENER-Problem, not KiCad specific!

Projects
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Hello,

I hope it is OK if I ask a question about a single component !?

I have replaced a ZENER 1N4731A (written on its body) with another 4.3V ZENER of the same size.
The resulting voltage was too small !

I tested both diodes with current according to their datasheets:
NEW 4.3V ZENER : approx. 4.3V @ 50mA OK
OLD 1N4731A : approx. 4.7V @ 50mA !

I checked the writing on the 1N4731A and the datasheets again and again and asked colleagues to confirm. A 4.7V Z-diode should be named 1N4732 !

Are there Diodes with wrong markings out there ??

Greetings from Chris

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So your question is “are there electronic components with defects or misprints”? Sure, happens all the time. Maybe the manufacturer of your pcb got the misprinted diodes for a discount. Cheap Chinese manufacturers use rejected products all the time.

3

Compare two SMB diodes: SMBJ15 and SM6T18.
SMBJ15 - working: 15V, breaking: 16.7-19.2, clamping: 24.4V/24A
SM6T18 - working: 15.3V, breaking 17.1-18.9 (typ: 18V), clamping: 25.2V/24A
In the BOM I specify them as acceptable substitutes even one name says 15V and second 18V.
We know nothing about NEW 4.3 ZENER to have a chance to compare datasheets.

For NEW you write ‘OK’, for old you write ‘!’.
If NEW is OK and old not OK then what is your problem?

4

Hi, maybe I was too confusing about this.

The 4.3V Diode behaves according to its marking: 4.3V@0.05A
The 1N4731 behaves different to its marking (which indicates 4.3V): 4.7V@0.05A

4.7V is obviously what I need for the circuit but the 1N4731 marking on the existing “old” PCBs made me buy new 4.3V diodes.

5

Or maybe the schematic (is there one?) specifies 1N4732 but the board text wrongly states 1N4731. Maybe the engineers said: Oh they sent us diodes with the wrong marking. Ok, we’ll just alter the silkscreen text so the assemblers don’t get confused. Who know what history this board has?

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sorry, again I was not percise enough. I have no diagram for that old circuit. I am buliding a replacement with some changes/enhancements.

The “1N4731A” is printed on the THT diode body itself. This was so convenient that I spent no time thinking about the value actually needed.

Its just that I have never personally encountered a component with false marking on it…

7

I rather suppose OP read it from diode and I was wondering whether 1 can be confused with 2 when reading is difficult or the inscription is partially blurred.
How old is that “old” PCB. Who knows may be those time for these diodes Zener voltage was measured with 5mA (like for example BZX84 serie) and those time 4V3 diode (at 5mA) was 4V7 (at 50mA).
Zeners have poor tolerance. It is also possible that someone was selecting diodes by measuring them and it happened some was 4V3 and others 4V7. In 80s I was measuring LM317 voltage and measuring 5% 180 ohm resistors and I paired them up.

8

Counterfeit parts ? poorly marked parts ? manufacturers doing their own thing ? look at this link, it shows a 1N4731A 4.7V

image

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Oh, thats interesting. Maybe the old 1N… code is not used as strictly as I expected.
(Or there simply IS a stock of these diodes with wrong labels on the market. The part itself is certainly OK if you know what you get)

10

Pull the diode out.
run it through a curve tracer. see what it is doing at different currents.

The dynamic resistance of zeners varies between mfr, types quite a lot.

11

This thread is nothing to do with KiCad so closing now

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