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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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14th Dec 2017, 4:54 pm | #1 |
Heptode
Join Date: Mar 2010
Location: Hemel Hempstead, Hertfordshire, UK.
Posts: 848
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Zener diode markings
I have been tasked with repairing a Clare insulation tester (has two transformers to produce 5kV) and there is a short circuit zener. I'm not sure about its markings as it shows C62PH which I have not been able to look up online. It's a small glass type. The P is a small p and I'm wondering if that means Philips.
Thanks in advance for any help with these markings. |
14th Dec 2017, 5:00 pm | #2 |
Rest in Peace
Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
Posts: 3,944
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Re: Zener diode markings
Usually the number after the "C" is the reference voltage. For example a BZX61C5V6 is a 5.6 volt zener, so perhaps yours is a 62 volt zener?
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14th Dec 2017, 5:03 pm | #3 |
Tetrode
Join Date: Apr 2013
Location: Cambridge, Cambs. UK.
Posts: 71
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Re: Zener diode markings
It's probably one of these
http://www.tekkna.it/product/20117/-...odo-Zener-.asp Something like a BZV85-C62 would probably do as a replacement. |
15th Dec 2017, 12:34 am | #4 |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,203
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Re: Zener diode markings
PH means Philips. If it's a small one (400mW), it is short for BZX79C62. A larger one would mean it's a 1W or 1.3W. In that case a BZV85C62 seems likely.
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15th Dec 2017, 7:49 am | #5 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,899
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Re: Zener diode markings
You don't want to fit a larger zener because the current they need to reach the knee in their curve is much greater, so the bigger part will start taking the amount of current the circuit is designed around at a somewhat lower voltage.
Just to make life difficult there are ranges of zeners with especially low operating current specs for the rated voltage. If replacing a zener other than with known like for like, then check the operating current of the circuit and the spec of the diode. This can save you some headscratching later. David
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15th Dec 2017, 2:58 pm | #6 |
Heptode
Join Date: Mar 2010
Location: Hemel Hempstead, Hertfordshire, UK.
Posts: 848
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Re: Zener diode markings
Thank you for the input. Sadly as its a discontinued and specialist bit of kit no circuit diagram exists. The problem arose when the mains input frequency was raised over about 100Hz then it went into shutdown (caused by this protect diode). Its only a small one so 400mA sounds about right.
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15th Dec 2017, 3:01 pm | #7 |
Tetrode
Join Date: Apr 2013
Location: Cambridge, Cambs. UK.
Posts: 71
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Re: Zener diode markings
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15th Dec 2017, 5:15 pm | #8 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,398
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Re: Zener diode markings
400mW 62V rating would imply maximum current of only around 7mA- though they apparently exist, that would seem to be low for an "electrical" piece of apparatus like this. A 1W device won't cost a fortune, if it proves to be inadequate in output or regulation terms a similarly inexpensive 400mW device could be tried. Does the surrounding circuit give any clues as to the expected operating current?
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15th Dec 2017, 9:23 pm | #9 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
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Re: Zener diode markings
400mW is a maximum rating rather than a target value. I suspect it's a zener designed for 5mA operation if used as a voltage reference.
David
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15th Dec 2017, 10:20 pm | #10 |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,203
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Re: Zener diode markings
This can only be determined by the dimensions (or by the operating parameters of the application), not by the marking C62. A 400mW zener is about the size of an 1N4148 or slightly larger in diameter while a 1W or more zener is obviously larger and probably has somewhat thicker legs as well.
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19th Dec 2017, 1:22 am | #11 |
Heptode
Join Date: Mar 2010
Location: Hemel Hempstead, Hertfordshire, UK.
Posts: 848
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Re: Zener diode markings
Thank you again for the help. Getting into work today I was able to take a photo of the diodes in place. I have ordered both the 400mW and 1.2W and to be honest I'm not really up to speed with diode characteristics and knees so this is a learning curve for me as well.
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23rd Jan 2018, 10:48 pm | #12 |
Heptode
Join Date: Mar 2010
Location: Hemel Hempstead, Hertfordshire, UK.
Posts: 848
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Re: Zener diode markings
Just to wrap up I fitted the new Zener and now the unit functions as it should. Sadly though it cannot take 300Hz mains input frequency (needed for a certain test) and the diode just goes dead short if you go over about 170Hz.
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23rd Jan 2018, 11:12 pm | #13 |
Heptode
Join Date: Mar 2009
Location: Portsmouth, Hampshire, UK.
Posts: 674
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Re: Zener diode markings
Sounds like you may have a 'Capacitive power supply' see Transformerless-Power-Supplies
for examples. Look for a large X2-rated capacitor and the absence of a mains transformer. Unfortunately these are designed for a specific frequency and running at higher frequencies will cause excessive current draw as you have found. Jim |
24th Jan 2018, 10:23 am | #14 |
Heptode
Join Date: Mar 2010
Location: Hemel Hempstead, Hertfordshire, UK.
Posts: 848
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Re: Zener diode markings
It actually has two step up transformers to generate 5kV from 250V input (and a diode / capacitor array for DC) and no X2 cap so in theory it should have worked. In fact we were told what we did is standard practice but our machine did not like it. I tried a lower input voltage but then the machine did not start the test and on about 200V input the diode blew. Below 200V I just got a small electrical snap sound when test engaged but the diode did not blow. We'll just have to rent something or design our own.
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