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zener diode replacement

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ravi17

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I need to replace 1N5274B zener diode. it is rated 130V. Can I replace with other zener diode with 130V? is there any general rule to place zener diode?
 

Pommie

Well-Known Member
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They don't normally have a current rating but a wattage rating. A 130V 0.5W zener can have a continual current not exceeding 0.5/130 or just under 4mA. The one I linked can take twice that current and would work fine.

Mike.
 

Superdat

Member
130V is the voltage at which it will break down (If you don't know, that's what zeners do). So 130V for your application isn't negotiable. When the reverse bias (130V) breaks down, the zener is essentially a short circuit so it will generate heat. The wattage indicates how much heat it can handle. This diode doesn't seem very popular so you might have to look about. You could fit a larger wattage as Pommie suggests but need to check its physical size and type. In other words will it fit.
 

Pommie

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Most Helpful Member
130V is the voltage at which it will break down (If you don't know, that's what zeners do). So 130V for your application isn't negotiable. When the reverse bias (130V) breaks down, the zener is essentially a short circuit so it will generate heat. The wattage indicates how much heat it can handle. This diode doesn't seem very popular so you might have to look about. You could fit a larger wattage as Pommie suggests but need to check its physical size and type. In other words will it fit.
A little confusing to say it's a short circuit at 130V. Better to say it will start to conduct around 130V and will conduct more and more as the voltage increases but will still have around 130V across the zener. Looking at the datasheet, it will start to conduct around 128V and will reach the rated 1W at about 134V.

Edit, Zeners are notoriously inaccurate, the one above having a tolerance of 5%, same as the one it's replacing.

Mike.
 

Superdat

Member
A little confusing to say it's a short circuit at 130V. Better to say it will start to conduct around 130V
Well confusing it may be but that is more or less what happens, that's why a current limiting resistor is usually if not always in circuit to stop the zener going pop!
Also what's the difference between a short circuit and conducting? Pretty much the same me thinks, a short circuit definitely conducts.
I was trying to make it easy for ravi17 (who is obviously new to the joys of zener diodes) to understand. I doubt he will be much interested in the excruciating exactness of a data sheet. Little steps, he wants to know which zener he can use.
 

Pommie

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Well confusing it may be but that is more or less what happens, that's why a current limiting resistor is usually if not always in circuit to stop the zener going pop!
Also what's the difference between a short circuit and conducting? Pretty much the same me thinks, a short circuit definitely conducts.
I was trying to make it easy for ravi17 (who is obviously new to the joys of zener diodes) to understand. I doubt he will be much interested in the excruciating exactness of a data sheet. Little steps, he wants to know which zener he can use.
That is not what happens. According to your explanation, a 16k resistor is a short circuit - check the maths. A short circuit has no resistance and no voltage across it! I answered the question asked by the OP without referring to "the excruciating exactness of a data sheet". I only referred to the datasheet as you don't seem to know how a zener works.

Mike.
 

Superdat

Member
My we are touchy.
While you were studying the datasheet did you notice that the zener you recommended is an SMD type whereas the OPs diode is a do-35 through hole?
It is about 3.5mm long against the DO-35 body of about 3.9mm so it's possible but would need to go on the oposite side.
An exact match for the current zener seems to be unlikely as they are obsolete but there are through hole versions @ 130V with a higher wattage.
Depending upon the usage these may be suitable and easier to fit.
http://uk.rs-online.com/web/p/zener-diodes/6256524/
http://uk.farnell.com/on-semiconductor/1n5381brlg/zener-diode-5w-130v-017aa/dp/2533358
https://www.rapidonline.com/Diotec-...:pid-50-0461&gclid=CMW_1aD5xtMCFUeZGwodTKAOXQ
 

crutschow

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My we are touchy.
I don't see that at all.
You are the one who seems to be touchy about being corrected. :rolleyes:
He was explaining the difference between conducting and a short circuit, which you were trying to gloss over.
On these websites we try to be a precise as possible in our definitions so as not to confuse others.
A short circuit has essentially zero resistance and zero voltage drop.
Now the incremental (dynamic) resistance of a Zener drops to a low value when it starts to conduct, but that's not the same as a short circuit.
 
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Superdat

Member
Not at all, I accept my comment was not (as you have alluded to) 100% technically correct, however for ease of understanding I simplified things, I was trying to emphasise the importance of using 130V. If a zener is not current protected and a voltage above its break down is applied it will usually go pop especially a low wattage version. Most people would consider that a short circuit shortly followed by an open circuit. No doubt you'll take exception to the use of open circuit and call it a high impedance. I do know what I'm talking about, I was merely simplifying it.
I was guessing that ravi17 was not very knowledgeable about electronics otherwise he wouldn't have asked the question.
I do admit to being irritated by devotees to the god of datasheets and unnessesary & irrelevant details, especially when minor issues like physical form and fit go unnoticed.
 
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Pommie

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If you read my post above yours you will see that I simply answered the OPs questions. Then you came along and posted completely wrong information which I went on to correct. Had you not done so you would not be " irritated by devotees to the god of datasheets and unnessesary (sic) & irrelevant details"!!!
 

Superdat

Member
You don't give in easily, the replacement you linked to is not really a good suggestion. Although OK electrically, it isn't the best option physically.
SMD is not a good replacment for through hole component.

Don't you like people offering an alternative view to your own?
 

Pommie

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Most Helpful Member
I didn't suggest a replacement and stated ANY 130V with a power rating of at least 0.5W will do. It's nothing to do with alternative views, it's about you posting complete nonsense.

Mike.
 

Colin

Active Member
Any combination of zener diodes in series that add up to 130v can be used. I use 10v zeners to make 30v to use up the thousands of surplus 10v zeners I have in stock.
 
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