yet another zener diode question

[pinkjimiphoton]

hey guys real quick,
i'm building a hm v3 which uses 12v zener diodes. i don't have any of those.
i know you can put diodes in series to get desired voltage levels, but do they have to be the same spec?

i need approx 12v, i have 9v and 3 v.... could i put them in series?

i've read that you can , but can't find any info on whether they all need to be the same voltage.

thanks!!!

[pinkjimiphoton]

for all intents, the circuit is a big muff without a tone stack pretty much. i doubt the diodes are that critical, as they're being used in a clipper function in a 9v pedal.

but i'm still curious. i've been googling and finding some conflicting info thats wayyyyyyy above my paygrade

[blackieNYC]

absolutely you can put them in series.
I once worked for an audio manufacturer who stacked ten 33v zeners for a 300v supply.

[pinkjimiphoton]

thanks blackie!1

BUT my question is...

for a 12v zener, can i use a 9v and a 3v in series? or do they all have to be the same voltage?
i think thats what i'm confused about.

i mean, i COULD use 4 3v ones in series, but it seems like a waste if i can go the other way.
either way, i'll probably just use the 9.1v ones i have

but i am curious if you can combine the different ratings to custom make specific voltage requirements

[blackieNYC]

Yes you can

[Fancy Lime]

Hi Jimi,

if the 12V Zener would actually be used for "zenering" to 12V, a 9V + 3V Zener combination would be the right choice. But if Zeners are used as antiparallel (not back to back, which is sometimes done with 2.7V Zeners) clipping diodes, you can just replace them with regular old Si diodes. This is because the reverse breakdown is never overcome. Consider this:


    |----->|-----|
A---|            |---B
    |-----|<-----|


The upper diode limits the Voltage difference between A and B to V(A)-V(B)=0.7V (assuming a forward breakdown of 0.7V). Therefore the Zener Voltage (which is the reverse breakdown voltage) of the lower diode is never reached, if it is >0.7V (2.7V are the lowest commonly available Zener Diodes). Long story short: Any Zener diode or small signal silicon diode (1N914, 1N4148...) will behave (nominally) identically in this application, the 12V should not even be specified in the schematic. Using two of any such diodes in series (per branch), on the other hand, will raise the clipping threshold from ~0.7V to ~1.4V, thus decreasing distortion and increasing volume. You might as well use a single LED instead of two series Zeners for much the same effect.

Hope that helps,
Andy

[antonis]

@Jim: In a 9V circuit, any Zener of reverse breakdown voltage equal or greater than 9V should act as ordinary Si diode...
(you can use your 9V1 Zeners without any difference from using 12V ones - IMHO, you can even use Zeners down to 8V2 with same results..)

P.S.
I refer to ONE way clipping of course, i.e. one diode from Collector to Base or GND..
For an antiparallel pair (like in Big Muff NFB loop) stands what Andy said..  


<2.7V are the lowest commonly available Zener Diodes>
It happens to have in my junkbox some beautiful BZX55Cs of 800mV RBDV.. 
Some of them exhibit a RBDV of down to 700mV so I use ONE of them as replacement for an antiparallel Si diode pair..

[EBK]

I'll throw this in just out of personal academic interest.  Maybe it will be useful to someone someday.

It acts like a variable zener diode, adjustable from 5 to 45V.

[antonis]

NO COLLECTOR CURRENT LIMITING RESISTOR... 
(I'll charge you for my burned out Zeners, Eric..) 

<adjustable from 5 to 45V>
Do you count on BC107 min/max V_CE...?? 

[EBK]

NO COLLECTOR CURRENT LIMITING RESISTOR... 
(I'll charge you for my burned out Zeners, Eric..) 

<adjustable from 5 to 45V>
Do you count on BC107 min/max V_CE...?? 

I let someone else do the math on that circuit.  I accept blame only for being lazy, not for being wrong.   

[pinkjimiphoton]

you  cats never cease to blow my mind... thanks for the info!!!

i figured the diode wouldn't matter... i can't see them ever seeing 12 volts, so i cheezed out with a couple 9.1v ones.
in this application, they do sound nice. like a real phat warm old school big muff.

great info to know, for when i'm,like , ricking-out in my laBORRRTatory blowing shit up.

thank you all once again!!
peace out!

[PRR]

> NO COLLECTOR CURRENT LIMITING RESISTOR...

It replaces a ZENER. A Zener has the same problem. You MUST have some system to limit current/dissipation. All workable Zener circuits have this.

A semi-objection to EBK's values is that it needs over 7mA just to start regulating. That may be more than some circuits send to the Zener. A little Ohm's Law can find a lower-current version. It also goes soft for much over 70mA(!). It adds a couple sources of "error" which would matter in precision work (not for pedal bias). It is a very framework.

[antonis]

> NO COLLECTOR CURRENT LIMITING RESISTOR...

It replaces a ZENER. A Zener has the same problem. You MUST have some system to limit current/dissipation. All workable Zener circuits have this.

That's exactly the reason for using capital letters..
(other than tease EBK a bit..)

Resting only on BJT's beta for calculating worst case situation (Vmin/full load - Vmax/no load) isn't wise enough..

[EBK]

That circuit served its academic purpose quite well, it seems.     We can safely put it back on the shelf and conclude that the best way handle a missing zener is to use it as an excuse to visit mouser.com (or substitute your regional equivalent or favorite merchant here). 

[pinkjimiphoton]

hahaha, well, at least *I* learned something today.

the haunting mids circuit really sounded good last nite, tho the damn thing broke down on me..i thought i'd fixed it, but seem to be losing the ground on the master volume.

but anyways, in this application, the zeners sound great. just like normal diodes. there does appear to be a bit more midrange warmth to the distortion, but that's more likely the rest of the circuit i'd imagine.

[TejfolvonDanone]

<2.7V are the lowest commonly available Zener Diodes>
It happens to have in my junkbox some beautiful BZX55Cs of 800mV RBDV.. 
Some of them exhibit a RBDV of down to 700mV so I use ONE of them as replacement for an antiparallel Si diode pair..

If you read the datasheet really into details you find that the ones lower than 2.7V are regular diodes with trimmed forward voltage drop. Been there done that.
I actually measured the forward and reverse voltage and if I remember correctly the end marked as cathode to the anode voltage was the "reverse breakdown" voltage but I couldn't measure a proper forward drop the other way around. Don't quote me on this though.

[antonis]

@ Szabolcs: You confused me..

Usually, it's easy to measure forward voltage drop via a multimeter but not reverse breakdown voltage (due to insufficient meter's current..)

Anyway, I can't see how a regular diode with trimmed forward voltage drop can act as a Zener..
(unless, of course, to place it "reversed" - like ordinary diodes)

[TejfolvonDanone]

@ Szabolcs: You confused me..

Usually, it's easy to measure forward voltage drop via a multimeter but not reverse breakdown voltage (due to insufficient meter's current..)

Anyway, I can't see how a regular diode with trimmed forward voltage drop can act as a Zener..
(unless, of course, to place it "reversed" - like ordinary diodes)

I didn't measure it it with just a DMM. And exactly that's what happens. They are just regular silicon diodes.
For reference I'm not talking complete nonsense:
http://www.surgecomponents.com/admin/pdfs/BZX55C0V8-BZX55C75.pdf?c=1 Last page note 2.

[amptramp]

T answer the OP, yes, you can put zener diodes in series (facing the same direction) and the voltage will be the sum of the zener voltages.  Since the same current flows through them, the power rating will be proportional to the voltage.  One more consideration is that zener diodes have a temperature coefficient that is at a minimum around 5.1 volts and is positive above that and negative below that.

[antonis]

For reference I'm not talking complete nonsense:
http://www.surgecomponents.com/admin/pdfs/BZX55C0V8-BZX55C75.pdf?c=1 Last page note 2.

Never said you're talking nonsense.. 

What puzzled me was the "conventional" cathode mark for a Zener and it's actual connection to the negative pole..


To "spam" a little more the OP..
(sorry Jim..)