Question about Zener diodes

[copperheadroads]

I'm building this pedal that uses a 1N5232  which is a 5,6v Zener   500mv     ,I don't have that diode can i use a 1N4734  which is a zener 5.6v  1 watt   . is the 500mv/1watt just the voltage rating it can handle ?

[antonis]

is the 500mv/1watt just the voltage rating it can handle ?

Not really..

500mV is the forward voltage drop, when Zener acts like an ordinary diode..
(biased with voltage higher on its anode than that of its cathode..)

1Watt is its power rating..
(which is its nominal reverse bias voltage drop, i.e. 5V6 times the current through it..)

edit: Did you, by any chance, make a mistake on 500mV..??
'Cause if it actually is 500mW, ingore the above striked-through said and proceed to 1W without fear..

[EBK]

Actually, that should have read 500mW, not 500mV.  The forward voltage is actually around 1V.

Yes, you can use the 1W part.
Antonis posted the same thing slightly before me.  Carry on (use the 1W part). 

[antonis]

That v instead of W resulted into striking through most of the clearly posted..

[duck_arse]

:beers: :beers: :beers:

[Rob Strand]

I'm building this pedal that uses a 1N5232  which is a 5,6v Zener   500mv     ,I don't have that diode can i use a 1N4734  which is a zener 5.6v  1 watt   . is the 500mv/1watt just the voltage rating it can handle ?

That's the spec and the simple answer, however, there's a hidden difference. 

For a given zener current the 1W zener will have a lower actual voltage than a 500mW zener.    The voltage on a zener is at a specific current, which chosen by the manufacturer. That current usually turns out to be a high current.  Many effects pedals operate the zener at much lower currents than the manufacturers spec and that means the zener voltage in the actual circuit is lower than the voltage marked on the zener.   

If you have a circuit which specs a 500mW zener and you use a 1W zener it pushes the voltage down further.  Sometimes that cause problems with the circuit.   A lot of people can only find 1W zeners from their local store.  If you sub a 1W for a  is pays to measure the zener in the circuit to see if it's too far off.   If you know the zener is operating at a low current in advance you might even buy a 1W zener with the next highest voltage rating to compensate for the fact it will drop.

You can try to wade through manufacturer's datasheet but often what you find is there's not enough data in the datasheets to work out the actual voltage when the zener is at low currents.

So in summary there's small  risk sub'ing a 1W zener for a 500mW zener.

[EBK]

But, Rob, we still don't know what the circuit is or how exactly it is using this zener diode.  I'm still betting the 1W part is fine (and I'd use it without hesitation), but...

copperheadroads, could you give us some more detail? 

(You know, we are just trolling our crusty wise elders here with this drawn out discussion of the idiosyncrasies of zener diodes.  One of them will yell at us soon.  )

[Rob Strand]

But, Rob, we still don't know what the circuit is or how exactly it is using this zener diode.  I'm still betting the 1W part is fine (and I'd use it without hesitation), but...

I'm only guessing it's a typical pedal but it's worth digging into the specifics.

[copperheadroads]

https://www.pedalpcb.com/docs/Valhalla.pdf This Valhalla pedal

[PRR]

Clipping diodes. Maximum dissipation is 0.2mA at <5.6V, 0.15 milliW (0.000,15W).

Nothing will blow up, for sure!

We actually have data for the knee impedance of the '5232 at 0.25mA, essentially the limit this circuit will reach. Say 2k@0.2mA makes about 6:1 reduction at the limit.


The double-size parts will be a little looser.

Yeah, try the over-size parts, but tack them in so you can get them out if you decide to try smaller diodes for tighter clipping.