Zener dilema, 1.5V's??

I have a small problem with a SSL Dynamics circuit that I'm trying to bring to life.

The schematic calls for a 1V5 zener diode between +5v/2K2 and GND. Trouble is, I haven't been able to locate a 1V5 zener anywhere. Lowest value I can find is around 3v's or so.

Here's the relevant section of the schematic, the RMS Detector; with the 1V5 highlighted.

Are there any alternatives to this like paralleling two values or substitution?

Mark
"Stumped in the Motor City"

Two bulk standard 1N400X diodes in series (roughly 0.7V each) is a 1.4V zener. Close enough.

[edit]

Clarification:

with the rings facing down in the above schematic.

It's often used to bring standard 78XX regulators to desired voltages like 7815 to 17V (takes three diodes). Even in commercial gear like mixers and their PSU's.

It should be easy to find a bandgap reference of that voltage. A red LED will fit as well; both will have lower tempco than two ordinary diodes in series.

Samuel

red led

I actually used a red LED for a low voltage reference in a kit I did back in the early '80s. I thought it was more than 1.5V but that was a long time ago and high efficiency LED technology may have changed some.

I'd be tempted to suggest rolling your own "whatever voltage" reference with a transistor and simple two resistor divider spanning across emitter collector with the junction of the two resistors connected to the base. The ratio of the two resistors will multiply the base emitter voltage to make anything you want, more than 1x Vbe.

Vce = 1+ Rbc/Rbe) x Vbe

JR

Red LED by itself is not a good answer.  A lot was left out.  What type of semiconductors is it made from?  The you need to look at the curves.

Found a 1.8VDC
http://www.onsemi.com/PowerSolutions/product.do?id=MMSZ4678T1G

I would look for a 1v5.  I see there is a connection to pins 5 and 7 of the IC  with a 75K

If you do sub a different diode etc in check it's voltage at at 1.6ma (3.5VDC/2.2K)

Gus said:

I would look for a 1v5.  I see there is a connection to pins 5 and 7 of the IC  with a 75K

If you do sub a different diode etc in check it's voltage at at 1.6ma (3.5VDC/2.2K)

Click to expand...

Any suggestions where I can find a good supply? I've been searching for a few days without any results.

Or are two 1N4001's back to back a good solution?

Mark

Biasrocks said:

Or are two 1N4001's back to back a good solution?

Click to expand...

It's cheapest and easiest. That's why they do it in commercial applications.

Since there is a trimpot after that voltage reference, the actual reference voltage does not seem very critical.

When I worked at Peavey I recall a dual diode in the system that was used for a specific application (bias strings for power amps) , I don't recall all the details but IIRC some temperature compensated zeners when operated backwards have two forward junctions so would bias up to roughly 1.2V.

I fear you are killing too many brain cells worrying over this. Probably any of the above solutions would work just fine. Pull out your dart board, flip a coin, or use what you have parts on hand to accomplish.

JR 

Okay, here's the updated schematic using 2 1N4001's in series.

Look okay?

Mark

Looks fine. In fact I'd prefer small-signal diodes (e.g. 1N914B) as these will have a higher forward voltage at a given current compared to large-geometry power parts. Much easier to fit on the PCB as well. But as JR wrote: things ain't critical here.

Samuel

LM4041DIZ-ADJ
http://www.national.com/ds/LM/LM4041.pdf

Get-a-grip TO92 package, <0.1mA-12mA. 1.225V, ADJustable

DigiKey has a thousand in stock at a buck a pop.

Indeed a couple diodes may be fine, and the "polarity" note may mean they really used 2-junction bias diodes instead of Zener.

Alright then, taking a cue from PRR


How's this look?

It looks like a dollar more than I would spend to do that, but it's only money...  enjoy... 

It's not often you can splurge like that for only a dollar.  ;D

JR

JohnRoberts said:

Since there is a trimpot after that voltage reference, the actual reference voltage does not seem very critical.

Click to expand...

Don't also overlook the 75kΩ (?) resistor going 'backwards' from the zener to the AC-to-RMS converter chip. -It doesn't 'see' the trimpot, and may use the reference for 'scaling' its output, I think.

Keith

so, what is the dynamics card not doing?  i  work on probably about 30 of these a year and have yet to have one of the zeners fail.  more often then not the little on board power supplies will go and not regulate everything properly.  i suggest redoing those and recap the whole shooting match if the thing is just dead.  I've never ever seen the AD chip go which is a good thing as they're expensive.  if just the comp or the gate is dead i've found that replacing the 914/4148's in their respective sections  will bring them back most of the time.

-justin

Bringing this thread back to life...

I've been searching around for 1v5 Zener diodes and haven't had much luck finding them, but I did manage to find some 0.75v 1.3W Zeners.

https://www.rapidonline.com/diotec-zpy1-zener-diode-1-3w-0-75v-50-0435

Two of those in series will be fine, right?

Lee_M said:

Bringing this thread back to life...

I've been searching around for 1v5 Zener diodes and haven't had much luck finding them, but I did manage to find some 0.75v 1.3W Zeners.

https://www.rapidonline.com/diotec-zpy1-zener-diode-1-3w-0-75v-50-0435

Two of those in series will be fine, right?

Click to expand...

Pretty much same answer as 8 years ago... I have never heard of a 0.75V zener, and that link didn't open for me.

A common way to make an odd voltage pseudo zener is a simple NPN transistor with a voltage divider between collector-emitter feeding the base. The ratio of resistors can make any voltage more than one Vbe (roughly 0.6V).

JR

JohnRoberts said:

I have never heard of a 0.75V zener, and that link didn't open for me.

Click to expand...

Huh, that's strange. It doesn't seem to have any issues loading on my computer.  ???

0.75v Zeners were a new one on me too, but the datasheet confirms their existence.  I was a little worried it was a misprint (mistype?) on the Rapid website, but it seems the ZPY1 is indeed 0.75v.

https://diotec.com/tl_files/diotec/files/pdf/datasheets/zpy1

JohnRoberts said:

A common way to make an odd voltage pseudo zener is a simple NPN transistor with a voltage divider between collector-emitter feeding the base. The ratio of resistors can make any voltage more than one Vbe (roughly 0.6V).

Click to expand...

That's a pretty interesting option, I'll have to remember that one for the future.

I was considering the LM4041 option that PRR suggested earlier in this thread, but Keith's mention of the 75k resistor made me cautious about fitting any extra resistors to ground from that node....I don't want to create an unnecessary voltage divider between the 75k resistor and the LM4041's resistive (18k3) voltage divider.

Lee_M said:

Huh, that's strange. It doesn't seem to have any issues loading on my computer.  ???

0.75v Zeners were a new one on me too, but the datasheet confirms their existence.  I was a little worried it was a misprint (mistype?) on the Rapid website, but it seems the ZPY1 is indeed 0.75v.

Click to expand...

OK opened that time...  Now I can no longer say I never saw one, looks like 0.7-0.8V ...  So two in series 1.4-1.6V

That's a pretty interesting option, I'll have to remember that one for the future.

Click to expand...

commonly done with trimpot to make variable bias voltage for power amp output stages.

I was considering the LM4041 option that PRR suggested earlier in this thread, but Keith's mention of the 75k resistor made me cautious about fitting any extra resistors to ground from that node....I don't want to create an unnecessary voltage divider between the 75k resistor and the LM4041's resistive (18k3) voltage divider.

Click to expand...

I wouldn't over think this... the 75k is coming from the regulated side of the 4041 so will probably work better than the original design. Zeners are generally not precision references.

IMO overkill but sometimes design overkill is just right.

JR