Zener diode question?

[Detailman]

I've got an application for a 14.6v zener.
On hand I have 16v.
Also I have 10v and 5v.
Could I series the 10v and 5v?

Are either of these options close enough to be workable?

Thanks.

 

[tcdriver]

Zener diodes generally have a tolerance. Many are + or – 10%. The zener voltage also varies with current through the diode and the temperature. You might find that the 16 volt zener is really 14.6 volts because of the tolerance. Connecting the 10V and 5V zener diodes in series may also give you a voltage near the 14.6 your application requires. Reducing the current through the zener will give you a lower voltage and increasing the current will give you a higher voltage. A little experimentation is in order.

 

[Hyperion]

The problem with using 2 diodes is that you are then subject to the drift of 2 semiconductor junctions, rather than one.

So, 1 diode is the ideal solution - and 16v ? - it depends on the application, but may be close enough when you take diode tolerance into consideration.

 

[EchoWars]

A 14V zener and a standard 1N4148 in series will give you about 14.6V.

14V axial zeners are only available in 1/2W, FYI.

 

[Tom Bavis]

The problem with using 2 diodes is that you are then subject to the drift of 2 semiconductor junctions, rather than one.

The temperature coefficient of 5V zeners is near zero - so the combination of a 5V and a 10V zener will give LESS temperature drift than a 15V one...

Whether 15V is close enough depends on your application - if the circuit wants a 2% part, then no. if it calls for a 10% part or doesn't specify... then it's probably OK.

 

[Hyperion]

Wow - Thanks Tom B - Learn a new thing every day

So, Ideally 3 x 5v zeners is better !

 

[EchoWars]

I believe it is the 6V or 6.2V zeners that have a zero temp drift. In any case, any value close to that will show little drift. But I'd suggest that drift probably isn't going to be a big problem.

If I needed 14.6V, I'd do it this way:

 

[cubby01]

For what it's worth, I had a service manual that listed a particular zener as "14.72v +/- .37" it also gave a part number. When I looked up the part number the part was described as 15v +/- some percentage.

 

[Hyperion]

Regarding zero temperature coefficient in Zener diodes - actually neither TB or EW are perfectly correct.

TB says 5v zeners are zero coefficient (or 'near zero' which is strictly correct)
EW says 6 or 6.2 zeners are zero coefficient

Wrong ! - the correct answer is 5.6v :yes:

Thanks for the lesson

 

[EchoWars]

I knew it was somewhere in there...

 

[ecluser]

Also I have 10v and 5v.
Could I series the 10v and 5v?

Yes, but don't forget that the 10V zener will dissipate twice as much power as the 5V zener.

If you have a stock of transistors, you can use the BE junction, reversed biased, and you will have a very good zener. A 2SA733 will give you nearly 9.5~10V.