Resistors, Capacitors, Zener diodes... Why the funny values?

[(*steve*)]

(*steve*) submitted a new resource:

Resistors, Capacitors, Zener diodes... Why the funny values? - An explanation of the E-series and why those funny values are used.

You might wonder why you can't always get the value of resistor you want. 6Ω sounds easy, right? What about capacitors. Why 470uF and not 500uF? Are these chosen at random? Why, why, why do they seem to want to make it hard for me? And why aren't there more resistor values between 1kΩ and 10kΩ than there are between 1Ω and 10Ω. Does that mean the higher value resistors are less accurate or something?

The numbers are not chosen arbitrarily at all. There is some (not a lot) of maths...

Read more about this resource...

 

[Arouse1973]

It might be a bit off topic but is it worth mentioning why we have strange values of voltage references like 1.024 V and 4.096 V etc. Also why zeners have the values they have e.g. 2.4, 3.3, 5.1,7.5 and the importance of the 5.6 Volt zener.
Thanks
Adam

 

[Georgy]

Any value be needed? So in paralel you can create needed value very simply. Only but not Zener.
Zener may be amplified to needed value. So 1024&4096 is for simplyfi calculations at ADC, DAC - there are two in the degree of N (N=10...12...)

 

[dorke]

A few notes:
1. "you cant start with 0!" that is true in the "theory" of the E series,
but a zero ohm resistor is available and very useful in many situations.

2. The 1-2-5 series is also used in currencies denominations,
like the Euro ,USD and many other decimal currencies .
The main issue here is to minimize the average effort required to make change.

 

[(*steve*)]

1) zero is not a value in the E series. But zero ohm resistors are available as are resistors that have values not in any E series.

2) to minimise change, a 1,2,4,8,16... series might be better. But given we have 10 fingers, 1, 2, 5 is a close estimate that repeats each decade. To maintain a fixed ratio between each range, a 1, 2.15, 4.64 if better, but makes reading values difficult. 1, 2, 5 is a close approximation. In both cases we end up with the same series, but for different reasons.

 

[dorke]

It might be a bit off topic but is it worth mentioning why we have strange values of voltage references like 1.024 V and 4.096 V etc. Also why zeners have the values they have e.g. 2.4, 3.3, 5.1,7.5 and the importance of the 5.6 Volt zener.
Thanks
Adam

Adam,

1. Voltage references which are "powers of 2"like 1.024 and 4.096 may be very useful in many applications like A/D and D/A conversions,they are not "strange" at all.

2. The voltage values of the zener diodes are about the same as the E series.

3. Why do you think 5.6v zener is special?
If at all,the value of 5V zener is "special".
That is because at about 5v we switch from the zener breakdown effect to the avalanche breakdown effect.
The importance comes from the change of the temperature coefficient from - to +.

 

[Arouse1973]

Hi Dorke
I knew the answers to these questions. It was meant for people new to electronics who may find the values strange, that's all. But thanks for answering
Adam

 

[(*steve*)]

I just so happen to have investigated some characteristics of zener diodes around the zener/avalanche voltage recently (not by personally doing experiments, but in advance of it).

One interesting factor is that manufacturing technique (and I guess, by extension, item by item variation) can affect the temperature coefficient. What is more surprising is that the temperature coefficient is also significantly influenced by the current at which the diode is operated.

 

[Kabelsalat]

Its because the values increases slightly exponentially for each step.

 

[(*steve*)]

exponentially

I'm pretty sure you mean "geometrically"

 

[Edward John]

yes they have odd values... If you’ve been around electronics for a while, you’ve probably noticed that components like resistors, capacitors, zener diodes, and inductors come in some odd values.

 

[martin de jong]

Wikipedia has a nice article about it, here: https://en.wikipedia.org/wiki/E-series_of_preferred_numbers

 

[WHONOES]

Resistor values are logarithmically spaced. There are a number of ranges all prefixed with E and they are E6, E12, E24, E48 and E96. This means that in the E6 range there are 6 values between1 and 10 then, E12 will have 12 values between 1 and 10 etc. Capacitor values follow the same principal except that it is rare to find standard values in ranges other than E6 and E12.
It is possible to get values that are not covered by these ranges but you will have to shop around to find them or in some instanced have them made specially. If you really need an odd value you may use paralleled or series values or a combination of both to achieve it.

 

[(*steve*)]

Resistor values are logarithmically spaced.

I'm pretty sure you meant "Geometrically"

 

[WHONOES]

No, I mean logarithmically.

 

[(*steve*)]

Well it's a geometric series. <-- edit, geometric sequence.

There is a constant multiplier between each value.

For the En series, the value is the nth root of 10.

 

[Terry01]

Holy smokes!! As a complete beginner this stuff makes my brain hurt! I get the jist of the values but as I've learned very quickly with electronics there's a lot more to take in. Pages and pages more! I find most of it very interesting and often end up reading about something that's nothing to do with what I started reading about! That's what keeps me interested...and usually up very late.

It amazes me most of you have this stored away in your head and are the same for topic after topic. I can't wait until I know that much When I'm about 200 years old!

I suppose that's what's great about electronics. There's always more to learn for everyone. Even the very clever guys who know everything

 

[kellys_eye]

Much of the impression you get of 'mass knowledge' is the result of 'application' of the basic theory that is learned then understood.

All electronics can be boiled down to basic circuit theory so your impression that we have intimate knowledge of 'everything' is actually our ability to derive the answer from basic principles - they key to 'understanding'.

 

[Fish4Fun]

(*Steve*),

Thanks! I always **assumed** the reason for the "odd values" involved +/- xx%, but it was fascinating to read the math behind how the particular values were selected. Again, Thanks!

I just so happen to have investigated some characteristics of zener diodes around the zener/avalanche voltage recently (not by personally doing experiments, but in advance of it).

I know the current trend in electronics is toward SoC ICs and further and further away from discrete components; however, spending a few hours with a breadboard, oscilloscope, VoM and a bag full of components is something I would suggest to anyone interested in electronics... Recently I spent an afternoon "testing" Zeners and "regular" diodes, and I learned way more about them than I had previously thought there was to know. Would love to read a resource dedicated to detailing proper Zener design techniques and perhaps a resource detailing diode forward voltage as a function of forward current & temperature.

How could diode forward voltage with respect to current be interesting? Take the common UF4007 Diode with the Datasheet stating typical forward voltage is ~1.7V @ 1A ... and you place 10 of them in series you might **assume** the forward voltage drop would be ~17V ... and if they were cold enough with enough current it might be close, but if current is limited to 10ma, the forward voltage drop is only 7.8V .. warm the diodes up a bit and the the forward voltage drop decreases to 7.2V ... with diodes nice and cool and a current of 500mA the forward initial voltage drop is ~12V ... as the diodes heat up the Vf drops steadily to ~10.5V .... with the diodes nice and cool and a current of 1A the initial Vf = 13V but quickly drops to 11V as the diodes heat up.

The list of things I didn't have right about diodes started with Forward Voltage DECREASING with respect to an increase in Temperature. I did not have a clue how current dependent Forward Voltage was, and Finally I had no idea that forward voltage might be less than 1/2 the Datasheet value. My experience with power semiconductors in general suggests relatively extreme de-rating from Datasheet maximum ratings, I would have expected this to be true for Diodes and would have expected a Vf of 1.7V to be optimistic.

I won't detail my findings with Zeners here, but suffice it to say, once again, despite years of successful designs employing them, I had some rather fundamental flaws in my understanding of how Zeners **actually** behave.

Fish

 

[Richard lee]

now i understand much better, thanks!