Hello, i know the basics of voltage dividers and KVL. I also understand that a zener diode works in reverse bias and it will have a consistent voltage drop that makes it ideal for voltage regulation circuits. Now voltage dividers don't make for good regulator because they dont offer any type of feedback to raise or lower voltage.
What is it about zener diodes that makes it good for voltage regulation and what type of basic circuit that i can implement a zener diode?
Thanks
tjones9163:
...and it will have a consistent voltage drop that makes it ideal for voltage regulation circuits.
A zener diode only has a constant voltage across over a limited current range.
And if the zener isn't about 5.6volt, then it also has a temp coefficient.
Zeners can be used as voltage reference,
but because of voltage/current/temp limitations are not often used as series or shunt regulators.
Leo..
Since the zener diode requires a current
limiting resistor to prevent damage due to exceeding maximum current, it (by itself) is not very usefull
as a voltage regulator. It's typical application is a voltage REFERENCE, NOT regulator. If you need a
regulator, buy a regulator. If you can't find one for your voltage then you can use an LM317 with a
zener diode to make a zener diode based regulator
If your required load current is < the zener diode operating current then of course a diode will work.
On the forum, it is usually more productive to simply start out by stating your end objective , rather than
simply asking questions as you go along , trying to solve the project by yourself.
Just say what you want to do and WHY a zener diode is of interest to you .
raschemmel:
Since the [If your required load current is < the zener diode operating current then of course a diode will work.
[/quote]Could you explain this please? Thanks for the response](https://www.vishay.com/docs/85816/1n4728a.pdf)
I think Raschemmel is trying to say that you can't draw more current through a zener diode than the max current rating of the zener diode (and/or the thermal limits of the zener diode).
Zener regulation is usually done as "shunt regulator" (Google that), to avoid the above.
Leo..
tjones9163:
Hello, i know the basics of voltage dividers and KVL. I also understand that a zener diode works in reverse bias and it will have a consistent voltage drop that makes it ideal for voltage regulation circuits. Now voltage dividers don't make for good regulator because they dont offer any type of feedback to raise or lower voltage.
What is it about zener diodes that makes it good for voltage regulation and what type of basic circuit that i can implement a zener diode?
Thanks
You'd be better off using a level shifter.
I'd a use Zener diode as a bias for a crowbar circuit:
You, might be able to see D1, a SCR, with its gate biased by D2, a zener.
You'd be better off using a level shifter.
I think that's a bit presumptious since we still have no idea what the OP's application is:
What is it about zener diodes that makes it good for voltage regulation and what type of basic circuit that i can implement a zener diode?
For that matter, show me where in the above there is any indication that there is an application
hidden somewhere in this post.
what type of basic circuit that i can implement a zener diode
It looks more like the OP was walking one day and found a zener diode on the ground and is wondering
what to do with it...
raschemmel:
I think that's a bit presumptious since we still have no idea what the OP's application is:For that matter, show me where in the above there is any indication that there is an application
hidden somewhere in this post.It looks more like the OP was walking one day and found a zener diode on the ground and is wondering
what to do with it...
No application in particular, I randomly saw a post about a zener diode and wanted to learn more about it.
I randomly saw a post about a zener diode and wanted to learn more about it.
Scroll down to the above label.
raschemmel:
Comparator Reference VoltagesScroll down to the above label.
Thanks a mega-ohm
So it is kind-of:
Zeners were useful when you needed some sort of voltage reference and there was nothing else - and accuracy wasn't really that critical. This was three or four decades (or more?) ago.
But then voltage regulators such as the 7805 and 723 came out with temperature-compensated reference circuits inside, so when you wanted a voltage regulator, it was much. easier to use them that to dream up a circuit using a Zener with comparatively poor performance. And there are precision voltage references where you need them, all in the form of ICs.
So you do not use Zeners in voltage regulators nowadays and only as a rough-and ready, imprecise over-voltage sensing device which triggers another component to respond to the overload. There really are very few applications as such.
Note: THe LM723 and LM7805 DID have internal Zener diodes... this was later replaced by constant current voltage references based on Voltage Dividers in later designs, such as the popular LT1117.
tjones9163:
No application in particular, I randomly saw a post about a zener diode and wanted to learn more about it.
The zener diode is a component that can be used in electronics ----- which has associated characteristics/behaviours --- just like resistors and capacitors etc have their own associated behaviours.
The zener diodes can be used as voltage references. They were popularly used as voltage references in voltage regulated power supplies. They can still be used for the same purpose if desired. The idea was to pass a suitable current through the zener diode in the reverse bias mode -- or zener mode of operation. This required a suitable raw voltage supply voltage -- eg. 8V, 10V or whatever to get a current to flow through the zener in reverse mode. A series resistance would be needed to set the current through the zener --- a current that the zener can happily handle.
The zener would then have a relatively constant voltage (the zener voltage) across it. It is temperature dependent. If the temperature stays relatively constant, then the voltage stays relatively constant. So this voltage would then be used within a negative feedback circuit, often involving an operational amplifier and power transistors (such as darlington pair), where a relatively constant output voltage could be generated by means of negative feedback action. A voltage regulated power supply could be made like this. And can still be made like this if somebody wants to.
Then, somebody came up with a voltage reference that didn't have much dependence on temperature --- the band gap reference. The improvement is basically getting the voltage reference as independent of temperature as possible.
Southpark:
It is temperature dependent.
That depends on zener voltage (as explained in post#1).
Below 5.6volt it's a negative temp coeficient, above 5.6volt it's positive.
5.6volt zeners are not temp dependent.
Leo..
Wawa:
That depends on zener voltage (as explained in post#1).
Below 5.6volt it's a negative temp coefficient, above 5.6volt it's positive.
5.6volt zeners are not temp dependent.
Leo..
Nice information Leo. Thanks for adding that.
Wawa:
That depends on zener voltage (as explained in post#1).
Below 5.6volt it's a negative temp coefficient, above 5.6volt it's positive.
5.6volt Zeners are not temp dependent.
7.15 V in the LM723 (with compensation).
There are definitely applications for zeners, level shifting and biasing networks for instance. They can
also be used to generate electronic noise. Whenever a low-precision voltage source is needed they are handy,
and they serve as snubbers for DC inductive loads with faster decay than a simple diode. Protection
circuitry can usefully employ zeners too.
Note that "zener diode" in common use covers two different types of diodes, true zeners which use
quantum tunneling and are low voltage only, upto maybe 6V or so, and also avalanche-breakdown
diodes which are used for higher voltages.
Avalanche breakdown diodes are noisier but have a much sharper knee in the response curve.
Both types of diode require a heavily doped pn-junction, so some diodes can exhibit both types of
reverse breakdown simultaneously. The emitter-base junction of BJTs can also exhibit zener-like
reverse breakdown at 5V or so (often this destroys the transistor!)
Many TVS diodes are effectively two high-power zeners stacked back-to-back to give a robust transient
clipping device that's unpolarized.