Re: Zener Diode Comprehension Issue: DZ=3V9, Voltage Drop, YouTube Instructional Videos

Question

Gentlemen and maybe ladies, on YouTube I watch instructional videos about the zener diode and when they connect it (e.g. DZ = 3V9) to a voltage of 1-12V, nothing appears behind the diode, and after exceeding 3.9V, the voltage does not increase any more despite giving more and more voltage, and...

brofran · Accepted Answer

It all depends on the configuration in which such a diode works (voltage and current distribution).
In general, the principle of its operation is such that after exceeding the rated voltage (3.9V in your case), such a diode begins to conduct current.

japycz321 · Accepted Answer

Ehh, from the beginning. If the diode is turned on in the forward direction, the drop on it is 0.6V. The charm of zenera is to use it in a negative direction. Its operation can be briefly described as follows: After exceeding the zener voltage, a breakdown occurs (it does not damage it by itself, of course) and the voltage on it no longer increases. If you turn it on in series with the resistor, then you will have a maximum of 3.9V on the diode. The rest will be lost on the resistor. And these 3.9V depends on the diode rating and will be constant regardless of the supply voltage, as long as it is higher than the 3.9V. It does not matter if you power such a 5V or 35 error, the diode will be 3.9V. Of course, you also have to watch over the current flowing through such a diode.

Anonymous · Accepted Answer

But in what arrangement? Where's the diagram? - because I know from experience that the descriptions of beginners are ... sucks. If the diode is inserted in series (reverse) - it will have a voltage drop of 3.9V, and the rest of the voltage (12-3.9 = 8.1V) will be put on this something that is connected in series with the diode - load, voltmeter, powered system, etc. But this something must limit the flowing (consumed) current so that the diode does not burn, because Pz = Iz x Uz. And if the diode is turned on in parallel (it must also have a current limiting element in series - but before the diode), then the output will have a voltage of 3.9V because the output is connected directly to the diode terminals, and there will be a voltage drop of 8.1V on the limiting element. Otherwise, you have to understand Kirchhoff's laws.

Andrzej42 · Accepted Answer

You think well, but in addition to voltage, you also have electricity and power. If you have a 24V power supply and 8V reception but let's say 1A, 1A will also flow from the 24V power supply, so the zener diodes will be 16V x 1A = 16W.
With low currents, you can lower the voltage with zener diodes or resistors, but with a certain power it is worth using step-down converters, especially as they are more and more available and cheap.

Dracov76 · Answer

But I still do not know what voltage to expect, I think E20 for a long time, I am well prepared despite the lack of practice, but it dawned on me that I do not know what voltage to expect for a zener diode in the system ... taking into account the voltage drop or stabilization: /

Dracov76 · Answer

Aaa ... now I think I understand
So in this diagram

D6AF369E-D...28458.jpeg Download (37.2 kB)
If the power source was 24V and the diode was, for example, 7.9V, then the resistor should be selected so that for a given current the voltage drop would be equal to about 16.1V. Okay, and the Voltmeter will show me 7.9V, because these are the zener diode terminals, so its voltage drop is probably correct ... I think I understand correctly ... such a large resistor), I can connect two zener diodes Dz = 5.9V + a resistor limiting the diode current On which voltage drop is 4V and behind this system I can connect something powered by 8V?

I think I understood, I hope I think well.

japycz321 · Answer

With the difference you gave, i.e. from these 24 to 8, only a step down. Even a linear regulator wouldn't work. Zener diodes are not suitable for lowering the voltage, but only for stabilizing it at a certain level.

Anonymous · Answer

It is suitable, but for small currents, because it results from its power - currently there are no zener diodes with a (real) power greater than about 1W, with a heat sink - several W, which means max current (for Uz = 8V) = approx. 0.5A. Very confused description, but I understand it like this: with + 24V in series, two 5.9V Zener diodes (they are not produced like that - the closest is 5.6V or 6.2V) and a resistor R. It makes no sense - Uwy will change because it depends on the current consumption of the receiver: Uwy = 24V-5.9V-5.9V-IR - i.e. Uwy = f (I). A resistor in series would suffice in this way. Besides, this resistor R does not limit the current - the current is determined by the receiver. If you want to break the voltage with the Zener diode (s): from + 24V in series the Zener diode 16V and then the receiver and ground. Zener diode selected for power P = IUz, where I is max. current consumed by the receiver. Instead of one 16V diode, you can give e.g. 2 pcs 5.1V and the third 5.6V (about 15.8V in total), which will reduce the power dissipated on each of them P = IUz - here the maximum power will be 5.6V on the diode. You can build a power zener diode from a regular low power diode and a power transistor (and 1 resistor). But all this does not make sense, because the power has to separate somewhere and it is better to do it with an element adapted to dissipate power - e.g. an integrated stabilizer of the LM78xx, LM317, 338, 350, etc. Power converters offer voltage conversion with much lower power losses. Besides Kirchhoff's laws, Ohm's law also bows. Principles of conservation of energy today do not teach in schools? - whether a resistor or a zener diode - the power must separate, and it is easier / safer to do it with a resistor. The zener diode has no magical properties.

japycz321 · Answer

Yes, only the maximum power that can be released on it is a problem and excludes it from many applications. Most often it can be done better. The higher the current, the less chance of using a zener diode

Re: Zener Diode Comprehension Issue: DZ=3V9, Voltage Drop, YouTube Instructional Videos

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