# Thread: apply kirchhoff's laws on Zener diode v. regulator circuit !

1. i read in a book talking about using zener diode as a voltage regulator
no problem in that !
the problem when the writer started to apply kirchhoff's laws on the circuit
he wrote:

the circuit is the most simple one, no thing changed .

the problem, why disappears from the second equation, while applying kirchhoff's laws ?

2.

3. Since the load would be parallel to the Zener diode, VL would equal Vz and would not add to the total Voltage in of Vi.

See this image:

but i think i got the idea, that voltage of the load should be equal to the voltage of the zener diode.

but Sorry again, in the case you described, i think that the second equation would be:

right ?

* the difference i mean is that the should be doubled !

but i think i got the idea, that voltage of the load should be equal to the voltage of the zener diode.

but Sorry again, in the case you described, i think that the second equation would be:

right ?

* the difference i mean is that the should be doubled !
No. Where did you get the 2?

In the circuit Janus posted, there is a source voltage, a series resistor, and the parallel combination of a zener diode and the load.

When you write Kirchoff's voltage law, you have to write it for a loop. You can choose your loop to include the source voltage, the resistor and the zener diode, or the source voltage, the resistor and the load. Not both at the same time.

6. I don't know why the image doesn't show for you. it shows for me and its a link (Not locally stored on my computer.

Anyway, parallel voltages do not add together in a circuit. Voltages add when in series. If I put two 1.5 v batteries in parallel to each other, they will still only put out 1.5 v. If I put them in series, then they will add to a total of 3 v output.

So, again, since VL and Vz are in parallel to each other, they do not add together when determining the total voltage of the circuit.

Currents, on the other hand add together when in parallel but not in series. Which is why IR is not included in the first equation. (It is in series and equal to Ii).

7. Originally Posted by Harold14370

but i think i got the idea, that voltage of the load should be equal to the voltage of the zener diode.

but Sorry again, in the case you described, i think that the second equation would be:

right ?

* the difference i mean is that the should be doubled !
No. Where did you get the 2?

In the circuit Janus posted, there is a source voltage, a series resistor, and the parallel combination of a zener diode and the load.

When you write Kirchoff's voltage law, you have to write it for a loop. You can choose your loop to include the source voltage, the resistor and the zener diode, or the source voltage, the resistor and the load. Not both at the same time.
Sorry, i got it now
the part i was missing is that kirchhoff's law being applied for a loop, now the idea is clear.

Originally Posted by Harold14370
I don't know why the image doesn't show for you. it shows for me and its a link (Not locally stored on my computer.

Anyway, parallel voltages do not add together in a circuit. Voltages add when in series. If I put two 1.5 v batteries in parallel to each other, they will still only put out 1.5 v. If I put them in series, then they will add to a total of 3 v output.

So, again, since VL and Vz are in parallel to each other, they do not add together when determining the total voltage of the circuit.

Currents, on the other hand add together when in parallel but not in series. Which is why IR is not included in the first equation. (It is in series and equal to Ii).
it still not visible !, you can post the link for me may be something blocking it, i'm using AdBlock Plus and NoScript, but they're correctly configured .
and about the voltages in series and parallels, the idea about that is clear.
As mentioned above, the part that was missing: Kirchhoff's Laws Being Applied On a Loop.

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