[sergey23 0]

Hello,given the  schematics below the zener diode gets reversed biased at 4.7 V.

so the current is I=(15-4.7)/R .
we automatickly assume we have 4.7V on the zenner, and we can calculate the current by the resistor.

under what conditions the zenner will not  enforce the 4.7V threw it?
Thanks.
https://www.mouser.co.il/datasheet/2/268/1N746A_1_1N759A_1_2c1N4370A_1_1N4372A_1-3442192.pdf

[1113 9]

10 minutes ago, sergey23 said:

under what conditions the zenner will not  enforce the 4.7V threw it?

there is only one condition - current through zenner must be Izt

[sergey23 0]

Hello, Where can i see the Izt?
I saw 20mA in the table shown below,but given the simulation  its working on much lower then 20mA

[1113 9]

7 minutes ago, sergey23 said:

Where can i see the Izt?

in datasheet

[sergey23 0]

In datasheet Izt is 20mA its the test current.

There is a logical problem.
In order to calculate the zener current  threw the limiting resistor we always assume that zenner is working properly.
how can i know mathematickly  the current without assuming i have proper 4.7V across the zener?
Thanks.

 

Изменено Воскресенье в 18:44 пользователем sergey23

[1113 9]

4 minutes ago, sergey23 said:

There is a logical problem

zener does not know what is your problem. there is only one thing - manufacturer guarantee that zener has Vz @ Izt

if you want get Vz you need put Izt

[sergey23 0]

 

Hello ,I have made  a plot shown below, I see that in 9mA current I have good 4.7V output as shown below.
In the lab I have a voltave source of 12V , how this plot will help me deside what current limiting resistor to choose?
Thanks.

Изменено Воскресенье в 19:04 пользователем sergey23

[1113 9]

1 minute ago, sergey23 said:

 

I see that in 9mA current I have good 4.7V output as shown below. how this plot will help me deside what current limiting resistor to choose?

R = (12-4.7) / 0.009

[sergey23 0]

Hello, There is a similar case in NPN,I swept the base current.
I want to decide what base limiting resistor to use.
I made plots shown below.
I have 12V voltage source i want base current 37uA.
that meens my resistor is 12/37uA=R which is very very large.
Is there a way to reduce the need for such a large limiting resistor?
Thanks.

[vervs 39]

Формально Rb = (V1 - Ue - Ube)/Ib ≈ (V1 - R1*(h21+1)*Ib - 0,6)/Ib = V1/Ib - R1*(h21+1) ≈ (12-0.6)/37u - 1k*(100+1) ≈ 210k, но так практически не делают.

[1113 9]

15 hours ago, sergey23 said:

There is a similar case in NPN

there is no similar case because to calculate resistor value by Ohm low you must know voltage on it

[sergey23 0]

Hello,Why In saturation Ic/Ib is so small as shown below.