zener diode

Thread Starter

hhsting

Joined Apr 25, 2024
156
In the circuit below Zenior Diode has breakdown voltage of 4.7V. When I take voltage between Zenior Diode I get 4.6V.

1714943908595.png

When I connect the transistor BSF as shown below I get voltage from the drain to the source of about 4.5V. I want to get 5.2V from drain to source while I want to get from gate to source voltage of zenior diode. How can I do this?

1714944314279.png
 

dl324

Joined Mar 30, 2015
17,122
Welcome to AAC!

1N750 voltage range at 20mA is 4.47-4.94V.

Didn't try to analyze the circuit because you've drawn it sideways and backwards and it's too much bother.
 

Thread Starter

hhsting

Joined Apr 25, 2024
156
I have load that is not shown that takes 5.2 vdc. The transistor turns load on or off depending upon the vgs. The zenior dido output controls the vgs. The 0.6V dc varies from 0 vdc to 1.8 vdc. I want transistor off when that voltage is 05vdc or higher and on from 0vdc to 0.5vdc
My question is how can I use the 5.2vdc which is constant to drive my load when transistor opens? I cannot connect 5.2vdc from source to drain it gives me some voltage less than 5.2vdc
 

crutschow

Joined Mar 14, 2008
34,837
I want transistor off when that voltage is 05vdc or higher and on from 0vdc to 0.5vdc
For that low and precise a voltage transition you likely need a comparator circuit, such as the LM339/393, along with a Zener or reference voltage IC.
Can you use those?
 

Thread Starter

hhsting

Joined Apr 25, 2024
156
For that low and precise a voltage transition you likely need a comparator circuit, such as the LM339/393, along with a Zener or reference voltage IC.
Can you use those?
I am trying to build comparator without using ICs, relays etc. I am confused how I can do it
 

crutschow

Joined Mar 14, 2008
34,837
I am trying to build comparator without using ICs, relays etc. I am confused how I can do it
Why no IC's?
A transistor differential comparator can be built, if necessary.
Example circuit below:
In place of D1 there would be a 0.5V reference voltage.

1715004979008.png
 

Thread Starter

hhsting

Joined Apr 25, 2024
156
Why no IC's?
A transistor differential comparator can be built, if necessary.
Example circuit below:
In place of D1 there would be a 0.5V reference voltage.

View attachment 321761
i dont follow your circuit. I dont have any AC voltages. All voltages are DC.

I want to learn how I can build comparator without Ics or relays and using minimum components as possible.

i am trying to build voltage comparator using only diodes and transistors where if its above 0.5VDC then I get 5.2VDC output and below 0.5VDC I get 0.5VDC output.

know of any such circuits?
 
Bjt itself works like this. It opens at 0.6V across BE.
If you insist to switch at exactly 0.5V input just use resistor divider R1:R2.

However, transistor Vbe changes with indoor/outdoor temperature in range 0.5 - 0.7V, so if temperaure is not stable it won’t be much precise.
 

Attachments

Last edited:

Thread Starter

hhsting

Joined Apr 25, 2024
156
Bjt itself works like this. It opens at 0.6V across BE.
If you insist to switch at exactly 0.5V input just use resistor divider R1:R2.

However, transistor Vbe changes with indoor/outdoor temperature in range 0.5 - 0.7V, so if temperaure is not stable it won’t be much precise.
Can you do anything with MOSFET that have positive vgs? Also I want transistor to open between 0V to 0.5V dc and close greater than 0.5vdc.

yours if less than 0.5vdc would close which is not what I want
 
Last edited:
Top