Circuit design MOSFET

Thread Starter

ridyzz

Joined Sep 24, 2021
4
I got a circuit and do not know the exact application of it. I would highly appreciate if you guys might help me with this.
Thanks a lot.
242676495_562481078322628_7933461327057155730_n.png
242676495_562481078322628_7933461327057155730_n.png
 

BobTPH

Joined Jun 5, 2013
3,769
No, you don’t have a circuit, you have a question asking you to design one.

The application is a power supply current limiter, but I doubt that iis what you are really asking

Since this appears to be homework, what have you done si far, or where are you stuck?

Bob
 

DickCappels

Joined Aug 21, 2008
7,836
It looks pretty straight forward to me. Use the components in the blue box along with the circuit shown to measure current and shut off the voltage to the load if the load draws more than 10 ma.

Hint: I think this problem presents a bad example using an opamp as a comparator.

A question for you: What would the MOSFET be used for?
 

BobTPH

Joined Jun 5, 2013
3,769
Actually the problem cannot be solved using only the given components. A voltage greater than 3.3V is required.

Bob
 

bertus

Joined Apr 5, 2008
21,587
Hello,

The LM358 seems to work from 3 to 32 Volts single supply:
LM358_features.png

The problem however is that the low can be near the 0 Volts, but the high is not at the supply voltage.

Bertus
 

Attachments

BobTPH

Joined Jun 5, 2013
3,769
Actually, if you read the question to mean that it is on at 10mA and off at 225mA with no specification for currents in between, and you get a typical part for the MOSFET, there is a solution that does not use the opamp!

Bob
 

DickCappels

Joined Aug 21, 2008
7,836
@click_here , you are right, it is 225 ma to shut it off. (When I went back to get the detail of the over-current condition I read the wrong number).

I think some of us have predefined concepts that are keeping some from seeing how this can be done. Let's let @ridyzz work it out without our idea of the "right way" getting in their way of finding the answer.
 
Top