I want to know how to design a current checker

Tahmid said:

What I gather from your post is that you want to design a sort of undercurrent and overcurrent protection.

You need a means of reading the current. You can do this using shunt resistor, current transformer or hall-effect sensor. Your method will depend on AC/DC and cost factor.

Then you need to compare the current to 2 references - one for 10A and one for 20A. And then take necessary action when current < 10A or > 20A. This can be done using comparators or microcontroller. If you don't use or haven't used microcontrollers, designing the circuit with comparators will be easier than using microcontroller.

Hope this helps.
Tahmid.

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