How can I add overload protection to my current limit circuit?

[mariuszoll]

Hi,

I made a current limit protection circuit at 1A, and I would like to improve it with an overload protection.
Could you give me please some ideas how to switch off the mosfet when the load current exceed 1A?

Thank you

 

[gnurf]

I made a current limit protection circuit at 1A, and I would like to improve it with an overload protection. Could you give me please some ideas how to switch off the mosfet when the load current exceed 1A?

Can you explain how the current limit protection circuit works?

 

[mariuszoll]

Hi,

under normal conditions transistor Q1 is blocked. R2 is used to sense the current through it. When current is 1A, the voltage drop over R2 is 0.7V and Q1 is turned on, which in turns increase the voltage on the gate of M1, and keep it at the limit of conduction.
R4 is used to limit the Q1 base current in case of a load short circuit.
R1 allows M1 to turn on and pass the voltage and current to the load.
And thus, the current limitation is made.

 

[gnurf]

What do you mean by overload protection and how is it different from what you already have?

 

[skeptic2]

I agree with gnurf. It looks like you already have a pretty effective overload protection circuit. What more do you want? Do you want it to shut down completely at some point? If so you have to define what it is that should cause the circuit to shut down.

 

[mariuszoll]

Hi,

Beside this current limitation, I would like also, to shut down the circuit when current becomes equal or higher than 1A.
If you could give me some ideas how to do it, I would appreciate it.

Thank you

 

[gnurf]

Beside this current limitation, I would like also, to shut down the circuit when current becomes equal or higher than 1A. If you could give me some ideas how to do it, I would appreciate it.

I think you're looking for a "latched overcurrent fault detector". In the article linked to below they use a latching comparator that turns off the FET when the current exceeds the limit. Hopefully that might give you some ideas!

http://powerelectronics.com/mag/510PET07.pdf
http://www.maximintegrated.com/datasheet/index.mvp/id/2204

 

[mariuszoll]

Hi gnurf,

Thank you for the articles, they are very good. Do you know how I can do the same thing but with discrete components?
I tried to improve the previous circuit, in order to switch off the mosfet, but without good results. You can find attached the circuit.

Thank you

 

[mariuszoll]

I think that there was a problem with the attachement.