Current Limiter

Hi Jimmy, 

We've got your request. Allow us some time to think about some possible solutions and get back to you. 

Best Regards,

Bala Ravi

Hi Jimmy,

I would recommend using OPA2990 for your current limiter circuit. Please find the device specs below. 

This device has an overload recovery time of about 1us. 

Here is an app note, that you may find useful: http://www.ti.com/lit/an/sbva011/sbva011.pdf.  

Best Regards,

Bala Ravi

Hi Bala,

Thanks for the reply on the solution. 

After going through the design, it cannot resolve my design problem.

Firstly, i am not able to modify the input power. In your design, the current limit is being control adjust by the voltage regulator, but in my current setup, i am not able to modify the input. 

Thus, I am looking for a way to increase the impedance of the supply line when it detect a over current so as to protect my MOSFET in me load.

Please advise if there is a way to resolve this

thanks

Hi Jimmy,

Please give me a clear picture of the system that you are trying to limit current.  Is this a power supply? A power amplifier? It will be good to know the application to come with appropriate solution.

You have mentioned in your first post that you would like to use a MOSFET and an op-amp. Do you have a circuit topology in mind? What is the level of current limit?

Have you chosen a MOSFET (NMOS or PMOS?) The size of the FET will depend on how much Voltage drop (RDSon) across the FET. If we are talking of small drop and large current then it has to be a big FET which also means big gate capacitance which will need to be compensated properly so that it does not cause an oscillation. 

A very simple circuit will be to put a resistor in series with FET and sense the voltage across this resistor based on the amount of current flowing through it (and the FET). Compare this voltage with the reference voltage (which is set for the current limit) with an OPAMP and control the gate voltage of the FET with the output of an op-amp hence closing the loop. The downside of this is you will have a voltage drop across the resistor (= current x Resistor). 

You said the input moves from 5V to 36V. If you put a MOS and resistor in series you will have a voltage drop on the other side. What is the level of voltage drop your system can handle across this MOSFET and resistor?  

Sanjeev

Hi Sanjeev,

Basically, i am driving a H-Bridge using two PWM channel 1 and 2. Channel 1 and 2 is always compliment of each other, and when implement on the H-Bridge, the cross over of the PWM will turn on the H-Bridge causing a short circuit.

There are ways using MCU, but as my circuit is kind of fix, i want to implement a overcurrent when that event happen. Thus i have request if able to use a opamp and current sense resistor plus gate to prevent a overcurrent at the cross over

Hope this is clear in my explanation