I am working on a project to do high-side current control. I had gotten help previously from Ron Simpson and others (Thank you all!) which was a low-side approach, a great help and worked well. However, it turns out that for reasons which are non-negotiable, the current through the sensor must be returned directly to system ground with no intervening resistors or components. I want to still use the IRLZ44N N-type MOSFET due to the relatively high current (36 DC amps), and the lower Rds-on compared to P-types. But this implies a bootstrapping function to provide the gate drive.

I need some guidance on components to flesh out a circuit which would include a high-side current sense IC, a high speed opamp, and some type of bootstrap function. I have included a rough conceptual sketch of how I envision this might come together, but I am out of my comfort zone on putting the details all together. Any comments and/or component suggestions are always most appreciated! Thanks.

 

How is the current sense circuit supposed to control the MOSFET switch?
You circuit won't completely shut off the output, just limit the current at some value, or perhaps oscillate at that current.
Is that what you want?

 

This looks like a linear circuit, and if it is controlling 36Amps @24V it's going to need a huge heatsink.
If the transistor is to work in linear mode, then Rds_on becomes immaterial, so you might just as well use the P-channel device. True, it is more expensive, but you don't need a complicated drive circuit.
If it is a switching circuit, and it is intended to produce a fixed current in a resistor, then you will need an inductor.

 

@crutschow: A microcontroller will send a 50 us pulse of 5V to the top of the voltage divider. The duty cycle of the circuit is low, say one pulse every 30 minutes.

@Ian0: As mentioned above, this ckt will be operating in response to a 50 us pulse, not continuous.

Thank you both.

 

A microcontroller will send a 50 us pulse of 5V to the top of the voltage divider. The duty cycle of the circuit is low, say one pulse every 30 minutes.

Great.

Okay we're into a game of 20 questions.

Don't just give us a circuit to figure out what its purpose is.
What exactly is the circuit supposed to do with that pulse and the output of the current-limit circuit?