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Current limiter for power switch

Hi and a happy new year to all

I am currently designing a solid state switch with current limiting (low side MOSFET switch and low side sensing resistor) with the following requirements:

- The current limitation shall be stable against capacitive, inductive loads, and short circuits

- The current limitation shall be active within 10-100us, allowing for brief inrush currents

- The current limit shall be insensitive to temperature variation and variation of bus voltage

- The current limit shall be adjustable at the time of design (first design is 10A). My approach for this is simply to adapt the size of the sense resistor, or the gain applied for the sense amplfication circuit

My current design is a simple feedback circuit with an amplifaction the sense voltage to 1V when activation begins. This is then used to drive a NPN (with emitter resistor to ground, in order to reduce sensitivty to BE voltage). The collector sinks the pull up current to 12V supply (the

12V will later be controlled in order to provide on\off functionality for the switch)

The schematic looks the following (made with AACircuit): VCC +------------------------------------++ | | | 12 V .-. + | | | | | R Load | '-' .-. | | | | 700 | | | '-' | | | | ||-+ | ||

Reply to
JF
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Gain in current limiting feedback loops is always treacherous. Why do you think you need to "gain-up" the voltage across the sense resistor? Just use an OpAmp or comparator capable of common-mode operation at ground. Or do it with some discrete transistors.

I'm immersed in my least favorite task today... final report writing :-(

If I have some time later today I'll post some ideas for you to try. ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
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Reply to
Jim Thompson

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