Timeline for High-side MOSFET drive in current-limited power supply
Current License: CC BY-SA 3.0
6 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Dec 9, 2016 at 5:43 | comment | added | NathanielJPerkins | @tummychow Did you ever solve the problem with differential amplifier across the current sense resistor? I have a similar problem now where I need to limit current to a load, but the voltage supply can be either of 2 sources, and one is a battery that might vary between some values. | |
| Sep 18, 2013 at 13:49 | comment | added | tummychow | Thanks for the clarification. The reason I wanted to use the differential amplifier was because Vin also varies. I'm designing a two-stage adjustable power supply with a switching regulator that feeds a linear regulator. The output of the switcher varies to match the dropout of the LDO (LTC3600 datasheet last page), and the current-limiting stage goes between them, so both sides of the current-sense resistor could shift up or down during normal operation. I'll fork that off into another question if I have to investigate it more seriously. | |
| Sep 18, 2013 at 13:37 | vote | accept | tummychow | ||
| Sep 18, 2013 at 12:57 | comment | added | Andy aka | @tummychow I see no advantage in using the current sense amplifier. It could also create stability problems too (ditto your original idea). Op-amps are designed to be close to the verge of stability at high frequencies and adding more silicon in the feedback loop is likely to cause sustained oscillations. Been here before!! You can turn the PFET off pretty much completely and if you have any worries about this, you can drive the PFET via a resistor from the op-amp and have another PFET there to clamp the gate drive to the positive rail. Be sure the op-amp has rail/rail i/p & o/p swing. | |
| Sep 18, 2013 at 12:41 | comment | added | tummychow | For a second I didn't know what you meant by "positive supply referenced" - it looks like you moved the sense resistor above the transistor in your diagram. Would it be possible to put a differential amplifier across the sense resistor and use that to drive the inverting input, as I did in my original diagram? Still works as intended? One other thing: I can turn the PMOS fully off (ie current limit of 0A) as long as the opamp's output can hit Vin, right? | |
| Sep 18, 2013 at 9:24 | history | answered | Andy aka | CC BY-SA 3.0 |