I don't think any of the TS posts state the voltage level of the sensed current. The LM358 input stage common mode range does not include its positive rail.
The voltage level of the sensed current is between 1.2 and 30V DC.I don't think any of the TS posts state the voltage level of the sensed current. The LM358 input stage common mode range does not include its positive rail.
For the LM358 to function correctly, the voltages at both input pins *must* be a couple of volts less than the voltage on the V+ pin. The value is on the datasheet. Your input voltage range exceeds both 12 V and 24 V operating voltages.The problem is that op amp 1 is not working as it should
I as not aware of this.For the LM358 to function correctly, the voltages at both input pins *must* be a couple of volts less than the voltage on the V+ pin. The value is on the datasheet. Your input voltage range exceeds both 12 V and 24 V operating voltages.
I'm currently designing a short circuit detection circuit for a bench lab PSU.
When the PSU's output goes above 1.5A the short circuit detection circuit will disconnect the load from the output and latch so until the load has been removed.
This is my current circuit:
View attachment 173502
Basically I pass the output through a 1Ohm power resistor and feed the voltage on both sides of the sense resistor into an op amp in differential configuration. After that the output of op amp 1 goes into the non-inverting input of a second op amp that is configured as a comparator against a reference voltage adjusted by a pot .
The problem is that op amp 1 is not working as it should and I think the issue might have something to do with the grounding.
The op amps are supplied by a separate 12V supply but the two voltages going into the differential op amp are referenced to the PSU ground.
Is it ok to feed in voltages that are referenced to a separate ground?
My question might sound a bit obvious to some people but I'm really not sure what the issue is.
All help is welcome
Thank you AK, I was not aware of this.Electrical Characteristics table: Input Common Mode Voltage Range. The minimum is listed as 0 V, an astounding feat in 1971. Note that while the 358 is described as a single-supply part, and even has its negative rail pin labeled GND (a disappointing mistake), it can function just fine as a traditional dual-supply part.
What would be suitable values for R1 and R3?In any of your schematics, increase the value of R1 and R3. this attenuated the input to be within the opamp's common mode range. Some integrated current sense parts have this built in, as do some general purpose instrumentation amps.
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