Improving Current limit

[jonnybgood]

Dear Jonny
The differential amp can use to obtain the difference between the voltage across the resistor and it can amplify you current error signal . but at that circuit because of that , the current sensor ( resistor ) is under the load to ground , i think it is not necessary to use diff amp , here .
All the best
Goldsmith

I was a littile bit scepticle of the differential amplifier because, I said that there will always be voltage across the current sense resistor except at no load. This will always create a positive output voltage irrelevant on the set closed loop gain and therefore I thought that this method can never be precise.. I am I right?

 

[mtwieg]

I was a littile bit scepticle of the differential amplifier because, I said that there will always be voltage across the current sense resistor except at no load. This will always create a positive output voltage irrelevant on the set closed loop gain and therefore I thought that this method can never be precise.. I am I right?

Well I'm not sure what circuit you're talking about (there are many posted in this thread so far), but I think I get what you're saying. The differential amp will normally just have the role of increasing the accuracy of the current sensing, and allowing you to use a current sense resistor that isn't ground referenced. It won't replace the function of the error amplifier, which should compare the output of the diff amp to a reference. I suppose it might be possible to use the current sense amp as the error amp as well, but it would require careful biasing...

 

[dselec]

Build the circuit many factors came out. Like voltage drop on secondary transformer output. This caused the voltage to drop than actually rise on the current sense resistor when the a resistor of 1.5 Ohms is put as a dummy load. The transformer I am using is from a car battery charger rated at 4Amps. I dont think I have control over this issue. I have a bigger transformer 12v output but it is very heavy. Is it the last option I have for this circuit to work or can I use another current limiting method?

Try out this circuit the current and voltage are in-depended and it also has a fold back option

 

[goldsmith]

Dear Friends
when we have no load , the out put of operational amplifier ( current limiter op amp ) , will be about zero .because v+ is zero and -vcc connected to the ground.
So there is not any problem.
Good luck
Goldsmith

 

[goldsmith]

Dear FvM
Again Hi
Thank you for your guide to us , but is it possible that you tell us your mean more clearly , please? and is it possible that you offer us , that what value can use for compensation network at this aim , please ? i think that RC network can shift the poles of this circuit to the left of S plane to improve it's transient response . but wee need your again guidance to select them.
Respectfully and with Appreciate.
Goldsmith