I used lm358 as a comparator and fed up in using it..I tried all kind of pull up resistor between non inverting input and o/p to avoid floating o/p,but wasnt able to..So i hav decided to look for an best comparator ic..Can anyone help me out in this...
Thank you,,
An LM358 is an old low power, low quality, slow dual opamp, not a comparator. Its outputs are push-pull so they never float.
Adding a resistor from its output to its non-inverting input simply adds positive feedback to make it switch faster or latch (it doesn't work when it latches).
I used lm358 as a comparator and fed up in using it..I tried all kind of pull up resistor between non inverting input and o/p to avoid floating o/p,but wasnt able to..So i hav decided to look for an best comparator ic..Can anyone help me out in this...
Thank you,,
Post your schematic. Since the LM358 is an opamp, not a comparitor, it shouldn't need any resistor on its output. An LM358 used as a comparator would be quite slow, but would work for non-critical applications.
Post your schematic. Since the LM358 is an opamp, not a comparitor, it shouldn't need any resistor on its output. An LM358 used as a comparator would be quite slow, but would work for non-critical applications.
Actually the problem was when i connected comparator circuit with my rectifier circuit ,the problem of comparator got arised..
When dc input of 3v was given to the comparator with reference of 2.5v,,the o/p of comp was 5v(it was to be +24v(high))..At the same time the ac voltage at that o/p was 3v ac..Now i got a point to say that ac is imposed on dc...so can u help me to reduce the ac voltage in the circuit before comming to the comparator..
I see that AG thought that I was referring to the op-amp based rectifiers.
To tell the truth, my poor little brain rebelled at the rest of the very badly draw circuit and did not bother analysing it.
Replacing the LM358 with a real comparitor is the least of your problems.
There is no filtering anywhere, on the +24V DC supply, on the output of the active rectifier, on the inverting input of the comparitor.
With out resistance values, I cant figure out what you are trying to do???
Thankyou everyone for sharing your time with me..but its not over yet...
I added a 1000 micro farad at the end of rectifier and amazingly the comparator worked very well...
But my circuit started working differently..The o/p of rectifier was 300mv dc for 250mv ac..But after adding capacitor,the o/p jumped to 700mv dc..I have attached the readings that i got(after adding capacitor)..Interstingly after reaching 900v dc, the o/p from rectifier stopped increasing..I couldnt relate the problem with my bad brain...Help plz??
None of your resistors have values so we don't know if the opamps are overloaded which will limit the output voltage.
We also do not know how much voltage gain you have in your active rectifier.
The text is too small to see if your power supply is AC or DC and we cannot see the voltage. If it is AC then the bridge rectifier needs a huge filter capacitor.
If the zener diode is connected with backwards polarity then it will limit the voltage to about 0.7V.
None of your resistors have values so we don't know if the opamps are overloaded which will limit the output voltage.
We also do not know how much voltage gain you have in your active rectifier.
The text is too small to see if your power supply is AC or DC and we cannot see the voltage. If it is AC then the bridge rectifier needs a huge filter capacitor.
If the zener diode is connected with backwards polarity then it will limit the voltage to about 0.7V.
I got my circuit working..I left pulsating dc till the amplyfing opamp and added capacitor filter in front of comparator...But couldnt justify how i got..Thankyou everyone...Very much appreciated