Hello everyone,
I have a precision rectifier for the front end of my circuit.The input to the rectifier is from 1 ohm resistor which is shorted to the current transformer. The rectifier i use converts ac voltage to pulsatting dc. So to make it into pure dc,i used a 1000micro f capacitor. Then my circuit was not linear as the o/p from rectifier was not proportional to the input..I have attached the circuit without the capacitor whwer it will be connected to pin 7 and ground...Help will be much appreciated
The circuit you posted is a half-wave rectifier although you show a full-wave rectified signal at the output stage. If you want a full-wave rectified signal then you need a different circuit.
You can't connect a capacitor directly to the output of an op amp and expect to get a linear DC output. The poor op amp is madly attempting to charge and discharge the large capacitor as it tries to follow the rectified signal level which means it's likely operating in an output current limit mode.
If you want the average value of the rectified waveform then add a resistor in series with the output of the op amp to the capacitor filter. The resistor must be large enough to keep the peak current below the output current rating of the op amp.
If you want the average value of the rectified waveform then add a resistor in series with the output of the op amp to the capacitor filter. The resistor must be large enough to keep the peak current below the output current rating of the op amp.
An average dc voltage is needed as output..and As crustchow told, Il add a HIgh range resistor to the o/p to the capacitor and check it out...Thank you...
That circuit will only measure the average and not true RMS of course, although you can adjust the resistor values to give the RMS value (similar to what an average responding DVM does).
That circuit will only measure the average and not true RMS of course, although you can adjust the resistor values to give the RMS value (similar to what an average responding DVM does).
OK. Just wanted to emphasize that the circuit generates a representative voltage of the RMS value based upon the average, not the true RMS. Perhaps I was overstating the obvious.
The circuit you posted is a half-wave rectifier although you show a full-wave rectified signal at the output stage. If you want a full-wave rectified signal then you need a different circuit.
Actually I got my problem solved..I added a high value resistor in series to line of parallel connected capacitor were crust how to.ld..
And I'm working on Eric Gibbs schematics and will check out the results..
Thanks everyone..much appreciated..
The circuit is a FULL-WAVE rectifier when it uses the LM358 opamp.
When the input is positive then the inverting opamp has its output diode disconnect it from the output so the output is simply half the input voltage due to the resistor values.
When the input is negative then the output of the opamp goes positive at half the voltage of the input.
The lousy old LM358 is low power and old so the circuit works only at low frequencies.
The circuit is a FULL-WAVE rectifier when it uses the LM358 opamp.
When the input is positive then the inverting opamp has its output diode disconnect it from the output so the output is simply half the input voltage due to the resistor values.
When the input is negative then the output of the opamp goes positive at half the voltage of the input.
The lousy old LM358 is low power and old so the circuit works only at low frequencies.
Yes,Audio guru,the circuit works well for low frequency due to the slow operation of lm358. In fact the circuit is used to detect the line current of commercial building using a ct(current transformer) with the frequency of 50hertz..so it works a lot better for me...
Are you using 741 opamp for the single supply or resistive discharge version? I have tried it but not getting the required output, although simulation on Multisim works fine, what's the reason for this, opamp selection or something else? Please also mention opamp model #