helpfull ideas for small signal amplifier please.
helpfull ideas for small signal amplifier please.
(OP)
i would like to amplify a 50Hz ac signal with a variable amplitude of anything from aprox 1mV to 25mV peak...why?... i am currently using a hall effect CT to monitor the output current from an ac generator. i get a dc mV signal from the CT that acts as the input to my prototype engine speed controller. the speed of the generator engine is increased at 4 preset increments depending upon the actual load current. i would like to replace the CT. i have been experimenting with a hall effect transistor. when the tr is placed within the magnetic field of the current carrying conductor an ac signal is imposed onto a 2.5V dc carrier voltage. when i decouple i get an ac signal of 2mV output (rms)for 1 amp of load current. the responce is linear and the max load current expected is 10 amps, giving 20mV AC signal. as i need a dc input of around 1 to 10 volts for my controler i want to amplify the ac mV signal to Volts and rectify / smooth as necissary. i know i can use an opamp to give a gain of up to 1000 but i do not want to add a dual polarity power supply to the circuitry. can i use an opamp on a single rail supply to solve my problem, and if so, how? i have spent a few hours tinkering but have not realy got anywhere. any help or suggestions would be greatly appreciated. thanks everyone.





RE: helpfull ideas for small signal amplifier please.
Use a MOS i/p op-amp like a CA3140 because its input current is lower than a bipolar such as a 741. Connect 2 x 470K resistors in series from Vdd to Vss, and connect their junction to the non-inverting i/p. Couple your i/p to that point with a 100nF capacitor. You will then have your 50Hz signal 'sitting' there at half rail.
Connect a 1M resistor from op-amp o/p to its inverting i/p, and from there connect a 1K resistor in series with a 100uF capacitor to Vss. The 1M/1K gives x 1000 gain and the 100uF gives DC isolation.
At the o/p you will then have your signal x 1000, again with its mean value sitting at half rail. You can then couple it with a 1uF capacitor and fit a resistor (100K?) from that point to Vss to give DC restoration. You can get the peak AC level using a diode and capacitor in the usual way.
RE: helpfull ideas for small signal amplifier please.
diode bridge. Generates 2* freq.
Want sketch? send fax #.
<nbucska@pcperipherals.com>
RE: helpfull ideas for small signal amplifier please.
RE: helpfull ideas for small signal amplifier please.
You mentioned DC restoration in your post. Can you suggest a good book that describes what it is and when it's good to use?
I'm looking for a good book or two that goes beyond the basic op-amp circuit fundamentals and delves into the workings of larger circuits.
Thank you,
Randy
RE: helpfull ideas for small signal amplifier please.
RE: helpfull ideas for small signal amplifier please.
Thank you again,
Randy
RE: helpfull ideas for small signal amplifier please.
RE: helpfull ideas for small signal amplifier please.
http://www.allaboutcircuits.com
RE: helpfull ideas for small signal amplifier please.
RE: helpfull ideas for small signal amplifier please.
RE: helpfull ideas for small signal amplifier please.
RE: helpfull ideas for small signal amplifier please.
http://us
RE: helpfull ideas for small signal amplifier please.
http://www.web-ee.com/primers/files/slod006b.pdf
RE: helpfull ideas for small signal amplifier please.
Thank you for your help. I too used to have a copy of the Op-amp cookbook but must have loaned it to someone and haven't gotten it back. I now have the new IC Op-amp cookbook and active filter cookbook on the way from Amazon.
I think I found the answer I was looking for in an old book about television circuits. I couldn't remember why DC re-insertion was required for some video signals but think I now know why. Boy oh boy, use it or lose it! :)
Thank you for your help, I appreciate it.
Randy