I was looking into gain, because I do get saturation. (I just lower R8.)
TL062 has 50 Ohm resistor on its output (but maybe I should add another.)
If values of C6 and C7 are the same, each should get half the energy (not counting voltage drop on D2).
Why should I increase energy on C7 ?
Hi,
More energy transferred to the output the more output voltage per unit ESR resistance, thus the sensitivity is increased. This isnt a critical issue though like the gain, which is more critical.
For the gain, here is the basic analysis..
The square wave generator generates a wave from 0v to +5v.
The transformer divides that down by a factor of 20, to 0.25v, or plus and minus 0.125v.
Given a low resistance we get all that across the second 10 ohm resistor, so that's plus and minus 0.125v.
The op amp U1B is biased at 2.5v, and the power supply is 5v, so we've got less than 2.5v headroom on the output.
That op amp gain however is 39, and 39 times 0.125 equals 4.875, so it becomes obvious that somebody made a mistake on the gain
because 4.875+2.5=7.375 and that voltage exceeds the op amp positive voltage supply so the op amp will saturate.
Furthermore, since the resistance of the ESR and second 10 ohm resistor reflects to the output as a simple ratio, given an ESR of 0.1 ohms we'll still see 99 percent of that output (given a higher supply voltage) at the output so that's still 7.3 volts which is still way too high.
Given the op amp output characteristics we'd have to look up the max output. Then we could decided what the gain should be, although there may be some variation in the transformer operation which attenuates part of the signal so maybe just short the ESR and adjust the gain such that the output of the op amp is within range of it's ability.
There could also be a problem using a TL062 op amp because the output swing may not make it up or down high enough even with lower gain. You'll have to do a test for linearity, but a rail to rail op amp would work better, or else increase the supply voltage to say 20v.
The output swing data for that op amp isnt very explicit so you'll have to test it, but be aware that if you build another one of these testers it may not work even though the first one works.