KeepItSimpleStupid
- Joined Mar 4, 2014
- 5,088
This http://cdn.teledynelecroy.com/files/appnotes/lab428.pdf might be useful as well.
That looks great! Thanks for sharing.You are correct about the op amp not being able to provide enough current, so it does require a buffer.
Also requires a plus and minus supply for the plus and minus AC waveform.
You may be able to offset it but that can get a little problematic to do.
Below is my take, using a transimpedance amp with buffer (LT1010) directly at the transformer output (I1) which avoid the diode drop voltage, giving 0V at the transformer output.
The transimpedance output then goes to an ideal full-wave rectifier circuit.
View attachment 144711
Thanks!This http://cdn.teledynelecroy.com/files/appnotes/lab428.pdf might be useful as well.
Looks great!Here's the circuit simulation with a +5V supply and a charge pump circuit to generate the -5V.
The LT1010 can only output about 3V max with a 5V supply, so I added some gain at the output to bring it up to near 5V peak.
Note that C1 should be ceramic, and C2, C3 should be ceramic or tantalum.
The simulation is quite slow (many minutes) due to the high frequency switching in the charge pump circuit.
View attachment 144770
That's good.I'm just curious to play with other ideas for practice.
Very true! I've already gone down a number of dead end streets trying unconventional approaches to circuits (mostly trying to solve problems from this forum.) So far, I've gained valuable knowledge from each of these attempts. Hopefully the trend continues!That's good.
It's how you learn.
Often you learn more by figuring out why something doesn't work than how something does.
Thanks again for all your advice and support!That's good.
It's how you learn.
Often you learn more by figuring out why something doesn't work than how something does.
So, my first attempt at building your circuit, using a TC7660 to create a negative supply, was a bit rocky. It was a significant improvement over previous error levels, but still had a lot of both offset and gain errors. Probing around with a multimeter showed some really odd behavior that I couldn't explain.In general rail-rail op amps cannot pull the output completely to ground with any significant load (such as the feedback resistors), as you found.
No, I had a larger decoupling cap across the two power pins instead of the two smaller caps to ground (being sloppy and lazy, I used what was in front of me instead of digging or shopping for the right thing .)Adding 10μF to stop the oscillation is a brute-force technique that's not recommended.
Do you have 0.1μF ceramic decoupling capacitors directly from all op amp power pins (both plus and minus) directly to ground with short leads?
If not, that can cause the observed op amp oscillations.
How about the protection diodes I added?Adding 10μF to stop the oscillation is a brute-force technique that's not recommended.
Do you have 0.1μF ceramic decoupling capacitors directly from all op amp power pins (both plus and minus) directly to ground with short leads?
If not, that can cause the observed op amp oscillations.
Well, I tried the improved decoupling, exactly as described, but it didn't stop the oscillation.Adding 10μF to stop the oscillation is a brute-force technique that's not recommended.
Do you have 0.1μF ceramic decoupling capacitors directly from all op amp power pins (both plus and minus) directly to ground with short leads?
If not, that can cause the observed op amp oscillations.
I must confess now that I'm guilty of discussing a circuit that differs from the schematic I've shared...It could be that the transformer inductance is a factor in the oscillation.
If the cap on the input suppresses the oscillation, then use it.
Sometimes you have to use what works, even if you don't understand why.
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