Marcel Duchamp wrote: >> I've seen small cheap transformers like this operate at near saturation, >> distorting the waveform. I had thought about including a switching power >> supply but it violates the simplicity rule. I wonder if I could keep >> current usage down and use a linear reg. direct from rectified AC. >> Probably not though - I think I'm going to use an 18F or 30F device >> which will use significant current (several mA perhaps). >> >> Thanks for looking at it. >> - >> Martin > > Using TR1 with the diodes attached will distort the waveform as you > mentioned. But you can do as Russell suggested and just include a > separate transformer for the purpose of sampling the voltage. > I could, but I want to measure things like PF and THD, and it's hard to do that if the voltage is distorted in the transformer: > You have an enormous range of gain on your amplifier circuits; is there > a good reason for this? > Not really, but A 1k resistor from pot->ground would be prudent. > C3 (and C4) are in the wrong place if you intend them for low pass > filtering. Think what happens at high frequency; the Xr goes down so > the stage gain goes up, right through the roof. It will be noisy at > best and likely will oscillate. If you are looking for low pass > filtering, put the caps in parallel with the 10k feedback resistors. > Yes of course.. dumb mistake. > Guessing here but are you trying to level shift the signal with your > output amps? Something else? It "just don't look right". You are > feeding the outputs with a ground referenced AC signal but have a > voltage divider that I can't quite figure out what you have in mind. > It does basically what I had in mind: CH2 is the input, CH1 is the output. I should have used VDD as the high side of the voltage divider though. > If you are trying to shift the output such that it is ready for unipolar > a/d conversion, consider using a reference for the bottom side of the > sensing transformers. If the desired output is +2.5V plus/minus the > signal, then put the bottom of the transformer at +2.5V. Or otherwise, > AC couple the signal maybe. > > Maybe a little more explanation of just what you had in mind will help > here. > It's an AC voltage and current sensing interface. Didn't I mention that? - Martin -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist