Electronics > Beginners
Op Amp Full Wave rectifier with Hi Pass question
alexg:
--- Quote from: Audioguru on June 26, 2018, 04:35:43 am ---Like all opamps, the opamp you are using has an absolute maximum negative input of only -0.3V when its negative supply (Vv-) is 0V.
In the circuit I posted, the inputs NEVER go negative (unless they have a very high level) so use this opamp in the circuit I posted.
--- End quote ---
I am just curious what effect will this have on the op amp of you let negative input go below -0.3V when supply is 0? It seems to work but does it mean that I am slowly killing it with every impulse below -0.3V ? I know datasheet says "Exposure to maximum rating conditions for extended periods may affect device reliability." and I understand that but I am curious if I am just lucky to have circuit that works fine even beyond max ratings or I am slowly killing op amp?
Benta:
Actually, I've seen this kind of opamp rectifier before. Certain amps phase invert when the input goes below zero. IIRC, is was the CA3130.
Audioguru:
Your input voltage is exceeding the maximum allowed input voltage so of course you are damaging the opamp.
alexg:
I built this circuit using following surface mount components:
Two resistors, 100k 0.5% both
Diode: NSVRB521S30T1G datasheet: http://www.onsemi.com/pub/Collateral/RB521S30T1-D.PDF
Op Amp: MIC 862 datasheet: http://www.microchip.com/mymicrochip/filehandler.aspx?ddocname=en580715
Op amp's power pin is decoupled with 10uF and 0.1uF and whole thing is powered with clean Lab power supply 3.3V
I get weird results, the wave does get rectified, however positive half of the wave has voltage drop somehow, I cannot figure out where does it come from, do I have a bad Op Amp choice, did it matter that I used 100k resistors in stead of 200k? there is not much else going on in this circuit, need help.
At the illustration with 1kHz sine wave on input, it comes form waveform generator, directly into "input" in original schematic.
oPossum:
Schottky diodes have high reverse leakage. Try a silicon diode like 1N4148 or 1N914 instead.
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