Timeline for OP Amp output voltage half
Current License: CC BY-SA 4.0
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| Dec 27, 2019 at 23:43 | comment | added | Frostiger | Yeah I don't know anymore, thanks guys for all the help but I have no clue what I'm doing wrong at this point, every setup I do isn't working, I'm doing what Russell said, with Vcc+ = 5v Vcc- = Ground, Rf1 = Rf2 = 10kohm Vin = 1.2 but when I put it in non inverting with that setup I get an extremely tiny voltage, and when I put it in inverting I get +3.5v. I've read a lot about it and tried all the setups but I can't figure out what's wrong. | |
| Dec 22, 2019 at 8:27 | comment | added | Circuit fantasist | @ Spehro Pefhany, I remember a similar problem with the ancient 702 (or 709)... where two diodes had to be connected back to back in parallel to the input... | |
| Dec 22, 2019 at 8:16 | comment | added | Circuit fantasist | @RussellMcMahon, I said it just because of "teasing":) It is clear that for the purposes of the initial introduction to the op amps, the supply voltage should be normal (large enough)... and the experimenter should focus on the principal things (though this is also something quite basic). | |
| Dec 22, 2019 at 8:07 | comment | added | Spehro 'speff' Pefhany | @Circuitfantasist There's a trap for young players in this. The LM324/358 is prone to phase reversal where a sufficiently negative voltage (outside the rated common mode range, negative wrt ground) on the inverting input will drive the output low, causing the output to latch low if it ever gets the chance. The TI SPICE model will allow this behavior to be simulated (in fact it will start up in a latched state). So some external parts should be added if the inverting configuration is used with inputs that are less than a few hundred mV. | |
| Dec 22, 2019 at 7:52 | comment | added | Russell McMahon♦ | @Circuitfantasist Hmmm. Obviously yes re Vcm and inverting input, which messes up my answer in this specific case. | This only applies while Vout is in controllable range - in this case slightly under 2.4V (as Vcc- = 2.4V and the '358 gets a bit weak around the knees when Vout is really close to V-. The OPs +1.6V should give -1.6V as shown which should be well within limits. | |
| Dec 22, 2019 at 7:18 | comment | added | Circuit fantasist | A very useful guidance for a beginner... Only to note that in the inverting configuration, the common-mode voltage is zero because of the virtual ground at the op-amp inverting input. Thus we can drive it with thousands of volts but it will stay zero (of course if we keep the same ratio R1/R2). | |
| Dec 22, 2019 at 0:08 | history | edited | Russell McMahon♦ | CC BY-SA 4.0 |
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| Dec 21, 2019 at 23:59 | history | answered | Russell McMahon♦ | CC BY-SA 4.0 |