| Electronics > Beginners |
| Struggling w. a Single Supply Integrator |
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| rstofer:
I am just guessing but in a single supply system, there are no negative voltages. So, why does your square wave not center around 2.5V and swing from 0V to 5V. The absence of input, what would be 0V in a dual rail configuration is 2.5V in the single supply design. You would expect that with the input held to 2.5V, the output would eventually become 2.5V You could post your .asc file so others could play with your circuit without having to create it from scratch. The latest simulation (just above) doesn't show a triangle wave at all. There is too much exponential stuff going on. |
| ogden:
--- Quote from: rstofer on December 12, 2018, 04:30:48 pm ---I am just guessing but in a single supply system, there are no negative voltages. So, why does your square wave not center around 2.5V and swing from 0V to 5V. --- End quote --- Many lo-end audio circuits are exactly like that - single supply, input capacitor, signal centered around ground ( 0V ). |
| Zero999:
Try increasing C2 to 10μF Increase R2 to 470k or even 1M. It only has to allow enough current through to bias the op-amp. If the op-amp isn't a bias compensated, J-FET or CMOS input, then there should be a resistor between Vref and the non-inverting input, with the same value as R2. I think the LT1001 is bias current compensated, so the resistor in series with the non-inverting input would make it worse, but if you're breadboarding it with the uA741 which isn't bias current compensated, then include it. |
| rstofer:
--- Quote from: ogden on December 12, 2018, 05:02:28 pm --- --- Quote from: rstofer on December 12, 2018, 04:30:48 pm ---I am just guessing but in a single supply system, there are no negative voltages. So, why does your square wave not center around 2.5V and swing from 0V to 5V. --- End quote --- Many lo-end audio circuits are exactly like that - single supply, input capacitor, signal centered around ground ( 0V ). --- End quote --- True, but they usually bias the input pin at Vcc/2. The problem with the circuit above isn't so much a matter of bias as the fact that the signal can go negative, below ground, and the integrator can't follow along. I don't see how adding bias to the input pin will work with the signal going below ground and I don't see how the bias will work at all without affecting the input - the reason the capacitor was put there in the first place, I suppose. I would like to see what happens when the input signal is changed to 0-5V and the input capacitor removed. But not enough to lay out the circuit from scratch. Analog computing, my main interest in op amps, is usually done with integrators using dual supply op amps but I don't see why it couldn't be done with single supply op amps just as well. It's just a case of Vcc/2 is the new 0V. I also don't see how the single supply design can get to the rails because rail-to-rail is a marketing term, not an engineering fact. In an analog computer scenario, we would probably leave a volt or so off of each rail so, for a Vcc of 5V, the signals would vary between 1V..4V and the center would still be at 2.5V ETA: I would adjust the signal source to center on 2.5 and have a 3V peak to peak amplitude. For the old 741 integrators, the supply was +-15V and the signals were constrained to +-10V. |
| eev_carl:
--- Quote from: Hero999 on December 12, 2018, 05:26:28 pm ---if you're breadboarding it with the uA741 which isn't bias current compensated, then include it. --- End quote --- It's an LT1001. 8) |
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