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I’m having some frustration with this circuit (Precision Full-Wave Rectifier) as shown in TI Precision Designs:, although I’m using an LM358N, the document references the OPA2211. I simulated the circuit in LTSpice with the LM358N and everything seems fine, but the problem arises when I move to hardware, where I don’t get any significant results. I’m sharing the breadboard assembly prints and the wiring diagram; am I making an obvious mistake here? By the way, I’m using a DSO153 to generate my input signal and analyze my output. Can anyone help me? Sorry for Image spam!

LTspice Simulation:

enter image description here

BreadBoard schematic:

enter image description here

Hardware circuit:

enter image description here

Input:

enter image description here

Output: enter image description here

positive supply rail: enter image description here

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  • \$\begingroup\$ Your diagram has an error -- the position of the lowest 1K resistor is off by one. However, this error is not repeated on the actual breadboard in the photograph. \$\endgroup\$ Commented Oct 18, 2024 at 21:56
  • \$\begingroup\$ Is your negative rail on the bottom connected? All I see in it is the 56Ω resistor, but we can't see the whole board. Is it connected at the other end and if so are the rails continuous (some boards break them in the middle)? Can you give us a pic that shows the whole board? \$\endgroup\$ Commented Oct 18, 2024 at 22:16
  • \$\begingroup\$ Hi, yes, It was connected to the other side of the breadboard, and even if I remove the 56-ohm resistor, apparently nothing changes! \$\endgroup\$ Commented Oct 18, 2024 at 22:31
  • \$\begingroup\$ @bananas867 The 50Ω resistor in the original circuit is for impedance matching with the signal generator, and will only attenuate the input (depending on your signal generator output settings). It won't alter the the behaviour of the circuit otherwise. \$\endgroup\$ Commented Oct 20, 2024 at 4:01
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    \$\begingroup\$ I don't see any wiring errors, so I am suspicious of the power supplies. I would like to see an oscillogram of the positive supply rail. \$\endgroup\$ Commented Oct 20, 2024 at 4:11

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The LM358 and the OPA2211 are very different notably at the inputs where one use PNP transistors while the other NPN. See their respective internal schematics. Their very small input current are not the same direction.

The LM358 is too slow so it oscillates.

If you want to use an LM358 for this function, use a circuit based on it (e.g. google LM358 full wave rectifier).

And always use decoupling capacitor near the op-amp.

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    \$\begingroup\$ The LM358N can work with dual supplies, according to TI and OnSemi datasheets. \$\endgroup\$ Commented Oct 19, 2024 at 19:47
  • \$\begingroup\$ @td127: It’s an ST LM358 which is in use here and pin4 Vcc- seem effectively connected to -12V. The data sheet confuse me as many things refer to ground and not Vcc-, sorry. \$\endgroup\$ Commented Oct 19, 2024 at 23:17

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