This circuit uses half of the TI dual OPA2626 (not showing the other half of the OP AMP). This dual OP AMP supposed to use 2mA, but it's pulling around 6.8mA (measured at the Grnd pin and also at the Vcc pin). The other half of the OP AMP is currently not used and none of those pins are connected to anything. Should they be pulled up or down in case that's where the current leak is?

The V-out is going to an Arduino digital pin and draws about 8.8uA, but even when I disconnect it the entire circuit is at 6.8mA. The current from the voltage divider (P1 potentiometer) to the OP AMP draws about 2.4uA and to N2 inductance (20 Ohm) is 0.1uA. Disregard the other (N1) inductance, it does not use any power from this circuit.

The other question: do you see any obvious problems as far as wasted power or noise sources, better solutions? This circuit supposed to amplify a 2-4mV to 4-8mV varying amplitude one-shot AC voltage sinus wave by 1000, and seems to work fine.

Thank you for any advice! enter image description here enter image description here


  • \$\begingroup\$ That R1 is kind of low, it’s only 10 ohm. Also in your simulation are you using the other half of the op amp or did you not even place it down? Also what is your peak output voltage? \$\endgroup\$
    – Leoman12
    Apr 26, 2020 at 3:12
  • \$\begingroup\$ Also if your output has some capacitance it’s advisable to add a low value resistor 10-20ohm between output of op amp and RL PLUS CL. \$\endgroup\$
    – Leoman12
    Apr 26, 2020 at 3:22
  • \$\begingroup\$ Try this, make a voltage divider of 100k and 100k between VCC and GND, connect this middle to non-inverting input of unused op amp, then connect inverting input to output. Then measure current drawn again. \$\endgroup\$
    – Leoman12
    Apr 26, 2020 at 3:25
  • \$\begingroup\$ Sorry, if I answer a bit slow, I need to digest the suggestions. My knowledge has some gaps. In the simulation I had the dual op amp, but removed the second half. On the proto-type breadboard I have the dual OP AMP 2626 vs the OP AMP 626. When N2 is "triggered" the output voltage spikes to 3-4Volts when measured with Oscope. (I need to limit it to 0-3.3V maybe using zener diodes not to damage the 3.3V Arduino) Come to think, the output waveform is Square, but the input is Sinus. So does this OP AMP work like a comparator instead of OP AMP? I thought I changed to OP AMP vs Comparator. \$\endgroup\$
    – TommyS
    Apr 26, 2020 at 3:59
  • \$\begingroup\$ When you say removed, you mean it’s no longer in your simulation environment? Or you just have it lying around in simulation window but unconnected ? Sounds like your clipping your signal to give square wave output. Too much gain or input signal too large. \$\endgroup\$
    – Leoman12
    Apr 26, 2020 at 4:08

1 Answer 1


First: second unused amplifier should be grounded, an output connect to inverted input, non-inverting input received '0' if dual , or half impedance if single power. if opamp unused, it doesn't mean it do nothing, in fact it can oscillate or locked to ether power rail. affecting crystal ...

next: Quiescent Current for datasheet pdf - a reference of opmamp in doing nothing state, like suspended, your RL resistor for example are some work to do, then, according to pdf it 2ma per 1 opamp, you have 2 so that at least 4ma. + consider wonky state of second opamp, and load of your schematic, like RL resistor.

If you trying to amplify, your power are single rail, means, you need to bias opamp input, half Vsuppl at least (after capacitor of course), and use a opamp for a single power supply. non inverting input grounded. Transformer second coil, bottom, on ground.

  • \$\begingroup\$ Thank you JamesBrown I get your first point along w/ @Leoman12 (thanks also) in regards to the other half of the OP AMP. Will try those suggestions. As far as your second point, I think I understand to move the P1 voltage divider to the inverting input after C1 & ground other side of N2 currently connected to the non-inverting input. Then ground the non-inverting input as well. Had similar setup with those inputs switched (comparator setup) but had noise/sensitivity issues: electronics.stackexchange.com/questions/493647/… \$\endgroup\$
    – TommyS
    Apr 26, 2020 at 4:11
  • \$\begingroup\$ nope you schematics , actually inverting with K amp = 6... but your link pointed to NON inverting with K amp = 1, it actually non inverting follower.. \$\endgroup\$
    – JamesBrown
    Apr 26, 2020 at 20:31
  • \$\begingroup\$ btw , for a proper design , need to know an input frequency, input \ output noise, transformer impedance, how it connected to opamp (like 20 meters long cable), , you K are not 1000, and where it connecting to ... and I'm not sure if opamp are suitable as well, it ADC driver and may not suitable to gain 1000, plus it dual. \$\endgroup\$
    – JamesBrown
    Apr 26, 2020 at 21:07
  • \$\begingroup\$ Please see me last comment above. Thank you both, I think it's in the home-stretch. Tested and incorporated some of your and @Leoman12 's suggestions. The cable is several feet now, but will be only a a few inches at the end. Frequency is between around 500H to 100KHz, but one-shot not continous. \$\endgroup\$
    – TommyS
    Apr 27, 2020 at 2:05
  • \$\begingroup\$ Yes read it, cant add on top comments, Just a note for this opamp, min V supply -2.7 - + 2.7, so it need at least 6Volt to run, (or maybe 5 V) , so if you find opamp +5 as normal \$\endgroup\$
    – JamesBrown
    Apr 28, 2020 at 5:35

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