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enter image description hereI want to understand why this circuit I have made works in the simulation (Multisim), but when I tested it in the protoboard it does not oscillate. If anyone can help me, I will be grateful.

(Sorry for the bad English)

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  • \$\begingroup\$ "Does not oscillate." Ok well what does it do? Care to share your data? \$\endgroup\$
    – Bort
    Commented Apr 17, 2018 at 18:00
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    \$\begingroup\$ +/-5 is pretty low supply voltages for a 741. Try it with +/- 15 V maybe? \$\endgroup\$
    – The Photon
    Commented Apr 17, 2018 at 18:06
  • \$\begingroup\$ @Bort Gets an unknown value of frequency in the oscilloscope and a 50mV Pk-Pk, otherwise, in the Multisim, gets an 146kHz and 425mV \$\endgroup\$ Commented Apr 17, 2018 at 18:21
  • \$\begingroup\$ So, is the signal at DC? What value? Is it a different waveform and has AC content? \$\endgroup\$
    – Voltage Spike
    Commented Apr 17, 2018 at 18:24
  • \$\begingroup\$ @ThePhoton Thanks for the help. I tried with 15V, but still not getting oscillation \$\endgroup\$ Commented Apr 17, 2018 at 18:57

2 Answers 2

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The 4.7uH inductor is swamping out the 470uH. If you are expecting a 741 on +/-5V to oscillate at 156kHz, that may be a bit on the optimistic side, as the typical bandwidth is only about that much at +/-15 and gain of 10. You might manage a feeble oscillation if you increase R8.

Try a better op-amp, or a lower frequency, by increasing the inductor value, not the capacitor value.

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  • \$\begingroup\$ Thanks, for the help. Which Op-Amp do you recommend? \$\endgroup\$ Commented Apr 17, 2018 at 18:53
  • \$\begingroup\$ ADA8022 is nice 100+MHz GBW, MC33078 cheaper 16MHz GBW. Don't go too high on GBW (not much above 100MHz), or you may get oscillation at higher frequencies than intended due to parasitics. As it is use good layout and bypass near the chip. \$\endgroup\$ Commented Apr 17, 2018 at 20:31
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    \$\begingroup\$ AD8022.......... \$\endgroup\$ Commented Apr 18, 2018 at 0:31
  • \$\begingroup\$ What SSRat said. \$\endgroup\$ Commented Apr 18, 2018 at 1:08
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I don`t think that the used opamp is the core of the problem. Rather, your circuit does not meet the classical oscillation condition (Barkhausen), which requires a loop gain of unity (or slightly larger with respect to a safe start of oscillations).

What is the problem? For an ideal tank circuit we have 100% positive feedback at the resonant frequency. However, at the oscillation frequency the positive feedback must be equal to the negative feedback (this condition is identical to the requirement of unity loop gain).

Therefore, place another resistor R6 in parallel to the tank circuit and select resistor values with R7/R8 < R6/R9 (R6/R9 only slightly larger, perhaps 2...5 %)

Further considerations: Of course, the used opamp must be able to work as desired at the oscillation frequency (small signal bandwidth as well as slew rate). Unfortunately, you did not mention the frequency of oscillation.

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