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I have been following these youtube tutorials on active rectification to learn more about the topic.

https://www.youtube.com/watch?v=VR456CsHYx4

https://www.youtube.com/watch?v=arvNukW-jeo

I simulated the final full wave active rectification circuit, in ltspice, with 4 mosfets and a mosfet driven by an op amp to prevent reverse current. However I am noticing that this design starts to fail for lower AC amplitudes.

35V active rectification:

Edit: Improved diagram from Audioguru

enter image description here

enter image description here

Take for example when the input voltage amplitude is 10V instead of 35V. there is a larger voltage drop and (some) distortion on the waveform. Why is this? Is Full wave active rectification for lower voltages achievable?

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Threshold voltage.

M2 and M4 do not begin to conduct until Vgs exceeds the FETs threshold voltage. This is the minimum gate-source voltage required for conduction at current levels greater than leakage. It is specified on the datasheet and can be determined from the charts. There usually is a plot of Vgs versus Rds.

In your 35 V case it is too small to see, but it always is there.

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  • \$\begingroup\$ imgur.com/a/uiC4O93 I believe this is the chart you are referring to. However the difference between Vgs=10V and Vgs=35 is a couple of milliohms, is that enough for a voltage drop of 0.5V ? \$\endgroup\$
    – Jirhska
    May 14 at 18:15
  • \$\begingroup\$ Do you check Vdio? Stabilizer circuit looks strange and fail-prone to startup. If the source is a transformer output, it may be possible to wind another coil with higher voltage for gate control. \$\endgroup\$
    – Vladimir
    May 14 at 18:21
  • \$\begingroup\$ @Vladimir Vdio looks fine, imgur.com/a/WzShy4B It could be that but I am not sure why, is that what the op-amp feedback circuit portion is called? a stabilizer circuit? It could be VGS on M3 not reaching a high enough threshold. \$\endgroup\$
    – Jirhska
    May 14 at 18:29
  • \$\begingroup\$ Purpose of U1 and M3 is unclear for me and it may be designed wrong. I thought that it should be voltage stabilizer. Power supply of opamp is discontinuous and negative input's potential is floating somewhere (?) \$\endgroup\$
    – Vladimir
    May 14 at 18:40
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    \$\begingroup\$ Then, IMO is better to use comparator and two voltage dividers, from Vin and Vout, going to +in and -in of comp. It's power should has capacitor and zener to ground. \$\endgroup\$
    – Vladimir
    May 14 at 18:55

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