about rectifier


I have a question about h-bridge rectifier.
first it is a url mosfet - Why does this Bridge Rectifier claim to have no [Diode] Forward Voltage drop - Electrical Engineering Stack Exchange

And http://www.analog.com/en/products/lt4320.html#product-overview

I'm just wondering those two of it are different.
I already know about that mosfet rectifier to replace voltage drope(when use diode).
But I don't know the necessary of using pulse wave.
I think it should have oscillator that consume power.

Does there any benefit to using pulse wave?

I would think the differences are:

  1. Just after a Zero crossing The Electrical Engineering bridge will not turn on the mosfet until the AC voltage is ~ 10 Volts. The LE4320 will turn it on a near zero volts.

  2. I believe the LT4320 limits the gate voltage where as the Electrical Engineering circuit puts the full voltage available on the Gate, therefore limiting the range of voltage the circuit is useful for.

JohnRob explained it but to polish the details just a bit:

The StackExchange circuit is just a proof concept and not practical, the peak applied voltage is limited to the Vgs rating of the mosfets and it can only drive a purely resistive load since there is no reverse current flow protection. This means pulsating dc output since you cannot hang a capacitor on the output to smooth it. This is what happens because you’re using the mosfets as switches. There is voltage drop with current flow due to the Rds rating of the mosfets.

The LT4320 actively controls the gates of the mosfets, elimating the reverse current flow allowing a capacitor for smoothing on the output. Why would you want an ideal rectifier? From the AD website:

Analog Devices’ ideal diode bridge controllers replace the four diodes in a full-wave bridge rectifier with a low loss MOSFET to drastically reduce power dissipation, heat generation, and voltage drop. The Schottky diode bridge rectifier is a classic circuit used for full-wave ac-to-dc rectification and dc polarity correction. Due to the ~0.6 V drop of each diode, the two diodes in the I/O path dissipate power (1.2 W per ampere), radiate heat, raise the ambient temperature, and complicate thermal design. At low input voltages, the two diode drops significantly reduce the voltage available to the downstream dc-to-dc converter. Ideal diode bridges eliminate or reduce heat sinking requirements, which helps shrink the overall footprint and provides significant cost savings.

The stack exchange circuit can probably drive an inductive filter though, as they tend to keep the current
flowing one way. Still big issue with Vgs limit of course, but a few resistors and zeners can fix that.

Adding one more diode can allow a smoothing capacitor, and it can be shottky for lower losses, and
has half the voltage losss of an all schottky bridge - but really you might as well for the the AD chip
and do things properly.