AC to DC conversion without diodes

Chapter and verse

Not directly in any efficient manner. You want to turn on the mosfets when the voltage is 0. Thich mosfet depends on the direction(sign of the derivative of the voltage). If the voltage is 0 for any long period of time you actually wan the mosfets to be off. This also causes a problem for near

It's better and easier just to use a controller. This way you can turn the mosfets on much more effectively by having them alternatate once per

The good thing about using a controller is that you can easily create a variable power supply PWM the mosfets among other things.

There is always motor generator sets.

Hmm I've taken a PNP and NPN set to be biased via an AC signal to produce a steady DC with no diodes.. The PNP simply derived the (+) directly with an R bypass over the NPN.. the NPN circuit was decoupled via a 90 degree shift circuit which also then, biased the PNP.. both were common E to the (+) and (-) rails.. I basically used that switch for a sensitive AC to DC switch which produced a nice DC saturated switch with fast response..

It works find If you're working with a small range of freq..

Just a thought..

"Jamie" wrote in = message news:Xzk%n.13500$ snipped-for-privacy@newsfe22.iad...

which=20

rails..

Just yesterday, I invented a chopper circuit which performs synchronous = rectification with 2N3904s. DC in, DC out, doesn't matter which = direction. It should work a few tenths of a volt negative as well = (i.e., a true ideal transformer for small signals).

Tim

--=20 Deep Friar: a very philosophical monk. Website:

snip

Could you please draw a diagram?

I would have to do one in Spice and spit it out here.

The above circuit description is a rough draft of what I did..

The original circuit used 2 PNP's from the (+) rail and one NPN circuit. The input signal was cap decoupled because of the signal source would've otherwise biased the first PNP to saturation...

A basic R from the base to the (+) rail and R in series to the cap of the input signal.

The 90 degree shift was a basic T network with cap and R which then input to a buffer amp, this amp then switched on the second PNP.

Both collectors of the PNPs are joined and both Emitters are joined to the (+) rail.. The second PNP base(B) is part of the 90 degree shift buffer stage. The (B) r for that transistor simply was the collectors R for the buffer stage which was inverted.

The shift was calculated for the lowest frequency of interest to insure the time domain would cross over at 90 degrees. Higher frequencies didn't need the shift to be exact due to the tome constants put in place for the final switch signal.

So when all said and done, I was able to get a wider pulse at the final output with a short gap in the signal. A final cap on the end into a comparator gave me the near perfect DC on/off I was looking for..

Basically I created a speed switch from a Eddy current motor that needed to have a very fast on response when the rotor started to turn with a very narrow gap in the pulse stream and voltages below .5 volts into a compressed safety circuit..

This was done years ago and I later on did basically the same thing using a 555 timer which worked out just fine...

This circuit isn't any good for a linear DC representation of AC levels.

I hope this was helpful enough, its a lot to do in Spice. I could look up the old print in the files at work when I return monday and photo scan that area and then post it. I will need to look in dirty place to find that one, yuk...