Driving common source MOSFets with OptoMosfet

You're missing an important element above, the stack of photodiodes required to receive the light and create an isolated gate voltage.

Yes, so tie both gates together, and connect them to the output of the PD stack, through a diode. The bottom end of the PD stack goes to the sources.

Yes, so add a high-value resistor across the PD stack, to pull it down to zero, and add a PNP emitter follower in parallel with the diode to pull down the FET gates following the high-value resistor. You can edit the drawing for us (or you can find one I posted here).

Yes of course, by reversing the polarities and using an NPN trannie.

--
 Thanks,
    - Win

Won't work- you need a floating VGS source referenced to the common source connection.

Hi

How would I go about driving a common source MOSFet configuration (Two N type) with the output of an Opto Mosfet (N type)

Basically, the schematic would be this:

| D ||-+ .------------. || ||

I did, but I actually two NC and two NO, hence I'm looking at different ways to achieve the same result. And yes, I know it would be easier to use a regular electromechanical relay, but there is no challenge here.

I only need two of each, and that's the main problem. My design is just for hobby, not for production.

You can't wire 2 N types like that.

What are you trying to do ?

Graham

Yes, but aren't these included into the package and not available on any of the pins of the package?

Fine.

Do you have a reference or a keyword for that message you posted here?

Indeed.

Thanks

Yes you can, see Solid State Relay schematics. It works because of the parasitic anti parallell diode in the Mosfet.

Turn On and Off AC signals (phone, actually)

Wassamatter with you, Graham, Of course you can! I've completed O'Bones drawing below. The result is a bog-standard ac SSR.

It runs deeper than that- your opto FET is bidirectional, sorry-assed p.o.s....

Why don't you use a simple bridge rectifier? Connect your AC source to the AC terminals of the rectifier, and let the opto-mosfet directly "short" the + and - terminals of the rectifier? If you can't afford the 2 diode drops, make a rectifier with

4 schottky diodes.

HTH Wolfgang

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Would you have a schematic for this?

Just buy a small solid-state relay or two. See cel.com for some examples.

John

Mr. Hill's drawing looked fine to me.

An open photodiode becomes forward biased when illuminated with the right wavelengths. This mode is called the photovoltaic mode.

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--Larry Brasfield
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Above views may belong only to me.

+-+---------+ A A | your AC load terminals o-----+ | D +-|| o-----(-+ ->|| Opto-MOSFET A A S +-|| | | | +-+---------+

so simple.... Just be sure to use a rectifier that can withstand the "open" AC voltage, and the "closed" current. Your opto-mosfet should also be capable of that....

HTH Wolfgang

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D'oh, so simple, should have thought of that before... Brain must have gone away, it's the end of the week after all...

Keep trying - I'm sure all SSR types are widely used in France, so find out who's selling them industrially. Post the question in sci.electronics.components

Hey, maybe you can get some free samples. :>)

--
 Thanks,
    - Win

Bummer. How can a country have a high-tech infrastructure if they make it hard for people to get parts? Do you have anything like Mouser or Digikey, small-quantity distributors?

John

What? NOBODY has the "p-types," because n-channel FETs are more suitable, and ac switches have no way to know if they're P or not.

--
 Thanks,
    - Win

Doing a mix of your proposition and Wolfgang's one, I came up with this:

In1 | N | .-----+-+ | ||-+ A A | || A | |R| | Vss | | - A | | | | +--- Out | | | | '-' | | ----' '-------+ | | '---------' | | .-----+-+ | | | ||-+ A A | Vss | ||-> | +---' '-||-+ +-)---. | A A | P '--+--+-+ | | | Vss | In2

I drive the Mosfet driver with whatever logic I want, and this will act as a SPDT "relay", selecting In1 if the LED is on, and In2 if the LED if off. The R resistor discharges the gates and cell when the LED is off, which effectively turns off the N mosfet and on the P one. Is there a specific value to use? Finally, to get a DPDT relay I simply duplicate the Mosfet + Brige part so as to switch the second line of the phone signal. Of course, the bridges and mosfets must whistand the voltage and amperage on the phone line. In my mind, this looks good, but please correct me if I'm wrong.

Thanks a lot for the help. Cheers Olivier

PS: Schematic created by AACircuit v1.28.5 beta 02/06/05

this soft is awesome