Re: Scopes Away! - mosfet diode

To: tesla-at-pupman-dot-com
Subject: Re: Scopes Away! - mosfet diode
From: "G.E. Leyh" <leyh-at-ix-dot-netcom-dot-com>
Date: Thu, 14 Sep 1995 13:29:14 +0000

Tesla List wrote:
> 
> >From 100624.504-at-CompuServe.COMTue Sep 10 22:29:57 1996
> Date: 10 Sep 96 15:39:11 EDT
> From: Alan Sharp <100624.504-at-CompuServe.COM>
> To: Tesla List <tesla-at-poodle.pupman-dot-com>
> Subject: Re: Scopes Away! - mosfet diode
> 
> Malcolm,
> 
> >>  Question - is there an easy way of destroying the diode without
> >>ruining the MOSFET? (Alan, anybody?). Alternatively, are there any
> >>devices without this built-in nuisance available (type/s please)?
> 
> The substrate diode is a property of the actual working
> bits of the MOSFET - it's not a separate component.
> 
> The simplest way to get rid of it is to put a diode in series with
> the mosfet.
> The alternative would be to go for a bipolar or IGBT device.
> 
> good luck,
> 
> Alan Sharp (UK)


The switching element in this application must be able to pass 
AC current, so a series diode cannot be used. A standard method
that is used in SS Relays when controlling AC current is to 
connect 2 MOSFETs in series source-to-source, where the 2 drains 
become the output terminals.  Connect the gates together, and apply 
>10V between the common-source and the common-gate to turn the 
switch on.  When off, the switch will also block voltage in
both directions.

I wonder, what's the upper pass freq limit on a standard SSR?

-GL