Re: MOT Voltage Doubler

• To: tesla-at-pupman-dot-com
• Subject: Re: MOT Voltage Doubler
• From: Jim Lux <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
• Date: Mon, 21 Sep 1998 18:17:08 -0600
• Approved: terryf-at-verinet-dot-com

Tesla List wrote:
> 
> Original Poster: "David Dean" <deano-at-corridor-dot-net>
> 
> >Original Poster: "Gregory R. Hunter" <ghunter-at-enterprise-dot-net>
> >
> >Dear List,
> >
> >I've been studying the half-wave voltage doubler circuit (MOT, cap,
> diode)
> >found in US-type microwave ovens, and I think I understand how it
> works.
> >What is the ultimate voltage developed by this thing.  Looks like 2.8 x
> >RMS.  Is that it?  If I'm correct, then it doesn't really "double"
> anything
> >does it?
> >
> >Greg
> >
> >
> nope. It is a simple half wave rectifier. It is not a voltage doubler.
> The topology is a little strange however, in that the diode is grounded
> on one end shorting the positive going half cycle. The negative going
> half cycle
> is conducted to the K (cathode or heater) of the magnatron by the
> capacitor.
> The capacitor is not used as a filter or as an energy storage device.

It sure is a voltage doubler, although with terrible regulation. During
one half cycle, the capacitor is charged through the diode to ground
(actually, only for the first half of the half cycle). (The magnetron
being reverse biased, as well). The next half cycle, the voltage on the
cap and the voltage from the transformer is applied to the magnetron
(which is also a diode).  Therefore, the peak voltage on the magnetron
is twice the peak voltage on the transformer winding, or 2.8xVrms, as
you pointed out.

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