On Mon, Dec 13, 2021 at 06:57 AM, Jim Adney wrote:
One note on the cap: Its value matters, as it is chosen to resonate with
the leakage inductance of the HV transformer.
Really? I've never heard this before. So they are expected to "ring" to give
higher voltage than would otherwise be expected? That seems like it would be
hard to control, even with a +/- 3% capacitor.
The magnetron wants roughly double the output of the transformer. (Cheap transformer here is the idea... to keep the cost of the transformer as low as possible...for the commodity domestic microwave oven market.)
And so...oven designers use a Villard doubler... designed/discovered by the same guy that discovered gamma rays! ... instead of a more expensive higher voltage transformer.
If you want to drive a square peg into a round hole... which I'm gonna do... you can look at the Villard doubler... as used in those old, 'big iron' transformer sporting ovens.. the ones with a lot of gravity... you can look at the Villard doubler in them... as 'like' a poor man's (poorly designed)... fixed frequency series resonant DC to DC converter. (Remember, I stipulated 'like.')
The goal is with a relatively s**t transformer... to try to get resonance at the fixed fixed frequency of operation... because that's where you would get maximum current... but, I'd say (because I haven't measured it) that's seldom the case. (These ovens are designed to maximise cheapness... not precision.)
Just the same with given transformer, and diode, and an arbitrary capacitance value... whose effect is to significantly 'detune' the circuit... well you won't get maximum current... and if you are too far off.... you won't get the rated power of the oven.
--
Roy Thistle
