Inverter Microwaves (not a product recommendation thread)

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elpenguino

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#2461085 14-Apr-2020 13:47

sidefx:

So I was under the perhaps mistaken impression from that document that the transformer wasn't required with the inverter circuit design and that's how they get the higher efficiency (because transformers are pretty inefficient at the high frequencies required to generate microwaves?)

You hit the magnetron with low frequency/high voltage AC and it resonates at Microwave frequency. The magnetron is modulated in time, not frequency. We're making an oven , not a radar :-)

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SomeoneSomewhere

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#2461217 14-Apr-2020 16:31

From that previous PDF:

In inverter-equipped microwave ovens, the power transformer is replaced by a
circuit board, which converts the 60Hz incoming line frequency to a variable rate
of 20 KHz to 45 KHz. A relatively small transformer is then required to increase
the voltage to the level required by a magnetron.

The transformer in a conventional microwave still runs at 50Hz; it's the magnetron that produces the 2.4GHz output.

I'm not really sure; I had a feeling they were DC but...

TwoSeven

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#2461289 14-Apr-2020 18:21

SomeoneSomewhere:

Actually, that's a fair point. I think there is a rectifier on the transformer output of a normal microwave.

Perhaps it's effectively an isolated DC boost converter then.

I think so, usually up to 380mA DC (depending on size of microwave) into a pulse width modulation inverter.

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TwoSeven

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#2461293 14-Apr-2020 18:27

elpenguino:

sidefx:

So I was under the perhaps mistaken impression from that document that the transformer wasn't required with the inverter circuit design and that's how they get the higher efficiency (because transformers are pretty inefficient at the high frequencies required to generate microwaves?)

You hit the magnetron with low frequency/high voltage AC and it resonates at Microwave frequency. The magnetron is modulated in time, not frequency. We're making an oven , not a radar :-)

From my understanding - a cavity magnetron is used - these are a central cathode surrounded by a circular anode. When the cathode it heated, electrons are emitted which try to jump to the anode.

underneath the magnetron is an electromagnet which creates a field pulling the electrons into a circular stream between the cathode and anode. As they pass the cavities they resonate releasing microwaves.

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sdav

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#2461467 14-Apr-2020 22:25

sidefx:

mains AC > rectifier > DC > INVERTER > variable frequency AC > magnetron

Ok, that seems to make sense to me! Thank you and to everyone else who answered!

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