Author Topic: Resonant Inverter: Amplitude to Voltage?  (Read 925 times)

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Offline johnywhyTopic starter

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Resonant Inverter: Amplitude to Voltage?
« on: May 20, 2023, 01:29:36 am »
I've read the Vout of a resonant inverter is lowered by increasing the oscillator frequency, pushing it above the resonant frequency of the LC tank.

Instead, why not lower Vout by reducing the amplitude of the square input oscillator, (and keep frequency the same)?
« Last Edit: May 20, 2023, 01:37:20 am by johnywhy »
 

Online johansen

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Re: Resonant Inverter: Amplitude to Voltage?
« Reply #1 on: May 20, 2023, 05:34:35 am »
The whole point of a resonant converter is to use switches to modulate a system under easy to switch resonant conditions.


Keeping above the resonant frequency is easier because you dont have diode recovery in the body diode of the igbt or mosfet to deal with.

You can decrease the power transfer by droppin below the resonant frequency as well as above.
 
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Offline temperance

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Re: Resonant Inverter: Amplitude to Voltage?
« Reply #2 on: May 20, 2023, 09:33:47 am »
This should clarify most of your questions concerning resonant power supplies:

https://www.youtube.com/playlist?list=PLMZ8LHWk_2jjYz1gM9x3dpLOb3E8GLVBq

Some species start the day by screaming their lungs out. Something which doesn't make sense at first. But as you get older it all starts to make sense.
 
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Offline johnywhyTopic starter

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Re: Resonant Inverter: Amplitude to Voltage?
« Reply #3 on: May 20, 2023, 09:51:27 pm »
This should clarify most of your questions concerning resonant power supplies:

https://www.youtube.com/playlist?list=PLMZ8LHWk_2jjYz1gM9x3dpLOb3E8GLVBq

Sam's great. I've watched a lot of his videos, but i don't always understand them.

Was there a particular video that explains why we don't vary amplitude to adjust Vout?

Thx!
 

Offline johnywhyTopic starter

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Re: Resonant Inverter: Amplitude to Voltage?
« Reply #4 on: May 20, 2023, 10:00:10 pm »
The whole point of a resonant converter is to use switches to modulate a system under easy to switch resonant conditions. Keeping above the resonant frequency is easier because you dont have diode recovery in the body diode of the igbt or mosfet to deal with. You can decrease the power transfer by droppin below the resonant frequency as well as above.

Sounds like an answer to me  :)

You're saying that, reducing pulse amplitude will cause diode recovery in the body diode of the igbt or mosfet?

I understand that raising fin is preferable, because if you lower fin, then harmonics of fin could sweep down into the passband of your resonant LC tank. Correct?
« Last Edit: May 20, 2023, 10:03:30 pm by johnywhy »
 

Online johansen

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Re: Resonant Inverter: Amplitude to Voltage?
« Reply #5 on: May 21, 2023, 05:16:45 am »
Pulse width stays the same. Amplitude is always the same. The switch is fully on or fully off. Anywhere inbetween is losses
 
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Offline johnywhyTopic starter

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Re: Resonant Inverter: Amplitude to Voltage?
« Reply #6 on: May 21, 2023, 05:05:29 pm »
Amplitude is always the same. The switch is fully on or fully off. Anywhere inbetween is losses

Right, of course, the switch must be fully on or off.

But you could vary the power supply.
 

Offline Weston

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Re: Resonant Inverter: Amplitude to Voltage?
« Reply #7 on: May 21, 2023, 06:24:03 pm »
Are you talking about a dc-dc converter using a resonant topology like LLC? Or an inverter with an AC output used for something like induction heating?

Either way, the same point applies:
One of the main goals of a power supply is to regulate the output with a varying input voltage.

You could regulate the input voltage and still use the resonant inverter, presumably to generate AC or to provide power across an isolation barrier. You are entirely correct in your understanding that it could be done.

However, this would require an additional power converter to adjust the input voltage. From a complexity and cost standpoint this is worse than just using the inherent frequency/amplitude characteristics of the resonant inverter.


 


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