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I want to try and make the output power of the following driver board adjustable. At full power it runs at 100watt I. The board itself does not have an option to reduce the power output. The output voltage is 220v (I think), output frequency is 40khz (most likely pwm square wave).

Here is the driver circuit board I'd like to use: https://www.aliexpress.com/item/33001673042.html?spm=a2g0o.productlist.0.0.3d644912VCTYPe&algo_pvid=1c2f1089-3691-4e06-88a1-95689226a60f&algo_expid=1c2f1089-3691-4e06-88a1-95689226a60f-36&btsid=07fe0fa2-3398-48aa-a224-770f018b1ea3&ws_ab_test=searchweb0_0,searchweb201602_5,searchweb201603_52 Image: enter image description here

I don't think it can be done by placing another pwm signal generator (/"dimmer) on either the input or output side. I'm quite sure it would mess up the output frequency of the driver board. Perhaps I could use a lot of triacs in series to get the desired voltage drop and in this way reduce the power but this is probably a bad way of doing it. Variable resistor is not an option I think due to the high power draw (approx 100w).

PS: I'd be using this driver/the high frequency transducer to try and build an ultrasonic cleaner.

Any suggestions on how to solve this problem will be greatly appreciated. Thank you very much!

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    \$\begingroup\$ Please provide a link to the manufacturer's datasheet for the board with a complete schematic. If you can't get the manufacturer's datasheet then you should look for a different board. \$\endgroup\$ – Elliot Alderson Sep 17 '19 at 12:19
  • \$\begingroup\$ The description of the item in the link clearly states that the amplitude is adjustable although without any detrails on how it is done. \$\endgroup\$ – Barry Sep 17 '19 at 12:23
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On the board, I see a "220V" input connector, rectifiers, and no smoothing caps. Thus I'm going to assume this runs directly from rectified mains. There doesn't seem to be any voltage regulation, and there are only two active devices.

Also the board has "110V" and "220V" versions, which means it can't adjust its power output for lower voltage.

So... if you want to reduce power, you could try powering it from an auto-transformer (variac) to reduce mains voltage. It probably needs some minimum volage value in order to run, though.

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  • \$\begingroup\$ If that is true and its chopping mains it is going to be putting a load of crap back into the mains unless it has really good filtering. Probably not legal under EMI regulations \$\endgroup\$ – Dirk Bruere Sep 17 '19 at 13:33
  • \$\begingroup\$ Well it has to be chopping mains since there is no big power supply capacitor to make some real DC... As for filtering, it looks like the PCB has a footprint for a choke (right besides the "40kHz" silkscreen) but it is populated with two wire straps....... \$\endgroup\$ – bobflux Sep 17 '19 at 15:11

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