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| Does this switch mode buck convertor design look OK? |
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| ogden:
--- Quote from: mosafet on January 20, 2019, 01:26:44 am --- --- Quote from: ogden on January 20, 2019, 01:23:10 am ---Source: http://www.learnabout-electronics.org/PSU/psu31.php --- End quote --- Cool, thanks! I'll put that in. It actually was something I thought of doing before but like I said, the examples I have don't ever show that and I wonder if it's actually necessary. --- End quote --- Sure. Upstream power source is usually omitted. Example design of the automobile wheel does not necessarily include drawing of the engine or other parts of the automobile power train. Actually you shall pay even more attention to buck converter topology. Notice that buck converter have common ground, high side switch transistor: Circuit of your converter does not look like that. --- Quote ---In case anyone is wondering, I'm using a 60W incandescent light bulb as a load. It pulls about 30W at 55V DC output. --- End quote --- 55VDC seems like 100% duty cycle for your buck converter which essentially means - it is not operating. You shall test at lower output voltage, like 12V. |
| mosafet:
--- Quote from: ogden on January 20, 2019, 11:29:57 am ---Actually you shall pay even more attention to buck converter topology. Notice that buck converter have common ground, high side switch transistor: Circuit of your converter does not look like that. --- End quote --- Right because you can use either a high-side or low-side design. That is a high-side circuit. Mine is using low-side because it's slightly easier to control the gate. This is fine if the load can float. --- Quote ---55VDC seems like 100% duty cycle for your buck converter which essentially means - it is not operating. You shall test at lower output voltage, like 12V. --- End quote --- Right, I was just giving that out as the max value (100%). At other voltages the wattage is less. It works. I also noticed that my schematic as drawn here is wrong. I did the breadboard first and messed up the MOSFET driver section when drawing the schematic. I'm considering other driver options if I can scrounge the parts. I really dislike P-FET's. :) |
| ogden:
--- Quote from: mosafet on January 20, 2019, 03:07:20 pm ---Right because you can use either a high-side or low-side design. That is a high-side circuit. Mine is using low-side because it's slightly easier to control the gate. This is fine if the load can float. --- End quote --- You may use low side buck for current supply like LED driver, but not for voltage supply which needs voltage monitor. Ground of your supply is not tied to ground of the microcontroller - how you can (correctly) measure output voltage? :-// --- Quote ---I was just giving that out as the max value (100%). At other voltages the wattage is less. It works. I also noticed that my schematic as drawn here is wrong. I did the breadboard first and messed up the MOSFET driver section when drawing the schematic. --- End quote --- Then fix your schematic and re-post it! :rant: Driver you are showing, with 10k pull-down resistor, is not able to switch power mosfet at high frequencies at all. If you say it is working then - could you please show 30% PWM duty-cycle voltage waveforms of power mosfet gate, output (virtual) ground and positive terminals? |
| mosafet:
--- Quote from: ogden on January 20, 2019, 03:23:06 pm ---You may use low side buck for current supply like LED driver, but not for voltage supply which needs voltage monitor. Ground of your supply is not tied to ground of the microcontroller - how you can (correctly) measure output voltage? :-// --- End quote --- OK, yes, I see the problem and I was not using the sense yet. Now THIS is why I asked if it looked OK because this is obviously something I need to fix. I'll re-sort it and rework the FET driver for high-side. More complexity :( :) |
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