| Electronics > Beginners |
| CCCV MOSFET Buck |
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| wraper:
--- Quote from: Leeroy on September 12, 2019, 04:43:15 pm ---Replace DAC and C5 with trim pot and you get what was reverse engineered from this module: https://www.aliexpress.com/item/1084552308.html --- End quote --- And what makes you think you can replace trim pot with capacitor and DAC? :palm: |
| wraper:
--- Quote ---I'm not sure how exactly I would implement current sense with less parts, I already have just a shunt and all-in-one amplifier. --- End quote --- Just place shunt on low side. Just like in TPS92512HV circuit in datasheet. |
| Leeroy:
--- Quote from: wraper on September 12, 2019, 04:52:22 pm ---And what makes you think you can replace trim pot with capacitor and DAC? :palm: --- End quote --- The fact that it was just producing variable reference voltage from 5V reg via voltage divider. --- Quote from: wraper on September 12, 2019, 04:55:47 pm ---Just place shunt on low side. Just like in TPS92512HV circuit in datasheet. --- End quote --- Will do. |
| wraper:
--- Quote from: Leeroy on September 12, 2019, 04:59:14 pm --- --- Quote from: wraper on September 12, 2019, 04:52:22 pm ---And what makes you think you can replace trim pot with capacitor and DAC? :palm: --- End quote --- The fact that it was just producing variable reference voltage from 5V reg via voltage divider. --- End quote --- Don't you still get that you put reference voltage into comparator which you made by omitting any DC feedback from opamp? It literally outputs logic ones and zeros with slew rate limited by 0,33uF capacitor and output impedance of DAC. |
| Leeroy:
--- Quote from: wraper on September 12, 2019, 04:00:01 pm ---Again. As simple as it gets. Usual shunt resistor which is selected according to current needed. Usual feedback input, you can modify circuit if you want current to be adjustable. --- End quote --- I mean look at this formula: This is ridiculous for a simple feature of current setting. Sub 1Ohm resistors are only easily accessible here in standart some shunt values like R100, R050, R005 and so on.. Ok let's say I went through all the trouble to calc and obtain the correct resistor for my 750mA. Then some time later I need to assemble myself a similar circuit for a 350mA LED and I should go through all that again every time? Fuck that.. --- Quote from: wraper on September 12, 2019, 05:10:13 pm ---Don't you still get that you put reference voltage into comparator which you made by omitting any DC feedback from opamp? It literally outputs logic ones and zeros with slew rate limited by 0,33uF capacitor and output impedance of DAC. --- End quote --- Yes. And my understanding is that it is enough since when current sense voltage is higher than reference IC either lowers the Ton or skips cycles depending on its capabilities. I don't know how hard it affect hysteresis and if it actually introduces the oscillation and noise. But judging by the fact that aliexpress module is stable it is acceptable. Maybe I should verify that I re-engineered it 100% correctly, since it was long time ago and in a hurry. Take a look at this thread: https://www.eevblog.com/forum/beginners/adding-cc-to-a-cv-buck-to-make-it-cccv/ |
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