Timeline for Use MOSFET as low frequency PWM variable resistor for step down regulator
Current License: CC BY-SA 4.0
15 events
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| Jan 20 at 23:52 | comment | added | hacktastical | The resistor DAC approach can certainly work, and on the low side too. | |
| Jan 20 at 22:05 | comment | added | arielnmz | Update: I couldn't find any available maxim chips in my country (or shipping was too expensive) however, I found a couple through hole DIP 2/2R based DACs: TLC7524 series. I assume I could just use that as an alternative to your BONUS suggestion, by wiring them appropriately? what is the catch? | |
| Jan 19 at 18:00 | comment | added | arielnmz | Can you elaborate a bit more on how to choose the resistor values for the PWM net current solution? I can identify two parts to it: the PWM voltage divider and the side of the FB pin, but what's the purpose of that 100R there? and the cap? | |
| Jan 19 at 2:42 | comment | added | hacktastical | Also, the way the PSU controls its 2-wire fan is with a PWM chop directly on the fan power supply. That’s a single big MOSFET between the fan (-) lead and ground. | |
| Jan 19 at 2:40 | comment | added | hacktastical | The feedback from the output is essential. It provides loop closure. As far as repurposing a fan from a dead PSU, your investment in both time and money just isn’t worth it when you consider how cheap a 4-wire PC fan can be, which you control directly with a PWM from your Arduino without messing with an additional power supply. | |
| Jan 19 at 2:20 | comment | added | arielnmz | By the way, I actually started exploring the idea of removing the feedback resistor network altogether and instead use PWM+Low pass filter to mimic the V_FB voltage and adjusting it from V_out via the analog input somehow... And it actually sounds a bit like the current sink/source you describe. Is that the case? Maybe I will ask a new question once I do the math for that approach. | |
| Jan 19 at 2:13 | comment | added | arielnmz | I salvaged this fan from a dead PSU, so I figured I could use it to move some air in my home lab rack by putting together a DHT11+this fan+an Arduino Nano somehow and learn more about electronics in the process. But I do agree, PWM is way easier. In fact, my first approach was to use an IRF520 and a 470uF cap to reduce the noise, then I went on to solve the problem of speed not corresponding linearly with PWM and here we are... | |
| Jan 18 at 23:59 | comment | added | hacktastical | Yes. Nevertheless I still think you'd be better off changing to a 4-wire fan. This will cost less than trying to hack the LM2596, and you'll get a better result. | |
| Jan 18 at 23:47 | vote | accept | arielnmz | ||
| Jan 18 at 23:46 | comment | added | arielnmz | Interesting, I didn't get far enough to explore the current sink/source solution to this, and it seems to be exactly the keywords needed to look for stuff like the DS4422 | |
| Jan 18 at 20:08 | history | edited | hacktastical | CC BY-SA 4.0 |
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| Jan 18 at 20:02 | history | edited | hacktastical | CC BY-SA 4.0 |
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| Jan 18 at 19:46 | history | edited | hacktastical | CC BY-SA 4.0 |
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| Jan 18 at 19:06 | history | edited | hacktastical | CC BY-SA 4.0 |
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| Jan 18 at 18:58 | history | answered | hacktastical | CC BY-SA 4.0 |