Electronics > Beginners
Filtering PWM to smooth DC
Rapsey:
Yes, I took the ESR or the inductor into account. The reason for using an inductor is that compared to a resistor, it seems to do a much better job of slowing down the capacitor charging while having less ESR, thus getting closer to 12V. The resulting ripple is more like a sine and less like a sawtooth.
R1 is indeed dissipating a lot of power in edit 4 but only during the off-portion of the PWM cycle. That way it does not hamper the max voltage at 100% duty cycle but the lower the duty cycle, the more it reduces the average output voltage. This way it's not like 10% duty cycle results in 90% output voltage.
An additional PWM circuit was my next option to explore. I haven't been able to find any PWM IC's that are also PWM-controlled (hardly surprising), they all seem to be voltage-controlled. Which brings me back to my original problem of how to convert the 500Hz PWM to a linear scaling voltage.
Do you have any examples of that diode+capacitor rectifier? I thought these things were for AC-to-DC conversion. Not entirely sure what there is to rectify when the wave function has no negative portion...
wraper:
--- Quote from: Rapsey on September 30, 2018, 07:18:54 am ---An additional PWM circuit was my next option to explore. I haven't been able to find any PWM IC's that are also PWM-controlled (hardly surprising), they all seem to be voltage-controlled. Which brings me back to my original problem of how to convert the 500Hz PWM to a linear scaling voltage.
--- End quote ---
Resistor + capacitor. What you've seen so far was not linear because pulling only to one side, not up/down and because of the load attached.
Rapsey:
--- Quote from: wraper on September 30, 2018, 10:33:00 am ---Resistor + capacitor. What you've seen so far was not linear because pulling only to one side, not up/down and because of the load attached.
--- End quote ---
I don't understand, without a load any DC supplied to the capacitor through a resistor would eventually charge it to 12V, regardless of the PWM duty cycle. What do you mean with pulling to one side vs up/down? It sounds like DC vs AC but that's probably not what you meant?
wraper:
--- Quote from: Rapsey on September 30, 2018, 02:55:36 pm ---
--- Quote from: wraper on September 30, 2018, 10:33:00 am ---Resistor + capacitor. What you've seen so far was not linear because pulling only to one side, not up/down and because of the load attached.
--- End quote ---
I don't understand, without a load any DC supplied to the capacitor through a resistor would eventually charge it to 12V, regardless of the PWM duty cycle. What do you mean with pulling to one side vs up/down? It sounds like DC vs AC but that's probably not what you meant?
--- End quote ---
It means pulling to GND as well, not leaving open circuit.
Gyro:
It sounds like a really fun discussion but are you sure you're not going a little OTT just to stop a fan whining? :)
Presumably the PWM changes in response to some kind of temperature sensing, so as long as the fan control range is able to keep up, then is there a problem?
Just asking. :)
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