Hello,
I am currently making a 2.1 system that is self-powered. I have built a previous system with class AB amplifiers, which have awesome power supply ripple rejection, however class D is another story. Right now I have a 200VA transformer full-bridge rectified to about 10uF of capacitance and I'm still getting about 60Hz hum at the speaker output. I know this is because of the switching properties of class d.
My question would be, if I take the v+ (the amp is single-supply tpa3118d2) going to the amp-chip and run about 4-7 lm317's in parallel to the chip from my ps and drop a little over the minimum voltage for the lm317 would my noise problem be solved a little?
Would also adding a bank of caps on the other side of the lm317 help too?
Thanks!
I am currently making a 2.1 system that is self-powered. I have built a previous system with class AB amplifiers, which have awesome power supply ripple rejection, however class D is another story. Right now I have a 200VA transformer full-bridge rectified to about 10uF of capacitance and I'm still getting about 60Hz hum at the speaker output. I know this is because of the switching properties of class d.
My question would be, if I take the v+ (the amp is single-supply tpa3118d2) going to the amp-chip and run about 4-7 lm317's in parallel to the chip from my ps and drop a little over the minimum voltage for the lm317 would my noise problem be solved a little?
Would also adding a bank of caps on the other side of the lm317 help too?
Thanks!
Try increasing the value of the 10uf cap to 470uf or higher and see if that clears up your hum problem. Most of the bridge rectifiers I have built or seen have bigger filter caps than 10uf.
I would suggest a MUCH higher capacitance.
What is the average current drawn from the power supply?
Since i = C dv/dt for an ideal capacitor and you can say that dt is approximately 1 / 2•fmains, you can pick what dv you want to tolerate and solve for an approximation of C:
C >= i / (2 dv fmains)
For example, if you pull 6 amps and you want 0.5 volt of 120 Hz voltage dip ("ripple") after the capacitance, then
C >= 6 / (2•0.5•60)
C >= 0.1 Farad
C >= 100000 uF
You don't yet know what dv value would solve your problem but I would start with 10000 uF (or whatever you have at hand) and go up or down from there, to see what works.
The regulators would not work with a too-small capacitance, because your ripple voltage amplitude would be so large that the input voltage for the regulator(s) would drop below the desired output voltage 120 times a second. Regulator input voltage must always stay above the desired output voltage PLUS the dropout voltage spec from the regulator datasheet, or the output gets very ugly.
What is the average current drawn from the power supply?
Since i = C dv/dt for an ideal capacitor and you can say that dt is approximately 1 / 2•fmains, you can pick what dv you want to tolerate and solve for an approximation of C:
C >= i / (2 dv fmains)
For example, if you pull 6 amps and you want 0.5 volt of 120 Hz voltage dip ("ripple") after the capacitance, then
C >= 6 / (2•0.5•60)
C >= 0.1 Farad
C >= 100000 uF
You don't yet know what dv value would solve your problem but I would start with 10000 uF (or whatever you have at hand) and go up or down from there, to see what works.
The regulators would not work with a too-small capacitance, because your ripple voltage amplitude would be so large that the input voltage for the regulator(s) would drop below the desired output voltage 120 times a second. Regulator input voltage must always stay above the desired output voltage PLUS the dropout voltage spec from the regulator datasheet, or the output gets very ugly.
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Here I am months and months later, having figured out all the problems on my PCB.
Firstly, I mis-typed my question at the beginning, I had 10mF of capacitance on the rails, which I later increased to ~25mF.
Turns out the hum was a bad value I had chosen for one of my lm317 active filter power supply caps.
I do thank you for your replies though.
Firstly, I mis-typed my question at the beginning, I had 10mF of capacitance on the rails, which I later increased to ~25mF.
Turns out the hum was a bad value I had chosen for one of my lm317 active filter power supply caps.
I do thank you for your replies though.
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