Hi, I’m aware of the fact that this topic has been already treated many times on this forum, but I wart to ask this question again. Is it worth to add capacitance to a symmetric SMPS? A member of this community some time ago told me that caps, for example, may partly solve the rail pumping problem of class d amps feeded by SMPS. Anyway, how should caps be connected to the power supply considering the two rails?
Many thanks in advance,
Gaetano.
Many thanks in advance,
Gaetano.
A well designed SMPS samples the output voltage at the root frequency, sometimes 350kHZ and does not require tank capacitors to keep the output stable. To add any extra is not a good thing except as decoupling.
Most cheap fleabay power supplies use voltage sampling to control the drive to the power supply but get it wrong and can produce a pulsing effect as it thinks it is being over loaded and they stumble producing ripple.
One gets what one pays for, if one is lucky!
Most cheap fleabay power supplies use voltage sampling to control the drive to the power supply but get it wrong and can produce a pulsing effect as it thinks it is being over loaded and they stumble producing ripple.
One gets what one pays for, if one is lucky!
Thank you for your kind answer. I built a power amp using Connex Electronic Smps800re and ljm l25d class d modules. Reading here and there, I found some infos about the potentially negative effects of class d rail pumping and that adding caps to smps could act as a “filter” for this kind of phenomenon. Thus from this, my idea to add one 125v 10000 uF cap per supply rail. Could this be right e/or useful?
Gaetano.
Gaetano.
In my experience, that will not be beneficial with a SMPS. Ideal with a linear PSU though.
If your amplifier is pumping, the PSU should be capable of producing the power and especially current required, to easily supply the amplifier. If you require large tank capacitors, there is a problem with the power supply.
If your amplifier is pumping, the PSU should be capable of producing the power and especially current required, to easily supply the amplifier. If you require large tank capacitors, there is a problem with the power supply.
The problem with adding capacitance on the output is the power up loading of the SMPS.
You can get to the point where it thinks there is a short on the output at power up so goes into protect mode.
You can get to the point where it thinks there is a short on the output at power up so goes into protect mode.
l25d amplifier with Power supply +/- 70v of how much current is needed to pull out 250watt of power ??? I don't understand how to size the transformer or smps power supply .... what is the calculation to know the current needed ??? and how to size fuses protection ????
It depends...
For amplifiers that draw a constant current (Class A), I like to use an RC or LC combination between the SMPS and the amp, with a large C. The resistance of the R or L should be enough to limit the inrush current to the C at startup, so that the SMPS does not go into protection mode. The LC or RC will also do a good job to reject any high-frequency noise from the SMPS.
For amps that do not draw constant current, an RC or LC will modulate the current variation to the rail voltages. Not good. You could insert a slow-start / inrush limiter between the SMPS and the big C to reduce the inrush current at startup. Once the C is charged to full voltage, the slow-start / inrush limiter gets out of the way, and tadaa -- you have an SMPS running with a large cap! I have never tried that, though, so I can't say if that's any good.
For amplifiers that draw a constant current (Class A), I like to use an RC or LC combination between the SMPS and the amp, with a large C. The resistance of the R or L should be enough to limit the inrush current to the C at startup, so that the SMPS does not go into protection mode. The LC or RC will also do a good job to reject any high-frequency noise from the SMPS.
For amps that do not draw constant current, an RC or LC will modulate the current variation to the rail voltages. Not good. You could insert a slow-start / inrush limiter between the SMPS and the big C to reduce the inrush current at startup. Once the C is charged to full voltage, the slow-start / inrush limiter gets out of the way, and tadaa -- you have an SMPS running with a large cap! I have never tried that, though, so I can't say if that's any good.