Hi,
I have a 12V / 2 A power supply. This must power a TPA3136 class D amplifier and also a TPS54302 DC-DC converter (5V/1A output). I'm afraid that the ripple generated by the converter will enter the amplifier, through the common supply. Is it possible to somehow isolate these 2 loads so that they influence each other as little as possible ? An LC filter or something ?

 

Yes, You can use a cascade of a common mode choke and a differential mode choke along with appropriate "Y" capacitors to achieve the desired result. This is quite common in avionics applications.

 

Ca you please show me an example ? I don't know what a "common mode choke and a differential mode choke along with appropriate "Y" capacitors" is, as I never worked with them...

 

This is my schematics...

 

The entire assembly will be powered by an SMPS source, because we are no longer in 1990 using classic iron transformers. Then, as if that were not enough, a DC converter also draws from that power supply. I would like to somehow isolate all of these from each other...

I thought about putting an LC filter on each consumer. And I started calculating the values for the amplifier. We already have a capacity of 200 uF that cannot be changed as recommended in the datasheet. Then, L = 33uH is needed. So far it is more or less ok. But! LC filters must be damped, because they generate an amplitude peak just before they start to attenuate. For this, an RC snubber in parallel with the C of the filter is recommended. But! The C in the snubber must have a capacity at least 3-4 times greater than that in the filter. So the result is a 600-800uF capacitor, which is absurd!

Another option would be to give up the snubber and put a resistor in series with the coil, which together with its wire resistance will result 0.3 ohms, and the 2 x 100uF capacitors should have at least 0.15 ohms ESR. But at 3A peaks of the amplifier I will have a voltage drop of 1V and dissipated power of 3W, so I have to put 5W resistors, which is again absurd!

So no matter what I do, it still doesn't work... Is there anyone who could help me with this, to somehow figure it out? Maybe I'm missing something...

 

Ca you please show me an example ? I don't know what a "common mode choke and a differential mode choke along with appropriate "Y" capacitors" is, as I never worked with them...

A series of video lectures by Robert Bolanos from a series on Flyback Converters, parts 9-12 is the best description of what is going on that I know of. There is too much information for a forum post. Here is a link to part 12

Analysis and Design of a Flyback Converter; Part 12 Input Filter

Watch part 12, then refer back to parts 9, 10, & 11 for more background information.

 

Is it possible to somehow isolate these 2 loads so that they influence each other as little as possible ? An LC filter or something ?

Try diode isolation.