Question: SMPS switching frequency with 41Hz Amp4

[DVBjunky]

Hi,

I am planning a small Tripath based Amp with the 41Hz Amp4 Kit but I am stuck with some questions about the SMPS?

1) I found some cheap MeanWell SMPS with 100W 24V 4,5 Ampere but with a switching frequency of 25 Khz. Is that too low?

Do I have to buy an SMPS with 50Khz, 63Khz or even 100Khz switching frequency?

2) Is 4,5 Ampere enough? 24V rail with 4 Ohm speaker? I have 89db effiency speaker.

3) Are they any cheap SMPS outhere? I Mean cheap and not Coldamp! :-)

Thanks and regards

Alan

[Eva]

Any switching frequency will be right as long as the SMPS does not leak substantial conducted or radiated EMI.

[nicoch58]

Hi

I use good MeanWell rs-150-24 with amp11,nice combo

[DVBjunky]

Does anyone used a notebook power supply with the Amp4 or Amp1?

90W - 20V - 3,5 Ampere - very small device, but I think the Ampere value is too low for 2 rails?

regards

Alan

[Corax]

@DVBjunky:

1) Any switching frequency above the audible frequency should be acceptable - harmonics are multiples of the switching frequency.

2) The answer is a little tricky: For 4 ohm loads Tripath recommends to parallel the outputs caused by the current limits of each channel but I guess the AMP4 isn't designed by Jan to have this option.
At 23.5V and a 6 ohm load you get just 23W (THD+N = 0.01%) at each channel, so a 108W SMPS (24V/4.5A) would do it easily. Assuming an efficiency of >80% you just need (23W + 23W) / 0.8 = 57.5W.

3) My source for cheap stuff is Pollin.de. You might give it a try. They have once in a while good bargains about SMPS.

Your last question) 20V is the lower end for the Tripath TK2050 chipset where it feels comfortable with the power supply voltage - however with further descreased output power. Therefore a 90W SMPS (20V/3.5A) will do a good job though.

Besides, If you connect a SMPS to the AMP4 make sure that the SMPS is stable when running on extremely large capacitiv loads (2x 10000µF(!!!) bulk capacitors). In case the SMPS acts a little "strange" (output voltage start to oscillate or, more likely, the SMPS just turns off when rapidly drawing current, because of current limit protection - if there is any protection scheme at all) you might have to remove the two 10000µF bulk capacitors.

[DVBjunky]

Hi,

thanks for the advice.

I missed the last Cheap Meanwell SMPS offers on Pollin last year. Damn...they were really cheap....a bargain.

Do you really think I have to remove the 2x 10000uF Caps or should I lower the value of the caps.......I am about to start the soldering, so it would take 2-3 weeks till I get there :-)

Tanks and regards

Alan

[Pafi]

Do not remove puffer caps, because then nothing will protect against supply pumping at reactive load!

[Corax]

@pafi:

In BTL (Bridge Tied Load) configuration you don't have any power supply pumping effect , except if the layout and wiring is badly designed - what I doubt if it concerns Jans skills.
That's by the way a reason why a design in theory and in simulations runs almost perfect but in a real and more practical design almost everything rises and falls with a good/bad PCB design.

Power supply pumping most likely happens at single ended amplifiers and at low output frequencies only - then the "revers" current must be "buffered" by the bulk(y) caps.

In a BTL design the "revers" current will be used by the other side of the bridge. Therefore it is necessary to have a short and low impedance track between the power supply tracks of the (+) and (-) output stage of each channel.


@DVBjunky:

If you're in doubt try to get a full datasheet of the SMPS your gonna use. In many (if not most) cases the manufacturer states the maximum capacitive load allowed for a stable and reliable operation of the SMPS.
In all my decades of experience in repairing/using/abusing SMPS I've seen just one SMPS which starts to oscillate as soon as the reactive load (capacity/inductivity) exceeds a certain level. Most likely current SMPS designs will limit the value of the max. output current. If the SMPS runs to long in that limit it expects a short at the output and just shuts down. How a certain SMPS will really react depends on the topology, the involved PWM controllers, and many other factors I won't list here.

[DVBjunky]

Okay,

I will try to get the datasheet of my mean well SMPS. Thanks.

regards

Alan

[Pafi]

Corax!

You are almost right, the strongest kind of supply pumping effect occures at SE amps, but not exclusively! Speaker load is not ohmic, but reactant (especially near resonance of woofer). Direction of energy transfer reverses for some part of period, and if it exceeds losses, then supply will start to increase, because most of SMPS-es are unable to sink current.