I think the problem is that the burst freq is dependent on the current drawn so it's hard to select what to put on the data sheet. The higher current the less it bursts, and as the current becomes high enough it never bursts b/c it needs to continously switch so the output doesnt droop.
So I dont think burst fequency is mentioned in data sheets, only the switching frequency. Vicor, Excelsys, and other high-end smps manufacturers might have such info, but I doubt it.
In my experience burst mode is only used by cheap single chip flyback converters of less than 100W. If you use a decent half bridge or similar converter with good open loop regulation burst mode is completely unnecessary and I don't know of any control chips for such converters that use it (queue damming evidence to the contrary).
IMOP the reason for the shortage of commercial products is due to the extremely expensive regulatory process required before such products may be sold on the open retail market and don't forget that all such power supplies now require the additional cost and complexity of power factor correction. Simply insufficient market to justify the investment.
IMOP the reason for the shortage of commercial products is due to the extremely expensive regulatory process required before such products may be sold on the open retail market and don't forget that all such power supplies now require the additional cost and complexity of power factor correction. Simply insufficient market to justify the investment.
Back in the mid 1980s when I was designing digital video broadcast gear which of course had analog I/O, we were forced to run the analog input and output sections with linear supplies. The SMPSs in those days were really rough noise wise. NTSC video is DC to about 6mhz. And those monsters used F-TTL to work at video speeds. 200amp +5volt power SMPS's were quite common.
Today, it's not really a problem anymore.
Today, it's not really a problem anymore.
With my latest project amp (Class AB) I started with both channels running off of regular transformers and rectifiers but then switched the left channel to run off of two new economical SMPS as a test. I was expecting it to turn out to be some sort of fire extinguisher class experiment. However it seems to work fine. I am struggling to identify an audible difference. They are cheap 24V 10A 240W SMPS using TL494, drive transformer, NPN switches and regular single LC after the rectifiers. When I opened it up I was a bit surprised how old the design looked for a brand new supply. Clean and neat looking, just old technology. They have an adjustment pot and both are running at 27.6V. (Which is ok for this experiment since I have 4 Ohm speakers.)
Can anyone advise on what to listen for or look for? So far I have not noticed anything from moving back and forth between the two speakers running the two identical amps with the different power supplies.
After the first couple of days I added a second LC. The channel with the SMPS did not change as far as I can tell. And the SMPS channel still sounds like the channel with the regular transformer and 22,000uF of capacitance. My meter reads about half the AC signal on the SMPS output (relative to the old fashioned supply).
I was hoping/expecting to be able to notice something (either positive or negative) from this experiment.
Can anyone advise on what to listen for or look for? So far I have not noticed anything from moving back and forth between the two speakers running the two identical amps with the different power supplies.
After the first couple of days I added a second LC. The channel with the SMPS did not change as far as I can tell. And the SMPS channel still sounds like the channel with the regular transformer and 22,000uF of capacitance. My meter reads about half the AC signal on the SMPS output (relative to the old fashioned supply).
I was hoping/expecting to be able to notice something (either positive or negative) from this experiment.
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You are testing in essence a DC power supply. You could try using the tip and barrel method to check the noise and ripple of the power supply output on a scope. Perhaps while it's under load (see the method described below). The tip and barrel method is used to avoid the capacitance of the ground test clip on the scope lead. The probe has to be as close to the source as possible.
Be careful where you put that barrel of the probe though, it's connected straight to mains earth and will short any power lines directly to ground, probably destroying the DUT. Using an isolation transformer would help prevent this.
Measurements like this are tricky, the noise/ripple is small and will be affected by where you place the probe.
In reality, if both the power supplies are adequate and have comparable output voltages then you shouldn't be able to hear any difference.
In order to test it objectively, then using a 4, 6 or 8 Ohm power load resistor (instead of a loudspeaker), and driving the amp using test tones and sweeps, viewing on an FFT, you can check the SNR, THDN, linearity etc. Normally this is done on an audio analyzer such as AP or dScope, but you can get an idea using a standard audio interface and suitable software on a computer. You will need to take care connecting an amplifier directly to a sound-card though, some interfacing or protection for the sound-card inputs will be required (the AP can handle the higher voltage, so there is no such protection shown in their diagrams).
There used to be a good PDF from Audio Precision on just this but I can't find it. This link will at least show you what I'm trying to describe above:
https://www.ap.com/blog/stereo-power-amplifier-test/
One thing I should point out - an SMPS generally has closed loop feedback to regulate the output voltage. Loop crossover frequency will generally be on the order of 1kHz or greater. This, and the higher refresh rate of an SMPS (>60kHz as opposed to 120 Hz), will result in less bass sag, and can enable using moderate local bypass caps at the amp PCB rather than a huge bank of filter caps.
If you configure the output regulation characteristic as constant power (it's easy to do a rough approximation of this), the output will sag rather than shut down if presented with an extreme overload. Of course you also need to properly size the power supply for the output to be delivered. For instance, if you are shooting for 100W RMS per channel, you will actually need 140 X2 or 280 watts from your power supply to handle the sine peak power.
Hello, do you mean the ground from the AC side with the ground on the DC side?
Or do you mean the combined ground of the two smps power supplies with the minus rail of the DC side?