Class D amp draws equally from + and -?

[eem2am]

Hi

Does a Class D amp, with a split supply, draw equal current from each half of the split....on average, over time?

[454Casull]

Should be the same as any other amp in that regard, no?

[Eva]

If input signal is symmetrical and the load is linear, yes.

[ssanmor]

Eva is right but I think that's not what you were asking. Most Class-D implementations draw more constant current from the negative rail due to the fact that the driver stage is fed with reference to the negative rail and the internal regulator usually takes power from GND.
For example, a no-signal current draw of 30mA from the positive rail and 80mA from the negative rail is not uncommon.

Our BP4078 was an example (with numbers similar to that), but other common modules behave the same. Our Sonora series are much more balanced in idle consumption. Anyway, it is not a problem provided that the PSU has proper cross-regulation of both positive and negative rail. Otherwise you can end with a +65V rail and a -55V rail only due to this fact if several modules are connected to the same PSU, specially if it is switching.

As for large signal, yes, the current drawn from each rail should be the same for same (different sign) inputs.

[eem2am]

Thanks to all.

Though i am worried now that a guitar amplifier may in fact be a non-linear load at times and give problems with drawing unequally from each of the rails.?

You see, our SMPS is one smps with the split rails cross regulated with weighted feedback from each....but if one is more loaded than the other in large signal, the cross regulation wont be good enough

[ssanmor]

Our first SMPS suffered the same problem due to different constant current draw as explained above, although in practice it was not important, you could get a couple of volts difference between + and - rails. We solved this years ago by using magnetic coupling between rails. Now you can draw nothing from a rail and a couple of amperes from the other and voltage remains virtually the same in both rails, even using one single feedback for the total voltage.
However, you should have no problem due to non-linear loads.
If you are interested, have a look at our SMPS at www.coldamp.com or drop us an e-mail.

[djk]

Music is asymetrical.

If you have problems with supply pumping, consider a bridged design.

[ssanmor]

Supply pumping is a different problem, related to low frequency-high power signals on low loads. In that case, a bridged design does help a lot, but the main problem is cross-regulation between rails per SMPS design.

[eem2am]

in a full-bridge smps, wit +50v and -50v rails, we oviosly have two output inductors.....would you completely couple both of these...or just couple a small bit of this inductance?

[AP2]

Hi,
Not all amp D class have symmetrical output current.
This depeand also from driver architecture,modulator and smps.
One smps that is developped precise for audio is a DPS-500 (sorry if I say this) is one that have linear regulators with two feedback.
No pwm use.
Regards