Single supply bridge UcD, referencing the signals

[Anthony C Smith]

HAs anyone tried using the HIP4080A; this has the comparator inside, the performance doesn't look to bad (the comparator that is) giving a true single chip amplifier!

[Ouroboros]

The HIP4080 only has a max peak output current of 2.5A, so it's limited in its output power. It also doesn't have any internal current sensing circuitry.

[luka]

Search, then ask

http://home20.inet.tele.dk/audio/HIP...p4080_soda.htm

[Anthony C Smith]

Originally posted by Ouroboros
The HIP4080 only has a max peak output current of 2.5A, so it's limited in its output power. It also doesn't have any internal current sensing circuitry.

I wasn't suggesting just the IC, I meant using a H bridge of fets from it.
I think I may give this a try as I can butcher one of my VA amplifiers which uses the 4081 and 319 comparators in a class BD solution.
Hmm got me thinking!!

[Ouroboros]

It should work well, and you could do a 'UCD style' amp if you wanted as both the + and - inputs of the comparator are accessible.

Pity that's not also the case with the IRS2092. If this had the comparator connected differently internally, then this also could be used for a UCD amp, but as it stands it isn't a great deal of use for this, even though it's ideal for a pre-filter feedback sigma-delta self oscillating design.

[Anthony C Smith]

I followed Luka's link; the guy opted for external comparator because of noise and "so it starts up silently when dis is removed"- checking the 4080a data sheet the comparator is not affected by the DIS pin so I fear other issues in the layout and decoupling were at the heart of the problems.
Still worth a quick try in UCD like mode- you never know!

[Cro maniac]

It seems that TL3016 I planned to use as modulator doesn't have rail-to-rail input (it is limited to 1,25-3,6V common mode input voltage when powered from 5V), so now I'm searching for another single supply fast differential comparator with r-r input.

[Ouroboros]

You don't need R-R input common mode. If you arrange your resistor values so that the self-biasing condition (allowing for the fact that the output of the amplifier will sit at an average voltage of Vsupply/2) will be at 2.5V (if your comparator supply voltage is 5V) then the actual signal swing at the input to the comparator will not go anywhere near the rails. The signal swing at the comparator input will be the audio output swing divided by the open-loop gain plus a small amount of the switching waveform. (Open loop gain is of course difficult to quantify in a UCD-style self-oscillating amplifier).

[Cro maniac]

The signal swing at the comparator input will be the audio output swing divided by the open-loop gain plus a small amount of the switching waveform.

Isn't the open loop gain in ucd proportional to attenuation of the output filter at switching frequency ?

Can you please explain what you mean ?
I don't understand why would signal at the comparator inputs be audio output swing divided by the open-loop gain. If I power my amp from 60V and set gain of 12 on each side I'll have 2,5V on both inputs of the comparator at idle. But what when output goes near the rails ? Won't I have 5V at one input and 0 at the other ?

[Ouroboros]

Yes, the open-loop gain is effectively that.

Regarding the swing at the actual input to the comparator. Here it is the O/L gain that matters. Just think of an op-amp. The actual differential swing directly at the op-amp input is the voltage at the op-amp output divided by the O/L gain of the op-amp at that particular frequency. In an op-amp inverter, normally the summing junction is considered as a 'virtual earth'. In reality, there is a signal at this point but it is tiny, and is the output divided by the O/L gain. In a bridged UCD circuit with differential input and differential feedback paths, then a similar state exists regarding the comparator inputs. If you SPICE it you'll see a fairly large component of the switching frequency (resulting from the post-filter ripple, and the NFB path attenuation) but a low component of the audio signal.