High speed comparator

[Jan-Peter]

Originally posted by Ouroboros
For a self oscillating design that I'm doing for my employer, I'm using a TLV7239 which is fast, very low power, and also has a low input offset voltage.

If you are using a UCD design with dc coupling (like the Hypex designs have), then it is often forgotten that the input offset voltage of the comparator will be multiplied by the gain of the amplifier. It is all too easy to find over 100mV of dc offset at the output of the amplifier. This is negligable when driving loudspeakers, but my designs are for driving step-up output transformers for 100V line loudspeakers. These transformers have very low primary dc resistance, so 100mV of output offset can cause almost 1A of dc to flow in the primary, which can cause problems with toroidal transformers. A slight redesign of the basic UCD circuit with ac coupling can drop the dc gain to unity, while keeping the desired gain at the audio frequencies. In this case the output offset will only be slightly greater than the comparator offset.

Hypex have an app-note showing how a dc-servo can be used with their amplifiers to reduce the dc offset when driving an output transformer.

Indeed...this application note is ONLY for customers who use our UcD modules......

Not for customer who design their own Class-D products, we are not a free design house......

Jan-Peter

[Ouroboros]

Apologies for mentioning this Jan. (Although of course the use of dc-servos in class-D amplifiers is a well-established practice).

[ak_47_boy]

Originally posted by ak_47_boy
What do you look for when choosing a comparator? What about the LM306, TL3116, or TL3016?

So just because an op-amp or comparator is fast does not mean is is good for audio? Can someone explain to me what to look for. Sorry for bumping a somewhat old thread but i don't think this question is worthy of a new thread.

[ChocoHolic]

I started to play around with the LT 1711 and must agree... they are fast! Sloping within 2ns, and just 5ns delay. Also they allow +/-5V even for the output stage (if needed). They really act like in the data sheet! Absolutely amazing stuff.
Pretty good, except the SMD micro-mini-killer-pitch ....

[Tahmid]

Hi,
You could give Maxim's MAX22427 a try. Its fast and very reliable.

[Tahmid]

Hi,
Texas Instruments (formerly Burr Brown) produces MAX22427 under the name of OPA22427.

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