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Workhorse 18th January 2006 01:41 AM

AD Vs BD Modulation in Class-D
Hi Everyone,

Whats your opinion regarding AD Vs BD Modulation in Class-D Bridged amps with External Clocked designs....Pros & Cons... 2 level & 3 Level PWM.......any helping great ideas.....

K a n w a r

Workhorse 19th January 2006 12:51 AM

:confused: :confused: :bawling: :bawling:

mirlo 19th January 2006 12:59 AM

Perhaps noone answered because they aren't familiar with the terms.

Here is a reference for anyone interested ...

-- mirlo

Workhorse 19th January 2006 01:27 AM

Thanks Mirlo...

vectorplane 29th January 2006 05:50 AM

I remember having seen somewhere some description of commercial design which used 3-level ( BD ) modulation.

When the audio signal was positive, the PWM switched between positive polarity and ALL OFF switches, rather than between positive and negative. With zero input signal, the switches were all in high impedance state, instead of alternately hitting both rails at 50% DC. It seemed to make more sense, also maybe lower DC offset at no signal, but it may be more complex to implement.

I can't recall what manufacturer was providing this info. I'll look through my collection of bookmarks to see if I can find it.


Wiebel 29th January 2006 11:38 PM

As I have not been aware of the AD Modulation I am surprised about it in several ways.
I am used to the "normal" analog opamp based amps (building headphone amps), so the AD Modulation comes more "natural" to me. Some points that comes to my mind:
You can half the suply Voltage with BD due to the use of the H-bridges. Things like this simply have to come with some drawbacks, the H-bridge adds some extra pice of hardware in the signal path which I would consider as a subotimal,also I could imagine that the zero transits may cause some problems. As mentioned I like Headphones so another bad thing comes in mind, the common ground which is simply impossible with BD design.

As I want to build some active speakers (possibly with additional headphone out) this informations comes in very handy, thanks for this enlightenment.

I would prefer AD design, now that I know of it ;), if the dimensioning of the PS is not a big issue.

Then again I'm very much a newbie to audio diy and I may be completely wrong.

Workhorse 3rd February 2006 10:10 AM

No one knows or there's some confusion
It seems that No one knows about my questionarrie....I just asked about Pros/Cons of 2 types of H-Bridge amp in which BD mode has Switching frequency in phase and AD mode has switching Frequency out of phase...thats all.

Hoping this time its little bit more simpler.....
K a n wa r

vectorplane 3rd February 2006 01:18 PM

Sorry, Kanvar

I think your topic may be a little over the head of most members, and everyone reading this knows less than you do about it.

You might try asking Eva, by interjecting an off-topic post in one of the SMPS forums she monitors. (Class D is not too different from SMPS).

You might also try emailing tech guys at a semiconductor house like, who actively promote class D design these days. Make sure to include a schematic or a mention that you use IR MOSFET part numbers in your design.
(make sure the diodes are IR part nrs also, not MUR...)

They're usually good with replying, and some of those guys feel so passionate about design, once you get them started, you can't stop them.


Workhorse 3rd February 2006 01:28 PM


Now I would Try these IRF babes...and get my chunk of info from them...... :D :D ;)

K a n w a r

vectorplane 4th February 2006 04:48 AM


Originally posted by Workhorse

Now I would Try these IRF babes...and get my chunk of info from them...... :D :D ;)

K a n w a r

Hey, Kanwar, when you do get a reply, I'd be curious to know the answer too...


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