Justification for the need for high voltage/power Class D amplifiers

Hi,

I am doing a study in Class D power driver. Currently, reviewing the
market feasibility. However, I have some questions.

1) What is the purpose of designing high voltage Class D power driver
if it is not for portable devices? Isn't a Class AB enough to meet
such requirements?

2) In what ways and why will Class D replace Class AB in the future?

I understand that Class D has the following advantages:

a)Compactness of overall design;
b)Lower heat dissipation/high efficiency;
c)Cost saving
d)Energy saving

Are there any other compelling reasons that Class D will replace Class
AB?

Appreciate any help.

Thanks.

 

One application is high power pro audio gear. Once you get into the 1kW+
range it starts making better sense.

It won't.

There is little correlation between physical size and method. In fact,
Class D usually requires more complicated circuitry to obtain decent
performance.

There aren't any compelling reasons for class D. Its just another method
that had advantages in some situations, and disadvantages in others.
Class D wont replace the other methods it is used in addition to the
other methods.

If your doing a study your supposed to identify the disadvantages as
well as the advantages. You seem to be assuming the Class D is god's
gift to amplifiers from the outset. It isn't.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

 

Off hand it smacks of homework.
They're probably also indoctrinating 'em that digital will always replace
analogue and that nothing worthy is designed below 10GHz and that microsoft
is the best thing since sliced bread.
regards
john

 

Matthew,

The efficiency is better but a close second is crossover distortion. True
Class D has no cross over distortion also the design is more simple over
the temperature range because one fet is switched full on or off.

Ray

 

Matthew,
Correction to my post. The other advantage to a switcher vs AB is the
voltage rating of the switch and size of the out put transformer along with
the power loss due to the bias current in the output transformer.
a very good pwm can be made with two 555s and one IR2111. driving two
totempole N fets.

Ray

 

Good article in EDN, Nov 11, 2004 called "Getting
the most from Class D multichannel audio amplifiers".
Mentions one aspect that I had not considered about
class D... they have *no* power supply rejection at all!
Whatever trash comes through the supply, comes out
the output because all these amps do is switch the
supply off and on.

I guess there are still a few legs (ie feedback) left to linear
circuits after all. <g>

Best regards,


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

 

This was made clear to me when I built a Class 'D' amp for a signal with a
constant amplitude of 121.6 Volts P/P and which had to degrade linearly down to
56.6 Volts P/P as the current went from 100% (nominal) to 300% of (nominal) and
shut off if the load increased further. As load current increased there was a
corresponding increase in ripple on the signal. The circuit was complicated by
the need to put 'ripple stripers' on both polarity outputs. MESSY!