Re: multi-supply audio amp

john larkin <JL@gct.com> wrote:

On Wed, 8 Jan 2025 00:09:51 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
 

john larkin <jl@glen--canyon.com> wrote:

On Tue, 7 Jan 2025 22:27:37 +0100, Lasse Langwadt <llc@fonz.dk> wrote:
 

On 1/7/25 20:19, john larkin wrote:

I recall that there was an audio power amp topology that used two
transistors and two power supplies for each polarity output. Low
voltage swings used a low voltage supply but it cut over to a HV
supply for big swings, with diodes or something.
 
What was that called?
 

 
class-G (or H) depending on who you ask
 
https://sound-au.com/articles/class-g.htm

 
Cool. Thanks.
 
I need a power amp that runs near ground most of the time but spikes
to higher output voltage occasionally. And runs 4 quadrant.
 
I have a switcher design that looks good, but it's slow. 

 
Our TEC controller is like that, 4-quadrant asymmetric bridge, but current
mode. Too slow for audio, but that’s mostly parts values.
Cheers
 
Phil Hobbs

 
My current design uses a TI DRV8962, which is a quad halfbridge. I'm
using two sections to make a full-bridge bipolar class-D amp. It's a
very cool chip, with lots of current limits and suppy lockouts and
stuff.
 
One of those chips would make a nice 200 watt stereo amp.
 
But they only recommend running it at 200 KHz max. I could go a lot
faster with a class G/H linear amp, of course at the cost of a heap of
complexity.

Looks like a nice part for reasonably noise-tolerant applications.  Class H
allows us to use Class-A noise rejection with very good efficiency.
Normally VDD is less than four tenths of a volt more than the differential
output voltage.

 
Why does a TEC driver run in the goofy quadrants? Does the cooler ever
act as a generator?

Yup. Not a very good one, of course—max thermodynamic efficiency of a
couple of percent. 

 
I'm designing a dummy load that looks resistive+inductive, like a
solenoid, so it usually runs in the odd quadrants, where the user is
pushing power into us. Sometimes we pretend that we stored some energy
and have to return it.

Cheers

Phil Hobbs



--
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics