amplifiers UcD / Hysteresis
There has been much talk
about the UcD amplifiers designed and patented by
Putzeys. Philips has made an application note, that in details describes the
circuit, and workings, and a demo board can be ordered. At the Class-D section
DIYAudio there has been several threads about the
UcD patent and the
Philips UcD Application note some of the more notably ones being by
johanps (probably forgot some, sorry).
Modules based on UcD are
developed and sold by Hypex.
The UcD circuit is
beautifully simple yet very powerful and in all a stroke of a genius. It uses as
few as discrete 14 transistors, and a handful of passive components.
The circuit is basically a
power comparator feeding the load through a 2. order passive filter. Feedback is
taken after the filter, which causes the oscillation and thereby modulation of
The circuit can be divided
into three blocks. The first stage is the comparator, which works from the PSU
rails, eliminating the need for a lower voltage PSU for the input.
Second stage is the power
stage. Here the MosFet drivers are made from discrete components, forming
two identical drivers, driving high and low switch. The lower driver is feed
from a 12V supply, but the upper driver supply is floating in order to provide
the needed Vcc+12V to properly switch the upper Fet.
Third stage is a second
order filter which demodulates the signal. Feedback is feed through a lead
network back to the comparator.
Read more on Hypex
Technology page for further information.
The basic circuit can be
adapted to work as a pre-filter hysteresis design, with very few alterations. As
I would like to investigate the difference in sound from these two quite
different working methods, I have decided to build a small construction which
can be configures for both. The intention is to build 4 amplifiers and try out
the two designs in a stereo A/B test.