Inverted Shunt Regulator - Tube CAD Journal

January 2001 ^^ TUBE CAD JOURNAL ^^
Volume 3 Number 1 >>
From this viewpoint, the ground is the signal
and any deviation from that signal at the output
is countered by the feedback until it is
eliminated.
So which is better? Better for what? Better for
needlessly heating the room? Better for using a
battery power supply? Better for isolating
delicate signal currents in an amplifier? Each
finds its own place in tube audio designer's
palette. My preference is to use kind for kind: a
shunt regulator for steady average current draw
circuits, for example Class A amplifier stages,
and a series regulator for variable current draw
circuits, for example Class AB, B output stages.
An Inverted Shunt Regulator
The usual topology is to place the series
resistor in between the load and the B+
connection, just as a choke would normally be
placed in a non-regulated power supply.
However, just as the choke can be placed at the
bottom, between load and negative power
supply, the shunt regulator's series resistor can
be placed at the bottom as well. What advantage
can be wrestled from this inversion? In the case
of the choke, the increased safety of moving the
choke closer to ground stands out as a large
advantage. With the choke at the top, its winding
sees the full B+ voltage and should the wire's
insulation breakdown, the voltage difference
between the B+ voltage and the chokes ground
level metal structure will make for some
fireworks. But when the choke is placed at the
bottom, the choke's winding and case only see
the voltage developed across the DCR of the
choke plus the ripple voltage, a total of 30 volts
let's say. Now, the insulation should not
breakdown and even if it did, 30 volts makes for
much smaller sparks.
+400vdc
0vdc