Handbook for Sound Engineers

678 Chapter 19

lated supplies may be simple shunt or series regulators
with 1–3% regulation or high gain supplies with
0.001% regulation and 0.001% ripple.

Power supplies may be connected in parallel, but to
protect the supplies, diodes are connected in the positive
lead of each power supply. When the diode is in its
normal conducting mode, it must be capable of with-
standing the short-circuit current of its regulator. The
piv rating of the diode must be equal to or greater than
the maximum open-circuit potential of the highest-rated
power supply.

Regulated power supplies can also be connected in
series if certain precautions are observed. The isolation
voltage rating of the individual power supplies must not
be exceeded, and the power supplies must be protected
against reverse potential. Diodes are connected in the
nonconducting direction across the output of each
supply unit. These diodes will start to conduct the
instant a reverse potential appears, providing a path for
short-circuit current. If possible, the regulating circuit
for one supply should be connected as a master and the
other as slaves. The voltages of the supplies do not have
to be the same.

All regulated supplies have a reference element and
a control element. The amount of electronics between
the two elements determines the quality and regulation
of the supply, Fig. 19-7.

The reference element is the unit that forms the foun-
dation of all voltage regulators. The output of the regu-
lated power supply is equal to or a multiple of the
reference. Any variation in the reference voltage will
cause the output voltage to vary; therefore, the reference
voltage must be maintained as stable as possible.

The control element is that unit that maintains the
output voltage constant. The regulator type is named
after the control element—namely, series, shunt, or
switching, Fig. 19-7A, B, C. The control element is an
electronic variable resistor that drops voltage either in
series with the load or across the load. Control element
configurations are shown in Fig. 19-8.
All regulated supplies draw standby current, which is
the current drawn by the power supply with no output
load. The input voltage to regulated supplies is filtered
dc. The smoother the input voltage is, the smoother the
output will be. The capacitor C 1 shown in Fig. 19-7A is
used to smooth the output or reduce ripple.
The comparison amplifier constantly monitors the
output, reducing ripple because the reference voltage is
smooth dc and the output ripple voltage appears to the
comparator like a varying load. The regulator or pass
transistor attempts to follow it, reducing ripple.

A constant-voltage regulated power supply is

designed to keep its output voltage constant, regardless

of the changes in load current, line voltage, or tempera-

ture. For a change in the load resistance, the output

voltage remains constant to a first approximation, while

the output current changes by whatever amount is

Figure 19-7. Regulated power supplies.

Pass

element

Reference

voltage

Transformer & rectifier

C 1 C 2

C 1 C 2

C 1 C^2

Comparator

amplifier

Pass

element

Pass

element

Transformer & rectifier

Transformer & rectifier

Comparator

amplifier

Constant current

comparator

amplifier

Current

reference

Current

reference

Voltage

reference

Constant voltage

comparator

amplifier

A. Block diagram for a constant voltage

regulated power supply.

B. Block diagram for a constant current

regulated power supply.

C. Constant voltage constant current regulated

power supply with automatic crossover

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