Radar System Engineering

SEC.14.8] VIBRATOR POWER SUPPLIES 581
itself of a booster armature winding and regulating field. A three-voltage
dynamotor is shown in the photograph of Fig. 14.24 and the circuit of a
dual-voltage machine is shown schematically in Fig. 1425. In any
multi-output dynamotor only one voltage can be regulated, but, except
in the event of very unevenly loaded circuits, the unregulated voltages
will closely follow the regulated voltage. Regulation can be handled in
several ways: (1) all output circuits have windings on the booster armature
although only one of them is controlled (Fig. 14”25); (2) only the
voltage to be regulated has a booster winding; and (3) the voltage to be
regulated is generated entirely in the windings of the booster armature.
The third method is practical only for low voltages, because of the large
number of turns and relatively high field current required to generate a
high voltage. 1
Over ranges of input voltage from 25 to 29 volts, from no load to
full load on the dynamotor, the output-voltage change will be approximately
3 per cent. The booster armature and regulating field increase
the size and weight of the dynamotor, but the regulator itself can be
considerably smaller than a series regulator because it carries only “the
field current rather than the line current.
14.8. Vibrator Power Supplies.—If relatively small amounts of power
are required, vibrator power supplies are useful. Conventional vibrators,
such as those used commercially in automobile radios, are capable of
supplying 50 to 60 watts of square-wave alternating current to a transformer.
The transformer output may be rectified and filtered to furnish
direct current of appropriate voltage.
Vibrator power supplies can, unlike dynamotors, supply a number of
different d-c output voltages without disproportionate increase in the
weight of the power supply. For example, it is possible to supply 2500
volts direct current at 5 ma, 250 volts d~rect current at 100 ma, and – 150
volts direct current at 5 ma, at approximately the same total weight as
that required for conventional power supplies designed to run from
115-volt 60-cps a-c lines. The vibrator power supply just described
weighs from 6 to 8 lb, depending on how it is packaged and on the degree
of filtering required.
The output voltage of a vibrator power supply can be regulated by
use of the series-tube type of electronic regulator, which is apt to be
wasteful of power. Further, output power is consumed by the rectifiertube
cathodes. Where a number of d-c output voltages are required,
I In any case, it is seldom practical to regulate the highest-voltage output since
current-limiting resistors are required in the regulator coil circuit, and at high voltages
the loss in them is excessive. It is also less important to regulate the higher vcdtages,
foc this can readily be done by regulating circuits in the radar set itself.