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SECTION IV
PRINCIPLES OF OPERATION
4-1
OVERALL BLOCK DIAGRAM DISCUSSION
(Figure 4-1)
4-2
Models 6110A and 6516A, as illustrated in
Figure 4-1, are constant voltage/current limited
power supplies that utilize a "piggy-back" regu-
lator design.
This design extends the usefulness
of the series regulating transistors rated for ap-
proximately 30 volts to short-circuit-proof power
supplies rated for 3, 000 volts.
The basic tech-
nique consists of placing the well-regulated low-
voltage "piggy-back" supply in series with a less
well-regulated high voltage doubler.
Notice,
however, that the amplified error signal from the
voltage input circuit is dependant upon the total
output voltage-not just the output of the "piggy-
back" supply alone.
Thus, the well-regulated
"piggy-back" supply continuously compensates
for any ripple, load regulation, or line regulation
deficiencies of the high voltage doubler, and ad-
justs the voltage across the series regulator so
that the total output voltage remains constant
de spite disturbances in the high voltage doubler.
4-3
For purposes of discussion the voltage
values of Model 6110A are used in the following
paragraphs, however, the theory pertains equally
well to both Models 6110A and 6516A.
The
"piggy-back" supply develops 200 volts, and the
high voltage doubler supply is capable of provid-
ing a maximum of 3200 volts.
With 30 volts nor-
mally dropped across the series regulatoP, the
maximum output of this supply is 3370 volts; 170
volts from the "piggy-back" supply and 3200 volts
from the high voltage doubler.
Thus, the series
regulator of the "piggy--back" supply has a voltage
range for accomplishing the dynamic changes nec-
essary to compensate for the variations of the
power source.
Short-circuit protection for the
series regulator in the "piggy-back" supply is
provided by the protection diode, which provides a
discharge path from the positive side of the power
supply to the positive side of the high voltage
doubler shunting the short circuit current around
the series regulator.
Whenever the load resist-
ance decreases to a value such that +S becomes
greater than -200 volts, the protection diode con-
ducts.
This prevents the output terminals of the
"piggy-back" supply from ever reversing polarity,
and the series regulator will never be called upon
to withstand a voltage strain greater than 200 volts
from its own rectifier.
4-4
The ac input line voltage is raised to the
proper level and coupled to the "piggy-back" sup-
4-2
ply. This supply converts the ac input to raw de
which is fed to the positive terminal via the series
regulator and current sampling resistor network.
The regulator, part of the feedback loop, is made
to alter its conduction to maintain a constant out-
put voltage or limit the output current. Voltage
developed across the current sampling resistor is
the input to the current limiting circuit. If the out-
put current that passes through the sampling net-
work
exceeds a certain predetermined level, the
current limiting circuit applies a feedback signal
to the series regulator which alters the regulator's
conduction so that the output current does not ex-
ceed the predetermined limit.
4-5
The voltage input circuit obtains its input by
sampling the output voltage of the supply at the
voltage control. Any changes in output voltage are
detected in the constant voltage input circuit, am-
plified by the error amplifier and driver, and ap-
plied to the series regulator in the correct phase
and amplitude to counteract the change in output
voltage. The reference regulator circuit provides
stable reference voltages which are used by the
constant voltage input circuit and the current limi-
ting circuit for comparison purposes.
4-6
The high voltage control circuit monitors the
voltage across the "piggy-back" supply, and alters
the conduction of transformer Tl so that the output
of the high voltage doubler can be varied between
0 and 3.2 kilovolts. For instance, if the high volt-
age control is adjusted for an output voltage in ex-
cess of the voltage supplied by the "piggy-back"
supply, the input to the high voltage control cir-
cuit becomes more negative. The high voltage
control circuit opens the control winding, and all
the energy appearing at the ac input of transformer
Tl is coupled to the secondary which is connected
to the high voltage doubler. The result is that the
output voltage of the high voltage doubler increases.
If the voltage control is adjusted for an output
which is less than the "piggy-back" supply, the
input to the high voltage control circuit becomes
less negative. The control winding of transformer
Tl becomes shorted impeding the transfer of energy
from the ac input to the secondary which is con-
nected to the high voltage doubler. Thus, the out-
put voltage of the high voltage doubler decreases.
4-7
In Model 6ll"OA, an oven houses the temper-
ature sensitive components in the supply to pro-
vide a low temperature coefficient which results
in excellent stability.
The oven control circuit
maintains the oven temperature at 65°C.
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