TM 11-6625-3081-23
1-21.
ELECTRONIC STATION (cont)
1-21
(3) Current Mode.
In the current mode of operation, the current comparator
amplifier senses any change in the output current by comparing an amplified sensing
voltage to a reference potential, developed by the current control amplifier. When a
change is detected, an error signal is amplified and becomes a control signal for the
driver stage.
The control signal is applied via the driver stage to the pass element,
which increases or decreases its conductance in response to the driver signal as
required to maintain the output current constant and vary the output voltage
proportionally.
(4) Output Control.
The internal feedback components in the voltage, as well as
in the current control channel, are such that a O to ±10 vdc signal applied to the
voltage comparator amplifier, or O to ±1 vdc applied to the current comparator ampli-
fier, controls the full output range. ‘For local (front panel) control of the output
quantities,
a control amplifier is used in a similar manner for the voltage as well as
for the current channel to produce the required O to ±10 vdc or O to ±1 vdc control
signal.
(5) Overvoltage.
A portion of the output voltage is taken from the sense ter-
minals and continuously compared at the overvoltage comparator to a reference voltage,
produced by the overvoltage reference amplifier, and adjusted by the CROWBAR SET LEVEL
control on the front panel.
The circuit is inactive as long as the output voltage
sample stays below the reference voltage.
If an overvoltage occurs, the overvoltage
comparator produces an output signal which turns the crowbar on, and lights the
CROWBAR indicator on the front panel. When the crowbar is on, the power supply output
is shorted and the front panel circuit breaker is tripped. The front panel CROWBAR
DISARM pushbutton (when depressed) disables the crowbar when adjusting the CROWBAR SET
LEVEL control.
The CROWBAR indicator is not affected.
e.
DC POWER SUPPLY ASSEMBLY 1A4
(1) General.
The dc power supply assembly 1A4 (FO-6) consists of four power
supplies (PS1-PS4).
PS1 supplies +28 vdc, PS2 supplies +15 vdc, PS3 supplies -15 vdc,
and PS4 supplies +5 vdc, for system operation.
Refer to FO-34 for dc power distri-
bution diagram.
Circuits of the four power supplies are identical, the following
description applies to all.
(2) Voltage and Current Control.
Source voltage of 115 vac is converted to a
usable level by the power transformer.
The power transformer is connected in series
with the pass element and the sensing resistor, thus producing dc output voltage.
(a) Output voltage is constantly compared to the reference voltage in the IC
regulator (adjusted by the voltage adjust) while the output current is monitored
across the sensing resistor.
Any variation in either the output voltage or the output
current produces an error signal which is amplified by its associated amplifier in the
IC regulator and transferred as a command to the driver.
(b) The pass element responds to the driver signal by changing its series
resistance.
It either corrects for variation of the output voltage or, if the signal
from the current amplifier is dominant, it tends to cut off the output, limiting the
output current to the preadjusted value of the current adjust.
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