Eberline ESP-1 - OPERATIONAL THEORY

6.
Low-Voltage Supply
The low-voltage supply regulates and provides the control point for the operating voltage for the
ESP-1 electronics.
C. OPERATIONAL THEORY
For the discussion that follows, please refer to Figures 7-1 through 7-12,
1.
Low-Voltage Power Supply
Power is supplicd to the ESP-1 electronics by six C-type batteries and regulated to 5.0 volts with
A101. The battery output limits are 9 volts for new batteries down to approximately 5.6 volts
for "dead" batteries. The lower limit is set by the voltage differential between the input and
output of A101 and enables A101 to maintain voltage regulation.
Computer voltage (Vc) is always applied to the computer to maintain its random-access memory
(RAM). With the ESP-1 off, battery drain consists of the normal leakage current of CMOS,
typically less than 50 microamperes. During a battery change, capacitor C1 (0.047 F) provides
power
for
RAM
for
about
20
minutes
(instrument
off).
This
power
maintains
all
the
operating
parameters at the values entered during calibration.
Pressing
the
ON/OFF
keypad
causes
the
microcomputer
to
initialize
the
program
at
BEGIN
(figure
7-8).
If the ESP-1 is operating when the keypad is pressed, it sets "PWR ON" to A1, HI (45 V),
turning
off
the
low
voltage
(Q101,
Q102,
Q103)
to
all
electronics
except
the
microcomputer
and
its program access (A1, A2, A3).
If
the
ESP-1
is
off
when
the
ON/OFF
keypad
is
pressed,
it
sets
"PWR
ON"
low
(0.0
volts)
turning
Q101
on.
This
supplies
the
operating
voltage
(+V)
to
the
amplifier,
high-voltage
control,
display,
and
speaker
circuitry.
It
also
switches
on
the
battery
voltage
(Vga)
to
the
HV
oscillator
and
battery
sense
via
0102
and
Q103. (АП
circuits
are
now
energized.)
Integrated
circuit
A11
converts
+V
to
a
negative
voltage
to
provide
a
bias
voltage
(V,)
to
the
display
(LCD).
Adjustment
of
V,
allows
the
operator
to
optimize
the
viewing
angle
of
the
display.
Battery
condition
is
monitored
by
one
of
the
comparators
in
A103.
Pin
15
is
connected
to
the
regulated
reference
(amplifier
"bias").
When
the
voltage
at
pin
14
falls
below
this
reference,
the
output
(pin
16)
goes
low.
This
voltage
transition
is
input
to
the
microcomputer,
causing
it
to
initiate
blinking
of
the
first
character
on
the
LCD.
The
blinking
indicates
a
low
battery
condition
to
the
operator.
This
switch
point
occurs
when
the
battery
output
is
approximately
5.8
volts
and
allows
the
instrument
to
operate
properly
for
about
another
four
hours
or
until
the
battery
voltage
reaches
its
minimum.
Pressing
the
LIGHT
keypad
lights
the
LCD
via
Q1
and
DS1.
Diodes
CR2
and
CR3
set
Q1
and
R3
as
a
current
source
that
maintains
a
constant
drain
on
the
batteries
and
prolongs
lamp
life.
ESP1.MAN/February 1992