CONTROL UNIT (X77-2120)
Digital-to Analog Converter Circuit
Various signals received from the CPU unit are
isolated b y PH1 to PH4. Vari ous control s ignals
are output by IC4 to IC6. Data extracted b y IC10
and IC11 is input to IC12 (reference DAC) and IC14
(monitor DAC), which convert the data into analog
signals.
Voltage and current monitor signals and CV/CC
status and other status signals are input to IC7 and
IC 8 and is olated by PH5. The remote O UTPUT
ON/OFF signals from the rear panel are isolated by
PH6 and PH7 and returned to the CPU unit.
IC9 is the EEPROM for storing the calibration data,
data set on the panel, etc.
CV/CC Control Circuit
The v oltag e and cur rent refer ence volt age o utpu t
by IC12 is ab out +2 .8 V a t the f ull sc ale, w hich i s
ampl ifi er t o a bou t 5 B by a re fer enc e am pli fie r
consisting of IC106.
In t he C V op erat ion mod e, t he v olta ge m onit ore d
by means of + sensing is compared with this
reference voltage by R139, R137 and R225. The
error amplifier IC105-1/2 output the CV control
signal.
In the CC operation mode, the current monitor signal
detected b y the p ow er unit is compared w ith this
reference voltage b y R140 and R141. The error
amplifier IC105-2/2 output the CC control signal.
In the slave operation mode, a signal input from the
master unit is used as the reference signal for control.
The C V or C C control signal is s elected b y D113
and D114 and sent to the pow er unit driv e circuit.
The operation voltage is about –3V.
Voltage, Current and “OVP S et
Voltage”
Monitor Circuit
The voltage detected by means of + sensing is
output as the voltage monitor signal (about +2.8 V at
the full scale) by the monitor amplifier IC107-2/2.
The current monitor signal detected b y the p ow er
unit
is output as the current monitor signal (about +2.8 V
at the full scale) by the monitor amplifier IC107-1/2.
The OVP signal set on the panel is output as OVP
set voltage monitor signal (about +2.8 V at the
maximum voltage) through the buffer amplifier
IC103.
This monitor circuit is a sequential comparator circuit.
Output monitor signals are selected by IC15,
compared with the monitor reference signal from
IC14 (monitor DAC) by IC16, and then returned to
the CPU unit. The OVP set voltage monitor signal
can only be selected w hen the OVP key on the
panel is pressed.
Alarm Circuit
Several protector circuit are used : Variable
overvoltage (OVP), maximum overvoltage (MAX
OVP), pre overvoltage (PRE OVP), overcurrent
(OCP), overheat (OHP) and pre
overheat (PRE
OHP). The pre
overvoltage, overcurrent,
ovrtheat and pre
overheat protector circuits output
alarm signals when they detect abnormalities.
Voltage of about +2.8 V is produced by IC104 and is
div ided by the semi-fixed v ariabl e resis tor on the
panel to make the set reference voltage of the OVP
circuit. The voltage detected by a comparator circuit
consisting of IC101 by means of + sensing is
compared with the reference voltage.
An alarm is output if such comparison results in an
error. The MAX OVP circuit runs in the same way on
the –3 V reference voltage determined by D108.
Output alarm signals, except OHP, are latched by
IC108 and IC109. A trip signal activates the main
switch control circuit to turn off the main switch.
Other Circuit
The circuit consisting of Q110 to Q112 output
signals for turning on or off the bleeder circuit of the
power nit.
When the output is off and the output level has
lowered sufficiently, PH106 functions to turn off the
bleeder circuit. IC112 and IC113 produce
5 V for
the digital ICs and DACs from
15 V.