Circuit Description; Control Unit; Digital-To Analog Converter Circuit; Alarm Circuit - Kenwood pds20-18 Service Manual

CONTROL UNIT (X77-2120)

Digital-to Analog Converter Circuit

Various signals received from the CPU unit are
isolated by PH1 to PH4. Various control signals
are output by IC4 to IC6. Data extracted by 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
IC8 and is olated by PH5. The remote OUTPUT
ON/OFF signals from the rear panel are isolated by
PH6 and PH7 and returned to the CPU unit.
IC9 is the EEPRO M for storing the calibration data,
data set on the panel, etc.
CV/CC Control Circuit
The v ol tag e and cur rent refer ence v olt 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 by the power unit is compared with this
reference voltage by 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 CV or CC control signal is selected by D113
and D114 and sent to the power unit driv e circuit.
The operation voltage is about –3V.
Volta ge , C urre nt a nd "OVP S e t
Voltage"
Monitor Circuit
The voltage detected by means of + sensing is
output as the v oltage monitor signal (about +2.8 V at
the full scale) by the monitor amplifier IC107-2/2.
The current monitor signal detected by the power
unit
PDS20-18/PDS36-10/PDS60-6

CIRCUIT DESCRIPTION

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.
Out put 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 O VP set voltage monitor signal
can only be selected when the O VP 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
divided by the semi-fixed v ariable resistor 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.
O utput alarm signals, except OHP, are latched by
IC108 and IC109. A trip signal activ ates the main
switch control circuit to turn off the main switch.
Other Circuit
The circuit consisting of Q 110 to Q 112 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
the digital ICs and DACs from
5 V for
15 V.
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