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CIRCUIT DESCRIPTION
circuit that consists of D6, D7 and D8.
6. PHASE CONTROL CIRCUIT
The PD series power source features a phase control circuit
to control the thyristors
D1
and D2 of the main power
source rectifying bridge, in order to minimize power loss of
the series control transistors (Q1-Qn) by maintaining the
voltage
between
the
Q1-Qn
collectors
and
emitters,
regardless of load. The GND
of this phase control circuit
consists of the emitter
of the series control
transistors
Q1-Qn, with an independent floating circuit from the unit
power source.
A stable +15 V is generated for the phase control circuit
power source by U10 and U11. A sawtooth wave that is
synchronized with the AC power source line is generated
by D42, D43 and U12. This sawtooth wave is applied to
U13 (2/2). (See Fig. 3)
The collector voltage (Vce detecting voltage) of the series
control transistor is applied to the error amplifier U13 (1/2).
The DC voltage of U13
(1/2) is added to the sawtooth
wave of U12 (2/2) and applied to the input of U13 (2/2).
The pulse width modulated (PWM)
output of U13 (2/2) is
finely differentiated by C64, etc., to drive the one shot
multi 014.
The output of U14 (trigger gate pulse) is separated from
the GND of the phase control circuit, and amplified by 022
and Q23 to drive the thyristors (D1 and D2).
Note:
GND indication of respective circuits
Case
+
Unit GND (Case or Chassis)
Ve
b
Voltage control circuit GND
Ie
¥
Current
control
circuit
GND
(one
end
—
point ''a'' of current detecting resistor R10)
thr
Phase control circuit GND
(emitter point of
series control transistors Q1-Qn)
Caution:
Do not short the insulation to the GND of the respective cir-
cuits when repairing breakdowns.
This may result in burning of the wiring and/or printed cir-
cuit board.
7.DPM UNIT (D type only)
The digital panel meter
unit consists
of the voltage in-
dicator circuit and current
indicator circuit,
which
both
function the same electrically.
U1 (U31) is the 3-1/2 digit indicaion A/D converter, with a
7 segment
LED driver incorporated.
U2
(U32) generates
the reference voltage.
The optimum
value is set with VR1
(VR31),
and VR2
(VR32) is for full scale adjustment. The A/D converter is
provided
with an external
circuit constant
to enable full
scale
indication
of
1999
when
1.999 V_
is_ input,
regardless of voltage indication, current indication and type
of unit. Namely, these circuit constants are R1 (R31), C3
(C33), C4 (C34) and C5 (C35).
The main amp output of the amp unit (X37) is fed to the at-
tenuator which
consists of R20 (R50)
and the amp
unit
R81 (R73). Voltage indication is 3-1/2 digits, but a 2nd at-
tenuator is provided for 2 step auto range in case of indica-
tion 20 V or higher. When the indication in the U3 circuit
exceeds
1999,
a range up signal is output, and a range
down signal is ouput when the indication is 1000 or lower.
This signal is latched to the RS flip flop which comprises
U4, is passed through Q1, Q2 and drives the decimal point
LED. Simultaneously, Q3 drives the analog switch Q4.
Since the ground levels for the meter output of the voltage
and current are different, the respective power supplies are
isolated.
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