FREQUENCY. CONTROLS CIRCUIT
This unit
is
composed by U201 which controlled frequency
in the instrument, but actually
it
is
achieved by controlling
voltage, V202 which undertakes this mission. U201
is
used for VCF
input invert amp. when VCF input
is
OV,
the
6th
pin of U201
is
also
OV.
If VCF input
is
+10V, the 6th pin
will
gain -13V voltage
and make control voltcge of VR202 controlled by VCF input voltage,
then input control voltage get by VR201, to constant current
generator circuit.
CONSTANT CURRENT
AND
TRIANGLE
WAVE
CIRCUIT
This unit
is
the heart of the instrument.
It
includes constart current
driving circuit U203, Q203, positive current source U204, Q202;
diode switch D201, D202; timing capacitor C203-C207; voltage
follower Q204-9206, differential level detector and flip-flop U301,
negative constant current
is
made
by
U205, Q203, which U203, Q203
is
called as current source.
As
far as U204, U205
is
concerned, U205
is
also called as "constant current driving circuitv.
As
circuit diagram Figure 6-1, differential input of OPA
f
OV,
so
Ve
=
-Vin,
Ie
=
Ic
+
IB;
and IcSIB, therefore
Ie
.i:
Ic.
If
Rc
=
Re
and to add equivalent voltage but contrary polarity
on
it
(
+15V and -15V
),
then
Ic
=
Ie
Vc
=
Ve.
This circuit uses OPA No. UA741, and
its
IE
current
is
only
approximate
O.1UA.
If Ic works within
mA
current range, then
Ic
=
Ie
is
reasonable. Now to change transistor to
FET,
IB
is
in
the staqe of PA
(UUA),
and therefore Vin
=
Ve
=
Vc.
i.e.
to control
not only Vin Voltage but also constant current
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