ln
general, quartz
controlled
oscillators, CR or LC oscillators
and
relaxation
oscillators are
popularly
used
to
regulate
speeds. The
quartz
oscillator oan
provide
maximum
stability
but is expensive. For accurate
control,
the CR oscillator requires
very
precise
and stable CR
components,
while
the
LC
(tuned)
oscillator is not
suitable
to
control
audio
frequencies.
The
thermally compensated PUT
relaxation oscillator
is a
practical
solution to these
prohrlems.
[1fl_
680K
512H2
o.oo39
0.0012
I
c
1M
10K
\
lrl
PUT
OSC Voltage
conversion
1
/2
frequencv
d ivider
Fis.
8-12
ln
the above
figure,
the oscillating
frequency
is
given
by:
,
1
,
i
._,
Josc
=
a*
(ln
1_
nl-'
Substituting for constants,
a=ffi=o+
R1
R1+R2
(stand-off
ratio)
1
6.8X
10s X
5.1 X
10-e
(,"#
t-t=
544H2
t
J osc Max
-
.fosc
Min
f
r"fif
-1
=
474H2
Thusthel00kSrpotentiometercanvarytheosciltatingfrequencyintherangefrom4T4HztoS44Hz.
-
3 Bridge-type
Motor
Drive
Circuit
PLL
logic
output
Slow Blow
Fuse
Fis.8-14
T
-r
P
resse d
Pinch roller
R e
lea sed
Bridge
motor
circuit
Fis.
8-13
i t\ruul
Motor vortase waverorm
A-n-,f\-,/\-
Motor
cu
rren
t
wavef
o
rm
#(a)
+(b)
Fig.
8-i
7
29
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