JUKI 6100 Technical Manual page 56

Fig.
7.9
is
the
schematic diagram of
the
+5
VDC
regulation
circuitry.
Unlike the
regulators for the other voltages in
the
6100, the
+5
volt circuit utilizes a
high
frequency
switching type
regulator.
A
complete
description
of the operation of
this
regulator
would
be very
difficult
because of
its
complexity, however,
a
few
general points will
be discussed.
The
voltage applied to
point
@
of
the
circuit
is
a
full
wave
rectified signal
of approximately
30
volts.
Transistor
Q6
acts
as
a
switch to periodically
apply the voltage to
the
filtering circuit
and
feed-back
networks.
The amount
of time during
which
Q6
is
turned
on determines
the
output
voltage. Fig.
7.10
illustrates
the relationship
between the
on and
off times
of the signal
which controls Q6.
The
output voltage
can be determined
by
the
following formula:
Output
Voltage = (tON
Divided
by T) x Input Voltage
When Q6
is
conducting, Coil
L5 and
Capacitor
C20
tend
to
smooth
the controlled
pulse voltage to a
DC
waveform.
When Q6
turns
off,
Coil
L5
releases
its
electro-
magnetic energy through
commutating
diode
D6.
Fluctuations
in
the input
voltage or the resulting
output
voltage are
detected
by
R24
and R25.
A
feedback
signal
which
is
supplied
at
the center of these
two
resistors
is
applied to the
IC
at
pin
1
and
the
tON
time
is
varied to
maintain
a
constant
output
voltage.
Over-
current protection
is
achieved by
monitoring
the voltage
between
R20
and R21
and comparing
it
with the voltage
between
R24
and
L6.
If
the resultant voltage
exceeds
a certain
preset value,
the
*ON
time
is
again
changed
to
reduce the
output
voltage. Fig.
7.10
also
shows
a
representation
of
the
output
voltage, the
amount
of
ripple
on
the
+5
volts
would
be only
a
few
millivolts.
GND
GND
Fig.
7.9
+5V
power
circuit
0V
—
T -
tQN
—
tQFF—
+5V
Stabilized
output voltage
!
Ripple
voltage
GND
Fig.
7.10
Q6
control voltage
-
53
-