REV.-A
The collector
of
05
is connected
to
the VB line (+5V) through inductance L 1 and the
emitter
is
grounded. When the transistor repeats
switching
on and off, therefore, a voltage
as
shown
in
Fig.
2-1 5 appears at the collector. This voltage is filtered
by
the electrolytic capacitor, C3,
through the diode
D1
to
a voltage
that
exceeds
VB.
This results in a potential difference across
the emitter, and base
of
the transistor
04,
which
causes the transistor
to
conduct,
outputting
a
DC
voltage
of
approximately
7V
at its collector.
Because
this
output
is connected
to
the constant-voltage circuit, consisting
of
the resistors R13
and R25, and the zener diode ZD5, the actual
output
voltage is fixed at
+5V
by the
5V
break-
down
voltage
of
the zener diode.
When
the
04
output
voltage rises above +5V, ZD5 breaks
down
at +5V,
putting
transistor
022
in conduction,
which
forces the
switching
signal
to
ground
level. The
output
voltage is always maintained
at
+5V
by disabling the
switching
of
05.
Varia-
tion
of
load is handled
by
the relatively large capacitance
of
capacitor C8
(220
J,lF),
connected
at the collector
of
04.
Clock
35
kHz
Switching
pulse
at
14D,
pin
14
Q5
emitter
Q4
collector
(before filtered)
5V
1----------'
I
G
1---------'
Zener breakdown
Fig.
2-15
+5V
Regulator
Voltages
2-22
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