5
Power Supply / Display
Overview
The power supply stage produces seven voltages when the CD Changer
is plugged into AC. Some of these voltages from the main board power
the FL Driver microprocessor IC701 and the FL indicator tube on the dis-
play board.
Power Supply
Power Supply Output
Output Voltage From Destination
1. +11.5Vdc Bridge Rectifier
D501-4
Regulator/Sw IC506,
+5V Regulator IC504,
Motor Driver IC503.
2. 13.5Vdc Bridge Rectifier
D501-4
Audio mute transistors
(Q325/e, Q327/e and
Q425/e), Motor driver
IC503.
3. +5Vdc Source Regulator IC504 Syscon IC501 (not shown),
FL Driver IC701.
4. +5Vdc Bridge D501-4 &
Zener D508
Mute transistors Q325/e,
Q327/e and Q425/e.
5. Reset +5V Reset IC505 Syscon IC501 (not shown),
FL Driver IC701,
LED Driver IC702 (not
shown).
6. 3.7Vac Power Transformer
T901
Fluorescent Display Tube
filament
7. -28V Q501/emitter Reference voltage for the
Fluorescent Display
+11.5V Source / -13.5V Source
When the CD Changer is plugged into AC, this voltage is applied to the
primary winding of T901. The secondary winding that is center taped
applies 20.6Vac to a four-diode bridge rectifier designated D501 to D504.
The positive output of the bridge rectifier is filtered by C501 to become the
+11.5V source voltage.
The negative output of the bridge rectifier is filtered by C502 to become
the –13.5V source voltage.
+5Volt Source
The +11.5V source voltage is reduced and regulated by IC504 to produce
the +5V source voltage for the CD Changer.
+5Vdc
The +11.5V source voltage is reduced by R505 and R508 and applied to
5.1 volt zener diode D508 for shunt regulation. Shunt regulation is when
a device like this variable resistance zener diode is placed in parallel with
the load. The zener diode resistance varies to keep the voltage at the
load reasonably stable.
This +5 volts that is output is used by the mute transistors Q325, Q327,
and Q425 to control the left and right channel audio muting at power ON
and OFF and when plugged and unplugged from AC.
D509 and C505 are used to insure there is sufficient voltage for the mute
operation when the unit is unplugged. C505 holds the +5V for the mute
transistors and diode D509 blocks this voltage from being used by the
loads on the 11.5V line (D509/anode).
Reset +5V
When the +5Volt Source voltage outputs regulator IC504, IC505 creates
a reset pulse using R506 and C507. Each one of these three parts has a
role in creating the reset pulse. When the source voltage is input IC505,
IC505 holds it output LOW for a fixed amount of time dependent upon
IC505’s design. This LOW grounds out C507 at the output. When the
IC505 releases ground, C507 is charged by R506 to +5V.
The reset output of IC505 is applied to the IC501 and IC701 microproces-
sors in this CD Changer. Generally, reset occurs when the reset input to
a device is held LOW while power (Vcc) is applied.
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