Automatic On/Off; Figure 2-2. Dc Power Distribution Block Diagram - Motorola CDM1550 LS+ Detailed Service Manual

Theory of Operation
FLT_A+
5VD
Figure 2-2. DC Power Distribution Block Diagram
5VI
VDDA
2-3
The INT SW B+ voltage from switching transistor 00661 provides power to the circuit controlling the
audio PA output. The voltage is monitored by the IJP through voltage divider R0671/R0672 and the
line battery voltage. Diode VR0671 limits the divided voltage to 5.6 volts to protect the IJP.
Regulator U0611 generates the voltage for the switched supply voltage output (SWB+) at accessory
connector J0501, pin 13. U0611 operates as a switch with voltage and current limit. Resistors
R0611 /R0612 set the maximum output voltage to 16.5 volts. This limitation is only active at high
supply voltage levels . The regulator output is enabled by a 0 volt signal at 00661, pin 2. 00641 and
R0641 disable the regulator when the radio is turned off. Input and output capacitors C0603 and
C0611/C0612 reduce high frequency noise.
Diode VR0601 protects against transients and reverse polarity of the supply voltage.
2.2.2 Automatic On/Off
The radio software and/or external triggers turn the radio on or off without direct user action . For
example, automatic turn on when ignition is sensed and off when ignition is off.
00661 provides the INT SW B+ voltage to the various radio circuits and to enable the voltage
regulators via transistor 00641 which contains a pnp and an npn transistor that provide an
electronic on/off switch. The switch is on when the collector of the npn transistor within 00661 is low.
When the radio is off the collector is at supply voltage level. This effectively prevents current flow
from emitter to collector of the pnp transistor. When the radio is turned on the voltage at the base of
the npn transistor is pulled high and the pnp transistor switches on (saturation). With the INT SWB+
voltage now at supply voltage level, transistor 00641 pulls pin 2 of the voltage regulators U0611 and
U 0641 to ground level, enabling their outputs.
The electronic on/off circuits are enabled by the IJP through ASFIC CMP port GCB2, line DC
POWER ON, emergency switch (line EMERGENCY CONTROL) , the mechanical On/OffNolume
knob on the control head (line ON OFF CONTROL), or the ignition sense circuits (line IGNITION
CONTROL). If any of the four paths cause a low at the collector of the npn transistor within 00661,
the electronic "ON" is engaged.