-
receive 5 volts (R5). During the receive mode, switch Q503 supplies
regulated 5volts (R5) to the receiver front end.
B+ Routing for
VOCON Boards and
Display Modules
Refer to Figure 3 and your specific schematic diagram.
Power for the radio is derived from a 7.5 volt battery, which is applied
to the transceiver board through J3. This Raw B+, or unswitched B+
(UNSW B+), is routed to J1 on the transceiver board and then on to
J401 on the VOCON board. Here the UNSW B+ is forwarded to the
radio’s control top on/off/volume knob through J901 and a flex
circuit. The on/off/volume knob controls B+_SENSE to Q206, which in
turn controls Q207. Transistor Q207 is a solid-state power switch,
which provides SW B+ to the VOCON board’s analog and transceiver
5V regulators, the audio PA, the display module, and back to the
transceiver board. In addition, UNSW B+ is routed to the main digital
5V regulator (U409); B+ SENSE provides for enabling or disabling this
regulator.
In the case of a secure radio model, SW B+ and UNSW B+ are also
supplied to the encryption module through J801.
Q207 is also under the control of the microcontrol unit (MCU - U204])
through a port on the SLIC IC (U206). This allows the MCU to follow
an orderly power-down sequence when it senses the SW B+ is off. This
sense is provided through the resistor network of R222 and R223,
which provides an input to the A/D port on the MCU.
The VOCON board contains two 5V regulators partitioned between
the digital logic circuitry and the analog circuitry. The 5V regulator for
the digital circuitry is comprised of U409, CR403, L402, C470, and
associated components. This circuit is a switched mode regulator.
Switched mode regulators use a switched storage device (L402) to
supply just enough energy to the output to maintain regulation. This
allows for much greater efficiency and lower power dissipation.
The analog circuitry of the ADSIC (U406) and the audio PA (U401) is
powered through a separate 5V linear regulator (U410).
It should also be noted that a system reset is provided by U407. This
device brings the system out of reset on power-up. It provides a system
reset to the microcomputer on power-down or if the digital 5V
regulator falls out of regulation.
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