Tait TM8000 Series, Service Manual

Page: 74 / 244

74 Circuit Descriptions TM8100 Mobile Radio Service Manual
May 2004 © Tait Electronics Limited
Supply Protection
Electrical protection to the radio is provided by the clamping diode
D600 and 10 A fuses in the positive and negative leads of the power
cable. This provides protection from reverse voltages, positive transients
greater than 30 V, and all negative transients. An ADC monitors the
supply and is responsible for the protection of internal devices, which
have an operating voltage of less than 30 V. The ADC also ensures
protection if the radio operates outside its specified voltage range of
10.6 V to 16 V.
Supervisory Circuit
The supervisory circuit comprises a reset and watchdog timer. The
circuit provides the reset signal
PSU SYS RST
to the digital section, which
in turn provides the watchdog signal
DIG WD KICK
required by the
supervisory circuit.
Internal Power
Supplies
There are nine internal power supplies:
■
one SMPS
■
five linear regulators ( +9
V
0 , +6
V
0 , +3
V
3 , +3
V
0
AN
, +2
V
5
CDC
)
■
three switched supplies (
+9
V
0
TX
,
+3
V
0
RX
,
+13
V
8
SW
)
The SMPS is used to regulate to 3.3 V from the external supply
+13
V
8
BATT
. The four lower voltages required are then further stepped
down with linear regulators. These all take advantage of the efficiency
gain of the SMPS. The 9 V regulator and the 13.8 V switched supply
are connected to
+13
V
8
BATT
. The two remaining switched supplies (9 V
and 3 V) use P-channel MOSFETs.
Control of Internal
Power Supplies
The radio can be turned on using the
ON
/
OFF
key on the control head or
by means of external signals. For the latter case hardware links are
required and there are several power-sense options; these are discussed
below. Some internal power supplies can be controlled by means of
digital lines depending on the mode in which the radio is operating.
Power-sense Options
There are five power-sense options for powering up and powering down
the radio:
■
battery power sense
■
auxiliary power sense
■
internal-options power sense
■
no power sense
■
emergency power sense
The emergency power-sense option can be used in conjunction with any
of the other four options. The
ON
/
OFF
key can be used with any of the
options, although the behaviour of the radio will depend on the option
selected. The links LK1 to LK4 on the main board are used to
implement the desired option. The power-sense options and the link
settings are described below.