Tait TM8235, Руководство по обслуживанию

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TM8100/TM8200 Service Manual Circuit Descriptions 81
© Tait Electronics Limited June 2006
3.6 Power Supply Circuitry
Introduction
For a block diagram of the power supply circuitry, refer to Figure 3.8 .
The power-supply circuitry consists of the following main sections:
■
supply protection
■
supervisory circuit
■
internal power supplies
■
control of internal power supplies
■
control of external power supply.
Supply Protection
Electrical protection to the radio is provided by the clamping diode D600
and by 20A fuses (for the 40W/50W radios) and 10A fuses (for the 25W
radios) in the positive and negative leads of the power cable. This provides
protection from reverse voltages, positive transients greater than 30V, 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
30V. The ADC also ensures protection if the radio operates outside its
specified voltage range of 10.8V to 16V.
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 eight internal power supplies:
■
one SMPS ( +3
V
3 )
■
four linear regulators (
+9
V
0
,
+6
V
0
,
+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 3.3V 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 9V regulator and the 13.8V switched supply are connected to
+13
V
8
BATT
. The two remaining switched supplies (9V and 3V) use P-channel
MOSFETs.
Control of Internal
Power Supplies
The radio can be switched 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.