Tait TB7100, Руководство по обслуживанию

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56 Circuit Descriptions TB7100 Service Manual
© Tait Electronics Limited October 2005
4.6 Power Supply Circuitry
Introduction
For a block diagram of the power supply circuitry, refer to Figure 4.6 .
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 base station is provided by the clamping diode
D600 and by 20A fuses (for the 50W/40W boards) and 10 A fuses (for the
25W boards) 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 base station
operates outside its specified voltage range of 10.8 V 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 3.3 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 13.8V switched supply are connected to
+13
V
8
BATT
. The two remaining switched supplies (9V and 3V) use P-channel
MOSFETs.