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56 Circuit Descriptions TB7100 Service Manual

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 10A 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 10.8V 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 (+3V3)

■ four linear regulators (+9V0, +6V0, +3V0 AN, +2V5 CDC)

■ three switched supplies (+9V0 TX, +3V0 RX, +13V8 SW)

The SMPS is used to regulate to 3.3V from the external supply +13

V8 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

BATT. The two remaining switched supplies (9V and 3V) use P-channel

MOSFETs.

Tait TB7100 Service Manual

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