T.E.M. A07B500S, Руководство пользователя

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A07B500S manual
Pag. 39
The voltages involved are very high and are unusual for transistor equipment; the power source has
been shielded from both an electrical and mechanical standpoint: it is impossible to reach points
having a voltage higher than 50V without switching off and disassembling the transmitter. The
most rigorous security regulations have been respected. A sensor cuts off voltage output when
temperature of the components reaches maximum limits and is controlled both by the value of input
and output current, thus protecting the circuit from overloads. Varistors protect the active circuits
from overloads above 400 V; a circuit limits the start-up current within the limits of maximum
absorbed current at full load. NO CURRENT PEAK EXISTS AT START-UP; there is rather a
gradual and smooth settlement of the rated value. Acting on the mains supply switch does not cause
immediate start-up of the transmitter; rather, it takes about three seconds, during which time the
nominal voltage value is reached gradually, and after which actual start-up takes place.
Using two 15A fuses, the card separately feeds two coupled power amplifier final stages, and using
a 2A fuse, feeds the fan and next card which generates all auxiliary voltages.
5.6 PW500 board
The purpose of the PW500 circuit is to generate the necessary voltages for the function of
the exciter; a voltage input of 48Vdc is reduced using two step-down regulators with values of +-
15Vdc and 5Vdc (U2 and U1).
On the same card, two amplifiers are also present which interface with the temperature sensor, the
detection of unbalance of the power amplifier final stages, the measurement of current and the
microprocessor.
5.7 A15 board
The module represents a 250 Watt coupled two-module driver. Its input power is 10dBm,
which comes from a synthesized SINTD oscillator; total output value is between 0 and 15 Watts. It
is comprised of three cascade stages, the first two of which have a variable voltage power source
with a command originating from the power control. All transistors have class A-B bias to produce
a smooth regulation and so that the parameters of the loop are as constant as possible, creating an
elevated margin of stability. The frequency of the loop is approximately 500Hz and, as such,
protection intervention for excessive SWR is triggered within a millisecond. Synchronous AM and
FM are likewise reduced for control of power.
The Q3 MOS-FET is able to supply more than 15 Watts of power and, if supplied with higher
voltage, could output more than 40 Watts; under such operating conditions, there is no need for
protection.