Crown FM150, Руководство пользователя

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4.9 Power Regulator Circuit Board
The power regulator board is the shorter of two boards mounted under the chassis toward
the front of the unit. The board has the isolating diode for the battery input, the switch-mode
voltage regulator for the RF power amplifier, and circuitry for PA supply current metering.
Illustration 6–10 and accompanying schematic complement this discussion.
Diode D4, in series with the battery input, together with the AC-supply diode bridge, pro-
vides diode OR-ing of the AC and DC supplies.
U1 and U2 form a switching regulator running at about 35 kHz. U1 is used as a pulse-width
modulator; U2 is a high-side driver for MOSFET switch Q1. Power for the two IC’s comes
from the 20–volt supply voltage for the RF driver (available when the Carrier switch is on).
The voltage is controlled at 16 volts by zener diode DZ1. Bootstrap voltage provided by D2
and C9 allows the gate voltage of Q1 to swing about 16 volts above the source when Q1 is
turned on. Current through the FET is sensed by R12A and R12B. If the voltage from pin 5
to 6 of U2 exceeds 0.23 volts on a current fault, drive to Q1 is turned off. This happens on a
cycle-by-cycle basis. The speed of the turnoff is set by C5.
U3 and Q2 are used in a circuit to convert the current that flows through metering shunt,
R19, into a current source at the collector of Q3. Forty milli-volts is developed across R19
for each amp of supply current (.04 ohms x 1 amp). Q3 is biased by U3 to produce the
same voltage across R16. The collector current of Q3 is the same (minus base current) as
that flowing through R22 resulting in 40 microamperes per amp of shunt current. R5 on the
metering board converts Q3 collector current to 0.1 volt per amp of shunt current (.04 ma X
2.49 k). (See section 5.4.)
4.10 RF Driver/Amplifier (FM30)
The RF Driver/Amplifier assembly is mounted on a 100 mm x 100 mm plate in the under
side of the chassis.
Illustration 6-14 and accompanying schematic complement this discussion.
The driver amplifies the approximate 20 milliwatts from the frequency synthesizer to 30
watts. An MHW6342T hybrid, high-gain, wideband amplifier, operating at about 20 volts,
provides about one watt of drive to a single BLF246 MOSFET amplifier. The BLF245 stage
operates from a supply voltage of 28 volts in the FM30.
The circuit board has components for input and output coupling and for power supply filter-
ing.
4-12 FM30/FM150/FM300 User’s Manual