Ecler PAM4100, Руководство по обслуживанию

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author:
Queralt
date:
010418
project:
EP04-99
product:
PAM4/6100
approved:
num:
52.0010
version:
01.00
title:
FUNCTIONING DESCRIPTION
ECLER
EPO4-99 Power Module. Functioning description.
Due to the high power level required on the output load, the amplifier final stage's
structure differs from the design used untill now. This is due to the breakdown voltage
limit on P-channel MosFET's, wich is 200V. This final stage is formed by several
shunted MosFET's, where those of the positive branch are common-drain configured,
and the negative branch are mounted in common-source configuration.
The system's controlling device is a NE5534-type operational amplifier, wich is
internally compensated in order to obtain gain levels equal or higher than three. The
amplifier's feedback is given by a resistor and a capacitor associated to the operational
amplifier's non inverting input.
Transistors BF587 and BF588 are common-base configured, forming a current supply
structure. This specific transistor type is used because of the higher Vce voltage level
required by this design. They perform simultaneously two functions: they polarize the
MosFET's gate-source junctions, keeping them on the conducting edge, and they
tranfer the OpAmp's output voltage variations referred to signal ground.
The signal variations normally reflected by Q107 and referred to the positive power
supply, are now needed to be floating variations, and referred to the outputs. This
function is done by Q109-110 (BF588), wich are mounted formig a Wilson-type mirror
current supply. This mirror current supply transfers all of the current variations detected
while descending through Q109's collector, to similar variations on Q110's collector
also downward current. Resistors R167 and R174 are used to balance the current
mirror, in order to avoid the use of transistors with forcibly the same beta value. C138
and C141 suppress their resistance when high frequency signal is processed. Diodes
D126 and D127 avoid the transistors to get saturated, and R171 eliminates the loads
on BF588's bases (Baker Circuit).
The system requires about 12Vdc additional voltage upon the usual Vcc level, this
allows a correct saturation and a symetric clipping at the higher MosFET's.
The correct polarization current value is adjusted by a 4K7 potentiometer connected to
the BF transistor's emitter. This adds an additional current to the current source output
on th BF transistor's loading resistors.
In order to maintain the appropiate stand-by current level against varying temperature
conditions, BD437-type transistors are used. As they have a particular temperature-
depending base-emitter voltage curve, this voltage is used to keep a correct voltage
reference for the current supply. As the temperature rises, the reference voltage level
decreases, the gate-source voltage also decreases and, finally, the bias current also
decreases.
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