Table of Contents
Advertisement
improved thermal performance by eliminating the insulating interface
underneath the power devices. The chassis itself is used as part of the
thermal circuit, and this maximizes utilization of the available resources.
Air flow in this amplifier is front to rear, also a departure from other
Macro-Techs. Fan speed is a function of ODEPIevel. AlthoughODEP
was covered in detail in the BASICS section of this text, the specif ics of
the MA-5000VZ ODEP circuit are unique and will be covered here.
Notes
OUTPUT STAGE CIRCUITRY
The MA-5000VZ, like other Macro-Techs, uses the grounded bridge. It
does differ, however, in certain aspects. For example, quadrants use
four devices ¡n parallel ratherthan the normal máximum of three. Output
stages are also physically built in a modular way, for ease of field
replacement.
Electrically, there are also a few differences. Bias servo networks
consist of two transistor devices per Vbe multiplier (one set for high side,
one set for low side). Also, ODEP affects the low side as well as the high
side by stealing low side bias and drive. Taking that a step further, any
protective action which limits, mutes, or shuts down the amplifier will
accomplish the same thing by stealing drive.
Circuitry on the positive and negative output modules ¡nclude bias
circuitry, current limit circuitry (the MA-5000VZ has two speed current
limit), last voltage amplifiers (LVA's), pre-driyers, drivers, and output
devices. Temperature sensors are also mounted to the heatsinks vía
the output modules. These deliver ¡nformation to the main module
which computes actual calibrated temperature for ODEP and
temperature measurement.
H-15V
R571
2.7K
Positive (NPN) Output Stage
Thermal Sensor Circuitry
U50O
V.
LM334 r
L
3
R572
r£
227
O.5OW
R584
2.7K
\
+TEMP1 :
The positive LVA's (Q501, Q502, and Q503)convert the negative output
of the voltage translator stage to a positive drive voltage for the NPN
High Side (HS) predriver. There are three LVAtransistorsin parallel due
to the very high voltages (therefor higher current and thermal
requirements) that are present when the power supply is in high voltage
mode. D522 prevenís the +LVA'sfromproducinga high negative output
to the HS NPN stage.
MA-5000VZ - 3
Advertisement
Table of Contents
