Crown Macro-Tech MA-5000VZ Owner's Manual download pdf (Page 3)

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

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