Crown Macro-Tech MA-5000VZ Owner's Manual download pdf (Page 11)

VZ

SUPPLY CIRCUITRY

For

simplicity,

only

channel

1

circuitry

will

be

covered unless noted

otherwise.

Circuitry.forthe

VZ

supply

(and

lowvoltage supply)

is

located

on

the

control module.

The

actual

VZswitch

circuit

is

located

on the VZ

switch

assembly.

In

this assembly

are the two

bridge

rectif

¡ers,

two f

ilter

capacitors, MOSFET

switches,

and

control diodes

D810

and

D811.

Three

MOSFETs

are

used

in

parallel

for

sharing

the

high currents

supplied

to the

rails.

WARNING:

From

a

sen/ice

standpoint,

'rt

is

critical

to

note that

VZ

switch

control circuitry

is NOT

ground referenced.

Any

attempt

to

take

voltage measurements using

a

ground reference

when

voltage

¡s

applied

will

not

only

be

unreliable,

but

may

be

extremely

dangerous.

Serious damage

to

equipment

or

personnel

may

occur

¡f

this

is

attempted.

The

output

of a 555

timer

(U703)

on the

control module determines

whether

the

MOSFETs

are

switched

on

(high)

or

off

(low).

This

555

device

and the

various sources that feed

the 555 are the

things that

make

the

articulation

work

wfíéh

and how

desired.

The

master

555

trigger

is

controlled

by the

output

of

U702A. S700,

physically

accessible

from

behind

the

front grille, determines

the VZ

operating

mode.

In

high voltage

mode

the

output

of

U702A

¡s

held

low.

This

in

turn keeps

the 555

output high

and the

MOSFETs

are

kept

on.

In

the

high current mode U702A

is

held

¡n the

opposite

polarity

keeping

the

output

of the 555 low and the

MOSFETs

off.

In the

AUTO position

of

S700,

the

audio

level

sense circuitry controls

the

threshold

and

reset

inputs

to the

555.

The 555

will then switch states

to

high voltage when

the

audio level

is

sufficient

and

will switch back down automatically when

Notes

Low

Voltage

Power

Supply,

including

DC

Pulse

network

for

Soft-start

and Fan

Control

circuitry.

MA-5000VZ

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