EVA
Manual
17
118144
‐
001
REV.
A
Chapter
4
EVA
HIGH
VOLTAGE
POWER
SUPPLY
PRINCIPLES
OF
OPERATION
The
EVA
series
of
high
voltage
power
supplies
utilizes
sophisticated
power
conversion
technology.
A
variety
of
analog,
digital
and
power
conversion
techniques
are
employed.
This
Principles
of
Operation
will
introduce
the
basic
function
blocks
that
comprise
the
EVA
power
supply.
For
details
on
a
specific
circuit,
consult
Spellman’s
Engineering
Department.
The
EVA
power
supply
is
an
AC
to
DC
converter.
Within
the
power
supply,
conversions
of
AC
to
DC,
high
frequency
AC,
then
to
high
voltage
DC
take
place.
By
reviewing
functionality
of
the
subassemblies,
a
basic
understanding
of
the
process
can
be
gained.
WARNING
THE
ENERGY
LEVELS
USED
AND
GENERATED
BY
THE
POWER
SUPPLY
CAN
BE
LETHAL!
DO
NOT
ATTEMPT
TO
OPERATE
THE
POWER
SUPPLY
UNLESS
THE
USER
HAS
A
SUFFICIENT
KNOWLEDGE
OF
THE
DANGERS
AND
HAZARDS
OF
WORKING
WITH
HIGH
VOLTAGE.
DO
NOT
ATTEMPT
TO
APPROACH
OR
TOUCH
ANY
INTERNAL
OR
EXTERNAL
CIRCUITS
OR
COMPONENTS
THAT
ARE
CONNECTED
OR
HAVE
BEEN
CONNECTED
TO
THE
POWER
SUPPLY.
BE
CERTAIN
TO
DISCHARGE
ANY
STORED
ENERGY
THAT
MAY
BE
PRESENT
BEFORE
AND
AFTER
THE
POWER
SUPPLY
IS
USED.
CONSULT
IEEE
RECOMMENDED
PRACTICES
FOR
SAFETY
IN
HIGH
VOLTAGE
TESTING
#510
‐
1983
.
4.1
Line
Rectification
and
Filtering
WARNING
LINE
VOLTAGE
IS
PRESENT
WHENEVER
THE
POWER
SUPPLY
IS
CONNECTED
TO
THE
INPUT
LINE
VOLTAGE.
BE
SURE
TO
DISCONNECT
THE
LINE
CORD
BEFORE
OPENING
THE
UNIT.
ALLOW
5
MINUTES
FOR
INTERNAL
CAPACITANCE
TO
DISCHARGE
BEFORE
TOUCHING
ANYTHING
CONNECTED
TO
LINE
REFERENCED
CIRCUITRY.
Simple
three/single
phase
rectification
provides
the
DC
buss
voltage
for
the
high
frequency
inverter.
An
input
line
cord,
circuit
breaker,
EMI
Filter
Assembly,
contactor,
inrush
limiting
circuitry,
bridge
rectifier,
electrolytic
capacitors,
rail
inductors
and
rail
capacitors
comprise
the
basic
components
required
for
input
line
rectification.
Three
different
input
voltages
are
available
for
the
EVA
Series.
If
the
user
is
unsure
which
input
voltage
is
required
for
the
unit
on
hand,
check
the
identification
tag
on
the
rear
of
the
power
supply.
The
customer
provided
AC
power
input
is
provided
to
the
unit
via
the
four
conductor
AC
line
cord.
Circuit
protection
is
provided
by
CB1,
a
fast
acting
magnetic
trip
type
circuit
breaker.
The
load
side
of
CB1
is
connected
to
EMI
filter
A2.
The
output
of
the
EMI
filter
connects
to
K1,
a
three
phase
contactor.
K1
provides
fail
‐
safe
type
disconnection
of
the
line
voltage
to
the
power
supply
rectification
circuits.
K1’s
coil
is
controlled
by
a
variety
of
circuit
conditions,
which
will
be
described
later
on.
The
load
side
of
CB1
is
also
connected
to
low
voltage
power
supply
assembly
A9,
which
provides
various
voltages
for
housekeeping
and
control
circuit
power.
When
contactor
K1
is
energized,
voltage
is
applied
to
isolated
bridge
rectifier
power
module
CR1,
used
for
line
voltage
rectification.
The
output
of
CR1
is
connected
to
aluminum
electrolytic
capacitors
C1
and
C2
for
line
filtering
purposes.
Capacitors
C1
and
C2
are
initially
charged
through
inrush
limiting
charging
resistors
which
is
located
on
POWER
PWB
–
A6.
After
an
appropriate
period
of
time
to
charge
C1
and
C2,
relays
on
POWER
PWB
–
A6
are
energized
to
short
out
the
inrush
limiting
resistors.
The
generated
DC
buss
voltage
is
supplied
to
the
inverter
circuitry
through
L2,
L3,
L6
and
L7.
The
inductors
provide
isolation
for
the
electrolytic
capacitors
C1
and
C2,
so
the
inverter’s
high
