Technical information

24
re-
ig
n
i
t
i
on vo
l
ta
g
e an
d
t
h
e current supp
l
y vo
l
ta
g
e
d
e
-
creases. I
f
the re-ignition voltage exceeds the supply
volta
g
e, the lamp
g
oes out
(
see also chapter 6.2.2
“Increase in re-ignition peak”
).
This means that P
O
WERBALL H
CI
®
m
us
t n
o
t
be
d
immed by reducin
g
the supply volta
g
e
,
as the
re-i
g
nition peak can cause earlier extin
g
uishin
g
o
f
the lam
p
or
f
licker
.
5.
2
.
2
Ph
ase contro
l
:
l
ea
di
n
g
e
dg
e, tra
ili
n
g
e
dge
Fi
g
. 26 and 27 show the decrease in e
ff
ective supply
vo
l
ta
g
e
b
y p
h
ase contro
l
w
i
t
h
l
ea
di
n
g
e
dg
e or tra
ili
n
g
e
dg
e.
Th
ere are a
l
so var
i
at
i
ons
i
n w
hi
c
h
t
h
e supp
l
y
volta
g
e is reduced in the middle and not be
f
ore o
r
a
f
ter the zero crossin
g
. In other versions, the supply
vo
l
ta
g
e
i
n t
h
e
l
ea
di
n
g
e
dg
e p
h
ase
i
s on
l
y
d
ecrease
d
a
n
d
n
o
t r
educed
t
o
z
e
r
o.
F
o
r th
e
phase control with leadin
g
ed
g
e
,
the result
-
i
n
g
i
nterva
l
s w
i
t
h
no current resu
l
t
i
n a
g
reater coo
li
n
g
down o
f
plasma end electrodes, thus increasin
g
the
re-i
g
nition peak, causin
g
the lamp to
g
o o
ff
earlier
.
Fo
r t
he
p
h
ase contro
l
w
i
t
h
tra
ili
n
g
e
dg
e
o
r
o
t
he
r
m
et
h
o
d
s w
h
ere supp
l
y vo
l
ta
g
e
i
s temporar
il
y sw
i
tc
h
e
d
off or reduced, suitable means are re
q
uired to
p
rovide
an un
i
nterru
p
te
d
,
“
smoot
h”
l
am
p
current to
p
revent t
h
e
lamp
f
rom
f
lickerin
g
and
g
oin
g
o
ff.
Increased blackenin
g
and there
f
ore a drop in luminous
f
lux must be expected in all versions compared to
f
ull
-
l
oa
d
o
p
erat
i
on
.
5.
2
.
3
I
ncreas
i
n
g
c
h
o
k
e
i
mpe
d
ance or
d
ecreas
i
n
g
l
am
p
curren
t
I
ncreas
i
ng c
h
o
k
e
i
mpe
d
ance re
d
uces t
h
e current
t
h
rou
gh
t
h
e
l
amp.
Th
e supp
l
y vo
l
ta
g
e rema
i
ns t
h
e
same so t
h
at t
h
e vo
l
ta
g
e
i
s st
ill
high
enou
gh
to re-
i
g
nite the lamp. The
f
latter zero crossin
g
o
f
the current
can
h
owever
b
e expecte
d
to cause
g
reater coo
li
n
g
down o
f
plasma and electrodes, with
g
reater blacken-
in
g
as a result o
f
the processes at the electrode durin
g
re-i
g
nition. The blackenin
g
there
f
ore causes a
g
reater
dro
p
in luminous
f
lux com
p
ared to
f
ull-load o
p
eration
.
The least disadvanta
g
es are to be expected by reduc-
i
n
g
current
i
n rectan
g
u
l
ar mo
d
e.
Th
e steep zero cross-
i
n
g
s mean t
h
at
l
ower re-
ig
n
i
t
i
on pea
k
s an
d
l
ess
bl
ac
k-
enin
g
f
rom sputterin
g
can be expected
.
I
f
a switchover to other chokes is used
f
or dimmin
g
l
amps w
i
t
h
a watta
g
e
>
400 W, the
y
must be le
f
t to
burn at 100
%
f
or at least 1 hour
.
5.2.4
C
han
g
e in frequency for hi
g
h-frequency mode
A
c
h
an
g
e
i
n watta
g
e w
h
en us
i
n
g
an
i
n
d
uct
i
ve
b
a
ll
ast
c
an also be achieved by varyin
g
the
f
requency o
f
the
power suppl
y
, as the inductive resistance o
f
the choke
d
epends on
f
requency. The chan
g
e in choke imped
-
a
nce at low
f
re
q
uencies has been dealt with in the
prece
di
n
g
c
h
apter 5.2.3
.
I
f
the chan
g
e in impedance is caused by chan
g
in
g
the
f
requency in radio
f
requency operation, in dischar
g
e
lam
p
s the
p
ossible occurrence o
f
acoustic resonances
h
as to
b
e cons
id
ere
d
.
R
esonance
i
n t
h
e
di
sc
h
ar
g
e
tu
b
e can cause t
h
e
pl
asma to start to osc
ill
ate
d
e
-
pen
di
n
g
on t
h
e arc tu
b
e
g
eometry an
d
p
l
asma tem-
perature. This can cause the lamp to
f
licker or
g
o o
ff
,
a
nd in extreme cases, destruction o
f
the lam
p
should
t
he
a
r
c
a
tt
ach
t
o
t
he
a
r
c
t
ube
w
all
due
t
o
se
v
e
r
e
r
eso
-
n
ance. This is wh
y
a currentl
y
proposed standard fo
r
e
lectronic o
p
eration o
f
metal halide lam
p
s limits the
a
mount o
f
hi
g
h-
f
requency oscillations.
It is di
ff
icult to
f
ind reliabl
y
resonance-
f
ree operat-
in
g
windows,
f
or various reasons: the resonance
f
requencies chan
g
e durin
g
the start-up and also dur-
Fi
g
. 26: Principle o
f
phase control with leadin
g
ed
g
e
(
idealized dia
g
ram
)
Fig
. 28:
A
mp
li
tu
d
e mo
d
u
l
at
i
on e.
g
.
by
c
h
o
k
e c
h
an
g
e
-
o
v
er
U
B
U,I
␣
␭
U
B
Supply voltage
U
L
Lamp voltage
␣ Ignition angle
␭ Current flow angle
t
U
L
Fi
g
. 27: Principle o
f
phase control with trailin
g
ed
g
e
(
idealized dia
g
ram
)
U
B
U,I
␣
␭
t
U
L
U
B
Supply voltage
U
L
Lamp voltage
␣ Ignition angle
␭ Current flow angle
l
t