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P
rimary Sectio
n
F
ilteri
n
g an
d
Overvoltage
P
rotectio
n
Thi s secti o n i s on schematic 4Α
Α line filter FL401 suppresses conducted RFI on the A C inpu t lin es .
Fu
se an
d
Switc
h
Th is section is on sche matic 4Α
B
ri
d
ge
R
ectifier an
d B
loc
k
ing Ca
p
acitor
HP 811 OA Se
r
vice G
u
ide
Thi s i s t h e p art of Figure 7-2 shown on th e
l
eft of the dotted- line.
RFI ge n erated by t he switchin g components of the
p
ow er s upply is
preven ted
f
ro m cond u ct ion b ack into the
A
C lin es by C401, C402,
C403, C404, LP 401, and C E 406, C E 407, CE408 .
P
o wer line
p
eak s are s upp ressed by th e v ari stor XS401,
p
reventing
over vol tage on capacitors C E406, CE 407, C E408 .
Fuse
F
401
i
s fitted in the phase line
f
or
p
rotection.
I
t is the only
p o w er li ne fuse .
S wi tch
S
W401 i s α double- pole switch which connects, or disconnects
t he s witching
p
ower supply from the ac
p
o w er .
Thi s sectio n is on schemati c 4Α
D
ep ending on the AC
p
ower input (90 VAC to 264 VA C) α rect ified
D C vo l tage
f
rom 100 VDC to 360 VD C is generated by the rect ifier
C R401 an d smoothed by
t
h e capaci tors C E 406, C E407, C E 408 . No
line se l ector swi tc h is requi red as
p
o w er conversio n is done in
o
ne
lin e- v ol tage range.
PWM
Control
U
nit, Switc
h
ing Transisto
r
s, a
nd
Transfo
r
mer
Thi s secti on i s on sche matic 4Α
The tra ns f or m er
p
ro vides e l ectri ca l i so l ati on bet w een t h e p rimary
v oltage/ p o w er an d the secondary v oltage/po w er. Th e phy sical
b e h aviour o f t he trans f ormer comp ares to α
c
h o k e wi t h α sing l e
p ri mary win ding Νρ, a n d on e or
m
ore secondary win dings N sek.
When t h e switching transistors Q404, Q405 are s witc hed on by t he
PWM contro l unit
U
401, t he
p
rimary winding of the transform er is
connected to th e rectified
D
C vo ltage (100 VDC to 360 VDC) for the
Ion-time' .
Due to the secon dary win ding
p
o larity
a
nd t he rect ifying diodes
C R408, CR409, CR 421, C R422, C R423 and CR424, the
p
rimary
win ding is ch arged . There is no
p
o wer tra nsmiss ion during the
I
on-time' .
Wh en
t
he s wi tc hin g transistors are off du ring the 'off time',
th e
p
o w er charge in t he
p
rimary win ding
i
s tra ns ferred into the
seco n dar y win d in gs.
F
unctio
n
al Desc
r
iptio
n
7-7
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