DELTA ELEKTRONIKA BV SM1540-D SM7020-D SM3004-D
Page 3 - 8 DESCRIPTIONS 1989 rev. May 2008
CIRCUIT DESCRIPTION
The 220 V AC line volt age is rec tified by a bridge
rectifier and smoothed by a large electrolytic ca paci-
tor. The 50 Hz choke in the in put cir cuit improves the
waveform of the in put, so that no low frequency dis -
tortion is produced on the line voltage.
Carefully de signed RFI fil ters protect the line and
the load from the high frequency in terference pro -
duced in side the power sup ply.
When the unit is switched on, the elec trolytic ca -
pacitor is charged via the resistor of the SOFT
START cir cuit, so no large in rush current will flow.
As soon as the volt age is suf ficiently high the power
supply starts working and the se ries re sistor is by-
passed by a triac.
The op erating switching fre quency of 100 kHz
has many ad vantages like small size, light weight,
low rip ple and fast reg ulation.
The rec tified 220 V (300 V DC) is chopped by the
transistors and transformed to a lower voltage. This
100 kHz power converter is of the feed forward type.
The reg ulation is achieved by pulse width mod ula-
tion.
Care ful de sign, over-rat ing of vi tal com po nents,
several built-in protections and cool op eration (be -
cause of the very high efficiency) make the SM se -
ries very re liable power sup plies which can be used
con tin u ously at max i mum rat ing.
fig. 3 - 31 Simplified functional diagram of SM1540-D, SM7020-D, SM3004-D
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