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DRX-1
CIRCUIT DESCRIPTION
1. Multi-Mode SOPS 50PS203
1.1. Why Multi-Mode SOPS?
Using ordinary SOPS results in a decrease of the
efficiency at low output loads due to the increase of the
switching frequency.
The Multi-Mode SOPS will reduce the switching frequency
at low loads but still preserves valley switching.
1.2. Block Diagram
Vi
MAINS
Overload
Overvoltage
protection
protection
7142
7143
1.3. Circuit Description
Input Circuit
The input circuit consists of a lightning protection circuit
and an EMI filter.
The lightning protection comprises R3120, sparkgaps
1124 and 1125. D6128, 6129, C2127 and R3129 are
optional.
L5110, L5115, C2120 and L5120 form the EMI filter. It
prevents inflow of noises into the mains.
Primary Rectifier/smoothing Circuit
The AC input is rectified by diodes 6151,6152, 6153, 6154
and smoothed into C2125. The voltage over C2125 is
approximately 300V. It can vary from 200V to 390V.
Start Circuit
This circuit is formed by R3125, 3126, R3141, C2140 and
R3132.
72
Rectifier
Lightning
Protection
EMI
FILTER
+ Vb
6140
3141
2140
7141
2141
7140
Control
6142
-Vreg
2151
6143
6200
5131
4
6210
2125
6215
2
7125
Power
switch
2146
feed forward
6220
Rsense
6230
8
6144
6240
7
7200
7251
Regulation
+12Vreg
Fig. 1
When the power plug is connected to the mains voltage,
the MOSFET 7125 will start conducting as soon as the
gate voltage reaches a treshold value. A current starts to
flow in primary winding 2-4. The MOSFET will be fed
forward via winding 7-8, R3150 and C2146.
+Vb Supply and Negative Regulation Voltage
The positive part of the voltage over winding 7-8 will be
rectified via R3150, D6140 and charged via R3140 into
C2140. The voltage over C2140 has a value of +30 till
+40V. This value depends on the value of the mains
voltage Vi and the load.
The negative part of the voltage over winding 7-8 will be
rectified via R3150, D6142 and charged into C2151. The
voltage over C2151 has a value of -15V and is used as
regulation voltage.
33Vstby
2260
6201
6211
+12Vstby
2211
2210
+12Vreg
+3V9
2214
6221
FLYB
7220
-5Nstby
2220
2222
-Vgnstby
2220
6231
2235
5.2Vstby
2241
2240
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