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Current mode power supply 30PS203
GB 56
DVD 950
10.
10. Current mode power supply 30PS203
10.1 Blockdiagram
Figure 10-1
10.1.1 Function description of the current mode power supply
MOSFET 7125 is used as a power switch controlled by the
controller IC 7110. When the switch is closed, energy is
transferred from the mains into the transformer. This energy is
then supplied to the load when the switch is opened. By control
of the switched-on time, the energy transferred in each cycle is
regulated so that the output voltages are independent of load
or input voltage variations. The controlling device MC44603P is
an integrated pulse width modulator. A clock signal initiates
power pulses at a fixed frequency. The termination of each
output pulse occurs when an analogue of the inductor current
reaches a threshold established by the error signal. In this way
the error signal actually controls the peak inductor current on
cycle-by-cycle basis.
10.2 General description of MC44603
The MC44603 is an enhanced high performance controller that
is specifically designed for Off-line and dc-to dc converter
applications. This device has the unique ability of automatically
changing operating modes if the converter output is
overloaded., unloaded, or shorted. The MC44603 has several
distinguishing features when compared to conventional SMPS
controllers. These features consist of a foldback facility for
overload protection, a standby mode when the converter output
is slightly loaded, a demagnetisation detection for reduced
switching stresses on transistor and diodes, and a high current
totem pole output ideally suited for driving a power MOSFET. It
can also be used for driving a bipolar transistor in low power
converters. It is optimised to operate in discontinuous mode but
can also operate in continuous mode. Its advanced design
allows use in current mode or voltage mode control
applications.
10.3 Pin connections
Figure 10-2
+6V Stand By
GNDs
Feedback
Voltage
Rsense
7201
7200
6230
6260
6250
6240
5131
7125
2121
REGULATION
EMI
FILTER
MAINS
+12V
-8V Stand By
R
Q
S
OSC.
+
+
-
-
2.5V
Error
Amplifier
latch
Lightning
Protection
Rectifier
1
5
7
9
Soft-Start
Control
Overvoltage
Mgmt
Mgmt
Demagnet.
Output
Sense
Current
Sense
Input
Buffer
Supply Init
Out
Gnd
7110
6129
6132
Vc
+5V
2240
2260
Stand By
+5V Stand By
-40V
+3V3
GND
7233
2250
7236
2230
6210
2210
6220
CL 96532065_064.eps
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Rref
R Frequency Standby
Voltage feedback Input
Error Amp Output
R Power Standby
Sof-Start/Dmax/
Voltage Mode
Sync Input
Overvoltage Protection(OVP)
Current Sense Input
Demag. Detection
Foldback Input
10
7
CT
8
9
6
5
11
12
Output
Gnd
VC
VCC
3
4
2
14
13
15
1
16
CL 96532065_057.eps
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