16
4. Power supply
MG5.1E
4.1 European power factor correction circuit
Figure 4-5
REGULATOR
DRIVE
BRIDGE
7104
2110
AC INPUT
350V DC OUT
6103
5109
CURRENT SENSE
5
3
7102
CL 96532100_086.eps
121199
The MG5.1 Power Factor correction circuit uses a Boost
regulator to smooth out the current draw from the AC line
improving the Power Factor to 0.99, which is accomplished by
drawing current from the AC source throughout the entire AC
cycle making the current waveform sinusoidal. (figure 4-5) Input
to the module is connected to the AC Mains. The output
supplies are approximately 350 volts DC to the Main and
Standby Switched mode Power Supply circuit. The Boost
Regulator circuit produces a higher output voltage than the
input voltage. The regulator drive circuit compares 6103's
output voltage, the input voltage from the bridge, and the
voltage across the current sensing resistors to control the On
time of 7104. This will maintain the output voltage at 350 volts
DC and limit the input current to acceptable levels. When 7104
is On, current flow through 5109 stores energy in the choke.
When 7104 turns Off, 5109 reverses polarity and charges 2110.
Using this type of regulation, current is drawn from the AC
source throughout the entire cycle, keeping the current
waveform sinusoidal. When the AC cycle is at its low point,
7104 is on for a longer period of time. When the AC voltage is
at its peak, 7104 is on for a shorter time to store the same
amount of energy in 5109 to maintain the output voltage at 350
volts.
If the Boost regulator circuit should become inoperative, due to
a loss of regulator drive, operating voltage is still applied to the
set. The supply voltage to the switching supplies will drop from
350 volt to approximately 329 volts depending on the Mains
voltage. Since the customer would not detect a failure, the
operation of this circuit should be checked after any repair of
the set.
