Toshiba 1997 G Series Handbuch zur Fehlersuche - Seite 6
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4. Outline of the Current Resonant Type
Supply
Fig. 3 shows the block diagram for the current resonant
switch mode power supply. The primary side is an LC
series circuit. It consists of the primary winding of the
transformer and a resonant capacitor in series. Two
power MOS FET's in a push-pull configuration drive
the primary side of the transformer.
The switching action on the primary side of the trans-
former produces the main B+ on the secondary side.
5. Fundamental Theory of LC Series
Resonant Circuit
The LC series resonant switch mode power supply is a
frequency regulated power supply operating above reso-
nance. When the the load increases on the secondary
side of the transformer, the frequency decreases (oper-
ates closer to resonance) and the current increases. Con-
versely, when the load decreases, the frequency increases
and the current decreases.
Fig. 4 LC series resonant circuit
The main B+ is regulated by negative feedback. The
main B+ is fed into an error amplifier and outputted to a
photo coupler. The output of the photo coupler is ap-
plied to the primary side of the power supply to control
the switching speed.
PHOTO
COUPLER
Fig. 3 Basic configuration
VL (v)
e
f=
4
B+
ERROR
AMP
Increased Load
Decreased Load
Resonant point
Normal
Operating
1
Frequency
2p
LC
Fig. 5 Characteristics
Frequency