Toshiba CF35E50, Technical Training Manual

Page: 101 / 139

101
4. OUTLINE OF CURRENT RESONANT
TYPE SUPPLY
Basic configuration of current resonant type power supply
used in CN32E90 is shown on figure 14-3. Basic operation
is as follow. Primary winding of converter trans and resonant
capacitor are connected in series to consist of LC series
resonant circuit. And this is drived by push-pull of two power
MOS FET’s. Converter transformer operates in forward
mode. Just when primary switching device turns ON,
converter trans produces the secondary output.
Automatic voltage control operation is done in such way that
+B voltage is detected by error amp. to be fed back to
the primary OSC circuit via photo coupler, then controls
frequency.
Fig. 14-4. LC series resonating circuit
Fig. 14-5. Characteristic
5. FUNDAMENTAL THEORY
Voltage generating on L of LC series resonant circuit has
characteristic which varies with frequency peaking at resonant
point f= 1/ (2
p
LC
) [Hz] as shown in figure 14-4. The
circuit utilizes this characteristic to control output
voltage. Actual operation is done at higher frequency than
resonant point. By this operation, variable range of voltage
across L ranges from maximum voltage of resonant point to
power line voltage.
Fig. 14-3. Basic diagram
O
S
C
D
R
I
V
E
PHOTO
COUPLER
+B
ERROR
AMP
VL
e
VL (v)
e
Resonant point
Frequency
1
f=
2
p
LC