FA5332M Fuji Electric holdings CO.,Ltd, FA5332M Datasheet - Page 6

• Manufacturer Part Number: FA5332M
• Description: Bipolar Ic For Power Factor Correction
• Manufacturer: Fuji Electric holdings CO.,Ltd

3. Current error amplifier and overcurrent limiting circuit
The current error amplifier forms a current loop to change the
input circuit current into sinusoidal waves. As Fig. 3 shows, the
multiplier output is connected to pin 2 (IIN –) through a resistor
(RA) to input the reference current signal. Pin 16 (IDET) is a
current input terminal. Design the circuit so that the voltage at
pin 16 will be within the range from 0 (GND potential) to –1.0V.
Connect a phase correction resistor and capacitors across pin
1 (amplifier output) and pin 2. See Fig. 4 for the expected gain
characteristics of the circuit shown in Fig. 3.
Here,
The voltage gain (G1) between Z and P of the circuit (gain
between pins 16 and 1) is given as follows:
Ensure an adequate phase margin by selecting C1 and C2 so
that the p/z ratio is about 10. The current error amplifier output
is used as an input to the comparator for PWM.
The overcurrent detection comparator (C2) limits an
overcurrent. The threshold voltage for overcurrent detection at
pin 16 is –1.10V. Connect noise filters Rn and Cn to prevent
the voltage at pin 16 from fluctuating due to noise, causing the
comparator to malfunction. For Rn, select a resistor of up to
27 . (See P66, 4. No-load operation )
4. Comparator for PWM
Figure 5 shows the comparator for PWM. When the oscillator
output (Va) is smaller than the current error amplifier output
(Vc), the comparator output is high and the output ON signal is
generated at pin 8. Pin 11 (CS) is a terminal for soft start. This
terminal charges capacitor C4 with the internal constant current
(10 A) for a soft start. Priority is given to Vb and Vc whichever
is lower.
5. Multiplier
The multiplier generates a reference current signal. Input a
fully rectified sinusoidal signal voltage into pin 3 (VDET).
Design the circuit to keep the peak voltage at pin 3 within a
range from 0.65V to 2.4V. The multiplier output voltage (Vm) is
roughly given as follows (see Fig. 6):
Vm = 1.25 – (Ve –1.55) • Vs .................................... (8)
As Fig. 3 shows Vm is internally connected to pin 2 (IIN–) of the
current error amplifier A2 through a 10k resistor. (See the
characteristic curve, page 67 for the input and output
characteristics of the multiplier.)
Z =
G1 = 20 • log
C =
p =
2 R5 • C3
2 R5 • C
C2 + C3
C2 • C3
1
1
10
{ 0.75 ( R5
.................................................. (5)
............................................. (6)
RA
+ 1) }
.................... (7)
Fig. 3 Current error amplifier and overcurrent limiting circuit
C3
Voltage gain
(dB)
detection
Rn
Current
G1
R7
R6
R5
V
C2
IN
CS
C4
Fig. 4 Voltage gain-frequency
Cn
3
11
4 16
1
2
Vb
Fig. 5 PWM comparator
Vs
Fig. 6 Multiplier
Ve
10k
RC
5k
Vocp
MUL
10 A
Vm
Z
RA
C3
MUL
15k
CURR.AMP(A2) output Vc
Oscillator output Va
RB
+
_
PWM comparator
CURR.AMP
A2
C2
OPC
ER.AMP(A1) output
VREF
5V
Vm
P
FA5332P(M)
comparator
Frequency
PWM
F.F
63