TRANSCONDUCTANCE AMPLIFIERS
The PFC voltage feedback amplifier is implemented as an
operational transconductance amplifier. It is designed to
have low small signal forward transconductance such that
a large value of load resistor (R1) and a low value
ceramic capacitor (<1µF) can be used for AC coupling
(C1) in the frequency compensation network. The
compensation network shown in Figure 3 will introduce a
zero and a pole at:
fZ
=
2π
1
R1C1
fP
=
1
2π R1C2
(2)
ML4833
PVFB/OVP
18
–
2.5V
+
R1
C2
C1
Figure 3. Compensation Network
EMI
FILTER
SINE
RAMP
CLK
PFC OUT
L
PIFB
2
–A
RSENSE
OUT A
14
SINE
+
–
SW2
SW1
RQ
VOUT
L
A
RA
M
INVERTER
LAMP
P
NETWORK
L
RB
A
M
P
18 PVFB/OVP
S
OSC
V TO I
CLK
PEAO –
+
VREF1
10 CRAMP
CRAMP
1
PEAO
R1
C2
C1
Figure 2. ML4833 PFC Controller Section
7