ml4835 Microsemi Corporation, ml4835 Datasheet - Page 8

• Manufacturer Part Number: ml4835
• Description: Compact Fluorescent Electronic Dimming Ballast Controller
• Manufacturer: Microsemi Corporation

ML4835
FUNCTIONAL DESCRIPTION
Setting minimum input voltage for output regulation can
be achieved by selecting C
current mode:
And for average current mode:
Where t is the dead time.
8
Figure 4. Simplified Model of ML4835 EOL Functionality
C
C
POWER LEVEL
RAMP
RAMP
TRIP POINT
PVFB/OVP
2.5V
=
=
PEAO
1
PEAO
22
22
K
Figure 5. Compensation Network
MAX
K
MAX
:
(
1
:
–
+
-
(
1
D Ts
-
)
D Ts
)
-
ML4835
D
-
t
?
D
!
t
?
2
V
P
!
IN
OUT
RAMP
2
V
P
IN
OUT
-

 
V
OUT
-

 
as follows for peak
V
2
-
OUT
2
L
R1
L
C1
POWER SHUTOFF
2
1
V
IN
1
(
1
POWER DETECT
-
(
1
D Ts
-
)
D Ts
)
"
# #
$
8
"
# #
$
(Continued)
8
´
´
R
R
SENSE
SENSE
C2
(1a)
(1)
OVERVOLTAGE PROTECTION AND INHIBIT
The OVP pin serves to protect the power circuit from
being subjected to excessive voltages if the load should
change suddenly (lamp removal). A divider from the high
voltage DC bus sets the OVP trip level. When the voltage
on PVFB/OVP exceeds 2.75V, the PFC transistor are
inhibited. The ballast section will continue to operate.
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
IQ –
Figure 7. Transconductance Amplifier Characteristics
gmV
2
IN
IQ +
Figure 6. Output Configuration
gmV
2
IN
i
IN
IN
O
0
CURRENT
CURRENT
MIRROR
MIRROR
LINEAR SLOPE REGION
OUT
OUT
V
IN
DIFFERENTIAL
io = gmV
IN