ml4836 Microsemi Corporation, ml4836 Datasheet - Page 7

• Manufacturer Part Number: ml4836
• Description: Compact Fluorescent Electronic Dimming Ballast Controller
• Manufacturer: Microsemi Corporation

FUNCTIONAL DESCRIPTION
The magnitude of the offset voltage that will appear at the
input is given by V
of 0.05 µW the input referred offset will be 20mV.
Capacitor C1 as shown in Figure 4 is used to block the
DC current to minimize the adverse effect of offsets.
Slew rate enhancement is incorporated into all of the
operational transconductance amplifiers in the ML4836.
This improves the recovery of the circuit in response to
power up and transient conditions. The response to large
signals will be somewhat non-linear as the
transconductance amplifiers change from their low to high
transconductance mode, as illustrated in Figure 5.
LAMP FB
2.5V
1
Figure 4. Compensation Network
–
+
OS
= io/gm. For an io of 1µA and a gm
PFC
Figure 6. Simplified Model of ML4836 EOL Functionality
R1
C1
LEAO
(Continued)
R9
C2
END OF LAMP LIFE
At the end of a lamp’s life when the emissive material is
depleted, the arc current is rectified and high voltage
occurs across the lamp near the depleted cathode. The
ballast acts as a constant current source so power is
dissipated near the depleted cathode which can lead to
arcing and bulb cracking. Compact fluorescent lamps are
more prone to cracking or shattering because their small
diameter can’t dissipate as much heat as the larger linear
lamps. Compact fluorescents also present more of a
safety hazard since they are usually used in downlighting
systems without reflector covers.
Figure 5. Transconductance Amplifier Characteristics
NETWORK
LAMP
ML4836
i
O
0
LINEAR SLOPE REGION
LAMP
V
IN
DIFFERENTIAL
ML4836
7