ML4836CS datasheet(7/15 Pages) MICRO-LINEAR

7 / 15 page

ML4836

FUNCTIONAL DESCRIPTION (Continued)

The magnitude of the offset voltage that will appear at the

input is given by VOS = io/gm. For an io of 1µA and a gm

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.

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 4. Compensation Network

Figure 5. Transconductance Amplifier Characteristics

–

2.5V

LAMP FB

LEAO

VIN DIFFERENTIAL

LINEAR SLOPE REGION

Figure 6. Simplified Model of ML4836 EOL Functionality

LAMP

NETWORK

LAMP

PFC

ML4836

ML4836CS Datasheet(PDF) 7 Page - Micro Linear Corporation