ML4835

8

Setting minimum input voltage for output regulation can

current mode:

C

PEAO

K

DTs

t

P

V

VV

L

DTs

R

RAMP

MAX

OUT

IN

OUT

IN

SENSE

=-

-

-

-









-



!

"

$##

´

22

1

1

22

2

18

()

()

D

:?

(1)

And for average current mode:

C

PEAO

K

DTs

t

P

V

V

L

DTs

R

RAMP

MAX

OUT

IN

OUT

SENSE

=-

-







!

"

$##

´

22

1

1

2

2

18

()

()

D

:?

(1a)

Where

Dt is the dead time.

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.

TRANSCONDUCTANCEAMPLIFIERS

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

Figure 5. Compensation Network

Figure 6. Output Configuration

Figure 7. Transconductance Amplifier Characteristics

–

+

1

2.5V

PVFB/OVP

R1

C1

C2

CURRENT

MIRROR

IN

OUT

CURRENT

MIRROR

IN

OUT

IQ +

2

IQ –

2

LINEAR SLOPE REGION

0

Figure 4. Simplified Model of ML4835 EOL Functionality

ML4835

POWER LEVEL

TRIP POINT

POWER DETECT

POWER SHUTOFF