ML4835 データシートの表示（PDF） - Micro Linear Corporation

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ML4835

Compact Fluorescent Electronic Dimming Ballast Controller

Micro Linear Corporation 

ML4835

FUNCTIONAL DESCRIPTION (Continued)

Setting minimum input voltage for output regulation can

be achieved by selecting CRAMP as follows for peak

current mode:

: ? !   "$## CRAMP

=

PEAO MAX

22K

(1- D)Ts - Dt

1

2POUT -

VIN

VOUT -

2L

2VIN

(1- D)Ts

8 ´ RSENSE

(1)

And for average current mode:

: ? !   "$## CRAMP

=

PEAO MAX

22K

(1- D)Ts - Dt

1

2POUT -

VIN

VOUT

2L

(1- D)Ts 8 ´ RSENSE

(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.

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

POWER DETECT

POWER LEVEL

TRIP POINT

ML4835

POWER SHUTOFF

Figure 4. Simplified Model of ML4835 EOL Functionality

CURRENT

MIRROR

IN

OUT

IQ

+

gmVIN

2

IQ – gmVIN

2

io = gmVIN

IN

OUT

CURRENT

MIRROR

Figure 6. Output Configuration

PVFB/OVP

1

–

2.5V

+

C2

R1

C1

iO

0

VIN DIFFERENTIAL

LINEAR SLOPE REGION

Figure 5. Compensation Network

8

Figure 7. Transconductance Amplifier Characteristics

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