Microsemi

Linfinity Microelectronics Division

11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570

Page 4

Copyright

© 2000

Rev. 0.3d,2000-11-30

RangeMAX

™

LXM1615-03-xx

A

M I CROSEM I

COM P A N Y

   

    



LAMP VOLTAGE & LAMP CURRENT – BURST MODE OPERATION

  – 50% Burst Duty Cycle

 – 2% Burst Duty Cycle

Rather than using the traditional dimming technique of

varying

lamp

current

magnitude

to

adjust

light

output,

RangeMAX inverters use a fixed lamp current value with a duty

cycle control method.

The lamp current burst width can be modulated from 100%

(continuous lamp current) down to a 2% duty cycle, allowing the

lamp to be dimmed to less than 1% of its full brightness.

As can be seen in Trace 4 of Figure 3 photo at right, careful

design consideration was given to controlling lamp start voltage

to softly start current flow. This eliminates current overshoot

that can result in premature cathode wear and reduce lamp life.

 ! – 2% Burst Duty Cycle (Expanded Time Base)

R a mp G en.

T ransfo rm er

Drive r

H igh Voltage

T ransfo rm er

C o mparator

Ra m p

+

-

I

SEN SE

V

SEN SE

V

LO

V

HI

V

BR IT E

.25 -

2.2V

DC

Figure 4 – RangeMAX Simplified Block Diagram

HIGHLIGHTS

voltage to pulse width converter that minimizes system

design work and system noise susceptibility.

This

provides a familiar and convenient interface while

reducing the potential for externally induced noise,

which can cause lamp flicker.

with the burst frequency synchronized to the video frame

rate.

This provides operation with no visible display

disturbances caused by beat frequencies between the

lamps and video frame rates. In this synchronous mode,

the inverter burst rate operates at twice the video refresh

rate, well beyond standard 50/60Hz video refresh rates

where the eye can perceive pulsing light.

onboard oscillator operates the inverter burst rate at

about 500Hz.

In this non-synchronous mode, minor

display disturbances can be found under certain video

conditions.

This performance may be acceptable for

many applications, but synchronization must be used

when no disturbance can be tolerated.