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CCFL inverters

Hi,

I am quite new in this subject but I have a question about a CCFL
inverter which I've tested. The inverter's current was measured to be
14 to 20 mA and the rms voltage was 520V. From most app. notes on CCFL
especially the Maxim note, the current stated usually in the region of
3mA to 8mA. What are the advantages and disadvantages of running the
inverter at 14 to 20 mA?

Cheers
Geoff
 
R

Robert Latest

Jan 1, 1970
0
On 19 Dec 2006 21:41:12 -0800,
in Msg. said:
I am quite new in this subject but I have a question about a CCFL
inverter which I've tested. The inverter's current was measured to be
14 to 20 mA and the rms voltage was 520V. From most app. notes on CCFL
especially the Maxim note, the current stated usually in the region of
3mA to 8mA. What are the advantages and disadvantages of running the
inverter at 14 to 20 mA?

How did you measure the RMS current and voltage? What does the user's
manual of the thing that you used to measure current and voltage have
to say about frequencies and waveforms?

robert
 
J

John Devereux

Jan 1, 1970
0
Hi,

I am quite new in this subject but I have a question about a CCFL
inverter which I've tested. The inverter's current was measured to be
14 to 20 mA and the rms voltage was 520V. From most app. notes on CCFL
especially the Maxim note, the current stated usually in the region of
3mA to 8mA. What are the advantages and disadvantages of running the
inverter at 14 to 20 mA?

You need to look at the bulb specifications, not (just) the inverter.

If run over-current, the bulb lifetime will be much shorter.
 
P

PeteS

Jan 1, 1970
0
Hi,

I am quite new in this subject but I have a question about a CCFL
inverter which I've tested. The inverter's current was measured to be
14 to 20 mA and the rms voltage was 520V. From most app. notes on CCFL
especially the Maxim note, the current stated usually in the region of
3mA to 8mA. What are the advantages and disadvantages of running the
inverter at 14 to 20 mA?

Cheers
Geoff

Most CCFL backlights operate at about 5-6mA, but there could well be
some that operate much higher.

Did you look at the waveform with a scope? Most CCFL devices require a
(fairly good) sinusoid, but your measurement may have distorted the
waveform (and therefore changed the crest factor so you got an invalid
measurement). [I know this was already mentioned :)]

Make sure it's already started before looking with even a HV probe - the
startup voltages required for CCFL backlights can be as much as 3x the
run voltage.

Cheers

PeteS
 
Hi,

The sine wave looks fine when measured by the voltage and current
probe. I have carried out the measurement using a Tektronix and Agilent
scope and both gave similar results. I believe the tube brightness was
measured to be 25000 nits but I can verify it when I start work next
year. The tubes used were straight and used in a 12 inch LCD panel. I
have another inverter which is used to drive another 12 inch panel but
when I increase the current by adjusting the PWM, the sine wave becomes
jagged instead of curved. Could this be caused by the inductance from
the transformer? Can someone direct me to link that describes about
this sine wave issue?

Cheers
Geoff


Hi,

I am quite new in this subject but I have a question about a CCFL
inverter which I've tested. The inverter's current was measured to be
14 to 20 mA and the rms voltage was 520V. From most app. notes on CCFL
especially the Maxim note, the current stated usually in the region of
3mA to 8mA. What are the advantages and disadvantages of running the
inverter at 14 to 20 mA?

Cheers
Geoff

Most CCFL backlights operate at about 5-6mA, but there could well be
some that operate much higher.

Did you look at the waveform with a scope? Most CCFL devices require a
(fairly good) sinusoid, but your measurement may have distorted the
waveform (and therefore changed the crest factor so you got an invalid
measurement). [I know this was already mentioned :)]

Make sure it's already started before looking with even a HV probe - the
startup voltages required for CCFL backlights can be as much as 3x the
run voltage.

Cheers

PeteS
 
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