Another Capacitor Value Question

[Tim]

Firstly, thanks to all you GURUS that help us out in this newsgroup from
time to time.

I have another Cap question for ya,

This guy is marked 10J 3KV

I know that it is rated at 3000 volts of course, but the 10J has me
stumped.

This is used in the final stages of a CCFL circuit in a LCD monitor. I
suspect that these are leaky and causing the HV to shut down after a
couple of seconds.

Thanks In Advance,

- Tim -

 

[Lostgallifreyan]

I have another Cap question for ya,

This guy is marked 10J 3KV

I know that it is rated at 3000 volts of course, but the 10J has me
stumped.

10J means 10 picofarads at 5% tolerance.

I am NEVER a guru, but I wanted an answer too so I looked and found this:
http://www.solarbotics.net/library/pieces/parts_elect_pass_cap_code.html

 

[Salmon Egg]

10J means 10 picofarads at 5% tolerance.

I am NEVER a guru, but I wanted an answer too so I looked and found this:
http://www.solarbotics.net/library/pieces/parts_elect_pass_cap_code.html

With my background, I would have taken the 10J to mean 10 Joules. My
background is in lasers and 10J at 3kV seems about right to pump flashtubes
for many small pulsed lasers. A helpful clue would be an indication of how
big the capacitor is.

I do not understand why an LCD would need a 3kV capacitor. But I do not know
that much about the nitty gritty of LCD displays. But I do not know what
CCFL means either.

Enlighten me.

Bill
-- Fermez le Bush

 

[Ross Herbert]

Firstly, thanks to all you GURUS that help us out in this newsgroup from
time to time.

I have another Cap question for ya,

This guy is marked 10J 3KV

I know that it is rated at 3000 volts of course, but the 10J has me
stumped.

This is used in the final stages of a CCFL circuit in a LCD monitor. I
suspect that these are leaky and causing the HV to shut down after a
couple of seconds.

Thanks In Advance,

- Tim -

Tim,

Some pics of a typical CCFL inverter on this page
http://www.crystalfontz.com/products/320240c/samples.html#CCFL1

The bottom 3 pics indicate a simple 2 transistor oscillator and
step-up transformer arrangement. A small blue high voltage cap is next
to the output socket. Is your unknown cap similar? If so then the
answer of 10pF 2kV proposed by Lostgallifreyan sounds right.

 

[Lostgallifreyan]

With my background, I would have taken the 10J to mean 10 Joules. My
background is in lasers and 10J at 3kV seems about right to pump
flashtubes for many small pulsed lasers. A helpful clue would be an
indication of how big the capacitor is.

Me too. Not with that level of experience, but it meant the same to me
too. And most of Google's results. I think that's maybe why the info wasn't
easy to find. I saw two occurences of 'picofarad' that helped me narrow it
down to find a decent page about it.

I do not understand why an LCD would need a 3kV capacitor. But I do
not know that much about the nitty gritty of LCD displays. But I do
not know what CCFL means either.

Enlighten me.

Cold Cathode Fluorescent Lamp. Those thin bright tubes used to modify
computer cases, car hi-fi's, backlight LCD's and give good spread of light
in tight spaces generally. They use a high voltage high frequency AC to
drive them, I think, closely related to the suppies used in
electroluminescent displays.

 

[PeteS]

Me too. Not with that level of experience, but it meant the same to me
too. And most of Google's results. I think that's maybe why the info wasn't
easy to find. I saw two occurences of 'picofarad' that helped me narrow it
down to find a decent page about it.


Cold Cathode Fluorescent Lamp. Those thin bright tubes used to modify
computer cases, car hi-fi's, backlight LCD's and give good spread of light
in tight spaces generally. They use a high voltage high frequency AC to
drive them, I think, closely related to the suppies used in
electroluminescent displays.

As I have a CCFL in an existing design...

Typical CCFL drive is at between 20kHz and 100kHz (it varies according
to load amongst other things) and the AC output ranges from perhaps
400Vrms to 750Vrms depending on model. [You have to choose the
appropriate parts for each different one or have quite spectacular
results ]

Note that during startup (strike, as it's known) the terminal potential
can be as high as 1.5kVrms.

Quoting the datasheet for my CCFL for which I designed the inverter:
"The Non-load output voltage (VS) of the inverter should be designed to
have some margin,
because VS may increase due to the leak current which may be caused by
wiring of CFL cables. (Reference value : 2015Vrms Min.)"

The spec table states that the unit will strike at 1550Vrms worst case,
0C.

As most (all?) controllers have an internal sequencer with operate and
short detection, a flaky output cap will cause the unit to shut down
almost immediately (the controller will sense a short). Usually the
strike is tried 3 or 4 times before autoshutdown (assumes no current
drawn), but heavy loading usually operates an electronic circuit
breaker.

Hope that helps

Cheers

PeteS

 

[Salmon Egg]

Hope that helps

That helps. I still hate cryptic acronyms.

Bill
-- Fermez le Bush

 

[PeteS]

That helps. I still hate cryptic acronyms.

Bill
-- Fermez le Bush

PCMCIA -> People Can't Memorise Computer Industry Acronyms



Cheers

PeteS

 

[Lostgallifreyan]

That helps. I still hate cryptic acronyms.

There was a time when the same thing could be said of 'LASER'. Not that
it would be true. New words can either come from Latin, Greek, Old High
German even, whatever is a good root with long standing, or, they can be
useful condensations. There is ONE reason the term laser became a word, and
that's because someone had the sense to know you had to be able to say it.
Similar things that formed true new words are Radar, Sonar. Some idiot
tried with Lidar, but that's just a cheap derivative, it feels like one,
no-one could actually drop that word in conversation without looking like a
dork. Even TLA
works better, as do some of the better TLA's like MRI, VGA, CRT, LCD...
They can be said, they make sounds like words. Can anyone say CCFL as a
word? Even the Welsh with practise at syllables with no vowels as most of
us know them would have trouble with it, and would know, more than most of
us, there is NO poetry to the term. In short, it sucks. If people really
want their technically creative legacy to last, they must think this stuff
through. It costs nothing, and being subject to copyright, it might be
better and longer lasting than a patent.

/end rant. I like rants. Without them I am useless, and that one is mine.

 

[Tim]

Yup, that's like the ones on my board. There are 4 of them, one for each
output I guess, as they are located at each connector. I'll just replace
them all just to be sure. The 3kv kinda threw me for a bit, but someone
explained about that HV spike at turn-on now that makes sense too.

Thanks,

- Tim -

 

[Tim]

Thanks for the info and the link. I bookmarked it for future reference.

- Tim -

 

[Tim]

Hey now I know why the cap has that 3kv rating.

Thanks for your input.

- Tim -

Me too. Not with that level of experience, but it meant the same to me
too. And most of Google's results. I think that's maybe why the info wasn't
easy to find. I saw two occurences of 'picofarad' that helped me narrow it
down to find a decent page about it.


Cold Cathode Fluorescent Lamp. Those thin bright tubes used to modify
computer cases, car hi-fi's, backlight LCD's and give good spread of light
in tight spaces generally. They use a high voltage high frequency AC to
drive them, I think, closely related to the suppies used in
electroluminescent displays.

As I have a CCFL in an existing design...

Typical CCFL drive is at between 20kHz and 100kHz (it varies according
to load amongst other things) and the AC output ranges from perhaps
400Vrms to 750Vrms depending on model. [You have to choose the
appropriate parts for each different one or have quite spectacular
results ]

Note that during startup (strike, as it's known) the terminal potential
can be as high as 1.5kVrms.

Quoting the datasheet for my CCFL for which I designed the inverter:
"The Non-load output voltage (VS) of the inverter should be designed to
have some margin,
because VS may increase due to the leak current which may be caused by
wiring of CFL cables. (Reference value : 2015Vrms Min.)"

The spec table states that the unit will strike at 1550Vrms worst case,
0C.

As most (all?) controllers have an internal sequencer with operate and
short detection, a flaky output cap will cause the unit to shut down
almost immediately (the controller will sense a short). Usually the

 

[Homer J Simpson]

There was a time when the same thing could be said of 'LASER'. Not that
it would be true. New words can either come from Latin, Greek, Old High
German even, whatever is a good root with long standing, or, they can be
useful condensations.

I think AIDS is the stupidest acronym ever.

Health aids? Home aides?

 

[Lostgallifreyan]

I think AIDS is the stupidest acronym ever.

Health aids? Home aides?

Yep, that one IS hard to beat, is it not?