CCFT dummy loads

[bob]

has anyone constructed a dummy test load for testing CCFL high voltage
power supples?

I have been running into more of these and would like a quick way to
load the inverter to see if its working, or shutting down due to bad tubes.

It seems to be a challenge to do this (short of just using another tube
as a load)

You would need some sort of zenar like device to start conducting at
about 1500 volts or so then drop down to the working voltage of 500/700
volts. With enough series resistance so not to overload the power
supply. maybe a TVSS gas discharge tube with a series resistance?
most of these supplies have a control chip that will try to strike the
lamp with a high voltage, then either lower the votage or shutdown due
to too much or too little current flow.

An OZ960 seems to be a popular controller.

Anybody thought about doing this and have any ideas?

bob

 

[Sjouke Burry]

bob wrote:

has anyone constructed a dummy test load for testing CCFL high voltage
power supples?

I have been running into more of these and would like a quick way to
load the inverter to see if its working, or shutting down due to bad tubes.

It seems to be a challenge to do this (short of just using another tube
as a load)

You would need some sort of zenar like device to start conducting at
about 1500 volts or so then drop down to the working voltage of 500/700
volts. With enough series resistance so not to overload the power
supply. maybe a TVSS gas discharge tube with a series resistance?
most of these supplies have a control chip that will try to strike the
lamp with a high voltage, then either lower the votage or shutdown due
to too much or too little current flow.

An OZ960 seems to be a popular controller.

Anybody thought about doing this and have any ideas?

bob
Try and find an old 10-15cm high transmitter tube, maybe

a radio amateur lives nearby.
connect a small neon tube to the input grit of the tube,feeding
the neon with~ 1megohm from 100-150V,
those neons are 50-100volt, acting like a zener diode,
and put in a cathode resistor to determine the plate current.
When you put a 10mohm pot across the neon bulb, you can
make the load current variable.
You can dispense with the neon tube by rectifying ~ 30-60 v
you get from an old transformer, you need one to supply the
kathode heater wire.
That 40-80 V voltage is enough to feed the potmeter, but the
load currrent from the tube becomes leess stable.

 

[mike]

bob wrote:

has anyone constructed a dummy test load for testing CCFL high voltage
power supples?

I have been running into more of these and would like a quick way to
load the inverter to see if its working, or shutting down due to bad tubes.

It seems to be a challenge to do this (short of just using another tube
as a load)
What's wrong with using a lamp as a load? Seems like a trivially easy way

to get a device that behaves exactly the way a lamp would.

You would need some sort of zenar like device to start conducting at
about 1500 volts or so then drop down to the working voltage of 500/700
volts. With enough series resistance so not to overload the power
supply. maybe a TVSS gas discharge tube with a series resistance?
most of these supplies have a control chip that will try to strike the
lamp with a high voltage, then either lower the votage or shutdown due
to too much or too little current flow.

An OZ960 seems to be a popular controller.

How about contacting the vendor to see what they use to test their chips.

Anybody thought about doing this and have any ideas?
You can buy discharge lamp testers that use RF to ignite the lamp.

Not sure if it's conclusive, but might make a good screening tool.

bob

 

On Mon, 11 Jan 2010 19:19:25 -0600, bob <sound@inetnebr.com> wrote:

has anyone constructed a dummy test load for testing CCFL high voltage
power supples?

I have been running into more of these and would like a quick way to
load the inverter to see if its working, or shutting down due to bad tubes.

It seems to be a challenge to do this (short of just using another tube
as a load)

You would need some sort of zenar like device to start conducting at
about 1500 volts or so then drop down to the working voltage of 500/700
volts. With enough series resistance so not to overload the power
supply. maybe a TVSS gas discharge tube with a series resistance?
most of these supplies have a control chip that will try to strike the
lamp with a high voltage, then either lower the votage or shutdown due
to too much or too little current flow.

An OZ960 seems to be a popular controller.

Anybody thought about doing this and have any ideas?

bob
It's been done. Testers are available commercially from online stores

that sell inverters and replacement tubes.

You don't really need a high voltage zener or eqivalent. The load
current and output voltage are not monitored for a couple of seconds
after the inverter starts. I'd suggest experimenting with a working
inverter and some resistors. Look up the specs of some CCFL tubes and
choose an appropriate resistor.

PlainBill