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CCFT dummy loads

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

Reply to
bob
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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.

Reply to
Sjouke Burry

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.

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

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.

Reply to
mike

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

Reply to
PlainBill47

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