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Survive ballast voltage?

Posted by: William Jansen on Thu, 03/08/2012

In Design Example Report 287, entitled T8 Tube Lamp Driver, the input specification is 180 VAC to 265 VAC at 60 Hz.

If the circuit is plugged into a fluorescent lamp fixture, the circuit will be connected to the fluorescent lamp ballast. For instant start ballasts, the initial voltage is 1000 VAC at 60 kHz (<- note killo Hertz). The voltage will eventually drop to 120 VAC, but the frequency is still 60 kHz.

How does the circuit survive the hit from the ballast?
Did you intend to remove the ballast?


Submitted by PI-Crumb on Thu, 03/08/2012


DER-287 provides design example for T8 Tube Lamp ***LED*** Driver. It is not meant to be used as a fluorescent lamp driver.

Submitted by William Jansen on Thu, 03/08/2012

I know that the circuit was meant to drive LEDs, not a fluoescent lamp.

It looks like the circuit was built to physically install in a lamp fixture in place of a fluorescent lamp. In the lamp fixture there is a ballast between the socket and the 120 VAC line.

If you simply put the circuit in the lamp fixture, the circuit is powered not from 120 VAC, it is powered from the ballast. If the ballast is a solid state ballast, the output frequency is in the 60 KHz range, not 60 Hz. The voltage is about 1000 Vp (2000 Vpp), until the ballast senses lamp ignition.

So, I was wandering hoe the circuit survived the ballast?
Or, did the note imply that the ballast must be removed?

I hope I conveyed my questions better this time.

Thank you.

Submitted by PI-Crumb on Thu, 03/08/2012


Thanks for the clarification. This design can work with magnetic ballast but unfortunately it is not designed to withstand such high voltage coming from the electronic ballast. The electronic ballast must therefore be removed from the fixture before using the LED driver.

Submitted by William Jansen on Fri, 03/09/2012

Thank you.