A
albert
- Jan 1, 1970
- 0
Good Day All,
I am trying to use a TI ucc3977 CCFL driver chip and I'm having
problems getting the output to go low enough.
I am using components removed from their evaluation pcb, so I am sure
my component values are correct.
While the standard use for this sort of chip is to supply 600v RMS AC
to power a CCFL, I am trying to use it to generate 100v p-p at much
lower current levels than a CCFL would use. The chip itself is drawing
about 1.3 ma, but the entire circuit draws 40 ma with a very high
value load resistor. The output is clipped despite the input being a
decent looking psuedo sine wave.
My problems seems to be one of excessive output voltage due to
overdriving the primary of the piezotransformer. They use outboard
mosfets to amplify the current output of the chip. Since I don't need
much output, I was wondering if I could hook the piezotransformer up
directly to the chip output pins and delete the external mosfets.
The chip itself sources or sinks 100 ma, which is much more current
than I need. I've posted the chips output stage schematic, the
schematic as suggested by TI and the schematic of what I'd like to try
in order to get the efficiency up.
The schematic is posted at:
http://www.uninets.net/~artky1k/piezo.PDF
Any comments are appreciated.
Al
[email protected]
I am trying to use a TI ucc3977 CCFL driver chip and I'm having
problems getting the output to go low enough.
I am using components removed from their evaluation pcb, so I am sure
my component values are correct.
While the standard use for this sort of chip is to supply 600v RMS AC
to power a CCFL, I am trying to use it to generate 100v p-p at much
lower current levels than a CCFL would use. The chip itself is drawing
about 1.3 ma, but the entire circuit draws 40 ma with a very high
value load resistor. The output is clipped despite the input being a
decent looking psuedo sine wave.
My problems seems to be one of excessive output voltage due to
overdriving the primary of the piezotransformer. They use outboard
mosfets to amplify the current output of the chip. Since I don't need
much output, I was wondering if I could hook the piezotransformer up
directly to the chip output pins and delete the external mosfets.
The chip itself sources or sinks 100 ma, which is much more current
than I need. I've posted the chips output stage schematic, the
schematic as suggested by TI and the schematic of what I'd like to try
in order to get the efficiency up.
The schematic is posted at:
http://www.uninets.net/~artky1k/piezo.PDF
Any comments are appreciated.
Al
[email protected]
