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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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23rd Aug 2018, 7:35 pm | #1 |
Pentode
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 165
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CCFL driver
please could more experienced brains than mine cast eyes over attached schematic which is the circuit of a backlight (CCFL) driver.
do any of the transistors TR700,1,2,3 form the pri oscillator? or is the pri osc "excite" signal more likely to be coming in via R750? many thanks |
23rd Aug 2018, 8:04 pm | #2 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,536
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Re: CCFL driver
702 and 703 are the oscillator- feedback from winding 1-5. The other two look to be a gate or possibly amplitude control- they do stuff to the dc conditions on the bases of the oscillator transistors at any rate.
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23rd Aug 2018, 9:03 pm | #3 |
Nonode
Join Date: Oct 2008
Location: Warsaw, Poland and Cambridge, UK
Posts: 2,679
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Re: CCFL driver
I agree that TR702 and TR703 are the oscillator. It looks like a Royer oscillator to me. TR700 and TR701 look to be set up to level-shift a PWM brightness signal from somewhere else. They're not biased into linear operation so the signal must be PWM, not a control voltage. R754/C704 then smooth the output of TR701 into a change in bias on the oscillator transistors, which presumably varies the brightness.
Chris
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24th Aug 2018, 10:39 am | #4 |
Pentode
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 165
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Re: CCFL driver
many thanks, all making sense now.
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