|
|
|
|
|||||||
| Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
 |
|
|
Thread Tools |
23rd Aug 2018, 7:35 pm
|
#1 |
|
Pentode
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 165
|
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: 16,535
|
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.
__________________
....__________ ....|____||__|__\_____ .=.| _---\__|__|_---_|. .........O..Chris....O |
|
|
|
23rd Aug 2018, 9:03 pm
|
#3 |
|
Nonode
Join Date: Oct 2008
Location: Warsaw, Poland and Cambridge, UK
Posts: 2,677
|
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
__________________
What's going on in the workshop? http://martin-jones.com/ |
|
|
|
24th Aug 2018, 10:39 am
|
#4 |
|
Pentode
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 165
|
Re: CCFL driver
many thanks, all making sense now.
|
|
|
