DIY Backlight Strobing [must read for experimenters!]
Posted: 13 Jan 2014, 16:21
It should be simple enough.
A signal generator with: duty cycle changer, phase shift (delay), and external frequency sync should do the trick.
The signal generator custom square wave should trigger the gate of a power transistor and strobe the leds as needed.
AKA Mosfet switch:
My train of thought goes like this:
Find the vsync clock on a working monitor with a small an oscilloscope like: This, (should be easy).
Take this vsync clock and send it to small a signal generator board with an external frequency sync input, like: This.
Generate a square wave signal with altered duty cycle (1ms - 4ms) and a delay (phase shift), to trigger the D-On cycle after the pixel transition time (should be fine tuned watching some moving UFO images.
This square wave should trigger the gate of a power mosfet to flicker the backlight.
Find the voltage output to the backlight, desolder it and connect it (or an external PSU) through the mosfet.
Find using a DVM the total Forward Voltage of the backlight diodes and select a resistor (Wattage should suit the current) accordingly (or a pot, for better brightness control).
Whaddaya' think?
EDIT:
It can be easier than I thought.
Looking at this thread: LCD LED Backlight
And this LED Driver IC schematic & Datasheet:
I can compare and understand that they are exactly the same, including the IC, Inductor, Diode, VCC, LED Ribbon, etc...
A typical Led Driving Circuit inside your monitor already there.
The only thing that needs to be done is:
Disconnect the PWM input to the Driver IC, and connect the vsync'ed Signal Generator output to that.
Thats it.
A signal generator with: duty cycle changer, phase shift (delay), and external frequency sync should do the trick.
The signal generator custom square wave should trigger the gate of a power transistor and strobe the leds as needed.
AKA Mosfet switch:
My train of thought goes like this:
Find the vsync clock on a working monitor with a small an oscilloscope like: This, (should be easy).
Take this vsync clock and send it to small a signal generator board with an external frequency sync input, like: This.
Generate a square wave signal with altered duty cycle (1ms - 4ms) and a delay (phase shift), to trigger the D-On cycle after the pixel transition time (should be fine tuned watching some moving UFO images.
This square wave should trigger the gate of a power mosfet to flicker the backlight.
Find the voltage output to the backlight, desolder it and connect it (or an external PSU) through the mosfet.
Find using a DVM the total Forward Voltage of the backlight diodes and select a resistor (Wattage should suit the current) accordingly (or a pot, for better brightness control).
Whaddaya' think?
EDIT:
It can be easier than I thought.
Looking at this thread: LCD LED Backlight
And this LED Driver IC schematic & Datasheet:
I can compare and understand that they are exactly the same, including the IC, Inductor, Diode, VCC, LED Ribbon, etc...
A typical Led Driving Circuit inside your monitor already there.
The only thing that needs to be done is:
Disconnect the PWM input to the Driver IC, and connect the vsync'ed Signal Generator output to that.
Thats it.