Dear forum,
using it for a full area local dimming back light we utilize several TLC59401 LED driver ICs to drive the individual LED strings. Basically they are working fine, but we encounter severe flickering which we cannot find the reason for. Here some information:
general:
- BL consists of 20 custom build panels using Nichia LEDs (4x14, 4 LEDs in series)
- VLED = 12~13 V (not defined yet)
- Driver IC is TLC59401 driving a column of 14 LEDs each (4 drivers per panel on 1 driving PCB)
- Channel current is limited to 10 mA by resistor
- VCC generated locally on each board (3v3)
- PWM frequency is fixed to 60 Hz (derived from video signal)
- Power rail and signal bus length ~2m
Observable issue:
- Flickering to human eye (maybe 10-15 Hz)
- Problem persistent if number of panels is reduced
- Also when using car battery as supply
Measurements taken:
- Light emission: PWM looks fine (w.r.t. frequency & duty cycle)
- Input voltage (locally): voltage drop (~0.5v observable switching @60Hz, but no modulation <60Hz)
What could be the reason for the system to flicker given the above data? Anyone encountered something like this before and was able to fix?
Best regards
Severin Völkl
