Driver Topology Influence on LED Luminescence Response Dynamics
Keywords:LED dimming, LED display electronics, LED video display, pulse-width-modulation
AbstractThe investigation light-emitting diode (LED) dimming temporal response when used in large scale LED video displays is presented. The aim was to find the response times for several driver topologies. Four driver topologies were considered: commercial constant current driver, passive driver, transconductance amplifier and constant current driver with tamper turn-off. 85 red Screen Master LEDs from Cotco were used in experiments. Measurement setup and circuit diagrams of the equipment used are presented. Measurement results for rise and fall fronts measurement are reported. Investigation results indicate that circuits possessing fast constant current drive (passive driver, transconductance amplifier and constant current driver with tamper turn-off) have similar performance for the front where this constant current source is operational: rise time. Average rise time for the aforementioned topologies is 62 ns, 54 ns and 56 ns accordingly. It was concluded, that average rise time is 283 ns and fall time was 111 ns when commercial driver MBI5026 was used. This is in high contrast with manufacturer specifications. Tamper turn-off produced very short fall time (4.2 ns) but this created large skew in light output response therefore it can be predicted that dimming linearity performance will be the worst. If passive driver is used then rise and fall response are 62 ns and 30 ns correspondingly. Lowest skew was obtained for transconductance amplifier-based topology.
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