For HDMI, Power is Still an Issue
HDMI wasn't designed to power peripherals -- watch what you're installing.
Long, active cable products continue to be popular, offering active equalization embedded into the HDMI connector on the cable.
But as we have mentioned many times, the power on the HDMI buss was never really designed into the interface to provide power to any HDMI peripheral.
Since the spec calls for a solid 5-volt supply with a 50-ma load, there is not much power left for peripherals.
If the 5-volt supply is pulled down below 4.7 volts, the risk of failure climbs astronomically. This power source needs to be preserved for the interface to function correctly.
We had one of these come in for examination because it was developing problems in the field.
After connecting the product up to our testing lab, we saw that a 20-meter active cable stole so much power away from the buss that the system flat out would not work.
Any advantage that the equalizer would have offered was lost due to the loss of the power supply. It had dropped to an all time low of 3 volts.
I can’t be anymore adamant about watching what you’re installing. Just because it worked once does not mean it will work for all.
Source and display products may or may not offer better supply currents. Don’t take the risk. If you see no external power, your alert ears should go up.
By way of white papers, knowledge-base Web sites and even this column, HDMI products continue to improve. Still, there are still a few out there that fail to move in the right direction.
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