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For HDMI, Power is Still an Issue

HDMI wasn't designed to power peripherals -- watch what you're installing.


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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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Article Topics

News · HDMI · Hdmi · All topics

About the Author

Jeff Boccaccio, President, DPL Labs
Jeff Boccaccio, president of DPL Labs, can be reached at jeff@dpllabs.com.

8 Comments (displayed in order by date/time)

Posted by Lee Distad  on  09/24  at  09:18 AM

Jeff, I’m not clear from your article on what, if any practical application in the field the +5v power carries.  Can you give me an example of a scenario of needing the the HDMI to run a peripheral?

In addition, isn’t a 20M HDMI cable pushing one’s luck in terms of functional length?  At what distance would you personally advise going with Cat5 or fibre extenders?

Posted by Crude Dude  on  09/24  at  07:56 PM

HDMI was never designed to power peripherals like USB(5v@500ma)...in fact I don’t know why there is a power lead at all.50ma is the same amperage as a 9v battery,it’s no surprise that it’s lost at 20m.

Posted by Jeffrey A Boccaccio  on  09/25  at  01:18 AM

Good question Lee. A perfect example is found with some long distance extenders. Some come with no power supply (wall wart). They use the on board 5 volt line to power the extender. You will also find this same set up with switchers, DA’s, and conditioners.

There are many products out there that due in fact run long lengths. I have see some do as much as 200 meters with the right cable and matched equalizers.

Posted by Ward  on  09/25  at  02:59 AM

Lee, the 5v line in HDMI (like DVI) is primarily to power on the display devices internal eeprom that stores the DDC/EDID data even when the display is turned off.  This way your source can receive the info it needs about the display even if you’ve forgotten to turn on the display first.
A more common problem I see now is when the display incorrectly allows the 5v input to ‘loop back’ to the player rather than being diode blocked per the format spec.
Timing issues surrounding the request and acknowledgment of DDC/EDID/HDCP data is less problematic every year but just like other published specs for PS2 & USB the mfg’s software implementation often falls short of being correct.
Good thing TV’s now come with a USB port for flashing the firmware, maybe drivers will be next <grin>.
The brute force type of active extension cables that Jeff mentions are generally powered by the source devices 5v output and overcome the distance limitation by adding pre emphasis to the data signals. These are very similar to the active USB extension cables you’ll find.

Posted by Lee Distad  on  09/25  at  09:50 AM

Great answers, thank you!

Posted by Goofo  on  04/29  at  10:44 AM

Hi.

i need to extend the hdmi run from my av receiver to reach my projector.

Could you please advise as to the effectiveness of the following scenario.

1. a Monster Cable 10.67m MC1000HD hdmi cable attached to receiever…

2. then either the Audioquest HDMI Extender or the Gefen EXT-HDMI-141SB HDMI Super Booster (both of which are unpowered) attached at the other end of the HDMI cable…

3. another (similar quality) HDMI cable of no more than 2m attached to other end of HDMI extender.

Note that the projector, receiver, and the hdmi cables i am using all support formats such as deep colour, truehd and dts-hd audio, etc.

I have heard that since these unpowered extenders have max video amplifier bandwith of only 165mhz that they do not support these formats whereas the powered extenders amp bandwiths of 225mhz can.

does this make sense? is that true?

any light on this topic would be much appreciated as my hdmi run needs extending to reach the projector and at present there is no additional power outlet at the source (projector) near the end of the long hdmi cable.

cheers.

Posted by Goofo  on  04/29  at  10:47 AM

...woops..


i forgot to insert point 4: the projector is connected to the other end of the shorter hdmi cable.

Posted by Steve  on  08/27  at  10:18 PM

I saw several multi-port hdmi switches on ebay. However, these had lights and circuits built into them, yet they don’t require an external power source. It appears that these switches are using the power from the hdmi bus to power the lights and circuitry. What’s your take on these devices? Could they possible draw too much current from the bus causing hdmi failures?

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