Can a passive device that does not use any active electronics, like a mechanical switch box, be compliant? The cost is a lot less.

Can a passive device that does not use any active electronics, like a mechanical switch box, be compliant? The cost is a lot less.

Can a passive device that does not use any active electronics, like a mechanical switch box, be compliant? The cost is a lot less. First lets discuss what a passive and an active device is, and what they are used for. An active device is electrically powered and divides the line level signal prior to amplification. A passive device is not active and uses no external power and results in insertion loss.

A device that is HDMI supported that has active electronics should have an external power provision in order to be compliant. For example, a receptacle that will allow the utilization of a standard power adapter, which may be called a power brick. There is a distinction to be drawn between active devices that actually have some powered electronics, and passive devices like some switches.

Some active devices, like actively powered HDMI cables, or in-line signal extender boxes, will attempt to get power for their electronics by taking it from the 5V line that is available on the HDMI connector by default. The HDMI specification requires that all source devices are to provide at least 55 milliamps of power on the 5V line for the main purpose of reading the EDID of a display. While 55mA is not enough power to operate most HDMI accessory devices as these usually require about 100 to 150mA, almost all the source devices on the consumer market today will provide significantly more current on the 5V line than is required by the HDMI specification. Because of this, most of the accessory devices can operate when interfaced with a source device that gives more than the required current on the 5V line. However, manufacturers should provide for a provision for their powered HDMI accessory devices to obtain external power as needed, and consumers are encouraged to look for this provision when purchasing these products.

Not all HDMI devices in the future may provide as much power over the 5v line. For example, as HDMI expansion happens into more and more portable applications like laptops, cameras, camcorders, etc., the power consumption often becomes much more of an issue, and such devices may not power the 5V line with the necessary power required by such “active” devices. Once again, consumers should consider verifying that their active HDMI accessory devices have a provision for external power before the purchase for this reason.

Any device, whether it is called active or passive, which performs any of the processing, amplification, or switching of the HDMI signal should use only actively powered electronics to perform reliably and be compliant. Most of the devices can use power that is supplied on the 5V line of the HDMI connector to function properly, however an external power source provision should be provided with any device purchased.

Non-powered, completely passive devices may be okay in various short cable length applications, but they are utilized at the user's own risk. Even if one configuration works great with a passive device, changing the cabling or equipment may make subsequent configurations fail.

The best advise is not to use passive devices at all. It is better to use active devices with a provision in place for an external power source. A passive device may solve the problem for the short term, but may lead to more time consuming issues later on. To be compliant, any device needs to have the external power source provision.