The HDMI interface was not designed to power external devices, but rather to supply sufficient power to complete the initial handshake, HDCP authentication and EDID Exchange. Whilst many source devices provide more than the specified 55 mA to perform these functions, they do not always provide enough additional power to allow the operation of external HDMI accessories such as Active HDMI Cables, HDMI to VGA Converters and HDMI Fibre Optic cables.