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I have an ongoing question on the Raspberry Pi SE site, in which I'm attempting to figure out how much current is available to devices connected to the HDMI socket of each Pi model. I think I've figured out every model aside from the Pi Zero.

There are no schematics available for the Zero but, following some extreme squinting, I think that the most likely candidate for HDMI power management is the component labelled D6. It's immediately below the white printed 'HDMI' label to the right of the mini HDMI socket, which is towards the bottom left corner of the board.

Raspberry Pi Zero

The part is marked 'F03 | CD'. Some stumbling in the dark on Google turned up the Diodes Incorporated DFLS130LQ / '1.0A SURFACE MOUNT SCHOTTKY BARRIER RECTIFIER', which has identical markings.

Is it plausible that this part might limit current to pin 18 of the mini HDMI socket? If so, what is the maximum current that it would allow to pass?

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    \$\begingroup\$ You might want to read up about on what diodes are and what they do... \$\endgroup\$ – PlasmaHH Jul 14 '16 at 12:09
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    \$\begingroup\$ It's common to use bus powered HDMI to VGA adapters such as this one to provide a cleaner audio output than the Pi's 3.5mm jack, which is garbage. They often don't work as the Pi can't supply enough power through the HDMI connector. It would be useful to know what the limits are. \$\endgroup\$ – goobering Jul 14 '16 at 12:20
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    \$\begingroup\$ @goobering: Usually on this site we expect people to research a bit of the basics first and then ask questions where they are stuck. \$\endgroup\$ – PlasmaHH Jul 14 '16 at 12:21
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    \$\begingroup\$ @PlasmaHH, we do the same on the Pi board. From here: '200mA is the limit for the BAT54 diode (D1) on the board'. From here: 'BAT54 diode D1 which has a max current rating of 200 mA'. From here: 'there is also a diode in-between the PI and the HDMI output to prevent the HDMI device from attempting to power the PI, and that diode is rated just 200mA'. Each referenced from my question on the Pi board. \$\endgroup\$ – goobering Jul 14 '16 at 12:31
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    \$\begingroup\$ Those who name these "current limiting diodes" "diodes" expose themselves as not having a clue about proper diodes. Naming these CRDs "diodes" is silly in my opinion. \$\endgroup\$ – Bimpelrekkie Jul 14 '16 at 12:43
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If the current limit is not documented, then the only way to determine it is empirically. Get yourself a variable load and plot the voltage-vs-current curve for the HDMI power terminal.

Assuming the circuitry is sophisticated enough to protect itself from overload, you'll find the current limit directly. The shape of the curve will give you some idea of how the current limit is implemented.

Otherwise, you'll reach the dissipation limit of some component on the RPi board, and this will determine the current limit. A thermal imager would be one way to monitor for "hot spots".

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