usb - Powering 12V device from 5/9/12V powerbank

I recently bought the Litionite Falcon powerbank that has one of its outs designed for 5/9/12V. The 12V is at 1.5A which I thought would be enough for my 12V/0.8A camera. However, connecting the camera to the charger with a USB to 0.7mm jack doesn't work. Indeed, I can measure only some 5.3V coming through the USB cable which explains why the camera doesn't recognise the power.

How do I get the 12V from the powerbank to charge my camera? Do I need a special USB cable? Do I need one with a step up? Or is it enough to wire the USB differently?

Answer

Your Litionite Falcon power bank uses the Qualicom proprietary Quick Charge 3.0 technology. To enable 9 or 12V, your device have to provide certain sequencing of voltage levels on D+ and D- data lines, aka "handshake". Since your camera doesn't do that, you need to make a device between your camera and the powerbank that generates the D+/D- signals.

The details of QC protocols are not publicly disclosed, and only occasional information is available on how to conduct the handshake. The most comprehensive details were eventually published in US patent Application US2014122909. If you can read the awkward patent language, you can start there.

Alternatively there are certain ICs that support the protocol, namely AP4370 by Diodes, NCP4371 by ONSemi, and CHY103 by Power Integrations. So some bits of information about actual protocol have been leaked. For example, Texas Instruments PMP9773 Reference Guide describes the protocol as follows:

According the description in the CHY100 datasheet, the processes to enter QC2.0 are: − Apply a voltage between 0.325 V and 2 V to D+ for at least 1.25 seconds − Discharge the D- voltage below 0.325 V for at least 1ms while keep the D+ voltage above 0.325 V − Apply the voltage levels in Table 3 to set the output voltage. (must keep the D+ voltage above 0.325 V)

The table of DC voltages that you need to set on on D+/D- wires looks like this:

To get an idea how the QC protocol has evolved to version 3.0, the following presentation can help. Version 3.0 introduces pulsing protocol, each pulse can decrement or increment VBUS by 200 mV.

So this is up to you which way to experiment with. Given your 12V@0.8A camera requirement, you probably be better off with a 5-to-12V booster from eBay.