The QC technology is very interesting for everyone who has a smartphone but also the DIY community can take profit from it.
QC itself is simple. If "the smartphone says -i need more power-" the QC charger increases the voltage. In the 2.0 version there are 5, 9, 12 (and 20) V. QC 3.0 can increase or decrease the voltage in steps of 200 mV.
Step 1: How It Works:
I think the best way to understand QC 3.0 is to read this (http://blog.rnix.de/12v-from-a-usb-powerbank/) article about version 2.0. Especially the "QuickCharge Handshake" part.
1. apply 0,4V-2V to D+ (D- is not connected)
2. apply the voltages to D+ and D- as shown in the table --> here we go, you can now enter the 9 or 12V (or 20V) mode (by the way it also woks with QC 3.0, because 2.0 is supported)
So what is the trick to select our voltage in steps of 200mV?
This datasheet (http://www.mouser.com/ds/2/308/FAN6290QF-1099224.pdf), page 12, shows us the way. We only have to enter "Continuous Mode" (as shown in the table |D+-->0.6V D- -->3.3V|). Now we are in continuous mode. To increase the voltage pull D+ to 3.3V for a short time. To decrease the voltage pull D- to 0.6V for a short time. (have a look at the diagrams from http://www.mouser.com/ds/2/308/FAN6290QF-1099224....
Step 2: Simple Circuit:
Here you can see a simple circuit. It is really important to choose buttons with less bouncing. The best way is to build up a breadboard with the circuit and test the buttons of your choice.
Step 3: Additional Notes
- the voltage-display is a simple one from ali (https://www.aliexpress.com/wholesale?ltype=wholesale&d=y&origin=y&isViewCP=y&catId=0&initiative_id=SB_20170424231520&SearchText=volt+meter&blanktest=0&tc=af
- if you want to go up to 20V choose another voltage regulator, this one can only handle 15V, but in the most case (like in mine) the QC device only supports up to 12V I think
- when connecting USB, disconnect D- before (the jumper in my circuit)
- Why don't use a step up? Because QC can provide more power.
- with the resistor values (as shown in the picture) you do not get the exact voltages, but for me they are working