DragonBoard was designed to accept a wide range of input voltages, anything between 6.5V, and 18V will work fine. Keep in mind that “Voltage” and “Power” are different things. The amount of Power your board will use is independent of the voltage, although it is highly dependent on your software. The "“Current” (I) required is a function of Power ( P) and Voltage (V), P=VI. As an example, if your board and software is drawing a current of 300mA while operating at 12V (Power=VI=12x300=3600mW), and you reduce the supply voltage to 9V, the current will increase to I=P/V=3600/9=400mA. The Power will remain constant.
Full disclosure: I am an employee of Qualcomm Canada, any opinions I have expressed in this or any other post may not reflect the opinions of my employer.