Official Raspberry Pi Page
https://www.raspberrypi.org/products/pi-zero/
Core Differences To The Raspberry Pi 2
Broadcom BCM2835 (as in Raspberry Pi 1, but @ 1GHz) single core processor instead of newer quad core BCM2836 (RPi 2).
512MB instead of 1GB RAM.
Processor
Broadcom BCM2835. This contains an ARM1176JZFS (ARM11 using an ARMv6-architecture core) with floating point, running at 1GHz, and a Videocore 4 GPU.
Memory
512MB LPDDR2 SDRAM
Connections
USB On-The-Go port
Mini HDMI
40pin GPIO header with identical pinout to Model A+/B+/2B
Unpopulated composite video header
CSI camera connector (newer version from May 2016)
LED
A single green LED. Normally on, turns off to indicate disk activity.
Power
The Zero uses similar power as the A+
Our tests using fresh installed Raspbian OS
HDMI + USB hub connected (no USB peripheral load)
Max current during boot up to command prompt (GUI not loaded): 197mA
Idle at command prompt (GUI not loaded): 95mA
Nothing connected other than power input:
Max current during boot up to command prompt (GUI not loaded): 185mA
Idle at command prompt (GUI not loaded): 82mA
Nothing connected other than power input, HDMI port and LED disabled (see here)
Max current during boot up to command prompt (GUI not loaded): 185mA
Idle at command prompt (GUI not loaded): 63mA
Powering with less than 5V
The RPi zero runs at 3.3V, there is an on board voltage regulator which creates this voltage from the 5V power input. Whilst the Raspberry Pi is generally specified as operating from 4.75V to 5.25V (the USB acceptable voltage range), the processor runs at 3.3V. No schematic is available at the current time for the RPi zero, but as it is simply just the processor and SD card, which both run at 3.3V, there should be no reason not to be able to power it with a voltage below 4.75V. It should be fine to power it with 3.3V directly via the IO connector 3V3 pin (we haven't tried, but no reason not to), or use its voltage regulator to create the 3.3V with an input voltage below 4.75V. The running current will be higher than at 5V as its voltage regulator is switch mode, but the voltage regulator should still do its job OK as long as there is a bit of voltage headroom to its Vout (3.3V).
Powering with 3.5V, HDMI disabled, USB hub connected
Powers up fine. 3.3V rail looks fine on an osciliscope.
RJ45 USB ethernet adaptor in the USB hub (powered by the USB hub not the RPi) works fine, SSH connection fine.
Max power consumption during boot: 268mA (this was just by watching PSU display readings by eye, most of the time was < 180mA but peeked at times – using an inline max/min multi-meter resistance caused too much voltage drop)
Power consumption idle: 98mA
Power consumption after sudo shutdown completes: 22mA
Powering with 3.4V, HDMI disabled, USB hub connected
Powers up fine. 3.3V rail looks fine on an osciliscope.
RJ45 USB ethernet adaptor in the USB hub (powered by the USB hub not the RPi) works fine, SSH connection fine.
Power consumption idle: 100mA
Power consumption after sudo shutdown completes: 22mA
Powering with 3.3V, HDMI disabled, USB hub connected
Powers up fine. 3.3V rail has a bit of wobble, min 3.16V and typ 3.29V on an osciliscope.
RJ45 USB ethernet adaptor in the USB hub (powered by the USB hub not the RPi) works fine, SSH connection fine.
Power consumption idle: 101mA
Power consumption after sudo shutdown completes: 22mA