Hardware Reference
In-Depth Information
Chapter 2
Power
One of the most frequently neglected parts of a system tends to be the power supply—at
least when everything is working. Only when things get weird does the power supply
begin to get some scrutiny.
The Raspberry Pi owner needs to give the power supply extra respect. Unlike many
AVR class boards, where the raw input voltage is followed by an onboard 5 V regulator, the
Pi expects its power to be regulated at the input. The Pi does include onboard regulators,
but these regulate to lower voltages (3.3 V and lower).
Figure
2-1
illustrates the rather fragile Micro-USB power input connector. There is a
large round capacitor directly behind the connector that people often grab for leverage.
It is a mistake to grab it, however, as many have reported “popping it off ” by accident.
Figure 2-1.
Micro-USB power input
Calculating Power
Sometimes power supplies are specified in terms of voltage, and power handling capability
in watts. The Pi's input voltage of 5 V must support a
minimum
of 700 mA (Model B). Let's
compute a power supply figure in watts (this does not include any added peripherals):
P = V × I
= 5 × 0.7
= 3.5 W
