Which voltage regulator?
With that much current, you probably want a switching regulator, also known as DC/DC converter.
Otherwise (9V - 5V) * 4A = 16Watts of power has to be dissipated as heat.
Which voltage regulator?
With that much current, you probably want a switching regulator, also known as DC/DC converter.
Otherwise (9V - 5V) * 4A = 16Watts of power has to be dissipated as heat.