Charging and power supply for mobile devices is disclosed. A USB-compliant
charging and power supply circuit includes switch-mode battery charging
circuitry for receiving power from an external power source and for
supplying output power through an output node to an electronic system of
an electronic communication device and a battery. Battery isolation
circuitry includes a semiconductor switch connecting the output node to
the battery. The battery isolation circuitry senses voltage at the output
node and variably restricts current to the battery when the voltage is
below a minimum voltage value by operationally controlling the
semiconductor switch as current passes through it. During variable
current restriction the electronic system is supplied required power with
said battery being supplied any additional available power.