Patent ID: 7426126

Claim:
An extension cord plug comprising: an outlet, being configured with an over-current protection circuit and a filter-rectify circuit, the over-current protection circuit being configured to sense the whole circuitry, the filter-rectify circuit beings configured to filter and rectify the inputted AC current and provide a steady DC current to a charge apparatus; and an USB interface outside the outlet and being connected to the charge apparatus; the charge apparatus, comprising: a power tube being configured to control an output voltage of a high-frequency transformer; a start-up circuit being configured to drive the power tube to work; an over-current sampling circuit being configured to sense the current flowing through the power tube to prevent the power tube from being damaged; a steady-voltage control circuit being configured to receive a sampling signal from the over-current sampling circuit to control a voltage of the power tube; the high-frequency transformer being configured to generate induced current and output voltage for a positive feedback circuit; the positive feedback circuit being configured to control a working status of the power tube according to an amplitude of the primary-side current flowing through the high-frequency transformer; an output filter-rectify circuit being configured to filter and rectify an AC power being outputted by the high-frequency transformer to output a steady DC power; a voltage sampling circuit being configured to sense variation of the output voltage; a photo-isolator being configured to receive a sampling signal from the voltage sampling circuit, transform the sampling signal into a photo signal for being transformed into an electrical signal and the electrical signal being transmitted to the steady-voltage control circuit; and a load sense circuit being configured to receive the DC power of the output filter-rectify circuit and being connected to the USB interface to check whether there is any load being connected to the USB interface, in which once there is load, the load sense circuit then drives a load monitor to present the status.