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In this paper, a low cost power control for LCC series-parallel inverters with resonant current mode control for HID lamps is presented. These kind of resonant inverters require controlling the power supplied to the lamp without exceeding the maximum power recommended by the manufacturer. The classical method measures the voltage and current of the lamp and they are multiplied, obtaining the power consumption. This control circuitry results very complex. Assuming a regulated input DC voltage (bus voltage) provided by the power factor correction (PFC) stage and a constant efficiency of the inverter, the power consumed in the lamp can be estimated and regulated properly measuring the average input current of the inverter. Also, the small-signal analysis performed allows obtaining the small-signal input impedance and the study of the stability of the connection with the PFC stage. A prototype for a 250 W HPS lamp has been implemented and tested to verify the power control method proposed.