Circuit for controlling a DCC converter in a power supply circuit for a discharge lamp of a motor vehicle headlight

A circuit for controlling a DC/AC converter of a power supply circuit for a motor vehicle headlight discharge lamp, the circuit comprising a primary circuit, voltage-feed means for feeding the primary circuit with voltage, and a secondary circuit coupled to the primary circuit by mutual induction, the secondary circuit delivering a voltage controlling the non-conductive and conductive state of a MOSFET type transistor of the DC/AC converter, the voltage that the power supply means deliver to the primary circuit constituting a modulated high frequency carrier voltage, the secondary circuit including means for converting the high frequency voltage delivered to the primary circuit into a control voltage for the transistor that is greater than or less than a given non-conductive or conductive threshold, as a function of the modulation of said high frequency voltage, the conversion means of the, secondary circuit including a switch connected between the grid and the source of the transistor, said switch being controlled by the voltage of the first capacitor means, the conversion means comprising means which charge said first capacitor means, when the high frequency voltage is delivered to the primary circuit, so that the voltage of said capacitor means maintains the switch in open circuit, wherein said conversion means also charge a second capacitor means when the high frequency voltage is delivered to the primary circuit, said second capacitor means discharging in the first capacitor means when the high frequency voltage disappears, the voltage of the first capacitor means thus charged by the second capacitor means being of such a value that it keeps said switch in the conductive condition.