Circuit for controlling a dcc converter in a power supply circuit for a

Abstract

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 open circuit while a high frequency voltage is being delivered to the primary circuit and short circuiting the grid and the source of said transistor when the said high frequency voltage disappears, said conversion means also including first capacitor means providing the control voltage to the switch, and second capacitor means which charge whenever the high frequency is being delivered to the primary circuit and which discharge into said first capacitor means when said high frequency voltage disappears, whereby said first capacitor means then keep said switch in the conductive condition.