Power regulation circuit for high frequency electronic ballast for ceramic metal halide lamp

A method of maintaining a power applied to a light emitting discharge tube within a range of a predetermined desired power magnitude during maintenance of a discharge arc in the discharge tube given that a resistance of the discharge tube varies with temperature during operation of the discharge arc, the steps of the method comprising:

• a) providing ballast circuitry including an oscillating inverter circuit for driving an LC tank network coupled to the discharge tube, the LC tank network applying a time varying voltage to the discharge tube to maintain the discharge arc, a peak-to-peak magnitude of the time varying voltage applied by the LC tank network being determined by a frequency of oscillation of the inverter circuit;
• and
• b) controlling the frequency of oscillation of the inverter circuit with power regulation circuitry inductively coupled to the inverter circuit, the power regulation circuitry varying the frequency of oscillation of the inverter circuit by controlling a current through a transformer winding coupled to the inverter circuit such that power applied to the discharge tube remains within the range of the predetermined desired power magnitude, wherein the power regulation circuitry is inductively coupled to the inverter circuit through the use of a transformer and a primary winding of the transformer is coupled to the inverter circuit and a secondary winding of the transformer is coupled to the power regulation circuitry.

A method of maintaining a power applied to a light emitting discharge tube within a range of a predetermined desired power magnitude during maintenance of a discharge arc in the discharge tube given that a resistance of the discharge tube varies with temperature during operation of the discharge arc, the steps of the method comprising:

• a) providing ballast circuitry including an oscillating inverter circuit for driving an LC tank network coupled to the discharge tube, the LC tank network applying a time varying voltage to the discharge tube to maintain the discharge arc, a peak-to-peak magnitude of the time varying voltage applied by the LC tank network being determined by a frequency of oscillation of the inverter circuit;
• and
• b) controlling the frequency of oscillation of the inverter circuit with power regulation circuitry inductively coupled to the inverter circuit, the power regulation circuitry varying the frequency of oscillation of the inverter circuit by controlling a current through a transformer winding coupled to the inverter circuit such that power applied to the discharge tube remains within the range of the predetermined desired power, wherein the frequency of oscillation of the inverter circuit exceeds a resonant frequency of the LC tank network and as discharge tube resistance decreases, the power regulation circuitry increases the frequency of oscillation of the inverter circuit to decrease the peak-to-peak magnitude of the time varying voltage applied by the LC tank network to the discharge tube.