Power control circuit for discharge lamp and method of operating same

A power control circuit for a discharge lamp to be operated by an electrical power supply having a d-c input stage with given voltage and an output power controlled by a switching frequency of power switch means in said power supply, said power supply including adjustable pulse creating means for creating current pulses at said switching frequency, said power control circuit comprising:

• means for sensing the instantaneous output current of said power supply itself, said output current comprising said current pulses at said switching frequency;
• means controlled by said sensed instantaneous output current of said power supply for creating a first signal with a value proportional to the actual power being supplied by said power supply to said lamp;
• means for creating a second signal with a value proportional to a set point power;
• means for creating an error signal having a value indicative of the difference between said first and second signals;
• and,
• means for adjusting said switching frequency in accordance with the value of said error signal whereby said output power of said power supply is continuously adjusted toward said set point power.

A power control circuit for a discharge lamp in a closed inductive loop and operated by an electrical power supply having a d-c input stage with a given voltage and an output power controlled by a switching frequency of a power switch means in said power supply whereby d-c current flows to said closed loop when said switch means is conductive and no current flows from said power supply to said closed loop when said switch means is non-conductive, said power control circuit comprising;

• means for sensing the current flowing through said switch means;
• means controlled by said sensed switch current for creating a first signal with a value proportional to the actual power being supplied by said power supply to said closed loop;
• means for creating a second signal with a value proportional to a set point power;
• means for creating an error signal having a value indicative of the difference between said first and second signals;
• and,
• means for adjusting said switching frequency in accordance with the value of said error signal whereby said output power of said power supply is continuously adjusted toward said set point power.

A method controlling the power supplied to a discharge lamp in a closed inductive loop and operated by an electrical power supply having a d-c input stage with a given voltage and an output power controlled by the switching frequency of a power switch means in said power supply whereby d-c current flows to said closed loop when said switch means is conductive and no current flows from said power supply to said closed loop when said switch means is non-conductive, said method comprising the steps of:

• (a) sensing the current flowing through said switch means;
• (b) creating a first signal from said sensed switch current, said first signal having a value proportional to the actual power being supplied by said power supply to said closed loop;
• (c) creating a second signal with a value proportional to a set point power;
• (d) creating an error signal having a value indicative of the difference between said first and second signals;
• and,
• (d) adjusting said switching frequency in accordance with the value of said error signal whereby said output power of said power supply is continuously adjusted toward said set point power.

A method of controlling the power supplied to a discharge lamp from a power supply including a d-c input stage and a power switch selectively switched between a conductive state to pass current through said lamp and a non-conductive stage whereby current passing through said lamp increased when said switch is in said conductive state and decreases when said switch is in said non-conductive state, said method comprising the steps of:

• (a) providing a current control means for creating a series of operating cycles (T) including a first driving portion (W) wherein said switch is rendered alternately conductive and non-conductive in succession and a quiescent portion (T-W) wherein said switch is non-conductive;
• (b) sensing the instantaneous current through said power switch and independent of said current passing through said lamp;
• (c) creating a first signal proportional to average of said sensed current;
• (d) creating a second signal proportional to a set point power;
• (e) creating an error signal indicative of the difference between said first and second signals;
• and,
• (f) adjusting the time of said first driving portion (W) of said operating cycle (T) in accordance with said error signal whereby the output power of said power supply is continuously adjusted toward said set point power.

A method of controlling the power supplied to a discharge lamp to be operated by an electrical power supply having a d-c input stage with given voltage and an output power controlled by a switching frequency of power switch means in said power supply, said power supply including adjustable pulse creating means for creating current pulses at said switching frequency, said method comprising the steps of:

• (a) sensing the instantaneous output current of said power supply itself, said output current comprising said current pulses;
• (b) using said sensed instantaneous output current of said power supply for creating a first signal with a value proportional to the actual power being supplied by said power supply to said lamp;
• (c) creating a second signal with a value proportional to a set point power;
• (d) creating an error signal having a value indicative of the difference between said first and second signals;
• and,
• (e) adjusting said switching frequency in accordance with the value of said error signal whereby said output power of said power supply is continuously adjusted toward said set point power.

A dimmer control circuit for a discharge lamp in a closed inductive loop resonant ballast and operated by a power supply having a d-c input stage with a given voltage and an output power controlled by a switching frequency of two sets of power switches in said power supply and operated alternately at said switching frequency whereby d-c current flows to said closed resonant loop when either of said switch sets is conductive, said dimmer control circuit comprising:

• means for sensing the current flowing through both of said sets of switches;
• means controlled by said sensed current for creating a first signal with a value proportional to the actual power being supplied by said power supply to said closed resonant loop;
• adjustable means for creating a second signal with an adjusted value proportional to a dimmer setting;
• means for creating an error signal having a value indicative of the difference between said first and second signals;
• and,
• means for adjusting said switching frequency in accordance with the value of said error signal whereby said output power of said power supply is continuously adjusted toward said dimmer setting.