Ferroresonant transformer ballast for maintaining the current of gas discharge lamps at a predetermined value

A ferroresonant transformer ballast for regulating the current across gas discharge lamps, the ballast comprising:

• a three-legged magnetic core having a center leg and outer legs;
• a first coil wound about the center leg of the magnetic core for supplying a changing input voltage;
• a second coil wound about the center leg of the magnetic core whereby the second coil is magnetically coupled to the first coil so as to induce a voltage across terminals of the second coil in response to a change in current from the first coil;
• an output capacitor connected across the terminals of the second coil for resonance;
• a third coil wound about the center leg of the magnetic core whereby the third coil is magnetically coupled to the second coil so as to induce a voltage across terminals of the third coil in proportion to the average voltage across the output capacitor;
• a gas discharge lamp connected across terminals of the third coil whereby a current of the gas discharge lamp is regulated in response to the average voltage of the output capacitor;
• a control inductor to be switchably coupled in electrically parallel relationship with the output capacitor;
• and
• means for switching the control inductor in a pulsing manner into and out of parallel relationship with the output capacitor in response to a current level of the gas discharge lamp to substantially maintain the current level of the gas discharge lamp when the lamp is operating in a steady state mode, the switching means including a switch having terminals coupled in series with the control inductor.

A ferroresonant transformer ballast for regulating the current level of gas discharge lamps, the ballast comprising:

• a magnetic core including cooperating E-shaped and I-shaped pieces, the I-shaped piece positioned across free ends of the E-shaped piece to form a three-legged magnetic core having a center leg and outer legs;
• a first coil wound about the center leg of the magnetic core for supplying a changing input voltage;
• a second coil wound about the center leg of the magnetic core whereby the second coil is magnetically coupled to the first coil so as to induce a voltage across terminals of the second coil in response to a change in current from the first coil;
• an output capacitor connected across the terminals of the second coil for resonance;
• a third coil wound about the center leg of the magnetic core whereby the third coil is magnetically coupled to the second coil so as to induce a voltage across terminals of the third coil in proportion to the average voltage across the output capacitor;
• a gas discharge lamp connected across terminals of the third coil whereby a current level of the gas discharge lamp is regulated in response to the average voltage of the output capacitor;
• a first magnetic shunt extending outwardly from the center leg of the magnetic core at a longitudinal position between the first and second coils, the first shunt serving as a leakage inductance shunt;
• a second magnetic shunt extending outwardly from the center leg of the magnetic core at a longitudinal position between the second and third coils, the second shunt serving as a lamp choke shunt;
• a control inductor to be switchably coupled in electrically parallel relationship with the output capacitor;
• and
• means for switching the control inductor in a pulsing manner into and out of parallel relationship with the output capacitor in response to a current level of the gas discharge lamp to substantially maintain the current level of the gas discharge lamp at a predetermined value when the lamp is operating in a steady state mode, the switching means including a switch having terminals coupled in series with the control inductor.