Electrodeless lamp operating circuit and method

In an operating circuit for an electrodeless lamp, means for providing a reverse-bias current to the winding of a magnetic core electric field inducing means in said lamp to reduce magnetic saturation of the core thereby to enhance electrical operating efficiency of said lamp comprising:

• (a) controlled switching means comprising a switch, an input lead, an output lead, and a control means effective for repetitively operating said switch at radio frequencies to provide periodic intervals of transmission between said input and output leads;
• (b) energizing means for applying direct current potential across the winding of said electric field inducting means when said switch is closed, said energizing means comprising a DC reference voltage bus and a ground terminal, said bus being connected to one terminal of said winding, said ground terminal being coupled to the output lead of said controlled switching means and said input lead of said controlled switching means being connected to the other terminal of said winding;
• (c) a voltage transformer having a primary and a secondary each with first and second sides, and providing a voltage across said secondary which is proportional to and of opposite polarity to that across said primary;
• (d) means connecting the first sides of both said primary and said secondary to said DC reference voltage bus terminal;
• (e) filtering means comprising:
• (i) a unidirectional conducting means having first and second electrodes, said first electrode connected to said second side of said voltage transformer secondary, and
• (ii) charge storage means connected between the first side of said voltage transformer secondary and the second electrode of said unidirectional conducting means;
• (f) isolation means connected between said second electrode and said other terminal of said winding, whereby a substantially constant DC current flows through the isolation means, charge is stored when said switch is closed, and the stored charge flows through said winding in a reverse-bias direction when said switch is open;
• and
• (g) reverse current blocking means connected between said second side of said primary and said other terminal of said winding, whereby
• (i) an energizing current is supplied to said winding when said switch is closed,
• (ii) said unidirectional conducting means prevents current flow through said secondary and said filtering means during opening of said switch,
• (iii) said isolation means prevents transients at said winding from reaching said filtering means during opening of said switch without short circuiting said DC reference voltage bus to said ground terminal upon closing of said switch, and
• (iv) said reverse current blocking means prevents currents developed by said filtering means from being conducted to said primary and thus allows substantially constant DC current to flow through said winding when said switch is open in a direction opposite to said energizing current thereby to minimize energy losses due to saturation of said core.