Abstract: A luminous power supply apparatus for driving gas discharge devices and the like with relatively high frequency voltages including an output transformer having a primary winding and a secondary winding across which a device to be powered may be connected, transistorized switches connected to the primary winding for providing pulses of alternating polarity thereto when driving, a pulse width modulator for driving the switches at an RF frequency, and a controller for selecting the width of the drive pulses to control the power applied to the device to be powered. The output transformer is comprised of: a pair of U-shaped core members having their corresponding ends joined together to form a unitary core; a primary winding wound about one side of the core and overlying a first junction of the pair of core members; a secondary winding wound about an opposite side of the core and overlying a second junction of the pair of core members; and potting means having a coefficient of resistance of 3.