Abstract: A circuit for energizing either a first or second lamp and for energizing a motor to position the energized lamp is comprised of first and second switches for supplying current to one of the lamps. Current sensors are provided to monitor the flow of current through each of the lamps. When current is flowing through one lamp and its associated switch, a biasing network assures that the other switch remains open. Upon the failure of the energized lamp, the other lamp is energized, a motor is energized so that the other lamp may be moved to a desired position within the optical system, and a visible indication that the lamp has failed open is provided.

Abstract: An apparatus for starting and operating an arc lamp used in health care applications includes means for producing a rectangular wave AC signal with a frequency controlled by external resistive and capacitive networks. Parallel-connected inductor and capacitor means form a resonant circuit to receive the rectangular wave AC signal. Additional capacitor means connected in series with the arc lamp is closed into the circuit when the arc lamp begins to conduct, thereby changing the resonant frequency of the parallel inductor-capacitor resonant circuit. The detection of current flow in the arc lamp causes a resistor to be switched into the resistive network controlling the frequency of the pulse-width modulated signal, thereby changing the frequency of the rectangular wave AC signal.

Abstract: A failure compensation circuit automatically reduces the output voltage of a power supply when a portion of a load drops out. The compensation circuit includes a circuit for generating a control signal representative of the desired voltage across the load. A power supply supplies voltage to the load in response to the control signal. An input signal representative of the current delivered to the load is produced which decreases whenever a portion of the load drops out. The circuit for generating the control signal is responsive to the input signal for adjusting the control signal such that when the current delivered to the load decreases, the voltage delivered to the load is automatically reduced.

Abstract: A compensation circuit includes a circuit for monitoring the current delivered to a load and for producing a switching signal whenever a current spike is detected. A control signal representative of the desired voltage across the load is produced. A power supply supplies voltage to the load in response to the control signal. The circuit for generating the control signal is responsive to the switching signal for adjusting the control signal such that when a current spike is detected the voltage delivered to the load is substantially instantaneously reduced.