Universal Manufacturing

Magnetek, Inc.

John Lindquist

Dahya Patel

A solid-state ballast for discharge lamps includes circuitry for limiting the maximum output voltage produced when a lamp is first being ignited or is removed. The ballast includes a signal controlled oscillator that provides the operating signal for a resonantly driven lamp load. The voltage across the load is sensed and a signal representing this voltage is fed back to a circuit when controlling the oscillator so as to limit the maximum load voltage during initial start-up and when a lamp is removed. In accordance with a second embodiment, the voltage is cycled between a low level and a level high enough to ignite the lamp, so long as the lamp is not ignited.

Electronic ballast with high voltage protection

A solid-state ballast for discharge lamps includes a device for sensing the instantaneous current flowing within the load to produce illumination. A signal representing this load current is differentially processed with an external control signal representing the desired illumination, to produce an removed signal which controls an oscillator that provides the operating signal for the load. In addition, the voltage across the load is sensed and the signal representing this voltage is fed back to a circuit which controls the oscillator so as to limit the maximum load voltage during initial start-up and when a lamp is removed.

Constant illumination, remotely dimmable electronic ballast

A circuit is provided to speed up switching of a capacitively coupled power transistor driven with a signal provided from a pulse width modulator. The speed-up circuit is provided across a buffer amplifier which is in series circuit between the pulse width modulator and the coupling capacitor. The speed-up circuit includes a time delay circuit which is activated when the output of the amplifier goes low. The delay circuit is coupled to actuate a clamp circuit at a predetermined interval after activation. The clamp circuit is connected to the input of the amplifier and, upon actuation, pulls up the voltage at the input of the amplifier so that it is at a level intermediate the extreme values of the pulse width modulator output signal. In a preferred embodiment the timer is a series RC charging circuit and the clamp is a transistor with its base connected to the junction between the capacitor and the resistor. The collector of the transistor is coupled to the input of the amplifier and its emitter is connected to a voltage source through a zener diode.

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Larkspur, CA, United States of America

John Lindquist