Magnetek, Inc.

Magneteck, Inc.

Bryce L Hesterman

Allan A Nostwick

George W Mortimer

Mihail S Moisin

Ben A Beer

Don V Folker

Antonio Marques

Dan Soule

John F Steel

A symmetry control circuit for a ballast driving a gas discharge lamp. The circuit controls the pre-heat time of a gas discharge lamp with heatable filaments by holding off the full striking voltage until the lamp has had sufficient time to pre-heat. The circuit is designed to work with electronic ballasts and especially electronic ballasts without boost power factor correction to properly pre-heat the lamp. A control circuit reduces the duty cycle in an inverter transistor, thereby keeping the voltage across the lamp low while allowing filament heating to occur. The control circuit is disabled after a time interval of about 500 ms, allowing the transistor duty cycle to increase to 50 percent, the lamp voltage to rise, and the properly pre-heated lamp to ignite.

Symmetry control circuit for pre-heating in electronic ballasts

A family of programmed start parallel-resonant electronic ballast circuits operate in a first mode during a preheat interval following application of power to the ballast, and then afterwards operate in a second mode. The ballast circuits can be based on any of the several forms of current-fed parallel-resonant inverters, all of which have a dc choke inductor. A first embodiment operates such that, during the first mode, the parallel-resonant inverter is inhibited, while an auxiliary transistor develops a trapezoidal voltage waveform across the dc choke inductor. Filament preheating is provided by windings coupled to the dc choke inductor. The ballast output voltage is essentially zero so that no destructive glow current is produced. During the second mode, the auxiliary transistor is inhibited, and the parallel-resonant inverter produces a sinusoidal output voltage. The rms magnitude of the filament heating voltage is reduced by about fifty percent as the waveshape changes from the trapezoidal shape to a form similar to that of a full-wave rectified sine-wave in which the dc component has been removed. In an alternative embodiment, the waveforms of the first embodiment are produced without using an auxiliary transistor. During the first mode, all of the switching transistors of the parallel-resonant inverter are operated in unison. During the second mode, they are switched in the normal out-of-phase manner.

Programmed-start parallel-resonant electronic ballast

A pulse-width modulator is disclosed which can be used, for example, in a power factor corrected electronic ballast circuit. The pulse-width modulator circuit combines a reference waveform signal with a second signal to form a composite waveform signal. The composite waveform signal is then compared with a reference voltage. The level of the pulse-width modulator's output depends upon the results of the comparison, such that a change in the level of the second signal causes an adjustment in the duty cycle of the output. In an electronic ballast application, the reference waveform can be a scaled version of the oscillator waveform found in the ballast's inverter circuit.

Pulse-width modulator circuit for use in low-cost power factor

A control circuit and ballasting means controls the light output of a gas discharge lamp in response to switches that are external to the ballast. The invention provides 3 levels of light output with single or multiple lamps. One embodiment of the invention can be mounted in a standard three-way socket for incandescent lamps. Another embodiment can be used to control multiple lamps in a ceiling-mounted fixture, replacing an inboard/outboard configured multiple ballast circuit. Other embodiments provide circuits that allow conventional dimming ballasts which are designed to be controlled with a low-voltage DC input signal to be controlled by a pair of switches connected to an AC power source.

Three-way fluorescent adapter

A two-winding, integrated-magnetic EMI filter provides damped common-mode and differential-mode inductances. The preferred embodiment of the filter has a magnetic core structure that incorporates a high-permeability C-core, a high-permeability I-core, and a low-permeability, lossy shunt. The three core pieces are assembled so as to form a structure that, similar to an E-I configuration, has two winding windows. The loss in the shunt aids in dissipating noise and it diminishes the effects of unwanted parasitic resonances by providing damping for the differential-mode inductance. Damping for the common-mode inductance is provided by losses in the C and I core pieces. Varying the reluctance of the shunt allows the differential-mode inductance to be adjusted separately from the common-mode inductance in order to tune the filter to remove desired noise frequencies. Another embodiment of the invention incorporates a high-permeability toroid core and a low-permeability, lossy shunt.

Integrated-magnetic filter having a lossy shunt

An electronic ballast includes a low cost circuit for power factor correction. A PWM circuit utilizes a wave form signal derived from the ballast inverter as a reference. The reference wave form signal is combined with a feed back signal to form a composite control signal that is compared with the reference voltage to create a pulse width modulated signal.

Diode clamping arrangement for use in electronic ballasts

An electronic ballast has a protection circuit particularly useful for smaller diameter gas discharge lamps including compact fluorescent lamps. The protection circuit prevents lamps from overheating by preventing the ballast from providing sustained output power when the magnitude of the ballast output voltage indicates abnormal lamp operation. The protection circuit has a voltage sensor which develops a voltage that is more negative than the negative DC supply terminal of the inverter so that an inexpensive low-voltage SCR can be used to turn off the inverter. The circuit provides automatic restarting of the ballast after a new lamp has been installed to eliminate the need for toggling the input power to the ballast.

Lamp protection circuit for electronic ballasts

A compensation circuit in a boost-type preregulator of the type having a power factor control circuit operating in a critical conduction mode by providing a triangular modulation of current according to a sine wave envelope, the compensation circuit in the form of a charge pump circuit acting as a frequency-to-voltage converter and including a capacitor, diode and resistor network providing AC coupled current pulses from the output to the input of the power factor control circuit to reduce crossover distortion during the zero-crossing of input current drawn from a sine wave power source. A capacitor at the current envelope input of the power factor control circuit operates to time-average integrate the current pulses to provide a load-current-dependent bias or compensation signal to the power factor correction circuit regulating the critical conduction mode of operation. In another embodiment, the compensation circuit includes an amplifier connected to a current feedback resistor and to a fixed reference to provide the compensation signal.

Power factor correction circuit

The present invention provides a method and circuit for controlling the flow of current through a load. In a preferred embodiment, an oscillator generates a pulse signal of constant frequency. A pulse width modulator adjusts the duty cycle of the pulse signal in response to a dimming level signal input indicative of the desired level of current flow through the load. A converter receives the pulse signal as an input and converts it into an AC signal, the frequency of which follows the frequency of the pulse signal and the symmetry of which varies with the duty cycle of the pulse signal. The load is connected into a resonant circuit tuned such that a change in the symmetry of the AC signal changes the level of current flowing through the load.

Symmetry control circuit and method

The present invention provides a low-cost power factor corrected electronic ballast circuit. A preferred embodiment includes a discontinuous conduction mode boost power factor correction circuit that is controlled with a simple pulse-width modulator (PWM) circuit comprising a few discrete components instead of an integrated circuit. The PWM circuit utilizes a reference waveform signal derived from the ballast inverter. The reference waveform is combined with a feedback signal to create a composite signal that is compared with a reference voltage to create a pulse-width-modulated signal. The feedback signal is used to regulate the bulk DC voltage. In an alternative embodiment, a feedforward signal that is proportional to the time-varying level of the rectified line voltage is added to the reference waveform and the feedback signal, and serves to modulate the pulse width of the boost circuit in a manner that reduces the harmonic distortion of the input current. In addition to the boost circuit, the power factor correction circuit can be realized with flyback and buck-boost topologies. The invention can also utilize several different types of inverter circuits.

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Fort Wayne, IN, United States of America

Bryce L Hesterman