News Column

Patent Issued for Ramp Controlled Driver for Series/Parallel Solid State Lighting Devices

July 30, 2014

By a News Reporter-Staff News Editor at Journal of Engineering -- General Electric Company (Schenectady, NY) has been issued patent number 8779689, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventors are Nerone, Louis R. (Brecksville, OH); Aurongzeb, Deeder (Mayfield Heights, OH).

This patent was filed on December 13, 2010 and was published online on July 15, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "Large area solid-state devices, such as organic light-emitting diodes (OLEDS), are becoming more popular for illuminating buildings, roads, and for signage and optical display applications. Large area OLEDs have large capacitances and connection of parallel OLED strings in a lighting array increases the capacitance seen by a driver circuit. In addition, the capacitance may vary as the OLED is bent or twisted because of changes in charge distribution. For a given large area lighting installation, moreover, adding further OLEDs in series requires higher drive voltages. Thus, while large area OLED installations typically include series/parallel configurations, practical limitations exist for the number of series-connected OLEDs that can be driven and for the number of parallel-connected strings of series OLEDs. Thus, a need remains for improved techniques and apparatus for driving large area OLED arrays."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "The present disclosure provides apparatus for driving OLED arrays in which a waveform generator slows the rise and fall times of the current control setpoint of a DC-DC converter stage, thus avoiding or mitigating current spikes seen by highly capacitive OLED panels of the array. This control apparatus advantageously serves to slow the rise of current when the device is turned on or anytime a lighting setpoint involves step or rapid changes to increase or decrease the lighting output. The waveform control concept may be employed to combat output current overshoot, which may be 40% of rated current absent the disclosed concepts. The improved ability to operate large capacitance outputs without excessive current spikes can advantageously mitigate premature device degradation and thus extend the usable service-life of a given lighting installation. Moreover, series-connected OLEDs often suffer from individual elements not consistently illuminating during startup.

"In accordance with one or more aspects of the present disclosure, an electronic driver apparatus is provided for powering an OLED array. The driver includes at least one DC-DC converter stage, along with a waveform generator providing a converter setpoint signal to a PWM circuit of the converter. The DC-DC converter has switching devices coupled in series between first and second DC input terminals, with first and second switching devices being joined at an internal node, as well as a driver which provides first and second switch control signals in complementary fashion to the switching devices based on a signal received at a driver control input. A PWM circuit provides a pulse width modulated signal to the driver control input according to a feedback signal and according to a converter setpoint signal from the waveform generator. The waveform generator receives an input setpoint signal, such as a user-selected dimming value representing a desired light output for the driven OLED array, and provides the converter setpoint signal based at least partially on driver setpoint signal, using minimum transition time values to avoid or mitigate current overshoot problems, where the converter setpoint signal has a specified rise and fall times that could be 1 us or more

"In certain embodiments, the waveform generator provides the converter setpoint signal having rise time and fall time values of 1 us or more and 10 ms or less, and the rise time and fall time values may be the same or may be different. In certain embodiments, the converter setpoint signal includes increasing and decreasing profiles, where at least a portion of the increasing and decreasing profiles are linear. In some implementations, moreover, at least a portion of the increasing and decreasing profiles may be nonlinear. The driver in some embodiments provides a second DC-DC converter between the ramp controlled DC-DC converter output and the OLED array.

"In certain embodiments, the driver includes two or more DC-DC converters receiving the DC input power and providing individual outputs to drive corresponding OLED arrays. The individual converters include switching devices, a driver, and a PWM circuit providing a pulse width modulated signal to the driver control input according to a converter setpoint signal and a feedback signal. In certain embodiments, the individual DC-DC converters have a corresponding waveform generator providing the converter setpoint signal to the PWM circuit at least partially according to the driver setpoint signal, with rise time and fall time values of 1 us or more. In certain embodiments, a shared waveform generator provides a common converter setpoint signal to the PWM circuits of the individual DC-DC converters with controlled rise and fall times of 1 us or more."

For the URL and additional information on this patent, see: Nerone, Louis R.; Aurongzeb, Deeder. Ramp Controlled Driver for Series/Parallel Solid State Lighting Devices. U.S. Patent Number 8779689, filed December 13, 2010, and published online on July 15, 2014. Patent URL:

Keywords for this news article include: General Electric Company.

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Source: Journal of Engineering

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