Patent Application
20120104975
The disclosure relates to lighting systems and more particularly to light source drivers or ballasts for powering LED arrays, fluorescent or high-intensity-discharge (HID) lamps. Many lighting system installations include a user-operated control unit, such as a wall-mounted switch or dimmer control, allowing controlled operation of a light source that is mounted remotely from the control device. Some light source control devices incorporate a variety of advanced features, including the ability to receive and act on control information transmitted to the device, such as from a radio frequency (RF) transmitter to allow a user to set the lights on or off or to a specific dimming level without being near the control unit. The control unit, moreover, may perform profile control for selectively turning lights on or off at certain times in a given day, or may perform lighting control operations based on sensed conditions such as ambient light levels and/or the sensed presence or absence of a person or vehicle in a given area near the light. Such advanced control devices (switch, dimmer) often include microprocessors and other circuitry that must be powered independently of when the lights are on, and thus require a certain amount of quiescent current flow from which to derive the off-state power. However, current flowing across the light source during such an off-state can cause abnormal operation (e.g. flashing or flickering) of the lamp or LED array. Prior attempts to address these problems involved dissipating excess off-state power in a resistive component in series with the control unit and parallel with the light source, but this approach reduces energy efficiency. Thus, there is a need for improved lighting systems to avoid inadvertent off-state flashing while providing quiescent off-state current to power advanced lighting control devices.
The present disclosure provides ballasts and driver circuitry with shunt circuits to selectively provide a bypass current path for quiescent current in the lamp or LED array off-state, while avoiding excess current dissipation in the on-state (including dimmed levels).
A ballast or driver is disclosed, having an input receiving AC input power, a rectifier converting the input power to provide a DC bus output, a DC bus capacitance, an output stage with one or more power converter circuits for powering a light source, and a shunt circuit. The shunt circuit includes first and second shunt circuit nodes coupled between the AC input and the DC bus capacitance. In certain embodiments, an LED driver is provided, where the output power stage includes a DC to DC converter circuit operatively coupled with the rectifier output terminals to convert the rectifier DC output power to provide DC driver output power to at least one LED light source. In other embodiments, a fluorescent lamp ballast is provided, with an output power stage including an inverter providing AC output power to at least one fluorescent light source.
In certain embodiments, the shunt circuit is connected between the rectifier output terminals and the DC bus capacitance. In other embodiments, the shunt circuit is coupled between the ballast or driver input and the rectifier.
The shunt circuit provides a high impedance when the AC input power is greater than or equal to a power threshold value, and provides a low impedance when the input power is below the power threshold value.
In certain embodiments, the power threshold is less than a normal operating power range for powering the light source and the power threshold is greater than an OFF-state quiescent power level of a light source control device coupled between an AC source and the ballast or driver. The disclosed configurations may be advantageously employed to allow quiescent current flow in the ballast or driver while inhibiting charging of the bus capacitance and thus prevent the output power stage from providing power to the light source to preventing or mitigating flickering or flashing in an OFF state when power is not to be delivered to the light source.
In certain embodiments, an active shunt circuit is provided, including a variable impedance circuit having a transistor coupled between the first and second shunt circuit nodes and a control terminal coupled to a sensing circuit including a zener diode and a resistance coupled between the first shunt circuit node and the control terminal to change the transistor impedance according to the voltage across the shunt circuit nodes.
In certain embodiments, a passive shunt circuit is provided, including a positive temperature coefficient (PTC) resistance coupled between the first and second shunt circuit nodes.
One or more exemplary embodiments are set forth in the following detailed description and the drawings, in which:
Referring now to the drawings, where like reference numerals are used to refer to like elements throughout, and wherein the various features are not necessarily drawn to scale. The present disclosure relates to ballasts and/or LED drivers for providing power to one or more sources, including a shunt circuit with a variable impedance to allow operation of the light source when the AC input power exceeds a power threshold value, and to provide a low impedance current path upstream of the power output stage when the AC input power is below the power threshold value to prevent an output power stage from providing power to the light source.
In certain embodiments, the apparatus 120 is an LED driver, with the output power stage 126 having a DC to DC converter circuit 127 coupled with the rectifier output terminals 124a and 124h to convert the rectifier DC output power to provide DC driver output power to at least one LED light source 130 via terminals 127a and 127b. In other embodiments, the apparatus 120 is a fluorescent lamp ballast, where the output power stage 126 includes a DC to DC converter 127 as well as an inverter 128 providing AC output power to one or more fluorescent light sources 130 via output terminals 128a and 128b. The DC to DC converter 127 may be omitted in certain ballast implementations, with the inverter 128 directly converting the output of the rectifier 124 to provide AC output power to the light source(s) 130. Where included, moreover, the DC-DC converter 127 may implement power factor correction to control a power factor of the ballast or driver 120, or power factor correction may be done in an active rectifier 124. In both situations, a controller 129 is provided to regulate the output power by controlling one or both of the DC to DC converter 127 and/or the inverter 128.
Some light source control units 110 include circuitry for sensing ambient light, detecting presence or absence of persons or vehicles, RF transceivers, and microprocessors or logic circuitry that require quiescent current flow across the ballast or driver 120 from the AC Mains source 102 for their proper operation, even in an OFF state in which power is not to be delivered to the light source 130. The control device 110 thus has an ON state in which power is delivered to the light source 130 and an OFF state in which a non-zero quiescent current is provided to the ballast or driver 120.
The exemplary ballast or driver 120 accommodates this situation via a shunt circuit 125 to provide a conduction path for such quiescent current flow upstream of the bus capacitance Cdc of the driver or ballast 120 so as to prevent the output power stage from providing power to the light source 130, and to thereby prevent or mitigate flickering or flashing of the light source 130 when the control device 110 is in an OFF state. The shunt circuit 125 senses or otherwise reacts to the ON or OFF state of the control unit 110, and during off-state, limits the voltage of the DC bus capacitor Cdc, thereby preventing undesired starting of the light source 130. When the control unit 110 changes to the ON state, the shunt circuit 125 provides a high impedance to allow the DC bus capacitor Cdc to charge and thus enables provision of power by the output stage 126 to the light source 130, without adversely impacting the ballast or driver power efficiency and the light output efficacy. The disclosed usage of the shunt circuitry 125 thus provides a solution to the above mentioned flashing problems with low power consumption to aid the proper operation of the light source control unit 110 in the ON and OFF states, and provides better lamp efficacy than prior solutions and better compatibility with control units 110 while meeting formal regulations.
As shown in
Referring also to
Referring also to
The active shunt circuits 125 of
In the normal (ON) state of the control device 110, the rectifier 124 provides a relatively high output DC bus voltage across the shunt circuit nodes 125a and 125b. In this condition, the DC voltage across the zener diode D5 exceeds the Zener voltage Vz of D5 and D5 conducts, creating a voltage across R3 such that the base emitter voltage of Q2 (Vbe) causes Q2 to turn on. With Q2 on, the collector voltage of Q2 (Vbe of Q1) is brought to ground or near-zero, and thus Q1 turns oft and does not conduct. In one implementation as exemplified in
When the control device 110 is placed into an OFF mode or state, power is not to be provided to the light source(s) 130. In this condition, the input power to the ballast or driver 120 is below the power threshold THP and the shunt circuit 125 provides a low impedance 202b (
Another embodiment is shown in
The above examples are merely illustrative of several possible embodiments of various aspects of the present disclosure, wherein equivalent alterations and/or modifications will occur to others skilled in the art upon reading and understanding this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, systems, circuits, and the like), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component, such as hardware, processor-executed software, or combinations thereof, which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the illustrated implementations of the disclosure. In addition, although a particular feature of the disclosure may have been illustrated and/or described with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, references to singular components or items are intended, unless otherwise specified, to encompass two or more such components or items. Also, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in the detailed description and/or in the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”. The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations.
