Digital addressable lighting interface short protection circuit

A timing circuit may be enabled when a static signal disables communication through a communications bus, the timing circuit producing a threshold level after being enabled for a predetermined time period, and a switch controlled by the timing circuit is configured to disconnect the static signal when the timing circuit produces the threshold level. A static signal may be used to enable a timing circuit upon the static signal disabling communication through a communications bus, and communication may be allowed through the communication bus by disconnecting the static signal using a switch controlled by the timing circuit, after the timing circuit has been enabled for a predetermined period of time.

The disclosed exemplary embodiments relate generally to lighting control systems, and more particularly to protection circuits for addressable lighting systems.

BACKGROUND

Lighting for homes, offices, commercial spaces, and public areas may be controlled to account for occupancy and ambient light at the light fixture, workstation, room, floor and building levels. Some systems have been implemented using the Digital Addressable Lighting Interface (DALI) which is a global standard for a lighting control data protocol and transport mechanism maintained as IEC 62386. The DALI standard specifies a two wire, bi-directional data bus connecting a DALI application controller with up to 64 DALI controlled devices, referred to as control gear, such as ballasts, occupancy sensors, photo sensors, wall switches, and dimmers. The data bus cable is mains rated and may be run next to mains conductors or in a cable with mains conductors. The DALI control gear are individually addressable and data is transferred between the application controller and the control gear using an asynchronous, half-duplex, serial protocol. Data is transmitted using Manchester encoding at a fixed data transfer rate of 1200 bits/s to ensure reliable communications. The DALI bi-directional data bus also provides power at 16 volts and 250 mA maximum current. DALI application controllers and control gear may be connected in a star or daisy chain configuration.

FIG. 1shows a block diagram of an exemplary DALI system100. An application controller105is connected to a number of control gear1100-11063by the bi-directional data bus115. Control gear1100-11063may control light sources125or other equipment or may be implemented as occupancy sensors, light sensors, wall switches or other lighting appliances. Mains power is provided through mains cable120. In some implementations, mains power is provided by or controlled by application controller105.

FIG. 2shows a schematic diagram of at least a portion of an exemplary DALI control gear205similar to control gear1100-11063. DALI control gear205may include a bus interface210and operating circuitry215. Bus interface210may isolate the operating circuitry215from the bi-directional data bus115using a diode bridge240and optocouplers. For example, optocoupler220R may be used for receiving commands or messages from application controller105to the control gear205, while optocoupler220T may be used for transmitting responses and messages from the control gear205to the application controller105. The control gear205may include a computer225, for example, a single chip microcontroller with a processor and memory230for exchanging information over the DALI bi-directional data bus115and for controlling lamps and other lighting equipment.

However, with this type of architecture, where one or more signals of the control gear are effectively coupled directly to the communications bus, some circuitry failures in the control gear may be capable of disabling the communications bus. In some failure modes of the control gear205, one or more inputs or outputs of the microcontroller225may be pulled to a low or ground state and may remain at that state until the failure mode is resolved. For example, the microcontroller225may fail, resulting in a transmit output235being forced to a low or ground state. In the exemplary control gear205shown inFIG. 2, this causes a static voltage to be applied across the LED of optocoupler220T which in turn causes the driver side of the optocoupler220T to remain in an “on” or conductive state. This effectively shorts the two wire bi-directional data bus115through the diode bridge240. As a result, no messages or responses may be conducted between the application controller105and the control gear205or any other devices that may be connected to the bi-directional data bus115. It would be advantageous to provide a mechanism to avoid these conditions.

SUMMARY

The disclosed embodiments are directed to an apparatus including a timing circuit enabled when a static signal disables communication through a communications bus, the timing circuit producing a threshold level after being enabled for a predetermined time period, and a switch controlled by the timing circuit and configured to disconnect the static signal when the timing circuit produces the threshold level.

The disclosed embodiments are directed to a method including using a static signal to enable a timing circuit upon the static signal disabling communication through a communications bus, and allowing communication through the communication bus by disconnecting the static signal using a switch controlled by the timing circuit, after the timing circuit has been enabled for a predetermined period of time.

DETAILED DESCRIPTION

The embodiments disclosed herein limit the time a signal may be held at a static level in the event of a failure. In one or more aspects, the present embodiments utilize a timing circuit and a switch to automatically disconnect a static signal after a pre-determined period of time.

FIG. 3is a schematic diagram of an exemplary control gear305incorporating the structures and techniques disclosed herein. The control gear305may include a bus interface310for isolating operating circuitry315from the bi-directional data bus115using a diode bridge340and receiver-transmitter circuitry360. As part of the receiver-transmitter circuitry360, optocoupler320R may be used for receiving commands or messages from application controller105to control gear305, and optocoupler320T may be used for transmitting responses and messages from the control gear305to the application controller105.

The exemplary control gear305may include a computer325, for example, a single chip microcontroller implemented as a reduced instruction computer with built in Universal Synchronous Asynchronous Receiver Transmitter (USART) capabilities. The microcontroller325may include a processor and a non-transitory computer readable medium in the form of a memory330with computer program code. The microcontroller325with the memory330and the computer program code may cause the control gear305to exchange commands and responses over the data bus115according to the disclosed embodiments, and to operate lamps and other equipment according to DALI protocol requirements. While computer or microcontroller325is shown and described as a programmable integrated circuit with on board memory, it should be understood that any suitable computing device may be applicable to the disclosed embodiments.

Still referring toFIG. 3, as a result of the illustrated implementation of bus interface310, a fault causing LED360to remain in a constant on state causes the two wire data bus to effectively become shorted, barring communication. To remedy this, a disconnect circuit345may be included to limit the time that transmit output signal335may be held at a static level. The disconnect circuit345may include a switch350in line with transmit output signal335, controlled by a timing circuit355. In operation, switch350is normally closed. The timing circuit355may be triggered when transmitting optocoupler320T of the receiver-transmitter circuit disables communication through the bidirectional bus, for example, by remaining constantly on. The timing circuit355may remain triggered as long as communication is disabled and after a period of time may cause switch350to open, disconnecting transmitting optocoupler320T and effectively turning it off.

As an example, microcontroller325may experience at least one fault condition where transmit output signal335may be forced to a constant low level. Because transmit output signal335is connected to LED360of optocoupler320T, LED360may remain continuously on causing the driver side365of optocoupler320T to continuously conduct and short the two wire bi-directional data bus115through the diode bridge340. If the condition persists, the two wire bi-directional data bus115remains inoperative, prohibiting communication between the application controller105and the control gear305or any other devices that may be connected to the bi-directional data bus115.

In this embodiment, when transmit output signal355transitions to a low level, timing circuit355is enabled. If transmit output signal335is forced to remain at a low level for a predetermined period of time, timing circuit355times out and causes switch350to open. Opening switch350allows the voltage across LED360to float, causing the driver side365of optocoupler220T. to go to a high impedance. The connection between the two wires of the bi-directional data bus115is removed and communication among devices attached to the bi-directional data bus115may be restored. Once the bi-directional data bus115is functional, the application controller105may begin diagnostic procedures to determine which control gear is defective and the failure cause.

FIG. 4shows another example of a disconnect circuit405. Disconnect circuit405may include a switch410implemented as a semiconductor, for example, a transistor, field effect transistor (FET), metal oxide semiconductor field effect transistor (MOSFET), or any other suitable device. In this example, a timing circuit415may include a capacitor420that discharges through a resistor425connected to transmit output signal335. During normal operations capacitor420remains charged, causing switch410to conduct transmit output signal335to LED360. If a fault condition forces transmit output signal335low for a predetermined period, capacitor420begins to discharge through resistor425. If the fault condition persists, the capacitor voltage will reach a threshold level below the gate threshold of the switch410. This results in a high impedance between the LED360and the transmit output signal line, effectively turning LED360off and removing the short between the two wires of the bi-directional data bus115. Communication on the bi-directional data bus115may then be restored and diagnostics may be performed.

While described in the context of a static signal that disabled communication through a communications bus, it should be noted that the disclosed embodiments may be used to disconnect any signal that remained static for a predetermined amount of time.

Various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. However, all such and similar modifications of the teachings of the disclosed embodiments will still fall within the scope of the disclosed embodiments.

Furthermore, some of the features of the exemplary embodiments could be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles of the disclosed embodiments and not in limitation thereof.