Patent Description:
Emergency lighting, sometimes referred to as egress lighting, is lighting that is activated in the event of power loss. One purpose of emergency lighting is to allow occupants of a building to safely exit the building in the event of a power outage or other emergency. Emergency lighting is mandated for use in commercial buildings by many electrical codes. Such codes generally specify the amount of light that must be provided in the event of power loss and the duration of time for which such light must be provided. For example, U. building codes require emergency lighting to provide one footcandle of light for a minimum of <NUM> minutes along the path of egress during a power outage.

Emergency lighting fixtures typically have a test button which temporarily overrides the unit and causes it to switch on the lights and operate from battery power even if the main AC line power is still on. Typically, the test button must be manually operated by a technician, and may be held down for the duration of the test.

In buildings, emergency lighting is commonly provided by battery-powered emergency light fixtures that are installed in a building along with the luminaires that provide light in non-emergency situations. In some systems, emergency lights are powered by a central bank of batteries. Building codes generally required the wiring from the central power source to emergency luminaires to be isolated from other electrical wiring.

For fluorescent lighting fixtures, emergency operation may be controlled by an emergency ballast that includes a backup battery. A typical fluorescent emergency lighting fixture is illustrated in <FIG>. The lighting fixture <NUM> includes an emergency ballast <NUM> that includes a backup battery <NUM>. A two-lamp instant start ballast <NUM> is connected to two fluorescent lamps 16A, 16B. A test switch <NUM> permits manual activation of the emergency ballast <NUM>.

As is known in the art, fluorescent lamp ballasts stabilize the current through fluorescent lamps, which have a negative resistance characteristic. The ballast provides a positive resistance or reactance that limits the current through the fluorescent lamp to an appropriate level. An instant start ballast, such as the ballast <NUM>, starts the lamps 16A, 16B without heating the cathodes of the lamps by generating a high initial voltage (around <NUM> V).

A fluorescent emergency lighting system can also be configured so that the emergency ballast <NUM> serves the function of both providing regular illumination and emergency lighting without the need for a separate lamp ballast.

<CIT>; <CIT>; <CIT>; <CIT> all show emergency lights with an alternate power supply or emergency light controls for switching a backup power system. <CIT> shows a driving circuit for LED lamps. <CIT> shows an exit sign illuminated by color LEDs.

The invention discloses an emergency lighting module for providing emergency power to a solid state luminaire, according to claim <NUM>, and a method of operating an emergency lighting module, according to claim <NUM>.

The invention according to the independent claims includes an emergency lighting module for providing emergency power to a solid state luminaire, the emergency lighting module comprising: a first output configured to supply a DC output voltage to the solid state luminaire responsive to a reduction of an AC line voltage; a first input configured to receive a DC input voltage from the solid state luminaire; and a second input configured to receive a status signal indicative of the status of the AC line voltage; wherein the emergency lighting module is configured to supply the DC output voltage such that an LED control module in the solid state luminaire can to drive LEDs on an LED board in the solid state luminaire responsive to a logical OR of the DC output voltage and the DC input voltage.

The signal indicative of the status of the AC line voltage may include an AC line signal and/or a rectified AC line signal.

The emergency lighting module may further include a charging circuit configured to receive the DC input voltage from the solid state luminaire and responsively generate a charging signal for charging a rechargeable battery coupled to the emergency lighting module.

The emergency lighting module may be configured to monitor the DC input voltage to detect a brownout condition of the AC line voltage.

The emergency lighting module may include a second output configured to supply a rectified AC signal to the luminaire.

The emergency lighting module may be configured to supply a control signal to the luminaire that disables an AC/DC converter of the luminaire in response to reduction of the AC line voltage.

The emergency lighting module may be configured to supply a dimming control signal to the luminaire in response to reduction of the AC line voltage.

The dimming control signal may include a pulse width modulation (PWM) control signal.

The emergency lighting module may further include a microcontroller configured to monitor the power status signal and to generate the PWM control signal in response to reduction of the AC line voltage. The microcontroller may be configured to generate the PWM control signal to have a target duty cycle.

The microcontroller may be configured to initially generate the PWM control signal to have a first duty cycle that may be lower than the target duty cycle and to increase the duty cycle of the PWM control signal from the first duty cycle to the target duty cycle. The first duty cycle may be less than about <NUM>%.

The microcontroller may be configured to increase the duty cycle of the PWM control signal from the first duty cycle to the target duty cycle in about <NUM> to <NUM> seconds.

The microcontroller may be configured to decrease the duty cycle of the PWM control signal from the target duty cycle to a final duty cycle that is lower than the target duty cycle.

The microcontroller may be configured to decrease the duty cycle of the PWM control signal from the target duty cycle to the final duty cycle over a period of at least <NUM> minutes. The final duty cycle may be about <NUM>% of the target duty cycle.

The microcontroller may be configured to maintain the duty cycle of the PWM control signal at the final duty cycle until the AC line voltage may be restored or until battery capacity may be exceeded.

The emergency lighting module may further include an AC detector configured to detect a presence of the AC line voltage and to supply an AC detection signal to the microcontroller in response to presence of the AC line voltage.

The emergency lighting module may further include an analog to digital converter configured to receive the DC input voltage and provide a digital signal indicative of a voltage level of the DC input voltage to the microcontroller.

The emergency lighting module may further include a charging circuit coupled to the microcontroller. The charging circuit may be configured to receive the DC input voltage from the solid state luminaire and to receive a charging control signal from the microcontroller, and responsively generate a charging signal for charging a rechargeable battery coupled to the emergency lighting module. The module may further include a voltage booster circuit coupled to the microcontroller and configured to receive a voltage booster control signal from the microcontroller and a DC battery voltage from the rechargeable battery and responsively generate the DC output voltage that may be supplied to the solid state luminaire.

The microcontroller may be configured to cause the voltage booster circuit to generate the DC output voltage in response to reduction of the AC line voltage.

The microcontroller may be configured to cause the voltage booster circuit to generate the DC output voltage to have a voltage level that increases from a first voltage level to a maximum voltage level at a first ramping speed in response to reduction of the AC line voltage. The first ramping speed may be between about <NUM> to <NUM> V/s. The first voltage level may be zero volts.

The microcontroller may be configured to cause the voltage booster circuit to generate the DC output voltage to have a voltage level that decreases from the maximum voltage level to zero volts at a second ramping speed in response to restoration of the AC line voltage.

The emergency lighting module may be configured to ramp the DC output voltage up from an initial voltage level to a target voltage level in response to detecting reduction of the AC line signal. The initial voltage level may be zero volts.

The emergency lighting module may be configured to ramp the DC output voltage up from the initial voltage level to the target voltage level at a ramping speed that may be between about <NUM> and <NUM> V/s.

The emergency lighting module may be configured to ramp the DC output voltage down from the target voltage level to zero volts in response to detecting restoration of the AC line signal.

An example related to the invention but not falling within the scope of the independent claims includes an emergency lighting module for providing emergency power to a solid state luminaire includes a microcontroller, an AC detector coupled to the microcontroller and configured to detect a presence of an AC line signal, a first input configured to receive a DC input voltage from the solid state luminaire, a battery charger coupled to the microcontroller and configured to charge a battery using the DC input voltage in response to a first control signal from the microcontroller, and a voltage booster coupled to the microcontroller and configured to generate a DC output signal in response to a battery voltage and a second control signal from the microcontroller. The emergency lighting module is configured to supply the DC output to the solid state luminaire in response to a reduction of the AC line voltage.

The emergency lighting module may be configured to supply a dimming control signal to the luminaire in response to reduction of the AC line voltage. The dimming control signal may include a pulse width modulation (PWM) control signal.

The emergency lighting module may further include a microcontroller configured to monitor the power status signal and to generate the PWM control signal in response to reduction of the AC line voltage.

The microcontroller may be configured to generate the PWM control signal to have a target duty cycle.

The microcontroller may be configured to initially generate the PWM control signal to have a first duty cycle that may be lower than the target duty cycle and to increase the duty cycle of the PWM control signal from the first duty cycle to the target duty cycle. The first duty cycle may be less than about <NUM>%. The microcontroller may be configured to increase the duty cycle of the PWM control signal from the first duty cycle to the target duty cycle in about <NUM> to <NUM> seconds.

The microcontroller may be configured to decrease the duty cycle of the PWM control signal from the target duty cycle to a final duty cycle that may be lower than the target duty cycle.

The microcontroller may be configured to maintain the duty cycle of the PWM control signal at the final duty cycle until the AC line voltage may be restored.

An emergency lighting module for providing emergency power to a solid state luminaire according to further embodiments includes a microcontroller and an AC detector coupled to the microcontroller and configured to detect a presence of an AC line signal. The emergency lighting module is configured to supply a dimming control signal to the luminaire in response to reduction of the AC line voltage.

The microcontroller may be configured to receive a module identification signal from the luminaire and to generate the dimming control signal in response to the module identification signal. The module identification signal may include a digital signal and/or an analog signal.

The microcontroller may be configured to receive a battery identification signal from a battery. The microcontroller may be configured to generate the dimming control signal in response to the battery identification signal. The microcontroller may be configured to control charging of the battery in response to the battery identification signal. The battery identification signal may include a digital signal and/or an analog signal.

The invention according to the independent claims further includes a method of operating an emergency lighting module (<NUM>) for providing emergency power to a solid state luminaire (<NUM>), the method comprising: receiving a status signal indicative of a status of an AC line voltage; monitoring the AC line voltage; and generating the DC output voltage in response to reduction of the AC line voltage; wherein the generating of the DC output voltage is performed such that an LED control module (<NUM>) generating of the DC output voltage is performed such that an can drive the LEDs on an LED board (<NUM>) in the solid state luminaire (<NUM>) responsive to a logical OR (<NUM>, <NUM>) of the DC output voltage and a DC input voltage, the DC input voltage being generated in the solid state luminaire responsive to the AC line voltage.

The method may further include generating a dimming control signal and supplying the dimming control signal to the solid state luminaire in response to reduction of the AC line voltage. The dimming control signal may include a pulse width modulation (PWM) signal. The method may further include generating the PWM control signal to have a target duty cycle.

The method may further include initially generating the PWM control signal to have a first duty cycle that may be lower than the target duty cycle and increasing the duty cycle of the PWM control signal from the first duty cycle to the target duty cycle. The first duty cycle may be less than about <NUM>%.

The method may further include increasing the duty cycle of the PWM control signal from the first duty cycle to the target duty cycle in about <NUM> to <NUM> seconds.

The method may further include decreasing the duty cycle of the PWM control signal from the target duty cycle to a final duty cycle that may be lower than the target duty cycle.

The method may further include decreasing the duty cycle of the PWM control signal from the target duty cycle to the final duty cycle over a period of at least <NUM> minutes. The final duty cycle may be about <NUM>% of the target duty cycle.

The method may further include maintaining the duty cycle of the PWM control signal at the final duty cycle until the AC line voltage may be restored.

An example related to the invention but not falling within the scope of the independent claims includes a method of testing a solid state luminaire including a test switch using an emergency lighting module including a battery includes monitoring the test switch for actuation, in response to actuation of the test switch, determining if the test switch was actuated for more than a threshold time, in response to the actuation of the test switch for more than the threshold of time, operating the solid state luminaire on battery power for a test period in excess of one hour without requiring continued actuation of the test switch during the test period, and supplying a dimming signal to the solid state luminaire during the test period. The dimming signal may cause the solid state luminaire to become more dim over a duration of the test period.

The dimming control signal may include a pulse width modulation (PWM) signal. The method may further include generating the PWM control signal to have a target duty cycle.

The method may further include initially generating the PWM control signal to have a first duty cycle that may be lower than the target duty cycle and increasing the duty cycle of the PWM control signal from the first duty cycle to the target duty cycle. The first duty cycle may be less than about <NUM>%. The method may further include increasing the duty cycle of the PWM control signal from the first duty cycle to the target duty cycle in about <NUM> to <NUM> seconds.

The method may further include in response to actuation of the test switch, checking a charge level of the battery, and in response to the charge level of the battery being less than a threshold charge level, ignoring the test switch actuation.

The method may further include in response to the actuation of the test switch for less than the threshold of time, operating the solid state luminaire on battery power for a shortened test period.

An example related to the invention but not falling within the scope of the independent claims includes an emergency lighting module for providing emergency power to a solid state luminaire includes a microcontroller, and an AC detector coupled to the microcontroller and configured to detect a presence of an AC line signal. The emergency lighting module is configured to supply a DC voltage and a dimming control signal to the luminaire in response to reduction of the AC line voltage. The module further includes a test switch coupled to the microcontroller. The microcontroller is configured to test operation of the emergency lighting controller in response to actuation of the test switch. The module further includes a wireless interface coupled to the test switch and configured to enable wireless actuation of the test switch.

The wireless interface may include a visible light detector that may be configured to actuate the test switch in response to a visible light signal, an infrared signal, a bluetooth signal, and/or a WIFI signal.

Other systems, methods, and/or computer program products according to embodiments of the invention will be or become apparent to one with skill in the art upon review of the following drawings and detailed description. It is intended that all such additional systems, methods, and/or computer program products be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate certain embodiment(s) of the invention. In the drawings:.

Embodiments of the present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

Recently, solid state luminaires that use light emitting diodes (LEDs) as light sources instead of fluorescent bulbs have been developed for general illumination. Accordingly, there is a need for emergency lighting systems that are suitable for driving an LED load.

Conventionally, emergency lighting for solid state luminaires has been handled through the use of a battery powered inverter connected to the luminaire. For example, as shown in <FIG>, an inverter <NUM> is coupled to a solid state luminaire <NUM>. The inverter includes a battery (not shown) that is charged by power received from an AC input (AC_IN) that also normally powers the luminaire <NUM>. As is known in the art, an inverter generates a sine wave or quasi-sine wave AC output in response to a DC power signal, such as a DC signal generated by a battery. The inverter <NUM> monitors the input voltage AC_IN and supplies an AC signal to the luminaire <NUM> in the event the AC_IN voltage is removed. One drawback of this type of system is that the solid state luminaire <NUM> is unaware of the power outage, and will continue to run at its full lumen level. Thus, in order to meet applicable code requirements, the inverter must be capable of supplying enough power to run the luminaire <NUM> at its full lumen output level for the entire time period required by code. This undesirably increases the capacity requirements, and therefore the cost, of the battery.

The present invention provides an emergency lighting module that provides DC power to a solid state luminaire and that controls operation of the luminaire in an emergency lighting mode. Some embodiments may also control dimming of the luminaire in a non-emergency mode. Referring to <FIG>, an emergency lighting module <NUM> provides emergency power to a solid state luminaire <NUM>. The emergency lighting module <NUM> connects directly to the LED array <NUM> of the luminaire <NUM> as well to an AC LED driver <NUM>, and provides a DC voltage signal DC_OUT to the LED array <NUM>. It will be appreciated that the emergency lighting module <NUM> and/or the AC LED driver <NUM> may be provided together with the LED array <NUM> as an integral part of an LED display or as separate components. Moreover, the LED array <NUM> may have any desired configuration and/or number of LEDs, including only a single LED.

In normal operation, an LED driver provides DC current to an LED array. As power is typically supplied via AC lines, it must be converted to DC. Referring to <FIG>, AC power is supplied via the AC_IN line. The AC power is passed to the AC LED driver <NUM>, which generates a DC drive signal DC_IN that is passed to the LED array <NUM> through the emergency LED driver <NUM> over the DC_OUT line.

When the AC power supplied over the AC_IN input is interrupted, DC power is drawn from an auxiliary source <NUM>, which may be a rechargeable battery pack, and passed to the LED array <NUM> over the DC_OUT line.

This configuration is an improvement over the configuration shown in <FIG> that uses an inverter to supply emergency AC power, as the emergency lighting module <NUM> can directly drive the LEDs with DC power at a lower current in the event of a power outage. However, in such a configuration, the emergency LED driver current is set at a fixed level. Thus, the lumen output of the luminaire <NUM> may vary depending on the configuration of the particular luminaire that the emergency module <NUM> is paired with. For example, if the luminaire <NUM> has <NUM> LEDs with a drive current of <NUM> amp, the lumen level output by the luminaire <NUM> during emergency operation will be different than the lumen output of a luminaire that has <NUM> LEDs with a drive current of <NUM> milliamps, because both luminaires would be run at the same reduced load current in emergency operation.

Some embodiments of the present invention provide digitally controlled emergency lighting modules (ELMs). Digital control may be accomplished by means of a microcontroller, a microprocessor, a field programmable gate array, or other suitable digital circuitry. The term "microcontroller" is used herein to refer to any suitably configured digital control circuitry. Microcontrollers are commonly employed in LED lighting systems for dimming control via remote communications. Some embodiments of the present invention provide a microcontroller based emergency lighting module for solid state luminaires in which a microcontroller performs emergency monitoring and control functions in addition to dimming control.

In an emergency lighting module according to some embodiments, the microcontroller and its firmware can provide comprehensive system monitoring and control functionality. Several semi-autonomous control systems/algorithms may be merged together to implement the system requirements.

Inclusion of a microcontroller in and emergency lighting module (with its accompanying input/output, peripherals, and firmware-based algorithms) allows for more sophisticated and integrated control than would otherwise be practical.

With a microcontroller and its associated input/output (I/O) capability and design flexibility, an emergency lighting module according to some embodiments may have the capability of handling multiple feature sets and technologies within the same product.

Emergency lighting modules according to embodiments of the invention are illustrated in <FIG>. Referring to <FIG>, an emergency lighting module <NUM>, <NUM>' is connected to and provides emergency power to a solid state luminaire <NUM>. The solid state luminaire <NUM> includes an AC/DC converter <NUM>, <NUM>' an LED control module <NUM> and an LED board <NUM>.

The AC/DC converter <NUM> of <FIG> receives a rectified AC signal and responsively generates a DC output signal DC_IN. The AC/DC converter <NUM>' of <FIG> receives a power line AC input signal, which may, for example, be an AC signal at <NUM> or <NUM> volts, and responsively generates a DC output signal while passing the AC input signal on to the emergency lighting module <NUM>. The DC output signal of the AC-DC converter <NUM>, <NUM>' is provided to an LED control module <NUM>. The LED control module <NUM> performs DC/DC conversion to generate a DC signal that is configured to drive LEDs in the LED board <NUM> at a desired level. The LED control module <NUM> may control the brightness and/or hue of light emitted by the LED board <NUM> by controlling the voltage and/or current supplied to various LEDs or groups or strings of LEDs in the LED board <NUM> via the LED DRIVE input to the LED board <NUM>.

The LED board <NUM> may include single and/or multiple strings of white, red, blue, green and/or blue-shifted yellow (BSY) LEDs as described for example in <CIT> and <CIT> the disclosures of which are incorporated by reference in their entirety.

Referring to <FIG>, the emergency lighting module <NUM> receives an AC line voltage signal AC_IN and responsively generates a rectified AC signal, which is provided to the AC/DC converter <NUM>. The emergency lighting module <NUM> also receives the DC_IN signal from the AC/DC converter <NUM>, which is used to charge a backup battery <NUM> (<FIG>). The emergency lighting module <NUM> further generates an ON/OFF control signal and a pulse width modulation (PWM) dimming signal PWM_OUT, which are applied to the LED control module <NUM> to control the operation thereof. The emergency lighting module <NUM> is also configured to generate a DC_OUT signal that is used to drive the LED control module <NUM> when the AC input signal is lost.

The DC_OUT signal generated by the emergency lighting module <NUM> and the DC_IN signal generated by the AC/DC converter <NUM>, <NUM>' are logic OR' ed by diodes <NUM>, <NUM> before being applied to the LED control module <NUM>. Accordingly, a higher of the voltages DC_IN, DC_OUT is applied to the LED control module <NUM>. This also prevents the back feed of DC_IN to DC_OUT or DC_OUT to DC_IN.

The emergency lighting module <NUM> also receives a module type signal MT that indicates the type and/or identity of the luminaire <NUM> to which the emergency lighting module <NUM> is attached. The emergency lighting module <NUM> may use the module type information to determine how much the luminaire <NUM> should be dimmed during emergency operation to meet minimum luminescent requirements for emergency lighting, as discussed in more detail below.

Referring to <FIG>, the emergency lighting module <NUM>' receives an AC signal from the AC/DC converter <NUM>' and a DC_IN signal from the AC/DC converter <NUM>'. The emergency lighting module <NUM> further generates ON/OFF control and PWM_OUT dimming signals, which are applied to the LED control module <NUM>. The emergency lighting module <NUM> is also configured to generate a DC_OUT signal that is used to drive the LED control module <NUM> when the AC input signal is lost.

An emergency lighting module <NUM> according to some embodiments is illustrated in more detail in <FIG>. As shown therein, the emergency lighting module <NUM> includes a microcontroller <NUM> that controls operations of the emergency lighting module <NUM>.

The microcontroller <NUM> may include, but is not limited to, a programmable microcontroller, microprocessor, field programmable gate array, or other suitable circuitry. In particular, the microcontroller <NUM> may be a general purpose programmable microcontroller, such as a model MSP430 microcontroller manufactured by Texas Instruments.

A conventional AC filter <NUM> filters and rectifies an AC line voltage AC_IN. The rectified AC signal is output by the AC filter <NUM>. An AC detector <NUM> is coupled to the AC filter <NUM> and detects the presence or absence of an AC input signal to the AC filter <NUM>. An output of the AC detector <NUM> is provided to the microcontroller <NUM>.

Brief reference is made to <FIG>, which illustrates an AC detector <NUM> according to some embodiments in more detail. As shown therein, the AC detector may include a rectifier circuit <NUM> having an input coupled to the AC filter <NUM> and an output coupled to a comparator <NUM> that drives an opto-coupler <NUM> for providing a signal S1 that is indicative of the AC line voltage. The opto-coupler <NUM> output will pulse at the line frequency rate as long as the AC voltage magnitude is above a predetermined cutoff level Vref. When the AC voltage drops below the cutoff level, the comparator <NUM> output becomes static, and no further pulses are generated through the opto-coupler <NUM>. The microcontroller <NUM> monitors the opto-coupler output signal for activity. If the opto-coupler output stops producing transitions at the line frequency, the microcontroller <NUM> may detect this as a loss of AC signal.

Referring again to <FIG>, the microcontroller <NUM> is also coupled to a battery charger <NUM> and a voltage booster <NUM>, and controls operations thereof. A DC input is provided to the battery charger <NUM>, while a DC output voltage DC_OUT is provided by the voltage booster <NUM>. The volatile and non-volatile memory requirements for the microcontroller <NUM> may be fulfilled with internal and/or external circuitry. The digital controller may use internal and/or external devices to convert analog and digital input/output signals.

A battery <NUM> is coupled to the microcontroller <NUM>, the battery charger <NUM> and the voltage booster <NUM>. The battery <NUM> may be a rechargeable battery, which may in some embodiments include a lithium-iron-phosphate (LiFePO<NUM>) rechargeable battery cell. Other types of battery technologies may be used, including, without limitation, NiCd, NiMH, lead-acid, etc. The battery <NUM> may be provided externally to the emergency lighting module <NUM> as illustrated in <FIG>, or may be integrated within the emergency lighting module <NUM>.

The battery <NUM> provides a battery type signal BT that indicates the type of battery that is connected to the emergency lighting module <NUM>. The microcontroller <NUM> may use this information to determine the battery type, voltage and/or capacity (e.g., in milliamp-hours) of the battery <NUM>.

The battery <NUM> and/or the emergency lighting module <NUM> may include a temperature sensor <NUM> that provides a temperature signal TEMP that is representative of the temperature of the battery <NUM> to the microcontroller <NUM>. The temperature of the battery <NUM> may be used by the microcontroller to improve the safety of the battery packs and also to improve charging performance. Using the temperature information it may be possible for the microcontroller <NUM> to tailor charging and discharging functions to increase efficiency for a given temperature. The microcontroller <NUM> may also disable the battery pack <NUM> in response to a temperature sensed by the temperature sensor <NUM> in the event of a malfunction.

An exemplary charging algorithm is illustrated in <FIG>, which is a graph of charging voltage versus charging current. Assuming a discharged battery has a discharged voltage level of V1, the battery is charged by applying a constant current I2 to the battery. In response to the charging current, the battery voltage may rise from V1 to V2 while the charging current is held constant. Once the battery voltage reaches a charged voltage level of V2, the battery voltage is held constant, while the charging current is reduced from I2 to I1.

The values of I1, I2, V1 and V2 may be determined or selected in response to a temperature sensed by the temperature sensor <NUM>. The determination may be made, for example, using a formula, a lookup table, etc. In particular embodiments, the values of I1 and I2 may be reduced when a high temperature is detected and increased when a low temperature is detected. Moreover, charging could be suspended if a temperature higher than a threshold temperature is detected. After a temperature based shutoff, charging may be retried after waiting a predefined period of time and/or waiting until the sensed temperature falls below a second threshold level.

Referring again to <FIG>, the microcontroller <NUM> has an input for a test switch and an output for battery status. The microcontroller <NUM> also generates the ON/OFF control and PWM_OUT dimming signals described above.

The microcontroller <NUM> is configured to monitor the status of the AC detector <NUM>, and, in response to a detected loss of AC input power, cause the voltage booster <NUM> to generate a DC output voltage DC_OUT to be supplied to the LED control module <NUM>. The microcontroller <NUM> also controls the level of light output by the solid state luminaire <NUM> by means of a PWM_OUT dimming signal.

An emergency lighting module <NUM>' according to some embodiments is illustrated in more detail in <FIG>. The emergency lighting module <NUM>' shown in <FIG> is similar to the emergency lighting module <NUM> shown in <FIG>, except that the emergency lighting module <NUM>' includes an AC detector <NUM>' that receives a rectified AC signal and responsively generates a signal indicative of the status of the AC power supply, which is provided to the microcontroller <NUM>.

As noted above, the AC/DC converter <NUM>, <NUM>' in the luminaire <NUM> (<FIG>) converts AC voltage to a DC voltage which is delivered to the DC/DC LED control module <NUM>. The LED control module <NUM> converts the DC input voltage to a controlled and regulated current for driving single or multiple LED strings in the LED board <NUM>.

In the configuration illustrated in <FIG>, the emergency lighting module <NUM>' receives an AC signal as an input. The AC signal is monitored for indication of loss of AC power for transition to backup operation and for charging the battery <NUM>. The microcontroller <NUM> detects the absence of an AC signal and in response transitions to emergency lighting mode. When emergency lighting mode is entered, the microcontroller <NUM> shuts off the AC/DC converter <NUM> via the ON/OFF control signal and delivers a pulse width modulated signal PWM_OUT to the LED control module <NUM> which determines the lumen level output by the fixture in an emergency mode. The microcontroller <NUM> also causes the voltage booster <NUM> to deliver a DC voltage DC_OUT to the LED control module <NUM>. This level of integration allows the reuse of existing electronics on the luminaire <NUM>, such as the DC/DC circuitry in the LED control module <NUM> and the AC/DC rectifiers in the AC/DC converter <NUM>. That is, only a single AC/DC converter and a single DC/DC LED control circuit may be needed between the emergency lighting controller <NUM> and the luminaire <NUM>.

Some existing fluorescent and LED emergency fixtures include a detection circuit that senses brown out conditions (as opposed to complete power loss conditions) that may cause a luminaire to go out even though the AC power has not completely gone away. It may be desirable for the emergency lighting to engage during brownout conditions to keep the light output at minimum levels.

According to some embodiments, the microcontroller <NUM> can monitor the secondary side DC voltage (DC_IN signal in <FIG>) that powers the LED strings. When this voltage begins to dip (indicating a potential brown-out condition), the digital controller can switch to emergency mode to ensure light output during brown outs that may cause other non-emergency LED lights to go out. Accordingly, as illustrated in <FIG> and <FIG>, the DC_IN signal may be provided to an analog to digital converter input ADC of the microcontroller <NUM>, which allows the microcontroller <NUM> to monitor the level of the DC_IN voltage generated by the AC/DC converter <NUM>.

The battery charger <NUM> may be implemented as a buck converter as illustrated, for example, in <FIG>. As shown therein, the battery charger <NUM> may include input and output capacitors C1, C2, a transistor Q1, which may be a N-channel enhancement mode MOSFET, a diode rectifier D1 and an inductor L1. It will be appreciated that the transistor Q1 could be any type of suitably configured current or voltage controlled switch, such as p-channel MOSFETs, bipolar junction transistors, etc. An input voltage DC_IN is drawn from the AC/DC converter <NUM>, <NUM>' of the luminaire <NUM>, as illustrated in <FIG>. An output voltage VCHG is provided to the battery <NUM>. The voltage generated by the AC/DC converter <NUM>, <NUM>' of the luminaire <NUM> is typically much higher than the voltage needed to charge the battery <NUM>. Accordingly, the battery charger <NUM> steps the voltage down to provide a desired voltage level VCHG for charging the battery <NUM>.

The operation of a buck converter is well known. Referring again to <FIG>, the transistor Q1 is operated as a switch under control of the microcontroller <NUM>, which monitors the output current and voltage of the battery charger <NUM> and responsively controls the ON/OFF state of the transistor Q1 through a control signal CTRL1 applied to the gate of the transistor Q1. By controlling the ON/OFF state of the transistor Q1, the buck charger circuit alternates between connecting the inductor L1 to the source voltage DC_IN to store energy in the inductor L1 when the transistor Q1 is in the ON (conductive) state, and discharging the inductor L1 into the output capacitor C2 (using current drawn through the rectifying diode D1) when the transistor Q1 is in the OFF (nonconductive) state. By measuring the output voltage VCHG, the microcontroller <NUM> can control the switch Q1 to have a duty cycle that maintains a constant output voltage on the output capacitor C2. As is well known in the art, "duty cycle" of a pulse train refers to the ratio of the pulse duration to the pulse period.

Conversely, during emergency operation, it is necessary to boost the output voltage VBATT provided by the battery <NUM> so that it can be used by the luminaire to drive the LED control module <NUM>. The voltage generated by the battery VBATT must therefore be boosted to the same voltage level that would otherwise be provided by the AC/DC converter <NUM>, <NUM>' of the luminaire before it can be output as a DC_OUT voltage signal.

Accordingly, the voltage booster <NUM> may be implemented as a boost converter as shown in <FIG>. A boost converter is a DC/DC converter that boosts an input voltage to a higher voltage level. Referring to <FIG>, the voltage booster <NUM> may include an input capacitor C3, an output capacitor C4, a transistor switch Q2, which may be an N-channel enhancement mode MOSFET, a diode D2 and an inductor L2. It will be appreciated that the transistor Q2 could be any type of suitably configured current or voltage controlled switch, such as p-channel MOSFETs, bipolar junction transistors, etc..

An input voltage VBATT is provided from the battery <NUM>, and the boost converter generates an output voltage DC_OUT that is provided to the LED control module <NUM>, as shown in <FIG>.

The state of the transistor switch Q2 is controlled by the microcontroller <NUM> via a gate control signal CTRL2 applied to the gate of the transistor Q2.

By controlling the ON/OFF state of the transistor Q2, the boost converter <NUM> causes the charge on the output capacitor C4 to increase to a higher level than the input voltage VBATT due to the tendency of the inductor L2 to resist changes in current. When the transistor Q2 is in the ON (conductive) state, current through the inductor increases rapidly, causing the inductor L2 to absorb energy, which is stored in the magnetic field of the inductor. When the transistor Q2 is switched to an OFF (nonconductive) state, the inductor L2 discharges stored energy through the diode D2 and into the output capacitor C4. The voltage generated by the inductor L2 during the discharge phase is related to the rate of change of current, and not to the original charging voltage, thus allowing the output voltage DC_OUT that is stored on the output capacitor C4 to exceed the input voltage VBATT.

By monitoring the output voltage DC_OUT, the microcontroller <NUM> can control the transistor Q2 to have a duty cycle that causes the output voltage DC_OUT to remain at a desired voltage level.

Referring to <FIG>, in some embodiments, the boost and charging circuits can be combined into a single bidirectional booster/charger <NUM> that acts to both charge the battery <NUM> under normal operating conditions and supply a DC voltage to the LED controller <NUM>, <NUM>' in emergency operation.

Operation of the bidirectional booster/charger <NUM> is controlled by two control signals CTRL3 and CTRL4 generated by the microcontroller <NUM>. In normal operation, the bidirectional booster/charger <NUM> acts as a battery charger. In particular, in normal operation, the bidirectional booster/charger <NUM> receives a DC input voltage DC_IN at terminal T1 and provides a charging voltage VCHG to the battery <NUM> at terminal T2. In emergency mode, the bidirectional booster/charger <NUM> acts as a voltage booster, in which case the bidirectional booster/charger <NUM> receives a battery voltage signal VBATT at terminal T2 and provides a DC output voltage DC_OUT to the LED control module <NUM> at terminal T1.

<FIG> is a circuit diagram of a bidirectional booster/charger <NUM> according to some embodiments. The bidirectional booster/charger <NUM> includes switching transistors Q3, Q4, which may be n-channel enhancement mode MOSFETs, although other types of suitably configured transistor switches can be used, including p-channel MOSFETs, bipolar junction transistors, etc. The bidirectional booster/charger <NUM> further includes capacitors C5, C6 and an inductor L3. A first input/output terminal T1 and a second input/output terminal T2 are provided.

In the bidirectional booster/charger <NUM>, the power moves either direction based on how the switching transistors Q3, Q4 are driven. There are a number of challenges to implementing this circuit effectively. The challenge first is being able to control the voltages in each direction. The two circuit topologies (charger and booster) have very different transfer characteristics requiring what amounts to two separate control loops. These two loops then have to work together seamlessly based on which direction it is desired for the power to move.

The microcontroller <NUM> monitors the voltage and current at each end of the booster/charger <NUM> and drives the transistor switches Q3, Q4 directly in response to the measured voltages and currents. In such an implementation, control of the transistor switches can be implemented in software, which enables the microcontroller to customize the operation of the booster/charger <NUM> based on the type of luminaire and/or battery to which the emergency lighting module <NUM> is connected.

The transistors Q3 and Q4 are operated as switches under control of the microcontroller <NUM>, which controls the ON/OFF state of the transistors Q3 and Q4 through control signals CTRL3 and CTRL4 applied to the gates of the transistors Q3, Q4, respectively.

In charging mode (normal operation), the circuit sees a voltage applied at terminal T1 and a load at terminal T2. In that case, the circuit steps the voltage level down from T1 to T2. When the transistor switch Q3 is in the ON (conductive) state and the transistor switch Q4 is in the OFF (nonconductive) state, the inductor L1 is connected to the source voltage DC_IN and energy is stored in the inductor L1. When the transistor switch Q3 is switched to the OFF (nonconductive) state, the transistor Q4 is switched to the ON (conductive) state, and energy is discharged from the inductor L1 into the output capacitor C6 using current drawn through the conducting switch Q4. Accordingly, in charging mode, the transistors Q3 and Q4 are driven with complementary control signals at a selected duty cycle Dchg.

By measuring the output voltage VCHG, the microcontroller <NUM> can control the switches Q3, Q4 to have duty cycles that maintain a constant output voltage on the output capacitor C6.

In charging mode, the output voltage VCHG is related to the input voltage DC_IN according to the following formula:
<MAT>.

In the boost mode (emergency operation), the circuit sees a voltage applied at terminal T2 and a load at terminal T1. In that case, the bidirectional booster/charger <NUM> causes the charge on the output capacitor C5 at terminal T1 to increase to a higher level than the input voltage VBATT applied at the terminal T2. When the transistor Q4 is in the ON (conductive) state and the transistor Q3 is in the OFF (nonconductive) state, current through the inductor L3 increases rapidly, causing the inductor L3 to absorb energy, which is stored in the magnetic field of the inductor. When the transistor Q4 is switched to an OFF (nonconductive) state and the transistor Q3 is switched to the ON (conductive) state, the inductor L3 discharges stored energy into the capacitor C5, which serves as an output capacitor in the boost mode. Accordingly, in boost mode, the transistors Q3 and Q4 are driven with complementary control signals at a selected duty cycle Dboost.

The voltage generated by the inductor L3 during the discharge phase is related to the rate of change of current through the inductor, and not to the original charging voltage, thus allowing the output voltage DC_OUT that is stored on the output capacitor C5 to exceed the input voltage VBATT. In boost mode, the output voltage DC_OUT is related to the input voltage VBATT according to the following formula:
<MAT>.

The charging subsystem of the emergency lighting module <NUM> includes the charger power supply electronics (i.e., the voltage charger <NUM> or bidirectional booster/charger <NUM>), the microcontroller <NUM>, an analog-to-digital converter (ADC), and a Pulse Width Modulation (PWM) output generator. The ADC and the PWM generator maybe implemented within the microcontroller <NUM> and/or as peripheral elements coupled to the microcontroller <NUM>.

The voltage charger <NUM> or bidirectional booster/charger <NUM> provides the voltage and current needed for the charging process. The microcontroller <NUM> monitors both the charging voltage and the charging current via the ADC. The microcontroller <NUM> monitors the ADC values, and adjusts the charger PWM signal output accordingly. The charger PWM output provides the control signal CTRL1 for the charger <NUM> (<FIG>) and/or CTRL3 and CTRL4 for the bidirectional booster/charger <NUM> (<FIG>).

Charging a Lithium-Iron-Phosphate (LiFePO<NUM>) battery requires precise monitoring and control. During an initial charging phase, the charging subsystem controls the PWM output to achieve a constant charging current in accordance with battery specifications. As the battery becomes charged, its voltage increases steadily under constant current conditions. Accordingly, the charging subsystem maintains a constant charging current while monitoring the battery <NUM> for increasing voltage.

Once the battery voltage reaches its target level, the charging subsystem modifies its output control to maintain a constant voltage on the battery <NUM>. During this constant-voltage phase, the charging subsystem adjusts the control output to hold the charger voltage steady. For a normal LiFePO<NUM> battery charged with this method, the charge current will steadily decrease during the constant voltage phase.

During the constant voltage (CV) phase, the charging subsystem monitors the charger current, and stops charging when the charging current drops below the CV minimum charging current threshold. The microcontroller <NUM> updates a status flag register to "charged" and continues to monitor the battery voltage. The charging algorithm reverts to charging (starting with constant current) in the event that the battery voltage drops below a "turn on charger" threshold. In some embodiments, the microcontroller may wait until the "turn on charger" threshold has been sustained for a certain period of time, such as minute, before charging is resumed.

Accordingly, some embodiments provide a microcontroller-controlled charging control loop for a rechargeable battery in an emergency lighting module for a solid state luminaire. The microcontroller may implement a charging algorithm specifically tailored for a LiFePO<NUM> battery; however, the charging algorithm may be adapted to any battery technology needs. The charging algorithm may utilize only a portion of the microcontroller's feature set and bandwidth for charging, so that the microcontroller may perform many other tasks concurrently with battery charging. Moreover, the charging algorithm may utilize a controlled ramp up of the charging signal to simplify and/or replace a hardware control loop.

With the wide variety of lumen levels supported in luminaires with which an emergency lighting module may be used, it may not be cost effective to use a single battery pack to support all of them. A single battery pack would have to be sized to support luminaires with the highest lumen rating, and may be significantly oversized for luminaires with lower lumen ratings.

One solution is to use multiple battery packs much more tailored to meet the needs of a narrower range of applications. To reduce inventory and cost, it is desirable to use the same emergency lighting module electronics to support a variety of different battery packs. In order to accomplish this, it is desirable for the microcontroller of the emergency lighting module to be able to identify the battery capacity.

Methods for generating the battery type signal BT are illustrated in <FIG> to I<NUM>C, and may include, but are not limited to, the use of an I<NUM>C communication channel between the battery <NUM> and the emergency lighting module <NUM> (<FIG>). The I2C channel is implemented using a programmable device <NUM> in the battery <NUM> which communicates with the emergency lighting module using POWER, CLOCK, DATA and GROUND lines. In other embodiments, fixed interface lines tied to either a logic '<NUM>' or a logic '<NUM>' such that they may be read back by a digital controller (<FIG>) may be used. In the example shown in Figure 13B, two of the data lines are tied to logic '<NUM>', while one is tied to logic '<NUM>'. With three data lines, up to eight different battery types can be recognized. In still further embodiments, a fixed resistor to which a current may be applied and the voltage read back by a microcontroller in the emergency lighting module <NUM> (<FIG>) is used to identify the battery <NUM>. Any of these approaches may enable the microcontroller <NUM> to identify the type or model of battery that is connected to the emergency lighting module <NUM> and to adjust the charging and boosting algorithms of the emergency lighting module accordingly.

An alternative method of providing the BT signal is via configuration during product assembly. For this method, when the Printed Wiring Board Assembly (PWBA) containing the ELM microcontroller <NUM> is to be combined into a system with a known battery input, the microcontroller receives configuration information about the battery specification, and stores that information in non-volatile memory, for use by its control algorithms during emergency operation.

The life span of the battery <NUM> is expected to be significantly less than the life of the luminaire or emergency lighting module with which it is used. In order to further reduce cost and increase the service life of luminaires and emergency lighting modules, an emergency lighting module according to some embodiments includes a field replaceable battery pack.

Referring to <FIG>, which is an exploded perspective view of a luminaire <NUM> including an emergency lighting module <NUM>, a housing <NUM> houses LED control circuitry <NUM> and the emergency lighting module <NUM>. An AC/DC converter <NUM> may also be enclosed within the housing <NUM>. A battery <NUM> is mounted in a battery cage <NUM>, which may be installed within the housing <NUM>. A lid <NUM> may be placed over the housing to cover the components mounted therein, and a cover retainer <NUM> may be placed over the cover <NUM> to hold the cover <NUM> in place. When the cover retainer <NUM> and the cover <NUM> are removed, the battery <NUM> may be exposed for field replacement by a service technician.

By monitoring the AC line voltage, an emergency lighting module according to some embodiments may automatically detect loss of AC power and transition smoothly to emergency lighting operation in which power is supplied to the luminaire from the battery.

Solid state light sources are most efficiently driven from voltages that are nominally much greater than voltages generated by most battery packs. Battery packs are most efficient and cost effective when limited to two to four cells. In order to achieve increased efficiency for both devices it is desirable to use a voltage boosting circuit to step the battery voltage up to levels required to drive the LEDs. To simplify the emergency lighting control algorithm, it is desirable to control the transitions to and from battery power. In some embodiments, the battery booster voltage may be gradually increased when transitioning to battery operation. Likewise, the battery booster voltage may be gradually ramped down when transitioning off of battery operation. This allows gradual transition of load between the battery booster and the AC/DC converter.

<FIG> illustrate an example of a transition from normal operation to emergency operation and back to normal operation. <FIG> is a graph <NUM> of an exemplary DC_IN voltage generated by an AC/DC converter <NUM>. As shown therein, the voltage DC_IN is generated by the AC/DC converter <NUM> at a voltage level V0. In some embodiments, V0 may be about <NUM> Volts; however, the level of V0 is dependent on the configuration of the LED control module <NUM> and the LED board <NUM>. In general, for solid state lighting applications, V0 may be between about <NUM> and <NUM> Volts.

At time T0, the AC line voltage input to the AC/DC converter <NUM> fails, at which point the DC voltage DC_IN begins to ramp down as capacitance in the AC/DC converter <NUM> discharges. At time T1, the AC line voltage is restored, at which point the voltage DC_IN begins to ramp back up to the V0 level.

<FIG> is a graph <NUM> of booster voltage DC_OUT generated by a voltage booster <NUM> or a bidirectional boost/charger <NUM> upon transition to battery power (emergency mode) and back to line power. Referring to <FIG>, at time T0, the microcontroller <NUM> detects a loss of AC line voltage. The loss of AC line voltage is detected directly from the line voltage or from a rectified AC output by the AC/DC converter <NUM> to the emergency lighting module <NUM>. Thus, the emergency lighting module may detect loss of AC power before the DC voltage DC_IN output by the AC/DC converter <NUM> has dropped too far.

<FIG> is a graph <NUM> of the voltage VDC that is actually applied to the LED control module <NUM>. As shown in <FIG>, the voltage VDC may be the diode-OR'ed product of DC_IN and DC_OUT. Accordingly, the voltage VDC may take the value of whichever of DC_OUT and DC_IN is greater. This may also prevent the back feed of DC_IN to DC_OUT or DC_OUT to DC_IN.

Referring again to <FIG>, when emergency mode is entered at time T0, the microcontroller <NUM> causes the voltage booster <NUM> or bidirectional boost/charger <NUM> to begin generating a boosted output voltage DC_OUT. The level of DC_OUT increases from time T0 up to a maximum level V0, which may be equal to the level of DC voltage that would otherwise be supplied by the AC/DC converter <NUM> of the luminaire <NUM>. The voltage level VDC supplied to the LED control module <NUM> may dip <NUM> when the DC_IN voltage drops. However, the DC_OUT voltage may begin to ramp up quickly enough that the voltage level VDC supplied to the LED control module <NUM> does not drop too far. For example, the DC_OUT voltage may ramp up quickly enough that the increasing level of DC_OUT exceeds the dropping value of DC_IN before the value of DC_IN drops by more than a predefined level ΔV, which may be about <NUM> Volts for a <NUM> Volt system. Ramping the voltage DC_OUT up to V0 may take about <NUM> to <NUM> seconds, and in some embodiments between about <NUM> and <NUM> seconds. Accordingly, the ramping rate up to V0 may be about <NUM> to <NUM> V/s. The DC_OUT level is maintained throughout emergency lighting operation until the battery is discharged or AC line power is resumed.

In the example illustrated in <FIG>, the microcontroller <NUM> detects the resumption of AC line voltage at time T1. At that time, the microcontroller causes the voltage booster <NUM> or bidirectional boost/charger <NUM> to begin ramping the voltage back down as the voltage DC_IN begins to ramp back up. However, ramping down the DC_OUT voltage may be delayed slightly to ensure that there is only a slight dip <NUM> in the VDC signal. Ramping the voltage back down from V0 may take about <NUM> to <NUM> seconds. A manufacturer may desire to use an emergency lighting module as described herein in connection with many different types of luminaires. Thus, it is desirable for an emergency lighting module to support different lumen levels for different applications.

In some embodiments, the luminaire <NUM> provides a feedback signal MT to the emergency lighting module <NUM>, <NUM>' which identifies the luminaire model, and which may be used by the emergency lighting module <NUM>, <NUM>' to determine the lumen level of the luminaire <NUM>. Based on the lumen level of the luminaire <NUM>, a PWM_OUT signal is generated to drive the luminaire at a desired lumen level for emergency lighting operation. This enables a single emergency lighting configuration to support multiple different lumen level luminaires and provide the same lumen level during emergency operation regardless of the lumen rating of the luminaire to which the emergency lighting module <NUM>, <NUM>' is connected.

For example, if the desired emergency lighting level is <NUM> lumens, a luminaire <NUM> rated at <NUM> lumens may be driven by the emergency lighting module <NUM>, <NUM>' at a fixed PWM duty cycle corresponding to <NUM> lumen operation. A luminaire rated at <NUM> lumens may be driven at a different PWM duty cycle for the same <NUM> lumen operation. This configuration may promote consistent emergency operation with the same battery size.

Methods for generating the module type signal MT are illustrated in <FIG>, and may include, but are not limited to, the use of an I<NUM>C communication channel between the luminaire <NUM> and the emergency lighting module <NUM> (<FIG>). The I2C channel is implemented using a programmable device <NUM> in the luminaire <NUM> which communicates with the emergency lighting module using POWER, CLOCK, DATA and GROUND lines. In other embodiments, fixed interface lines tied to either a logic '<NUM>' or a logic '<NUM>' such that they may be read back by a digital controller (<FIG>) may be used. In the example shown in <FIG>, two of the data lines are tied to logic '<NUM>', while one is tied to logic '<NUM>'. With three data lines, up to eight different luminaire types can be recognized. In still further embodiments, a fixed resistor to which a current may be applied and the voltage read back by a microcontroller in the emergency lighting module <NUM> (<FIG>) is used to identify the luminaire <NUM>. Any of these approaches may enable the microcontroller <NUM> to identify the type or model of luminaire to which the emergency lighting module <NUM> is connected, and thereby infer the rated lumen level of the luminaire.

It will be appreciated that in place of an I<NUM>C connection, an Ethernet, synchronous or asynchronous serial or parallel interface, or any other communication protocol may be employed.

An alternative method of providing the MT signal is via configuration during product assembly. For this method, when the Printed Wiring Board Assembly (PWBA) containing the ELM microcontroller is to be combined into a system with a known light output, the microcontroller receives configuration information about the light output requirement, and stores that information in non-volatile memory, for use by its control algorithms during emergency operation.

While in emergency lighting mode, the emergency lighting module monitors the battery voltage and current while driving the LED control module <NUM> via the dimmer pulse width modulation signal PWM_OUT generated by the microcontroller <NUM>.

<FIG> is a graph of duty cycle versus time for a PWM signal generated by a microcontroller <NUM> of an emergency lighting module <NUM> according to some embodiments. When switching to battery power, the microcontroller <NUM> may start the dimmer PWM_OUT signal at a low initial duty cycle (for example about <NUM>%), and may thereafter ramp the PWM_OUT signal to a desired duty cycle, (e.g., <NUM>%) shown in <FIG> as TARGET. Ramping the PWM_OUT signal may avoid start-up issues with the driver circuit in the LED control module <NUM>. Once the microcontroller <NUM> has ramped the PWM_OUT signal to the target duty cycle, the target duty cycle is maintained for an initial period, which may in some cases be about three minutes. At the end of the initial period, the microcontroller <NUM> may begin a gradual ramp down of the duty cycle to achieve a final PWM duty cycle of nominally <NUM>% of the target duty cycle at ninety (<NUM>) minutes after the emergency lighting module <NUM> entered the emergency lighting mode. For example, if the target duty cycle is <NUM>%, the ending duty cycle will be about <NUM>% at the <NUM> minute mark. The ramp down may be linear, quasi-linear, parabolic, piecewise linear, exponential, or may follow any other waveform. The final PWM_OUT duty cycle is maintained until either power is re-applied, or the battery drops below the fully-discharged level. If the battery level drops to the fully discharged level, the microcontroller <NUM> shuts down the lamp drive and enters low power mode until power is restored.

The ramp down of the PWM_OUT dimming signal described above meets the Underwriters Laboratories UL924 standard requirement that the final light output of an emergency egress light be <NUM>% of the initial value. In addition, by ramping down the dimming, the emergency lighting module <NUM> conserves power, which allows for a smaller capacity battery (and lower cost) than would be required if the dimming signal were held steady for the entire <NUM> minutes.

Ramping down the PWM_OUT dimming signal causes the light emitted by the luminaire <NUM> to decrease over time, which provides a visual indicator to building occupants that the emergency lighting power is decreasing, which may encourage occupants to exit the building sooner.

With the use of a digital controller additional operational improvements can be made by sensing the light output and/or temperature of the luminaire <NUM> directly. The LED string current and voltage may be adjusted in response to sensor measurements to maintain optimal efficiency and light output quality.

In some further embodiments, the power good output of the lighting controller may be monitored by the emergency lighting controller <NUM>, which may respond to abnormal conditions and improve overall efficiency and reliability.

Referring again to <FIG>, an emergency lighting module <NUM> according to some embodiments includes a test switch <NUM> that may be used to initiate test operation of the emergency lighting module <NUM>. Implementation of test functions may be necessary to comply with product certification requirements. The emergency lighting module <NUM> may also include a status indicator <NUM>, which may be an LED status indicator, that can provide feedback to the user as to the status of the emergency lighting module, the level of charge currently available on the battery, etc. Charge status of the battery may be indicated, for example, by flashing an indicator lamp at an increasing rate as the battery takes more charge, by providing a series of indicator lamps and progressively lighting indicator lamps in the series until the battery is charged, etc..

The emergency lighting module test switch subsystem includes the test switch <NUM> and the microcontroller <NUM> which implements an algorithm for managing the test switch <NUM>.

In some embodiments, , the microcontroller <NUM> may respond to actuation of the test switch by initiating a battery test only if the battery is fully charged. However, in other embodiments, the battery may not need to be fully charged before a test is initiated.

From an initial state, the microcontroller may measure the duration of a test switch signal. When the test switch is de-actuated (e.g., a pushbutton switch is released), the microcontroller may activate either a "monthly" or "yearly" test, depending on duration of the test switch actuation. The monthly test may be a brief (e.g. thirty second) test to ensure that the luminaire will operate on battery power in response to a loss of the AC line voltage. The yearly test may be a more thorough test that verifies the luminaire will continue to run for a full ninety minutes on battery power after loss of the AC line voltage.

For example, if the test switch is actuated momentarily (e.g., a pushbutton switch is held down for less than ten seconds), the microcontroller <NUM> may initiate the "monthly" test; if the button is actuated for more than ten seconds, the microcontroller <NUM> may initiate the more exhaustive "yearly" test. In other embodiments, if the button is held down for more than a predefined period of time, the emergency light module will begin a test that operates only so long as the button is held down.

Once a battery test is initiated, the microcontroller <NUM> may activate a five second timer during which it ignores additional button presses (the "cancel lock-out period").

Subsequent the cancel lock-out period, the microcontroller <NUM> may resume monitoring the test switch <NUM>. If the user actuates the test switch after the <NUM>-second cancel lock-out period has elapsed, the microcontroller <NUM> may proceed to cancel the battery test.

If the battery test fails, the microcontroller may place the emergency lighting module <NUM> in a "fail wait" state until the test switch <NUM> has been pressed and released.

If the test switch <NUM> is actuated for more than ten seconds, the emergency lighting module <NUM> may switch to emergency (battery power) mode for a full ninety minutes.

The microcontroller <NUM> may be configured to ignore requests to initiate battery testing unless the battery is fully charged and the AC line voltage is present.

Test switch handling is illustrated, for example, in the flowchart of <FIG>. As shown therein, the microcontroller <NUM> monitors the status of the test switch <NUM> (block <NUM>). If the switch is activated (block <NUM>), operations proceed to block <NUM>. Otherwise, the microcontroller <NUM> continues to monitor the status of the switch.

After activation of the switch, at block <NUM>, the microcontroller <NUM> checks to see if the battery <NUM> is fully charged. If not, the microcontroller ignores the switch, and operations return to block <NUM> to continue to monitor the switch status.

If the battery is fully charged, the microcontroller <NUM> then checks to see if the switch was actuated for more than a threshold time, such as for more than ten seconds (block <NUM>). If not, a monthly test is initiated (block <NUM>), and if so, a yearly test is initiated (block <NUM>).

The microcontroller then starts a cancel lockout period, such as five seconds, during which time it ignores further button presses (block <NUM>). After the end of the lockout period, the microcontroller <NUM> again monitors the switch status (block <NUM>). If the switch is activated again, the microcontroller <NUM> will cancel the current test (block <NUM>). If the switch is not activated, the microcontroller checks to see if the test is complete (block <NUM>), and if not returns to block <NUM> to check the status of the test switch at block <NUM>. If the test is complete, the operations of <FIG> may be restarted from the beginning.

The battery testing simulates an on-battery (i.e., emergency lighting) scenario. In a yearly test scenario, the emergency lighting module <NUM> operates as described above, ramping from the initial value to <NUM>% of the initial value over the course of the <NUM>-minute battery test.

Although described above as a pushbutton switch, the test switch <NUM> may be implemented in a number of different ways, as illustrated in <FIG>. In particular, some embodiments provide a wireless interface for actuating the test switch <NUM>. Referring to <FIG>, the test switch <NUM>, which is coupled to the microcontroller <NUM> in an emergency lighting controller <NUM>, may be actuated by an infrared receiver 360A in response to an infrared signal 355A transmitted by an infrared transmitter 350A.

Similarly, referring to <FIG>, the test switch <NUM> may be actuated by a Bluetooth receiver 360B in response to a Bluetooth signal 355B transmitted by a Bluetooth transmitter 350B.

Referring to <FIG>, the test switch <NUM> may be actuated by a WIFI receiver 360C in response to a WIFI signal 355C transmitted by a WIFI transmitter 350C.

Referring to <FIG>, in other embodiments the test switch <NUM> may be actuated by a visible light detector 360D in response to a visible light signal 355D transmitted by a light emitting device 350D, such as a flashlight, laser pointer, etc..

Providing a wireless interface to a test switch of an emergency lighting module may be particularly beneficial for installations where the luminaire is mounted out of reach, so that a technician is not required to physically climb up to the location of the luminaire in order to manually engage a pushbutton switch.

Referring again to <FIG>, the emergency lighting module <NUM> may further include a status indicator <NUM>, which may include one or more light emitting diodes of different colors.

Using the status indicator <NUM>, the emergency lighting module <NUM> may display information about various machine conditions, including battery charging, battery charged, battery test in progress, "on battery" (i.e., emergency) operation, battery failure, etc..

In some embodiments, the status indicator <NUM> may include one red and one green LED for indicating the state of the emergency lighting module <NUM>. With two LEDs, there are many possible combinations of distinct LED flashing sequences, allowing greater detail to be displayed and easily interpreted. For example, an alternating red and green pattern may be used for indicating a test sequence. Table <NUM> lists several possible LED indicator combinations for use in the emergency lighting application.

In other embodiments, the status indicator may include an alphanumeric LCD display that can display status information alphanumerically under control of the microcontroller <NUM>.

In many environments, dimming is an important feature for a light fixture to implement. Various different dimming technologies have been developed for both incandescent and fluorescent lighting, which represent the vast majority of installed commercial lighting facilities today. As solid state lighting fixtures are developed and become more available as a replacement technology for incandescent and fluorescent lighting, it is desirable for solid state luminaires to respond appropriately to dimming signals generated by various different types of dimming systems.

One rudimentary method of dimming control is referred to as step dimming. Step dimming uses multiple switches that allow a user to select one of several (e.g., two or three) different brightness levels for a light fixture by appropriate setting of multiple switches. For example, in a three-bulb fluorescent fixture, one switch may control the two outer bulbs, while another switch may control the single inner bulb. By setting the switches appropriately, the user can turn on one, two, three or no bulbs in the fixture at one time, effectively providing four levels of dimming.

<NUM>-<NUM> V dimming is an electronic lighting control signaling system that enables continuous dimming between brightness levels. A <NUM>-10V dimming switch generates a DC voltage that varies between zero and ten volts in response to a user setting, such as the position of a slide switch or a dial connected to a potentiometer. The controlled lighting fixture typically scales its output so that it emits full brightness in response to a <NUM> V control signal and is off (zero brightness) in response to a <NUM> V control signal. Dimming devices may be designed to respond in various patterns to the intermediate voltages, such as giving output curves that are linear for voltage output, actual light output, power output, perceived light output, etc..

Dimming fluorescent ballasts and dimming LED drivers often use <NUM>-<NUM> V control signals to control dimming functions. In many cases, however, the dimming range of the power supply or ballast is limited.

Digital Addressable Lighting Interface (DALI) is a technical standard for network-based systems that control lighting in buildings. It was established as a successor for <NUM>-<NUM> V lighting control systems. The DALI standard, which is specified in the IEC <NUM> standard for fluorescent lamp ballasts, encompasses the communications protocol and electrical interface for lighting control networks. A DALI network consists of a controller and one or more lighting devices (e.g., electrical ballasts and dimmers) that have DALI interfaces. The controller can monitor and control each light by means of a bi-directional data exchange. Data is transferred between controller and devices by means of an asynchronous, half-duplex, serial protocol over a two-wire differential bus.

A luminaire may be designed to respond to multiple types of dimming control signals including, for example, step dimming control signals, <NUM>-10V dimming control signals, DALI dimming control signals, and other dimming control signals. In addition, a luminaire may be designed to respond to a PWM_OUT dimming signal generated by an emergency lighting module as disclosed above.

<FIG> illustrates an emergency lighting controller 500A according to some embodiments that is connected to a power board 400A of a luminaire according to some embodiments. The power board 400A includes the AC/DC converter <NUM>, <NUM>' and the LED control module <NUM> described above in connection with <FIG>, but does not include the LED board <NUM> of the luminaire. The emergency lighting module 500A may be configured in a similar manner as the emergency lighting modules <NUM>, <NUM>' described above, except that the emergency lighting module 500A is additionally configured to output a dimming signal source select signal SELECT to the LED board 400A as described in more detail below.

The LED board 400A may be configured to handle dimming signals generated by many different types of dimming systems, including step dimming, <NUM>-10V dimming, DALI dimming, and/or other types of dimming signals. For example, the LED board 400A may include a step dimming interface <NUM> that detects the presence of AC signals on multiple switched AC lines corresponding to the state of one or more step dimming switches. The LED board 400A may also include a <NUM>-10V interface <NUM> that is configured to process a <NUM>-10V dimming signal. Alternatively or additionally, the LED board 400A may also include a DALI dimming interface <NUM> that is configured to communicate with a DALI controller (not shown) and to receive and process DALI dimming signals.

The step dimming interface <NUM> may include one or more AC detectors that detect the presence of AC voltage on multiple switched lines based on AC signals provided by the AC filter <NUM> in the emergency lighting module 500A. In response, the step interface <NUM> is configured to generate a PWM signal indicative of the state of the switched lines to a multiplexer <NUM>. For example, in the case of two switched lines, the step interface <NUM> may generate a PWM signal having a duty cycle of <NUM>% if both switched lines are powered, a PWM signal having a duty cycle of <NUM>% if only one switched line is powered, and a duty cycle of <NUM>% if neither switched line is powered. Other arrangements are also possible. For example, the step interface could generate a PWM signal having a duty cycle of <NUM>% if switched line <NUM> is powered and switched line <NUM> is unpowered, and a PWM signal having a duty cycle of <NUM>% if switched line <NUM> is unpowered and switched line <NUM> is powered.

The <NUM>-10V interface <NUM> is configured to detect the voltage level provided by a <NUM>-10V dimmer and generate a PWM signal having a duty cycle related to the level of the <NUM>-10V signal. For example, the duty cycle of the PWM signal generated by the <NUM>-10V interface <NUM> could be directly proportional to the voltage level of the <NUM>-10V signal (e.g., generates a <NUM>% duty cycle in response to a 5V signal, a <NUM>% duty cycle in response to a 6V signal, etc.). In other embodiments, the duty cycle of the PWM signal may be related in a linear or nonlinear fashion to the voltage level of the <NUM>-10V signal in order to provide, for example, PWM signals that result in linear changes in voltage output, actual light output, power output, perceived light output, etc., of the luminaire. The PWM signal output by the <NUM>-10V interface <NUM> is provided as an input to the multiplexer <NUM>.

The DALI interface <NUM> may include circuitry for communicating with a DALI controller using asynchronous, half-duplex, serial protocol over a two-wire differential bus, and processing the DALI signals to generate a PWM signal in response to dimming commands received over the DALI interface. The PWM signal output by the DALI interface <NUM> is also provided as an input to the multiplexer <NUM>.

It will be appreciated that in a particular installation, only one type of dimming control will be available. Thus, the multiplexer <NUM> will receive only one PWM input from the step interface <NUM>, the <NUM>-10V interface <NUM> and the DALI interface <NUM>. The DALI interface may be a standard DALI interface. The <NUM>-10V interface may include an analog to digital converter that converts an analog <NUM>-10V signal to a digital signal and a microcontroller that reads the digital signal and responsively generates a PWM signal that is provided to the multiplexer <NUM>. Similarly, the step interface may include analog and/or digital circuitry that converts a step voltage signal to a PWM signal. The design of such interface circuits is well known in the art.

The PWM dimming control signal PWM_OUT generated by the microcontroller <NUM> is also provided as an input to the multiplexer <NUM>. The multiplexer <NUM> selects a PWM dimming control signal from either the PWM_OUT signal generated by the microcontroller <NUM> on the one hand or an available one of the PWM signals generated by the step interface <NUM>, the <NUM>-10V interface <NUM> or the DALI interface <NUM> on the other hand and supplies the selected PWM signal to the LED control module <NUM> in response to the SELECT signal output by the microcontroller <NUM>. Accordingly, in the event of a power loss, dimming control of the luminaire may be taken over by the emergency lighting module 500A. In that case, dimming of the luminaire is based on the PWM_OUT dimming signal output by the microcontroller <NUM>, and any dimming signal generated by the normal dimming system (e.g., step, <NUM>-10V or DALI) is disregarded by the luminaire.

An emergency lighting controller 500B and a power board 400B of a luminaire according to further embodiments are illustrated in <FIG>. The emergency lighting controller 500B and power board 400B shown in <FIG> are similar to the emergency lighting controller 500A and power board 400A shown in <FIG>, except that in the embodiments illustrated in <FIG>, some of the dimming control functionality is moved to the emergency lighting controller 500B.

Referring to <FIG>, the emergency lighting controller 500B includes an analog to digital converter <NUM> that receives the <NUM>-10V signal from a <NUM>-10V dimmer (not shown) and generates a digital value that is proportional to the level of the <NUM>-10V signal. It will be appreciated that the ADC <NUM> can be integrated in the microcontroller <NUM> and/or implemented as a separate peripheral component thereof. The emergency lighting controller 500B also includes separate AC detectors 512A-512C for detecting the presence of AC voltage on multiple switched lines (switched line <NUM> and switched line <NUM>) as well as an unswitched AC line. The microcontroller <NUM> can determine the state of a step dimming control based on the detected presence or absence of AC voltage on the switched lines.

The microcontroller <NUM> may therefore generate the PWM_OUT dimming signal in response to a step dimming signal, a <NUM>-10V dimming signal, or in response to a loss of AC power on the unswitched AC line. The PWM_OUT signal may therefore be generated by the emergency lighting module 500B during normal operation, and not just during emergency operation. However, since the power board 500B still includes a DALI interface <NUM>, the microcontroller <NUM> still generates a SELECT signal to cause the multiplexer <NUM> to select between the PWM_OUT signal generated by the microcontroller <NUM> and the PWM signal generated by the DALI interface <NUM>. A jumper setting in the emergency lighting module 500B may be used to indicate to the microcontroller <NUM> which type of dimming control is being used. In other embodiments, configuration data that is written to a programmable device at the time of manufacture may be used to identify the type of dimming control that is used.

An emergency lighting controller 500C and a power board 400C of a luminaire according to further embodiments are illustrated in <FIG>. The emergency lighting controller 500C and power board 400C shown in <FIG> are similar to the emergency lighting controller 500B and power board 400B shown in <FIG>, except that in the embodiments illustrated in <FIG>, all of the dimming control functionality is moved to the emergency lighting controller 500C.

Referring to <FIG>, the emergency lighting controller 500C includes a DALI interface that communicates with a DALI controller (not shown) to receive and process DALI dimming control commands. In this embodiment, all dimming by the power board 400C is controlled by the PWM_OUT signal generated by the microcontroller <NUM>. Accordingly, power board 400C does not include a multiplexer and the microcontroller <NUM> does not have to generate a SELECT signal to control its operation.

Claim 1:
An emergency lighting module (<NUM>) for providing emergency power to a solid state luminaire (<NUM>), the emergency lighting module (<NUM>) comprising:
a first output configured to supply a DC output voltage to the solid state luminaire (<NUM>) responsive to a reduction of an AC line voltage;
a first input configured to receive a DC input voltage from the solid state luminaire (<NUM>); and
a second input configured to receive a status signal indicative of the status of the AC line voltage;
wherein the emergency lighting module is configured to supply the DC output voltage such that an LED control module (<NUM>) in the solid state luminaire (<NUM>) can drive LEDs on an LED board (<NUM>) in the solid state luminaire (<NUM>) responsive to a logical OR (<NUM>, <NUM>) of the DC output voltage and the DC input voltage.