Patent Description:
An emergency lighting system may use a battery-backed lighting device which switches to a battery automatically when a power failure is detected.

An emergency light is necessary in order to provide illumination when the power provided by regular power supply, e.g. mains supply, fails. Emergency lighting devices require a kind of energy storage device, for example a battery, such as a rechargeable battery, which provides electrical energy to the lighting device, during the mains failure.

Modern emergency lighting devices can be provided in commercial buildings and residential buildings. The lighting devices often include one or more clusters of high-intensity LEDs.

A conventional emergency lighting device driver supplied by a mains voltage can comprise an electromagnetic interference EMI filter circuit followed by a power factor correction circuit (PFC), which supplies a converter circuit, for example a flyback converter, which powers LEDs used as lighting devices. The flyback converter can also separate the mains supply on one hand and a low voltage side on the other hand by means of an isolation barrier.

The isolation barrier provides safety extra-low voltage (SELV - also separated extra-low voltage) by separating circuitry with high voltages, e.g. a mains supply voltage, from circuitry with low voltages. A SELV circuit can include electrical-protective isolation (double insulation) from all circuits other than SELV, particularly all circuits that may carry higher voltages and simple separation from other SELV circuits.

State of the art lighting devices make use of specific additional discrete components designed to provide a means for detection for mains presence in order that an ASIC or microcontroller uC can use this information. This is particularly critical in emergency control gear as this detection is often used to switch to the battery supply for an emergency event (such as loss of mains).

<CIT> discloses an isolated, primary side switched driver having a mains detection. <CIT> and <CIT> each disclose an isolated, primary side switched driver including a capacitor connecting ground potentials of primary and secondary circuits, with no such mains detection.

<CIT> discloses an isolated primary-side-switched driver which is suitable for lighting means and which detects a mains failure on the primary side, and passes a mains failure signal to the secondary side for the purpose of saving parameters using the remaining energy stored in a capacitor.

<CIT> discloses detection of mains voltage and/or DC supply voltage by monitoring the current flowing through a capacitor connected between the primary and secondary ground potentials of a flyback converter, a capacitor network and an amplifier being used to monitor said current.

Particularly in emergency drivers with a flyback topology this detection can be relatively slow if implemented on the secondary side.

Thus, it is an object of the present invention to provide for an improved isolated, primary side switched driver for lighting means.

According to a first aspect, the invention relates to an isolated, primary side switched driver for lighting means, wherein a mains voltage is connectable to the primary side of the isolated driver, the isolated driver comprising: a primary circuit having a switch, a secondary circuit, an isolation barrier separating the primary circuit and the secondary circuit, wherein a ground potential of the primary circuit and a ground potential of the secondary circuit are connected via a capacitor, and a control circuit on the secondary side, configured to monitor a current to/ from the capacitor to the ground potential of the secondary circuit and configured to issue a mains failure signal in case the current does not meet predefined conditions, preferably in case no such current is detected, wherein a shunt resistor is connected in series between the capacitor and the ground potential of the secondary circuit.

The capacitor bridging the isolation stage is dimensioned to be within regulatory requirements for SELV barriers.

This provides the advantage that instead of using extra discrete circuitry specifically for the purpose of detecting a mains failure, the same result can be achieved almost instantly by the use of an existing capacitor, for example a class Y capacitor, connected across the SELV barrier together with a resistor or bead used for EMI purposes. Moreover, physical space is used efficiently and costs are reduced. Moreover, embodiments of the invention allow for a fast and reliable mains detection without the need for specific circuitry to do so. It can use existing circuitry that is present on SELV rated emergency drivers and only simple signal processing circuitry may be needed to allow secondary control. In an embodiment of the primary side switched driver according to the first aspect, the mains failure signal causes the activation of an emergency lighting operation stage supplying an emergency lighting means.

This provides the advantage that a very fast mains detection of both mains presence and mains loss is made possible.

Advantageously, components are saved since the same components are used for doing multiple tasks. Furthermore, cost are minimised and the very fast detection of mains present and mains loss allows to provide lighting in emergency devices in a very fast and efficient way.

In an embodiment of the primary side switched driver according to the first aspect, the mains voltage is connected to an electromagnetic interference, EMI, filter on the primary side circuit.

In an embodiment of the primary side switched driver according to the first aspect, the EMI filter is connected to a full- or half-bridge, wherein the full- or half-bridge is connected to the ground potential of the primary circuit.

In an embodiment of the primary side switched driver according to the first aspect, the full- or half-bridge is connected to a primary side switching circuit and wherein the primary side switching circuit is connected to the capacitor.

In an embodiment of the primary side switched driver according to the first aspect, the isolation barrier is a safety extra-low-voltage, SELV, barrier.

In an embodiment of the primary side switched driver according to the first aspect, the capacitor is a class Y capacitor.

In an embodiment of the primary side switched driver according to the first aspect, the control circuit is further configured to measure an amplitude of the mains voltage.

In an embodiment of the primary side switched driver according to the first aspect, the control circuit is further configured to derive a timing signal with regard to a frequency of the mains voltage.

According to a second aspect, the invention relates to a method for operating an isolated, primary side switched driver for lighting means, wherein a mains voltage is connectable to the primary side of the isolated driver, comprising: separating a primary circuit and a secondary circuit, wherein a ground potential of the primary circuit and a ground potential of the secondary circuit are connected via a capacitor, wherein a shunt resistor is connected in series between the capacitor and the ground potential of the secondary circuit, monitoring a current to/from the capacitor to the ground potential of the secondary circuit, and issuing a mains failure signal in case the current does not meet predefined conditions, preferably in case no such current is detected.

Aspects of the present invention are described herein in the context of an isolated, primary side switched driver for lighting means.

Various aspects of an isolated, primary side switched driver for lighting means will be presented.

The term "LED luminaire" shall mean a luminaire with a light source comprising one or more LEDs. LEDs are well-known in the art, and therefore, will only briefly be discussed to provide a complete description of the invention.

Now referring to <FIG>, an isolated, primary side switched driver <NUM> for lighting means <NUM> is shown according to an embodiment. The driver may implement e.g. a flyback or boost topology.

The isolated, primary side switched driver <NUM> for lighting means <NUM> comprises a primary circuit 100a having an actively controlled switch in series to a primary side winding, a secondary circuit 100b, an isolation barrier <NUM> having said primary side winding and a secondary side winding, and separating the primary circuit 100a and the secondary circuit 100b. A ground potential of the primary circuit 100a and a ground potential of the secondary circuit 100b are connected via a capacitor <NUM>.

Moreover, the driver <NUM> comprises a control circuit <NUM> on the secondary side 100b, monitoring a current to/from the capacitor <NUM> to the ground potential of the secondary circuit or side 100b and issuing a mains failure signal in case the current does not meet predefined conditions, preferably in case no such current is detected.

The mains failure signal may e.g. cause starting the operation of the lighting means off the battery power.

The switch on the primary side is controlled by a primary-side control circuit which may perform a feedback-control of a secondary side current or voltage, using a feedback signal obtained at the primary side or the secondary side.

The control circuit <NUM> may control e.g. a converter for driving the LEDs off the battery power.

This provides the advantage that instead of using extra discrete circuitry specifically for this purpose, the same result can be achieved almost instantly by the use of an existing capacitor <NUM>, for example a class Y capacitor, connected across the SELV barrier <NUM> together with a resistor or bead used for EMI purposes.

Furthermore, the primary side 100a comprises an EMI filter <NUM> supplied by the mains <NUM> voltage, a bridge <NUM>, the primary side switching circuit <NUM> and a primary side controller <NUM>. The primary side controller <NUM> can be configured to control the primary side switching circuit <NUM>. The bridge <NUM> can be a half- or full-bridge.

The secondary side 100b comprises a secondary LED driver <NUM> configured to drive the LED load <NUM>. Moreover, a battery <NUM> can be provided which is charged by a secondary side battery charger <NUM> and which is configured to supply the LED load <NUM> in case of a mains <NUM> failure.

Embodiments of this invention make use of existing EMI improvement techniques such as class Y capacitors and series resistor/ bead between primary 100a and secondary circuits 100b) to, then, measure a voltage on the secondary side 100b due to the residual current flow through the class Y capacitor. The AC current can be rectified and filtered, if necessary, to provide a DC voltage to the secondary side microcontroller <NUM>, for example. This current only flows when the mains <NUM> is present and stops flowing when the mains <NUM> fails. The amount of current is directly proportional to the mains voltage level.

This provides the advantage that use is made of existing circuitries, in particular capacitor <NUM>, to provide a second function directly without the need for a separate circuit. Moreover, physical space is used efficiently and costs are reduced.

Moreover, embodiments of the present invention allow for a very fast mains detection (both mains presence and mains loss). Moreover, advantageously, components are saved since the same components are used for doing multiple things. Furthermore, cost are minimised and the very fast detection of mains present and mains loss allows to provide lighting in emergency devices in a very fast and efficient way.

Moreover, embodiments of the invention allow for a fast and reliable mains detection without the need for specific circuitry. It can use existing circuitry that is present on SELV rated emergency drivers and only simple signal processing circuitry may be needed to allow secondary control.

Thus, in case mains voltage is present at the primary side 100a, an AC current will flow through the class Y capacitor <NUM> across the SELV-isolation barrier <NUM>. Therefore, when arranging a resistor or bead <NUM> on the secondary side 100b, through which this AC current is directed to flow, the voltage drop across this resistor or bead <NUM> can be used in order to analyze the mains voltage (indirectly) with regard to at least one of the following aspects:.

Therefore, in embodiments of the present invention, no dedicated (primary side 100a) mains detection circuitry is required, but rather the presence of the already present class Y capacitor <NUM> across the SELV-isolation barrier <NUM> can be used for the mains voltage detection.

<FIG> shows a method <NUM> for operating an isolated, primary side switched driver for lighting means <NUM> according to an embodiment.

All features of all embodiments described, shown and/or claimed herein can be combined with each other.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only and not limitation. Numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described embodiments. Rather, the scope of the invention should be defined in accordance with the following claims and their equivalence.

Claim 1:
Isolated, primary side switched driver (<NUM>) for lighting means (<NUM>),
wherein a mains voltage is connectable to the primary side of the isolated driver, the isolated driver comprising:
- a primary circuit (100a) having a switch;
- a secondary circuit (100b);
- an isolation barrier (<NUM>) separating the primary circuit (100a) and the secondary circuit (100b), wherein a ground potential of the primary circuit (100a) and a ground potential of the secondary circuit (100b) are connected via a capacitor (<NUM>); and
- a control circuit (<NUM>) on the secondary side (100b), configured to monitor a current to/from the capacitor (<NUM>) to the ground potential of the secondary circuit (100b) and configured to issue a mains (<NUM>) failure signal in case the current does not meet predefined conditions, preferably in case no such current is detected, wherein a shunt resistor (<NUM>) is connected in series between the capacitor (<NUM>) and the ground potential of the secondary circuit (100b).