Patent Description:
State of the art emergency converters typically comprise at least two controllers. Moreover, safety standards require a battery connection in any emergency converter such that each battery replacement should be performed in Separated Extra Low Voltage (SELV) conditions. Therefore, the design of the converter should provide a galvanic (physical) isolation between the electrical grid and the battery connections. This is usually accomplished by using isolated converter topologies such as flyback, forward, LLC, etc..

In <FIG>, a known example of an isolated emergency converter with two controllers and a flyback topology is shown. In general, such an isolated converter requires a first controller (or primary-side controller) in order to operate, such as, for example, an off-the-shelf analog or mixed analog-digital controller. Moreover, a second controller (or secondary-side controller) should be used in order to guarantee the changeover between a maintained and charging operation and an emergency operation, the control of the battery charge, and the lamp operation.

The maintained operation is the operation of the lighting means off the main voltage (in non-emergency state).

For this purpose, a microcontroller is usually used. Therefore, at least two controllers are present in such emergency converters of the prior art.

In order to control an isolated, primary side switched DC-DC converter by a secondary side controller, there is an issue regarding the start-up of this controller from an OFF mode to a full operation mode. After all, the secondary side controller is supplied by a secondary side voltage which is only present once the switched converter has start its operation, as controlled by said secondary side controller.

Therefore, in view of the above mentioned prior art converters, the following question arises: how to turn ON the secondary-side controller from an unpowered mode or OFF mode to a full operation mode.

In general, a start-up circuit for such a secondary side controller plays a significant role in voltage and current reference circuits. The start-up circuit brings out the reference circuit from a dead (zero current) operating point to its normal operating point and, then, is no longer used once the reference circuit starts operating properly. A conventional start-up circuit continues to consume constant current even after giving start-up and, thus, increases the total power consumption of the circuit. This power can be significant when multiple numbers of bias generator circuits are employed in a single chip, consequently reducing battery life.

Moreover, most isolated DC-DC converters are primary-side controlled due to the start-up supply (see <FIG>). When starting-up, the circuit should be energized before the switching of the converter starts. This is normally achieved by drawing current directly from the rectified mains. This also means that the secondary-side controller, disadvantageously, becomes impractical, and many time difficult or expensive to implement. Therefore, a prior art solution provides a start-up oscillating circuit that drives the switching of the isolated converter initially (see <FIG>), thus establishing a secondary side voltage which can be used to supply the secondary side control circuitry. Then this known start up circuit transfers the control of the switching of the isolated converter to the secondary-side controller.

However, this approach requires anyway a controller. In some cases, integrated circuits can be used, in other cases use is made of discrete components. Moreover, this circuit can be expensive, difficult to control, and unreliable. Furthermore, if the handover of the control does not happen correctly, both controller could try, and act over the same switch, and this might have destructive consequences.

As shown in <FIG>, some circuits may also use a secondary transformer in order to transfer energy to the secondary-side controller. In particular, in the OFF mode, the secondary-side controller has no supply. In fact, since there is a physical separation between the primary-side and the secondary-side, there is no energy in order to power-up the secondary-side controller. Therefore, this solution provides a separate transformer that transfers a small amount of energy to start-up the secondary-side controller. This can be done with a high frequency transformer, and an oscillating circuit, or a low frequency transformer without power electronics. However, this approach is expensive due to the fact that, effectively, there are two converters in parallel, requiring a galvanic isolation, and some level of control, especially if a low frequency transformer is used.

As it can be taken from above, the vast majority of converters, such as in LED lighting means, uses primary-side controllers, irrespective of the presence of a secondary-side controller, limited by the need for a biasing energy to start the controller. Applications with secondary-side controllers may also use an additional transformer, in particular an isolation transformer, and additional circuitry to draw energy form the primary-side to the secondary-side. However, afterwards, the circuit is not used anymore. <CIT> discloses a primary-side switched isolated converter according to the preamble of independent claim <NUM>.

Therefore, disadvantageously, the state of the art solutions require the presence of a primary-side controller, irrespective of the presence of a secondary-side transformer or provide more expensive solution with an additional isolation transformer in order to provide bias to the secondary-side controller.

Thus, it is an objective to provide for an improved LED converter comprising a secondary-side controller which, in particular, overcomes at least partially the above mentioned disadvantages.

According to a first aspect, the invention relates to a primary-side switched, isolated converter for supplying an LED load, having a primary-side having terminals for supplying a mains voltage, a secondary-side controller arranged on a secondary-side of the isolated converter, wherein the secondary-side controller is configured to issue a control signal for a primary-side switch of the switched isolated converter, a secondary-side circuitry on the secondary-side of the converter comprises terminals configured to directly or indirectly supply the LED load, and a battery configured to supply the secondary-side circuitry, and a start-up circuitry configured to supply the secondary-side controller off the battery, wherein the start-up circuitry has a control terminal for supplying a start-up signal transmitted from the primary-side to the secondary-side via an isolation stage of the converter.

This achieves the advantage that a controller is provided in the secondary-side which reduces costs by combining the operation of a primary-side controller and a secondary-side controller in a single controller. Another advantage is the direct access to the feedback signals such as voltages and currents.

According to the invention, the isolated converter comprises a secondary-side switch, wherein the secondary-side controller is not configured to control the secondary-side switch.

According to an embodiment, the primary-side of the isolated converter does not comprise a switch control circuitry.

This provides the advantage that the complexity of the converter is reduced.

According to an embodiment, the isolation stage comprises an optocoupler.

This provides the advantage that a simple, and cheap device, such as an optocoupler, can be used to transmit the start-up signal in the isolation stage.

According to an embodiment, the isolation stage comprises a transformer.

According to an embodiment, the switched isolated converter is a flyback-, forward-, or LLC-converter.

This provides the advantage that well known typologies of converters can be used.

According to an embodiment, the secondary-side controller is a microcontroller.

According to an embodiment, the primary-side switched isolated converter is designed as an emergency lighting LED converter.

This provides the advantage that the battery, which is needed for the emergency operation of the emergency lighting LED converter, can be used. Thus, the energy which is necessary for the start-up of the secondary-side converter can be taken off from this battery.

According to an embodiment, the battery is configured to be connected such that the LED load is driven off the battery.

According to the invention, the start-up signal is supplied to an input terminal of a control terminal of the secondary-side switch, such as e.g. a transistor, which, upon being supplied by the start-up signal, is configured to connect the battery to a voltage supply terminal of the secondary-side controller.

This provides the advantage that a component, such as the battery, which is already present in the circuitry of e.g. emergency converters, can be used in order to start-up the secondary-side converter. Thus, this reduces the complexity of the circuitry of the converter.

According to a second aspect, the invention relates to a LED module comprising a primary-side switched isolated converter for supplying an LED load according to the first aspect and anyone of the implementation forms thereof and a LED load.

According to a third aspect, the invention relates to a method for switching a primary-side isolated converter for supplying an LED load, comprising the following steps: supplying a mains voltage; issuing a control signal for a primary-side switch of the isolated converter from a secondary-side controller of the isolated converter; supplying a secondary-side controller of the isolated converter from a start-up circuitry off a battery, wherein the start-up circuitry has a control terminal for supplying a start-up signal transmitted from the primary-side to the secondary-side via an isolation stage of the converter; and supplying directly or indirectly the LED load.

The method according to the third aspect provides the same advantages as the converter according to the first aspect.

Aspects of the present invention are described herein in the context of an LED converter.

Various aspects of an LED converter will be presented. However, as those skilled in the art will readily appreciate, these aspects may be extended to aspects of LED converters without departing from the invention.

The term "LED luminaire" shall mean a luminaire with a light source comprising one or more LEDs and/or OLEDs.

Now referring to <FIG>, an exemplary embodiment of an LED converter <NUM> according to an embodiment of the invention is shown.

<FIG> shows a flyback converter as an example of a primary-side switched, isolated converter <NUM> for supplying an LED load (not shown in <FIG>). The converter <NUM> comprises: primary-side terminals <NUM>, <NUM> for supplying a mains voltage, a secondary-side controller <NUM> arranged on a secondary-side of the isolated converter <NUM>, wherein the secondary-side controller <NUM> is configured to issue a control signal for a primary-side switch <NUM> of the switched isolated converter <NUM>. Thus, the control signal crosses the isolation barrier from the secondary side to the primary side of the converter.

Moreover, a secondary-side circuitry on the secondary-side of the converter <NUM> comprises: terminals configured to directly or indirectly supply the LED load, and a battery <NUM> configured at least to supply the secondary-side circuitry, and a start-up circuitry <NUM>, <NUM> configured to supply the secondary-side controller <NUM> off the battery <NUM>, wherein the start-up circuitry <NUM>, <NUM> has a control terminal for supplying a start-up signal transmitted from the primary-side to the secondary-side via an isolation stage of the converter <NUM>.

Typically, the converter <NUM> is an emergency lighting converter. In this case, this battery <NUM>, or one or more additional batteries are used to drive the lighting means once the main voltage fails. The batteries on the secondary side are typically charged off the mains voltage, using the shown e.g. flyback converter or any other suited charging circuit. The charging of the batteries may also be controlled by the secondary-side controller <NUM>.

The converter <NUM> can be a maintained mode energy LED-converter as well as a non-maintained mode energy converter. The maintained mode emergency converter <NUM> is a converter configured to provide with energy the LED-module (off the mains voltage) in the case where the mains is active, and in an emergency case of a failure of the mains (off one or more batteries). In this embodiment, a recharge of the battery <NUM> may be necessary, as soon as the mains is available again. Moreover, in this case, the converter <NUM> should be high started in order to make sure that the illumination takes place.

The non-maintained mode refers to a mode wherein the converter <NUM> is configured to maintain the LED module n case of an emergency, when a failure of the mains occurs. In this embodiment, a recharge of the battery <NUM> may be necessary, as soon as the mains is available again.

Moreover, the converter <NUM> can be used to monitor the presence of the mains, so to recognize if, and which, voltage is available at the input terminals of the converter <NUM>.

Advantageously, a solution to bias the start-up circuit <NUM>, <NUM> of the isolated converter <NUM> is proposed comprising the secondary-side controller <NUM>, in particular, in battery powered devices. This is applicable for any topology of converter <NUM> with a galvanic isolation, such as flyback, forward, push-pull, SEPIC, half-bridge, etc..

In an embodiment, the converter <NUM> is an emergency converter, having the secondary-side controller <NUM> and obviously also the secondary-side battery <NUM> for powering the LED lighting means. Therefore, some embodiments, especially, deal with the supply of the power and energy for the secondary-side controller <NUM>.

The isolated signal transmission path is provided from the primary-side having the start-up circuit <NUM>, <NUM> to the secondary-side (see <FIG>), wherein on the secondary-side, the signal from the isolated signal transmission path triggers the power up from of the secondary-side controller <NUM> off the secondary-side battery <NUM>.

In an embodiment, also a transformer could be used to make the start-up signal cross the isolation barrier, however, this is more costly than the preferred implementation using an optocoupler <NUM>, <NUM> or the isolated signal transmission.

Preferably, the secondary-side controller <NUM> may control the primary-side switch <NUM> which controls the power transmission across the main transformer <NUM>.

Advantageously, assuming the presence of a battery <NUM>, there is no need for an energy transfer from the primary-side to the secondary-side. Only a control signal is needed. In particular, in power-down mode, the battery <NUM> is disconnected from the secondary-side controller <NUM> via a controlled switch <NUM> (e.g., a transistor such as e.g.a MOSFET). To start-up the device <NUM> from the battery <NUM>, the control signal is used to turn ON (i.e. conductive) the secondary-side switch <NUM> and allow the energy to flow from the battery <NUM> to the secondary-side controller <NUM>. The controller <NUM> will the start the operation of the primary-side switch of the converter, such that energy is transferred to the secondary side. Thus a voltage will be established at the secondary side which can be used to supply the controller <NUM> after the start-up phase, thus that the supply off the battery, in one example, will be stopped, e.g. interrupted.

This provides the advantage that a simple and relatively small device <NUM>, <NUM> (smaller than any SELV transformer), can be activated by the presence of mains voltage (diode side) and it can be configured to turn ON the secondary-side switch <NUM> that connects the battery <NUM> to the secondary-side controller supply <NUM>. From this point, the controller <NUM> can start e.g., an AC-DC converter <NUM> for normal operation and stop using the energy of the battery.

For example, the switch <NUM> can be a P-channel MOSFET switch (see <FIG>). In yet another embodiment, the switch <NUM> can be a PNP battery switch <NUM>. In a yet another example, a regulator <NUM> (see <FIG>) between the battery <NUM> and the controller <NUM>, e.g., a microcontroller supply, is provided, since the battery voltage has a wide range, and the microcontroller only works at a specific value.

Therefore, some embodiments make use of the existing battery <NUM> (e.g., in emergency converters) to bias the secondary-side controller <NUM>, before the converter <NUM> starts switching. The biasing circuit can be executed with standard cheap components like optocoupler <NUM>, <NUM> and MOSFETS <NUM>. The circuit <NUM> is controlled by the presence or absence of the main electric supply V1 (see also description of <FIG>).

Thus, advantageously, there is no need to use two controllers, since only a controller <NUM> may be arranged on the secondary-side of the converter <NUM>, as is the case of emergency lighting means. In fact, in the case of emergency lighting means, a secondary-side controller <NUM> is used in order to operate the battery charge, and the emergency light.

This provides the advantage that it is cheaper to use only one controller <NUM> in the LED converter <NUM> than two, as is the case of the prior art solutions.

Moreover, in the schematic representations shown in <FIG> and <FIG>, the converter <NUM> further comprises a resistor <NUM>, the transformer <NUM>, a rectifying diode <NUM>, and a smoothing capacitor <NUM>.

<FIG> shows a further exemplary embodiment of an LED converter <NUM> according to an embodiment.

In this embodiment, the mains V1 is used in order to turn on the switch <NUM> connected to the battery <NUM> that is configured to provide supply to the secondary-side controller <NUM> during the start-up of the converter <NUM>. In this way, the secondary-side switch <NUM> can be controlled through the isolation barrier <NUM>. The example presented uses optocouplers <NUM> (U1), <NUM> (U1) and U2, U2, but other means might be used, such as a transformer.

The mains voltage V1 passes through a rectifier comprising the diodes D1, D2, D3, and D4. Afterwards, the resulting signal passes through a first capacitor C1 in parallel to a resistor R1, and a further capacitor C3. Moreover, when the mains V1 is present, the diode U1 is polarized, turning the secondary-side switch Q2 on.

The battery <NUM> can be connected to the controller supply directly or indirectly through a regulator <NUM> (as shown in the embodiment of <FIG>), turning on the secondary-side controller <NUM>. A microcontroller can be used as the secondary controller <NUM>, U3. In general, batteries <NUM> have enough voltage to start-up the microcontroller or controller <NUM>. However, if the design requires higher voltage than the battery <NUM> can supply, than a voltage step-up regulator can be used, such a charge pump or boost regulator.

The start-up signal can be supplied to an input terminal of a control terminal of the secondary-side switch <NUM>, such as e.g. a transistor, which, upon being supplied by the start-up signal, is configured to connect the battery <NUM> to a voltage supply terminal of the secondary-side controller <NUM>.

From this point, the controller <NUM> can start switching the mains switch Q1 of the converter <NUM> through an isolated converter, using the optocoupler or a gate converter transformer. The same microcontroller can drive a lamp or the battery charger, advantageously eliminating the need for another controller.

In an example, only the battery <NUM> is required for the converter <NUM> to start. Moreover, once the converter <NUM> is operating, the battery <NUM> can be removed.

Moreover, the converter <NUM> shown in <FIG> comprises a transformer <NUM>, a smoothing capacitor <NUM> and a rectifying diode D5.

Summarizing, a circuit is provided to power up a secondary-side controller <NUM> of an, e.g., insulated DC/DC converter <NUM> using a battery <NUM> as source of energy, wherein:.

<FIG> shows a schematic representation of a method <NUM> for driving an LED according an embodiment.

Claim 1:
A primary-side switched, isolated converter (<NUM>) for supplying an LED load, having:
- a primary-side having terminals (<NUM>, <NUM>) for supplying a mains voltage (V1),
- a secondary-side controller (<NUM>) arranged on a secondary-side of the isolated converter (<NUM>), wherein the secondary-side controller (<NUM>) is configured to issue a control signal for a primary-side switch (Q1, <NUM>) of the switched isolated converter (<NUM>);
- a secondary-side circuitry on the secondary-side of the converter (<NUM>) comprises:
∘ terminals (Vout) configured to directly or indirectly supply the LED load, and
∘ a battery (<NUM>) configured to supply the secondary-side circuitry, and
- a start-up circuitry (<NUM>, <NUM>) configured to supply the secondary-side controller (<NUM>) off the battery (<NUM>), characterized in that
the start-up circuitry (<NUM>, <NUM>) has a control terminal for supplying a start-up signal transmitted from the primary-side to the secondary-side via an isolation stage (<NUM>) of the converter (<NUM>), wherein
the isolated converter (<NUM>) comprises a secondary-side switch (<NUM>),
the secondary-side controller (<NUM>) is not configured to control the secondary-side switch (<NUM>), and
the start-up signal is supplied to an input terminal of a control terminal of the secondary-side switch (<NUM>) which, upon being supplied by the start-up signal, is configured to connect the battery (<NUM>) to a voltage supply terminal of the secondary-side controller (<NUM>).