WO2017114646A1

WO2017114646A1 - Driver circuit, lamp and dc grid system

Info

Publication number: WO2017114646A1
Application number: PCT/EP2016/080274
Authority: WO
Inventors: Johannes Adrianus Cornelis Misdom
Original assignee: Philips Lighting Holding B.V.
Priority date: 2015-12-29
Filing date: 2016-12-08
Publication date: 2017-07-06

Abstract

The invention describes a driver circuit (1) for driving a load (2), comprising a first stage (11) realized for power factor correction and to convert an input voltage (VAC) to a DC bus voltage (VBUS) for a second stage (12), which DC bus voltage (VBUS) comprises a high voltage wire (VB_hi) and a low voltage wire (VB_lo); a second stage (12) realized to convert the DC bus voltage (VBUS) to a load voltage (VLOAD) for the load (2); and a surge detector circuit arranged to detect the voltage amplitude of the DC bus voltage (VBUS) to detect the occurrence of a surge on the input (VAC), wherien said surge detector circuit output a voltage difference; and a micro controller unit (14), connected to the surge detector circuit and configured to poll the output of the surge detector circuit continuously and configured to compare the voltage difference with a threshold;or the surge detector circuit is configured to compare the voltage difference or a variation rate of the voltage difference with a threshold, and the driver further comprises: an interruption generating circuit, for generating an interruption when the voltage difference or a variation rate of the voltage difference is above the threshold; and a micro controller unit (14), connected to the surge detector circuit and to the interruption generating circuit, configured to poll the output of the surge detector circuit when receiving the interruption and configured to compare the voltage difference with a threshold. The invention further describes the surge detector circuit comprieses a common-mode surge detector circuit (13) and a differential-mode surge detector circuit (15).

Description

Driver circuit, lamp and DC grid system

FIELD OF THE INVENTION

The invention describes a driver circuit for driving an electrical load. The invention further describes a surge detector circuit. BACKGROUND OF THE INVENTION

In a device that operates off mains power, the device is usually designed to withstand surges or transients to some degree. A surge appearing on the mains supply will propagate into any device connected to that supply, and may result in immediate or accumulated damage. The mains supply can be a household supply, for example an AC mains supply with the usual line (L), neutral (N) and earth conductor wires, and for example an DC grid. The earth conductor of an AC mains supply is generally referred to as the protective earth (PE) or "safety earth". When this input earth conductor is available at the power connector to a device, it can be directly connected to a metal housing of the device to ground the electrical equipment. When a protective earth or safety earth conductor is not available, for instance when the power connector only comprises line and neutral conductors, the neutral serves as a functional earth (FE) and is connected to the metal device housing. Some devices also make use of a functional earth that can be connected to the metal housing in order to reduce electromagnetic interference (EMI), for example, or to improve surge response. The two main kinds of surge that can occur on the mains supply are a differential- mode (DM) surge in which the voltage on the line wire is elevated with respect to neutral, and a common-mode (CM) surge in which the voltage on both line and neutral wires is elevated at the same time with respect to protective earth.

A surge can propagate into any device operating off the mains, for example into a driver that implements a converter to convert the mains voltage into a two-wire DC voltage for a specific load, whereby an internal device DC voltage is measured between a "high" wire and a "low" wire (device ground potential). A CM surge in the mains supply causes the voltage on both wires of a device DC voltage to elevate with respect to the protective earth. In the event of a DM surge at the mains input, a spike will usually appear on the "high" wire of a DC voltage, relative to the internal ground or the low wire of the DC voltage. A DM surge in an electrical device can originate from switching of other heavy-duty electric circuitry in the neighbourhood - such as an electric motor, welding equipment, cosine-phi capacitor banks, etc. A CM surge generally results from an external event such as a lightning strike in the vicinity. Electronic equipment used outdoors is susceptible to both DM surges and lightning-related CM surges.

A switching event or lightning strike can briefly elevate the voltage on a wire by several kilovolts, and the wire becomes very hot as a result of the attendant current spike. Each surge effectively places stress on the electrical device, and damage can result.

Following one or more surges, for example, the insulation on the wire experiencing the high voltage and current may be damaged. In the case of a CM surge, the insulation between line and PE wires, and between neutral and PE wires, can overheat. Insulation damage can accumulate over time, ultimately leading to device failure. To protect electrical or electronic devices from severe damage resulting from surges, various measures can be deployed.

A surge-protector device (SPD) reduces or limits the mains surge voltage that is applied to the input pins of an electrical or electronic device. The effect of an SPD is to absorb or divert most of the surge energy. The remaining amplitude of the surge should be significantly reduced, and a complete suppression is rarely possible. By ensuring that the remaining voltage does not exceed a certain threshold level, a longer useful lifetime of the device can be achieved. Including such protective measures generally adds to the cost of a device, but a low-cost device without such protective measures will have a significantly shorter lifetime. A surge protector can implement a metal-oxide varistor (MOV) to shunt current away from sensitive circuitry in the event of a surge. In addition to a current-diverting function, some kinds of surge protectors are able to count surges. This can be important when the surge protection circuitry uses expendable components that wear out after being repeatedly exposed to surges. A surge protector generally has a limited lifetime regarding the number of surges it can handle, for example an MOV will wear out eventually after being exposed to too many surges. Such a surge protector can provide feedback to an operator of the device, for example to indicate when an expendable component of the surge protector is approaching its end-of-life. However, these measures generally cannot provide feedback regarding the stress to which a device has been exposed.

In one approach of US20050269999 to detect surge in a single-stage power converter, the controller of a power-factor correction (PFC) stage is also used to detect the occurrence of a surge by observing the rectified input voltage to the PFC stage and to shut off a boost function of the power converter in the event of a surge. Therefore, it is an object of the invention to provide an improved way of detecting a surge experienced by an electrical or electronic device.

SUMMARY OF THE INVENTION

The above mentioned prior art is only has one power conversion stage namely the PFC stage, more particular a boost converter. It does not discuss how to detect surge in a two-stage architecture.

The application aims to handle surge in two-stage architecture. A basic idea of the application is detecting the surge by measuring the intermediate voltage between the two stages. More specifically, the first stage is a PFC stage and the second stage is a converting stage that converts the intermediate voltage to a load voltage.

One prior art US20110051462A1 discloses a two stage architecture with a boost converter as a first stage and a DC-DC half bridge converter as a second stage. The voltage between the first stage and the second stage is detected for overvoltage protection. The overvoltage detection is implemented by a voltage divider, a comparator, and a latch circuit.

It may be advantagous to detect the surge by using MCU, which has already be used widely in the two stage architecture. In order to address the above concern, in a first aspect, it is provided a driver circuit for driving a load, comprising a first stage realized to perform power factor correction on an input voltage to provide a DC bus voltage; a second stage realized to convert the DC bus voltage to a load voltage for the load; and a surge detector circuit arranged to detect the voltage amplitude of the DC bus voltage to detect the occurrence of a surge on the input, wherien said surge detector circuit output a voltage difference; and a micro controller unit, connected to the surge detector circuit and configured to poll the output of the surge detector circuit continuously and configured to compare the voltage difference with a threshold. In this aspect, a solution detecting surge in two-stage architecture is proposed. The intermediate voltage between the two stages, not the input voltage of the PFC stage is measured to detect the surge by a micro controller unit, or MCU, by continusly polling. This provides a very fast detection.

Alternatively, the surge detector circuit is configured to compare the voltage difference or a variation rate of the voltage difference with a threshold, and the driver further comprises: an interruption generating circuit, for generating an interruption when the voltage difference or a variation rate of the voltage difference is above the threshold; a micro controller unit, connected to the surge detector circuit and to the interruption generating circuit, configured to poll the output of the surge detector circuit when receiving the interruption and configured to compare the voltage difference with a threshold. In this embodiment, the micro controller unit does not need to monitor the surge detector circuit all the time but is triggered by an interrupt to do so, thus the workload of the micro controller unit is decreased.

In a further embodiment, wherein the surge detector circuit comprises a first detector circuit coupled to a low voltage wire or a high voltage wire of the bus voltage and coupled to a protective earth terminal and configured to detect a first voltage difference between the protective earth terminal and the low voltage wire or the high voltage wire as a common mode surge detector.

This embodiment provides a first detector circuit for detecting common-mode surges. Common mode surge is the surge between the line/neutral and the protective earth. Since the DC bus voltage after the power factor correction is relevant with line/neutral, this aspect can detect the common-mode surges accurately.

In a further embodiment, the first detector circuit comprises: a sniffing capacitor for storing the first voltage difference between the protective earth terminal and the low voltage wire or the high voltage wire and an integrator circuit arranged to integrate or smooth the voltage on the sniffing capacitor.

This embodiment discloses a more specific structure of the first detector circuit. It can also provide a stretched high voltage for a ease of detection.

In a further embodiment, the micro controller unit is connected to the first detector circuit and configured to poll the output of the first detector circuit continuously and configured to compare the first difference with a first threshold.

In an alternative embodiment, the first detector circuit is configured to compare the first difference or a variation rate of the first difference with a first threshold; and the interruption generating circuit further comprises: an first interruption generating sub- circuit, for generating an interruption when the first difference or a variation rate of the first difference is above the threshold; and a micro controller unit, connected to the first detector circuit and to the first interruption generating sub-circuit, configured to poll the output of the first detector circuit when receiving the interruption and configured to compare the first difference with a first threshold.

In a further embodiment, the first detector circuit is configured to compare the first difference with the first threshold and comprises: a comparator with a first input connected to the integrator circuit and a second input connected to a reference source of the first threshold, an output of the comparator is the output of the first interruption generating sub-circuit.

This embodiment realizes the first detector circuit by an integrated comparator.

Alternatively, the first detector circuit is configured to compare the variation rate of the first difference and comprises: a capacitor connected to the integrator circuit and for differentiating the first difference; a transistor with a base connected to the capacitor and a collector as the output of the first interruption generating sub-circuit.

This embodiment realizes the first detector circuit by discrete components.

In another embodiment, the said surge detector circuit further further comprises a second detector circuit coupled to a low voltage wire and a high voltage wire of the DC bus voltage and configured to detect a second voltage difference between the high voltage wire and the low voltage wire as a differential mode surge detector.

This embodiment proposes a detector circuit for detecting differential mode surge between the line and neutral.

In an embodiment, the micro controller unit is connected to the second detector circuit and configured to poll the output of the second detector circuit continuously and configured to compare the second difference with a second threshold.

In this embodiment, the micro controller unit detects polls output of the second detector circuit continuously. The micro controller unit can be the existing controller in the driver with an additional programed function. Thus the additional cost for the surge protection function is very low.

Alternatively, the second detector circuit is configured to compare the second difference or a variation rate of the second difference with a second threshold; and the interruption generating circuit further comprises: an second interruption generating sub- circuit, for generating an interruption when the second difference or a variation rate of the second difference is above the second threshold; and a micro controller unit, connected to the second detector circuit and to the second interruption generating sub-circuit, configured to poll the output of the second detector circuit when receiving the interruption and configured to compare the second difference with a second threshold.

In this embodiment, the micro controller unit does not need to monitor the second detector circuit all the time but is triggered by an interrupt to do so, thus the workload of the micro controller unit is decreased. In an embodiment, the second detector circuit is configured to compare the first difference and comprises a comparator with a first input connected to the integrator circuit and a second input connected to a reference source of the second threshold, an output of the comparator is the output of the second interruption generating sub-circuit.

This embodiment realizes the second detector circuit by an integrated comparator.

Alternatively, the second detector circuit is configured to compare the variation rate of the second difference and comprises: a capacitor connected to the integrator circuit and for differentiating the second difference; a transistor with a base connected to the capacitor and a collector as the output of the second interruption generating sub-circuit.

This embodiment realizes the second detector circuit by discrete components.

In a further embodiment, the micro controller unit is configured to connect at the same pin to the first and the second interruption generating sub-circuits via a logic.

This embodiment can save the pin number of the micro controller unit.

In a further embodiment, the micro controller unit is further configured with a surge counter for counting the occurrences of surges on the bus voltage.

In a further embodiment, said micro controller unit is further configured with a diagnostic module for analysing surge-related data provided by a surge detector circuit of the driver circuit.

In a further embodiment, the driver comprises an output interface for providing surge-related diagnostic information to a user.

In a further embodiment, the first stage comprises a PFC which is a boost converter, a buck converter or a flyback converter, and the second stage comprises a down converter for reducing the DC bus voltage to a DC load voltage.

Further, the micro controller unit can be the existing controller in the driver with an additional programed function. Thus the additional cost for the surge protection function is very low. This conroller is also used to control the operation of the PFC of the first stage and the down-converter of the second stage.

In a second aspect of the invention, it is provided a lamp comprising a driver circuit according to the above first aspect and embodiments and LED as the load of the driver circuit, wherein the first stage is adapted to receive the input voltage of alternating current or direct current. In a third aspect, it is provided a DC grid system comprising a DC power supply and at least one lamp according to the second aspect which is connected to the DC power supply.

Other objects and features of the present invention will become apparent from the following detailed descriptions considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for the purposes of illustration and not as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a first embodiment of a driver according to the invention;

Fig. 2 shows an exemplary embodiment of a CM surge detector circuit according to the invention;

Fig.3 shows a second embodiment of a driver according to the invention; Fig. 4 shows exemplary waveforms relating to a common-mode surge on an AC input;

Fig. 5 shows exemplary waveforms relating to a differential-mode surge on an

AC input;

Fig. 6 shows exemplary waveforms relating to an embodiment of the common-mode surge detector according to the invention;

Fig. 7 shows a first exemplary embodiment of an interrupt generator circuit for use in the driver according to the invention;

Fig. 8 shows a second exemplary embodiment of an interrupt generator circuit for use in the driver according to the invention;

Fig. 9 shows a conventional device with a differential-mode surge detection means.

In the drawings, like numbers refer to like objects throughout. Objects in the diagrams are not necessarily drawn to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Fig. 1 shows a first embodiment of a driver 1 according to the invention. The driver 1 is incorporated in an LED lighting device 3 and serves to drive an LED load 2. Here, the driver 1 is connected to the line L, neutral N and protective earth PE phases of a mains or household AC power supply. It should be noted the input is not limited to AC mains, but is also applicable with DC grids. In a physical realisation, a metal chassis or housing of the device 3 is connected to the protective earth PE. In this exemplary embodiment, the driver 1 comprises a first stage 11 for power factor correction and for providing a DC bus voltage to a second stage 12 connected to the LED light source 2. Here, the first stage 11 is shown to include an optional EMI filter 110, a rectifier 111, and includes a PFC 112. The PFC 112 may be realized as a boost converter, for example, and the second stage 12 may be a buck converter. It should be understood that any other combinations of the first PFC stage 112 and the converter 12 are also applicable. For example, the PFC 112 may also be flyback converter or buck converter. The first stage 11 and second stage 12 are connected in the schematic by a high voltage wire VB hi and a low-voltage wire VB lo of a device DC bus voltage VBUS generated by the first stage 11. The low- voltage "wire" VB lo acts as a device-internal reference ground. A microcontroller unit 14 is used to control the operation of the PFC 112 and a down-converter of the second stage 12. The microcontroller unit 14 may be a general purpose MCU or a dedicated MCU. The blocks can be connected as illustrated to exchange information and commands.

To collect surge-related diagnostic information, the driver 1 comprises a CM

(common mode) surge detector circuit 13, or called as the first detector circuit, connected between the protective earth PE and the low bus wire VB lo. The CM surge detector circuit 13 can detect the occurrence of a common-mode surge by comparing the voltage levels on the protective earth PE and the low bus wire VB lo to detect any alteration. Fig. 2 shows an exemplary embodiment of the CM surge detector circuit 13, indicating a first input terminal 13 PE that is connected to the protective earth PE, and a second input terminal 13 GND connected to the device ground, i.e. to the low bus wire VB lo. The CM surge detector circuit 13 comprises a sniffing capacitor CI to detect any voltage anomaly, and a double- sided envelope detector Dl, D2, C2, R2 to detect positive and negative common-mode surges and to stretch or extend a surge pulse. The sniffing circuit 13 acts as a capacitive divider with a ratio given by CI :C2. The capacitances of the sniffing capacitor CI and the envelope detector capacitor C2 can be chosen to give a ratio of 1 : 1000, for example capacitor CI could have a value of 47 pF and capacitor C2 could have a value of 47 nF. Resistor Rl acts as a current limiter in case there are very high dV/dt signals on the protective earth wire of the AC input. Resistor R2 acts to discharge capacitor C2 after a surge.

In case of a negative surge (the voltage at device ground VB lo is lower than zero or protective earth PE), the surge voltage is applied via diode D2 to the output capacitor C2. In case of a positive surge (the voltage at device ground VB lo is higher than zero or protective earth PE) the surge will flow via Dl and thus charging CI only. Once the positive surge has diminished, the right-hand side of the sniffing capacitor CI will become positive and the output capacitor C2 can charge via diode D2. In this way, both positive and negative surges can be detected. Either way, a stretched surge voltage 13_MCU appears at the output terminal 13_MCU.

In Fig. 2, when a CM surge occurs, the CM surge detector circuit 13, especially the capacitor CI and C2 provides a stretched version 130 of the surge voltage on its output terminal 13 MCU as described above, connected to an appropriate pin of the microcontroller 14. The microcontroller 14 can then start collecting information. For example, the microcontroller 14 may be configured to continuously poll the output 130 of the CM surge detector 13 circuit. Using a built-in ADC, the microcontroller 14 can detect the amplitude of the stretched voltage 130 to compute the total energy of the CM surge. This can be stored in a tracking module of the MCU 14, or provided to an external data collection unit over a suitable interface 140.

Fig. 3 shows a lighting arrangement 3 with a driver 1 according to a second embodiment of the invention. In this exemplary embodiment, the driver 1 is connected via a surge protection device 4 to the live L, neutral N and protective earth PE phases of an AC power supply. The surge-protector device 4 can be used to protect the electronic equipment, for example by limiting the maximum voltage or current to the driver 1 and/or by shunting much of the spike current to bypass the driver 1. Here also, the driver 1 comprises a first stage 11 for power factor correction and for providing a DC bus voltage to a second stage 12 connected to an LED light source 2. The first stage 11 optionally includes a rectifier 111 and an EMI filter 110, and include a PFC 112 as described above. As described above, the first stage 11 and second stage 12 are connected by a high voltage wire VB hi, and also a low- voltage wire VB lo connected to device ground.

In this embodiment, the driver 1 comprises a CM surge detector circuit 13 connected between the protective earth PE and the low bus wire VB lo similar as above, and also a DM (differential mode) surge detector 15 connected to both of the high voltage wire VB hi (optionally via a voltage divider as shown) and the low voltage wire VB low, realised to detect the occurrence of a differential-mode surge on the high voltage wire VB hi with respect to the low voltage wire VB low and output a signal 150. In this realisation, in order to reduce processing work load of the MCU 14, the MCU 14 does not continuously poll the connections 130, 150 from the detector circuits 13, 15, but is triggered instead by an interrupt to start polling a detector circuit output 130, 150. To this end, the driver 1 also comprises an external interrupt generator 16 that generates an interrupt 160 to trigger the MCU 14 to commence polling on its input pins connected to the detector circuit outputs 130, 150.

Alternatively, for differential mode surge, the MCU 14 also has two connections to the high voltage wire VB hi (optionally via a voltage divider as shown) and the low voltage wire VB low thus it can detect the voltage drop between the two wires on its own. As already explained, the CM surge detector circuit 13 provides a stretched version 130 of a common- mode surge voltage to the microprocessor 14, and the DM surge detector circuit 15 provides a stretched version 150 of a differential-mode surge voltage to the microprocessor 14 thanks to a normal buffering capacitor (not shown) at the output of the PFC 112, so that whenever the MCU 14 is triggered by the external interrupt generator 16, it reacts by summing or integrating the voltage appearing on either the CM surge detector output 130 or the DM surge detector output 150. In this way, the energy of each detected surge can be logged and stored for later retrieval, for example over an interface such as a DALI interface. Each surge event can be recorded by incrementing a counter, for example a DM surge counter and a separate CM surge counter. Diagnostic information such as surge count, surge energy etc. over a certain time period can be read out by a user over the interface 140. In order to save pin number of the MCU 14, the two outputs 130 and 150 can be in the form of logic high/low and connected via a logic and to the same pin of the MCU.

Fig. 4 shows exemplary waveforms for a common-mode surge on an AC power supply, for example a 220 V household power supply. The diagram shows waveforms 40 L, 40 N, 40 PE for the line wire, the neutral wire and the input earth conductor (the protective earth in this case) respectively. In the event of a common-mode surge due for example to a lighting strike, a spike 40 will appear on the line wire, and a spike 41 will simultaneously also appear on the current-carrying neutral wire (a voltage spike on the line/neutral can easily reach 10 kV or more and is not drawn to scale in these diagrams). When these waveforms are applied to the first stage of a driver of the type discussed in the above, the potential on both bus wires VB hi, VB lo will be elevated as a result of the voltage spikes 40, 41.

Fig. 5 shows exemplary waveforms for a differential-mode surge on an AC power supply. Here also, the diagram shows waveforms 50 L, 50 N, 50 PE for the line wire, the neutral wire and the protective earth wire respectively. In the event of a differential- mode surge due for example to a switching event, a spike will appear on the line wire. When these waveforms are applied to the first stage of a driver of the type discussed herein, only the potential of the high bus wire VB hi will be elevated with respect to the low bus wire VB lo. The common-mode surge detector circuit according to the invention makes use of this distinction, and monitors the low bus wire VB lo relative to the protective earth wire of the AC input to detect the occurrence of a common-mode surge. The driver can also monitor the high bus wire VB hi relative to the low bus wire VB lo to detect the occurrence of a differential-mode surge.

Fig. 6 shows exemplary waveforms relating to an embodiment of the common-mode surge detector 13 according to the invention, incorporated in a driver 1 as described in Fig. 1 or Fig. 3 for example. The upper part of the diagram shows the voltage 60 at the second input 13 GND, i.e. the voltage on the low bus wire VB lo, during a common- mode surge event. The peak voltage of a lightning-related common-mode surge can typically reach 10 kV or more. After detection and stretching by the inventive CM surge detector circuit 13, a stretched version 61 of the surge is provided at the output terminal 13 MCU. This can be integrated as described above to estimate the total energy to which the device was exposed as a result of the surge.

Fig. 7 shows an exemplary embodiment of the combination of a surge detector and an interrupt generator circuit 7 that generates an interrupt signal INT DM, INT CM for the MCU 14 in the event of a surge. This embodiment uses a comparator 70, 71 to compare a voltage to a threshold voltage. As shown in the lower drawing of figure 7, to generate an interrupt in the event of a CM-surge, the interrupt generator circuit 7 is connected across the outputs of the CM surge detector circuit 13 via its negative input terminal. The positive terminal of the comparator 70 is connected to a reference source. If the CM surge is higher than the reference source, the comparator would generate a negative/low level. To generate an interrupt in the event of a DM-surge, as shown in the upper drawing in figure 7, the interrupt generator circuit 7 is connected at the voltage divider between the high bus voltage VB hi and the low bus voltage VB lo. The output of the comparator 70 and 71 is biased by a positive voltage. In the event of a surge, a comparator output INT DM, INT CM goes low, i.e. the interrupt pin triggers the MCU 14 to start polling the input connected to the relevant surge detector circuit 13, 15. If the comparator 70, 71 has an open collector output in each case, the outputs INT_DM, INT_CM of the two interrupt generator circuits 7 can be wired- AND logic, requiring only one interrupt pin of the MCU 14.

Fig. 8 shows a further exemplary embodiment of an interrupt generator circuit 8 that generates an interrupt signal INT DM, INT_CM for the MCU 14 in the event of a surge. This embodiment is based on a dV/dt approach using discrete components. A dV/dt capacitor C8 detects a sudden rise on an input (VB hi in the case of a DM surge; the output 130 of the CM surge detector circuit 13 in the case of a CM surge) and generates a current, which switches on a transistor Q8 to output an interrupt trigger signal INT DM, INT CM to the microcontroller unit 14. The collector of the transistor Q8 is biased by a positive voltage. In case of surge, the collector of the transistor Q8 will be pulled to low/the ground. The MCU 14 detects this low level and then commences to poll the relevant surge detector circuit output 130, 150. In this case also, the outputs of the two interrupt generator circuits 8 can be wired- AND logic, requiring only one interrupt pin of the MCU 14.

The interrupt generator circuits 7, 8 of Fig. 7 and Fig. 8 can be used to decrease the workload of the MCU 14, since it does not need to poll the surge detector outputs 130, 150 continuously, but only when necessary i.e. in the event of a surge.

The DM surge detection can be standalone without the CM surge detection. Fig. 9 shows a device, with an SPD 4, a load 2, and a driver with first PFC stage 11 and second stage 12 to convert an AC input to a load voltage. This arrangement can detect DM surges.

Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention. Other driver topologies may be used, for example a driver topology in which a power-factor correction function is integrated in the down converter. When mains input power is supplied by a DC grid, a rectifier is not necessary, but the first stage of the power converter still implements a PFC and down converter.

For the sake of clarity, it is to be understood that the use of "a" or "an" throughout this application does not exclude a plurality, and "comprising" does not exclude other steps or elements. The mention of a "unit" or a "module" does not preclude the use of more than one unit or module.

REFERENCE SIGNS:

1 driver circuit

2 load

3 LED lighting arrangement

11 first stage

110 EMI filter

111 rectifier

112 PFC unit

12 second stage

13 CM surge detector circuit

13 PE input terminal

13 MCU output terminal

130 CM surge detector output

14 MCU

140 diagnostic information

15 DM surge detector circuit

150 DM surge detector output

16 interrupt generator

40 L, 40_N, 40 PE CM surge input waveform 40, 41 CM surge

50 L, 50 N, 50 PE DM surge input waveform

60 detected CM pulse

61 stretched CM pulse

7 interrupt generator circuit

70, 71 comparator

8 interrupt generator circuit

VAC AC input

L line

N neutral

PE protective earth VBUS DC bus voltage

VB hi high bus wire

VB lo low bus wire, device ground

D1,D2 diode

R1,R2 resistor

C1,C2, C8 capacitor

Q8 transistor

INT CM, INT DM interrupt signal

Claims

CLAIMS:

1. A driver circuit (1) for driving a load (2), comprising

a first stage (11) realized to perform power factor correction on an input voltage (VAC) to provide a DC bus voltage (VBUS);

a second stage (12) realized to convert the DC bus voltage (VBUS) to a load voltage (VLOAD) for the load (2);

a surge detector circuit arranged to detect the voltage amplitude of the DC bus voltage (VBUS) to detect the occurrence of a surge on the input (VAC), wherien said surge detector circuit is adapted to output a voltage difference; and

a micro controller unit (14), connected to the surge detector circuit and configured to poll the output of the surge detector circuit continuously and configured to compare the voltage difference with a threshold;

or

the surge detector circuit is configured to compare the voltage difference or a variation rate of the voltage difference with a threshold, and the driver further comprises:

an interruption generating circuit, for generating an interruption when the voltage difference or a variation rate of the voltage difference is above the threshold;

a micro controller unit (14), connected to the surge detector circuit and to the interruption generating circuit, configured to poll the output of the surge detector circuit when receiving the interruption and configured to compare the voltage difference with a threshold.

2. A driver circuit according to claim 1, wherein the surge detector circuit comprises a first detector circuit (13) coupled to a low voltage wire (VB lo) or a high voltage wire (VB hi) of the bus voltage (VBUS) and coupled to a protective earth terminal, and configured to detect a first voltage difference between the protective earth terminal and the low voltage wire (VB lo) or the high voltage wire (VB hi) as a common mode surge.

3. A driver circuit according to claim 2, wherein the first detector circuit (13) comprises: a sniffing capacitor (CI) for storing the first voltage difference between the protective earth terminal and the low voltage wire (VB lo) or the high voltage wire (VB hi) and;

an integrator circuit (D2, C2, R2) arranged to integrate or smooth the voltage on the sniffing capacitor.

4. A driver circuit according to claim 2, wherein the micro controller unit (14) is connected to the first detector circuit and configured to poll the output of the first detector circuit continuously and configured to compare the first difference with a first threshold;

or

the first detector circuit is configured to compare the first difference or a variation rate of the first difference with a first threshold;

the interruption generating circuit comprises a first interruption generating sub-circuit, for generating an interruption when the first difference or a variation rate of the first difference is above the threshold;

the micro controller unit, connected to the first detector circuit and to the first interruption generating sub-circuit, configured to poll the output of the first detector circuit when receiving the interruption and configured to compare the first difference with a first threshold.

5. A driver circuit according claim 2, wherein

the first detector circuit is configured to compare the first difference and comprises:

a comparator (71) with a first input connected to the integrator circuit and a second input connected to a reference source of the first threshold, an output of the comparator is the output of the first interruption generating sub-circuit;

or

the first detector circuit is configured to compare the variation rate of the first difference and comprises:

a capacitor (C8) connected to the integrator circuit and for differentiating the first difference;

a transistor (Q8) with a base connected to the capacitor and a collector as the output of the first interruption generating sub-circuit.

6. A driver circuit according to the claim 1 or 2, wherein said surge detector circuit comprises a second detector circuit (15) coupled to a low voltage wire (VB lo) and a high voltage wire (VB hi) of the bus voltage (VBUS) and configured to detect a second voltage difference between the high voltage wire (VB_hi) and the low voltage wire

(VB low) as a differential mode surge.

7. A driver circuit according to claim 6, wherein

the micro controller unit (14) is connected to the second detector circuit (15) and configured to poll the output of the second detector circuit (15) continuously and configured to compare the second difference with a second threshold;

or

the second detector circuit (15) is configured to compare the second difference or a variation rate of the second difference with a second threshold;

the interruption generating circuit comprises: a second interruption generating sub-circuit, for generating an interruption when the second difference or a variation rate of the second difference is above the second threshold;

the micro controller unit (14) is connected to the second detector circuit (15) and to the second interruption generating sub-circuit, configured to poll the output of the second detector circuit (15) when receiving the interruption and configured to compare the second difference with a second threshold.

8. A driver circuit according to claim 7, wherein the second detector circuit is configured to compare the first difference and comprises:

a comparator (70) with a first input connected to the integrator circuit and a second input connected to a reference source of the second threshold, an output of the comparator is the output of the second interruption generating sub-circuit;

or

the second detector circuit is configured to compare the variation rate of the second difference and comprises:

a capacitor (C8) connected to the integrator circuit and for differentiating the second difference;

a transistor (Q8) with a base connected to the capacitor and a collector as the output of the second interruption generating sub-circuit.

9. A driver circuit according to 7, wherein the micro controller unit is configured to connect at the same pin to the first and the second interruption generating sub-circuits via a logic.

10. A driver circuit according to claim 1, wherein said micro controller unit is further configured with a surge counter for counting the occurrences of surges on the bus voltage (VBUS).

11. A driver circuit according to claim 1 , wherein said micro controller unit is further configured with a diagnostic module for analysing surge-related data provided by a surge detector circuit (13, 14) of the driver circuit (1).

12. A driver circuit according to any of the preceding claims, comprising an output interface for providing surge-related diagnostic information to a user.

13. A driver circuit according to any of the preceding claims, wherein the first stage (11) comprises a PFC (112) which is a boost converter, a buck converter or a flyback converter,

the second stage (12) comprises a down converter for reducing the DC bus voltage (VBUS) to a DC load voltage (VLOAD), and

said micro controller unit (14) is further used to control the operation of the PFC (112) of the first stage (11) and the down-converter of the second stage (12).

14. A lamp comprising:

a driver circuit according to any one of claims 1 to 13 and

LED as the load of the driver circuit,

wherein the first stage is adapted to receive the input voltage of alternating current or direct current.

15. A DC grid system comprising a DC power supply and at least one lamp according to claim 14 which is connected to the DC power supply.