Driver circuit, system and method for controlling solid-state lamps

Abstract

Solid-state lamp driver circuit (302) comprising: a switching regulator having a buck converter; an input detector (308; 600; 700; 800) configured to receive an input power supply (306) and output a control signal that depends on a frequency of the input power supply (306); and a control device (310) configured to receive the control signal and activate an operation of the switching regulator or short-circuit the switching regulator according to the control signal, wherein, when short-circuited, the buck converter provides a DC path and the driver circuit (302) acts as a linear regulator.

Description

TECHNICAL FIELDThe present disclosure relates to a system and a corresponding method for controlling solid state lamps.BACKGROUNDSolid state lamps replace fluorescent and incandescent lamps because of their higher efficiency. The light emitting element in a solid-state lamp comprises semiconductor material in which light is emitted by electroluminescence. Various types of light emitting elements may be used, such as light emitting diodes (LEDs) of various types (including silicon, organic, and polymer LEDs). The present disclosure discusses in particular the case of an LED, but it is obvious that it applies generally to other types of solid state lamps.The current through a solid state light emitting element must be controlled to ensure that a minimum amount of power is provided so that light of the required brightness is emitted, but also that a maximum amount of power is not exceeded to prevent damage to the element and the circuit. To take this into account, an LED driver circuit is provided.For example, CN 201615369 U shows an exemplary LED driver circuit. In order to simultaneously enable a suitable exchangeability between different ballasts and power supply units, the above-mentioned driver circuit additionally provides a passive component network and a power supply, which can adapt to the output characteristic of an existing electronic ballast.Furthermore, a current limiting circuit is also shown by way of example in CN 204231704 U, which current limiting circuit can convert a conversion of high-frequency alternating current supplies, which drive a fluorescent lamp, into a direct current power supply required for LEDs by means of a rectifier circuit.Ballasts are also frequently used in lighting systems. A ballast is a device or circuit that limits the amount of current supplied to a load. They are frequently used in devices which exhibit a negative resistance characteristic, such as gas discharge lamps, where limiting the current is important to prevent the lamp from being destroyed or failing. However, ballasts are also useful for limiting current in ordinary positive resistor circuits, including for use with solid state lamps. The ballast is usually integrated with a luminaire housing for coupling to the driver circuit of a solid state lamp via suitable electrical connectors when the solid state lamp is inserted into a socket of a luminaire housing.FIG. 1 shows an LED lighting system 100 in which an LED driver circuit includes a linear regulator 102 that supplies power to a series of LEDs 104, generally shown as LED 1 through LEDn. The linear regulator 102 is coupled to the grid supply 106 provided by an electrical grid (or alternatively, a grid independent power supply). A linear regulator can be connected to an AC power supply, but has low efficiency and high power loss, resulting in high heat dissipation. When connected to a ballast, the linear control must be adjusted to balance the input and output power of the LED driver circuit.FIG. 2 shows a lighting system 200 in which a switching regulator 202 is used to control the power supplied to the LEDs 104. The switching regulator has a switching element that serves to selectively charge or discharge an energy storage element and selectively couple the energy storage element to the load to regulate voltage or current characteristics and control the power supplied to the load. Various other circuit topologies are known, including, without limitation, a buck converter, a boost converter, a buck-boost converter, and a single-ended primary inductor converter (SEPIC). A switching regulator 202 is more energy efficient than a linear regulator.A switching regulator 202 works well with an AC power supply or with a magnetic ballast operating at a similar frequency. However, if directly connected to an electronic ballast, the switching regulator 202 may cause flicker, erroneous output voltage and output current, unstable and unreliable operation, or even damage to the circuit. This is because switching regulators are designed to operate with an AC input or a magnetic ballast, both of which are voltage sources. However, an electronic ballast acts as a current source and thus, when connected to a ballast, the input energy and further the input voltage of the switching regulator 202 depends on its output portion. If there is a mismatch between the input power and the output power, the switching regulator 202 has either an insufficient input voltage or an excessive input voltage.It should therefore be noted that existing LED driver circuits are designed to be used either exclusively with a mains supply or with an electronic ballast. If an LED driver circuit is designed for use with a power supply, it will not function properly with a ballast, and vice versa.This creates a problem for lamp interoperability and for retrofitting lamps. A solid state lamp is normally provided in a lamp housing and includes the driving circuit and the light emitting element. A lighting system may include a luminaire having a housing and a socket for receiving a lamp. Ballast is normally provided as part of the luminaire for electrical connection to a lamp being inserted via suitable mating electrical connectors provided through the lamp housing and the luminaire socket.A major concern in installation and maintenance of lighting equipment is interoperability of lamps with various types of ballasts. A luminaire may or may not have a ballast and the driver circuit of a solid state lamp may or may not be compatible with a ballast. This means that the compatibility of the lamps and lighting installations must be carefully checked. This increases a requirement for users and introduces complexity for manufacturers who must manufacture, manage and support multiple different products to accommodate the different combinations that are possible.Thus, it would be very advantageous if a solid state lamp driver circuit could function if coupled to either a ballast or an AC supply as an input.SUMMARYAccording to a first aspect of the disclosure, there is provided a solid-state lamp driving circuit, comprising: a switching regulator including a step-down converter; an input detector configured to receive an input power supply and output a control signal depending on a frequency of the input power supply; and a controller configured to receive the control signal and enable an operation of the switching regulator or short-circuit the switching regulator according to the control signal, wherein when short-circuited, the step-down converter provides a DC path and the driving circuit functions as a linear regulator.Optionally, the control device is configured to activate an operation of the switching regulator when the control signal indicates that a frequency is detected within a first range, and is configured to short-circuit the switching regulator when the control signal indicates that a frequency is detected within a second range, the first range being lower than and non-overlapping with the second range.Optionally, the control signal has a first logic state when a frequency is detected within the first range and a second logic state when a frequency is detected within the second range.Optionally, the first frequency range corresponds to an operating range of a mains supply and / or of a magnetic ballast and the second frequency range corresponds to an operating range of an electronic ballast.According to a second aspect of the disclosure, there is provided a method of driving a solid state lamp, comprising: receiving an input power supply; and activating an operation of a switching regulator or short-circuiting a switching regulator according to the frequency of the input power supply. The switching regulator includes a buck converter, wherein when shorted, the buck converter provides a DC path and the driver circuit acts as a linear regulatorOptionally, the method comprises outputting a control signal based on the frequency of the input power supply and activating an operation of a switching regulator or short-circuiting a switching regulator according to the control signal.Optionally, the control signal has a first logic state when a frequency is detected within the first range and a second logic state when a frequency is detected within the second range.Optionally, the method comprises: enabling operation of the switching regulator when a frequency of the input power supply is within a first range; shorting operation of the switching regulator when a frequency of the input power supply is within a second range; wherein the first range is lower than and non-overlapping with the second range.Optionally, the first frequency range corresponds to an operating range of a mains supply and / or of a magnetic ballast and the second frequency range corresponds to an operating range of an electronic ballast.According to a third aspect of the disclosure, there is provided a lighting system comprising: one or more solid-state lamps; and a driving circuit for driving one or more of the solid-state lamps; wherein the lamp driving circuit comprises: a switching regulator comprising a step-down converter; an input detector configured to receive an input power supply and output a control signal depending on a frequency of the input power supply; and a control device configured to receive the control signal and enable an operation of the switching regulator or short-circuiting the switching regulator according to the control signal, wherein when short-circuited, the step-down converter provides a DC path and the driving circuit (302) functions as a linear regulator.The third aspect may include any combination of features of the first and second aspects.BRIEF DESCRIPTION OF THE DRAWINGSThe present disclosure will now be described by way of example with reference to the accompanying drawings, wherein: FIG. 1 shows a first existing LED lighting system with a driver circuit with a linear regulator; FIG. 2 shows a second existing LED lighting system with a driver circuit with a switching regulator; FIG. 3 shows a lighting circuit according to a first embodiment of the disclosure; FIG. 4 shows a portion of a lighting circuit according to an aspect of the disclosure, wherein a control device having two switching elements is provided; FIG. 5 shows a portion of a lighting circuit according to an aspect of the disclosure, wherein a control device is provided with a switching element; FIG. 6 shows a first example input sensing circuit for use with the lighting circuit of FIG. 4 ; FIG. 7 shows a second example input sensing circuit for use with the lighting circuit of FIG. 5 ; and FIG. 8 shows a third example input sensing circuit for use with the lighting circuit of FIG. 5.DETAILED DESCRIPTIONAccording to the disclosure, a lighting system includes a solid-state lamp and a driver circuit for controlling power input to the solid-state lamp. The driver circuit includes a switching regulator (for example, a buck converter), an input detection circuit, and a controller. The input detection circuit monitors the power supply input to the driving circuit and outputs a control signal based on the detected frequency. The control device then acts on the control signal to either activate the switching regulator or short-circuit it. When the switching regulator is short-circuited, the driver circuit acts as a linear regulator. If the input to the driver circuit is provided directly by a mains supply or by a magnetic ballast, the input detection circuit determines that the input has a relatively low frequency and activates the switching regulator. However, if the input to the driver circuit is provided directly from an electronic ballast, the input detection circuit determines that the input has a relatively high frequency and shorts the switching regulator. A solid state lamp incorporating such a driver circuit can therefore operate with any of a power supply, a magnetic ballast or an electronic ballast and changes its operation accordingly to ensure proper operation.A power supply varies in frequency from country to country, but for the present disclosure we assume that it is between 50 and 60 Hz. To avoid doubt, other power supplies are not excluded from the present disclosure.Ballasts are used in various contexts to limit and control current through electrical loads. There are two main types of ballasts: magnetic and electronic. Magnetic ballasts include inductors that provide reactance to the electrical current provided to a circuit. They operate at a frequency that is synchronized to the line frequency. Electronic ballasts use solid state circuits and are often based on a switching mode power supply topology that rectifys the input power and chopped it at high frequency. An electronic ballast may allow dimming by techniques such as pulse width modulation. An electronic ballast typically supplies power to a lamp at frequencies of several tens of kilohertz, usually 50 kHz or higher. While there may be variation between specific frequencies of power supplies, magnetic ballasts and electronic ballasts, the frequency of an electronic ballast is always an order of magnitude (or more) higher than that of the power supply or a magnetic ballast.FIG. 3 shows a lighting system 300 according to a first embodiment of the disclosure. A driver circuit 302 is provided between an input 306 and a series of LED lamps 304 which form the load for the driver circuit 302. Any number of light emitting elements may be provided. The diodes D1 to D4 serve to rectify the input, and the diode D5 is a blocking diode which prevents current from flowing back from the load to the input. An inductor (L) and a free wheeling diode (D6) are also provided. The switch S provides overvoltage protection and is used to selectively decouple the input from the output. The driver circuit 302 includes an input detection circuit 308 and a controller 310.The input detection circuit 308 detects whether the frequency of the input 306 is low or high. In a preferred embodiment, a low frequency is defined as being in a range of frequencies that can be supplied by a power supply or a magnetic ballast, and a high frequency is defined as being in a range of frequencies that can be supplied by an electronic ballast. The low frequency range may comprise frequencies on the order of 100 Hz and the high frequency range may comprise frequencies on the order of 10 kHz.The controller 310 operates to control the power supplied to the load. The controller 310 may be switched between different modes depending on the output of the input detection circuit 308, which in a preferred embodiment may include high or low logic signals representative of whether a high or low input frequency is detected. More sophisticated outputs may be provided in alternative embodiments, including quantifications of the actual detected frequency for more sophisticated control.When it is detected that the input is an electronic ballast, the controller 310 shorts the switching regulator. In this case, the driver circuit operates as a linear controller. When it is detected that the input is a power supply or a magnetic ballast, the controller 310 activates the switching regulator so that normal switching mode regulation can be used.The control device comprises in one aspect two switching elements, one of which is activated to activate the switching regulator and the other is activated to short-circuit the switching regulator and provide a linear regulator.An exemplary embodiment of such an aspect is shown in FIG. 4. Here, a lighting circuit 400 includes a control device having two switches Q 1 and Q 2. Q1 is used for a switching function and Q2 is used for a short-circuit function. The input sense circuit is not shown here (and discussed below), but it receives an input from the AC_DETECT node and provides a control signal G_MOS to the gate of Q2. Q1 is controlled by another switching regulator.When the input signal is provided from a power supply or a magnetic ballast, the input signal detection circuit outputs a low signal level to the gate of Q2. The circuit operates in a buck mode, with switch Q1, inductor (L) and diode (D6) forming a buck converter circuit. Q1 operates in a high frequency switching state and Q2 remains off. When the input signal is derived from an electronic ballast, the input detection circuit outputs a high level signal. Q1 is controlled and held in the off state. Q2 remains on and resistor R1, inductor L and output capacitor C act as a linear regulator. This circuit takes advantage of the fact that a buck converter can form a DC path when short-circuited.In another aspect, the controller may include a single switching element that changes operating states to either function as part of a switched regulator or to remain in a state where the switched regulator is shorted and the driver circuit operates as a linear regulator. An exemplary embodiment of such an aspect is shown in FIG. 5. Here, a lighting circuit 500 includes a control device including a switching element Q 1. The input sense circuit is not shown here (and discussed below), but it receives an input from the AC_DETECT node and provides a control signal G_MOS to the gate of Q1.When the input signal is provided from a power supply or a magnetic ballast, the input detection circuit outputs a low level signal to G_MOS. The gate of Q1 is then controlled by G_MOS, which may be a regulated pulse width modulated signal, for operation of the buck circuit. When the input signal is from an electronic ballast, the input detection circuit outputs a high level signal. Q1 remains on, effectively shorting the buck circuit. The resistor R1, the inductor L and the output capacitor C act as linear regulators. Again, this circuit takes advantage of the fact that a buck converter can form a DC path when shorted.Any suitable frequency discrimination or detection circuit may be used for the input detection circuit 308. Fig. 6 shows a suitable example suitable for use with the two-switch controller of Fig. 4 or 5.Here, a low frequency AC signal is blocked, but a high frequency AC signal is allowed to pass. The input source voltage is divided by C3, C4 and R5. When the frequency is low (power supply or magnetic ballast), the voltage of C4 is lower than 0.7V; when the frequency is high (electronic ballast), the voltage of C4 is about 10V.When the input signal is the AC power supply or a magnetic ballast, the input detection circuit 600 of FIG. 6 outputs a low level signal to the terminal G_RI, which activates the buck converter of FIG. 4, as noted above. When the input signal is from an electronic ballast, the input detection circuit 600 outputs a high level signal, the switch Q2 of FIG. 4 remains on and in a short-circuit mode. Q1 is controlled and held in an off state.FIG. 7 shows another embodiment of an input detection circuit 700. This may be used together with the circuit of Fig. 4 or 5.FIG. 8 shows another embodiment of an input detection circuit 800. This may be used together with the circuit of Fig. 4 or 5. The drive signal G_Ri is obtained from a switching regulator integrated circuit so that when VCCof IC is low, the gate is pulled to ground to protect the main circuit. When G_ Is high, G_MOS is high, but when VCC is low and when G_D is low, G_MOS is not controlled.The circuit of Fig. 8 shows a means by which Q1 is maintained in a normal closed state, in the meantime the down-drive circuit may be disabled, but this is not a requirement.Various improvements and modifications may be provided to the above scope of the disclosure.

Claims

A solid state lamp driver circuit (302) comprising: a switching regulator comprising a buck converter; an input detector (308; 600; 700; 800) configured to receive an input power supply (306) and output a control signal depending on a frequency of the input power supply (306); and a controller (310) configured to receive the control signal and enable operation of the switching regulator or short-circuit the switching regulator according to the control signal, wherein when short-circuited, the buck converter provides a DC path and the driver circuit (302) functions as a linear regulator.The solid state lamp driving circuit of claim 1, wherein the control device is configured to activate the operation of the switching regulator when the control signal indicates that the frequency is detected within a first range, and is configured to short-circuit the switching regulator when the control signal indicates that the frequency is detected within a second range, the first range being lower than and non-overlapping with the second range.The solid-state lamp driver circuit (302) of claim 2, wherein the control signal has a first logic state when the frequency is detected within the first range and a second logic state when the frequency is detected within the second range.The solid-state lamp driving circuit according to claim 2 or claim 3, wherein the first frequency range corresponds to an operating range of a power supply and / or a magnetic ballast, and the second frequency range corresponds to an operating range of an electronic ballast.A method of driving a solid state lamp having a driver circuit (302), comprising: receiving an input power supply; (306); and activating operation of a switching regulator or shorting the switching regulator depending on a frequency of the input power supply (306), wherein the switching regulator comprises a buck converter, and wherein when shorted, the buck converter provides a DC path and the driver circuit (302) functions as a linear regulator.The method of claim 5, comprising outputting a control signal based on the frequency of the input power supply and enabling operation of the switching regulator or shorting the switching regulator according to the control signal.The method of claim 6, wherein the control signal has a first logic state when the frequency is detected within a first range and a second logic state when the frequency is detected within a second range.The method of any of claims 5 to 7, comprising: enabling operation of the switching regulator when the frequency of the input power supply is within a first range; shorting the switching regulator when the frequency of the input power supply is within a second range; wherein the first range is lower than and non-overlapping the second range.The method of claim 8, wherein the first frequency range corresponds to an operating range of a power supply and / or a magnetic ballast and the second frequency range corresponds to an operating range of an electronic ballast.A lighting system comprising: one or more solid state lamps; and a driver circuit (302) for driving one or more of the solid state lamps; wherein the lamp driver circuit (302) comprises: a switching regulator comprising a buck converter; an input detector configured to receive an input power supply and output a control signal depending on a frequency of the input power supply; and a controller configured to receive the control signal and enable operation of the switching regulator or short-circuit the switching regulator according to the control signal, wherein when short-circuited, the buck converter provides a DC path and the driver circuit (302) functions as a linear regulator.

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