CN210124030U

CN210124030U - Circuit arrangement for operating a lamp and dimming circuit for a light-emitting diode

Info

Publication number: CN210124030U
Application number: CN201920015555.1U
Authority: CN
Inventors: C·内森松; G·萨沙; K·克莱米斯; L·弗兰克; M·帕特里克; M·马库斯; N·哈拉尔德; W·奥利弗
Original assignee: Tridonic GmbH and Co KG
Current assignee: Tridonic GmbH and Co KG
Priority date: 2018-01-25
Filing date: 2019-01-04
Publication date: 2020-03-03
Anticipated expiration: 2029-01-04
Also published as: AT18059U1; DE202018100418U1

Abstract

The utility model relates to a circuit arrangement for operating lamps and lanterns and be used for emitting diode's dimmer circuit, this circuit arrangement includes: -a converter circuit designed to transfer electrical energy from an input (101) of the converter circuit to an output (103, 104) of the converter circuit that can be coupled to a luminaire (200), wherein the converter circuit comprises an electrical storage device (107); -zero-crossing detection means (110-113) designed to generate a zero-crossing signal (115, ZCD) as a function of the current output by the accumulator means (107); -a timer device (150) having an input, wherein the input receives the zero-crossing signal (115, ZCD), wherein the timer device (150) is designed to generate a timer signal depending on level variations in the zero-crossing signal (115, ZCD) at the input; -a locking means (180) designed to prevent a level change at the input of the timer means (150) depending on the timer signal.

Description

Circuit arrangement for operating a lamp and dimming circuit for a light-emitting diode

Technical Field

The present disclosure relates to a circuit arrangement for operating a luminaire, in particular an LED luminaire.

Background

For operating, for example, light-emitting diode (LED) based luminaires, circuit arrangements are generally employed which generate a voltage suitable for operating the luminaire and/or a current suitable for operating the luminaire from a mains voltage or a supply voltage (for example an alternating voltage or a direct voltage in the range of 120-. In connection with LED luminaires, such circuit arrangements are often referred to as LED converters or LED transformers. For example, such a circuit arrangement may comprise a buck converter, in which case a desired output voltage or a desired output current may be regulated by the duty cycle of the switching means in the buck converter. It is also desirable to adjust the brightness of an LED fixture. Such adjustment is also referred to as "dimming". Such dimming can also be adjusted by the duty cycle of the switching device in the case of a buck converter.

Especially when using a buck converter in combination with a dimmable LED luminaire, it may be necessary to operate the buck converter in a so-called Discontinuous Current Mode (DCM), also called intermittent operation. In intermittent operation, the current through the accumulator (usually the coil) of the buck converter drops to zero in each pulse period. The period of time during which no current flows through the accumulator is called dead time (Totzeit) and is usually set by a timer which is started as soon as the current through the accumulator drops to zero. This time is also referred to as the "zero crossing". The determination of this instant is detected by a so-called zero-crossing detector. However, oscillations in the overall circuit arrangement may cause interference when detecting the zero crossing, so that the timer for the dead time cannot be started or started repeatedly as specified.

It is therefore an object of the present invention to improve the zero crossing detection or to improve the control of a timer for dead time in accordance with the zero crossing.

SUMMERY OF THE UTILITY MODEL

According to the invention, this task is achieved by a circuit arrangement for operating a luminaire according to claim 1. The dependent claims define embodiments of the invention.

According to one embodiment, a circuit arrangement for operating a luminaire comprises a converter circuit, zero-crossing detection means, timer means and locking means. The converter circuit is designed to transfer electrical energy from the converter circuit input to the output of the converter circuit connectable to the lamp. The converter circuit includes an electrical storage device. The power storage device includes, for example, an inductor or a coil. The converter circuit may comprise, for example, a so-called buck converter. The luminaire may be, for example, an LED luminaire, and the circuit arrangement may be designed to operate at least one light emitting diode. For this purpose, the circuit arrangement can be designed, for example, such that a voltage and/or a current suitable for operating one or more light-emitting diodes is provided at the output of the converter circuit.

The zero-cross detection means is designed to generate a zero-cross signal in accordance with the current output by the electrical storage device. In particular, the zero-cross detection means may be designed to generate the zero-cross signal when the current output by the electrical storage device falls to zero.

The timer means has an input receiving a zero crossing signal. The timer means are designed to generate a timer signal in dependence of level variations in the zero crossing signal at the input. In other words, the timer means are designed to generate a timer signal upon detection of a certain level change at the input. The timer signal may for example indicate and control a so-called dead time for the buck converter.

The locking means are designed to prevent a level change at the input of the timer means in dependence of the timer signal. For example, the locking means may be designed to keep the level at the input of the timer means at a constant value as long as the timer signal from the timer means has a defined value. For example, the locking means may maintain the level at the input of the timer means at a constant value during the inactive time.

The aforementioned circuit arrangement enables the realization that, upon detection of a level change of the zero-crossing signal at the input of the timer device, the timer device outputs a timer signal, for example, having a predetermined inactive time length. By means of the locking means it is ensured that the timer means are not disturbed by subsequent level changes in the zero crossing signal which may occur due to oscillations in the circuit arrangement. It is thereby ensured that after the detection of the first zero crossing of the current flowing through the electrical storage device, the dead time starts and is not disturbed by subsequent level changes in the zero crossing signal, in particular is not additionally triggered and thus is lengthened. Especially in dimming of LED luminaires, a reliable realization of the dead time is of utmost importance for maintaining a constant brightness and avoiding flicker.

In another embodiment, the converter circuit further includes a diode coupled to the electrical storage device by a wire. When the converter circuit for example comprises a buck converter, the diode is a so-called freewheeling diode. During charging of the electrical storage device, no current flows through the diode. The potential at the connection between the diode and the energy storage device may in this case, for example, substantially correspond to the ground potential, for example, at the output of the converter circuit. During discharge of the electrical storage device, the electrical storage device is a voltage source and current flows through the diode. The potential at the connection between the diode and the storage means drops substantially to zero or ground potential. When the electrical storage device discharges, the potential at the connection between the diode and the electrical storage device increases again. This is the moment when the dead time starts. Therefore, the potential rise at the wiring between the diode and the electrical storage device can be used as a trigger to start the dead time. The zero-cross detection means may generate the zero-cross signal based on a potential comparison between a potential at a wiring between the diode and the electrical storage device and a reference potential. The reference potential may be, for example, a voltage between a ground voltage and a desired output voltage of the converter circuit.

In order to generate the zero-crossing signal, the zero-crossing detection device may comprise a further diode which is connected, for example, on one side (for example, the cathode) to a connection between the diode and the electrical storage device and on the other side (for example, the anode) to a reference potential, for example, via a voltage divider. The zero crossing signal may be provided, for example, at the center tap of the voltage divider. In this way, a zero-crossing signal can be provided by simple and inexpensive means, which indicates the discharge of the electrical storage device and thus the start of the dead time in terms of a potential change (for example a rising edge).

In yet another embodiment, the converter circuit comprises a switching device. The switching means is controlled in dependence of a timer signal. The switching means may for example comprise a transistor, in particular a MOSFET.

The switching means may be controlled in a switching manner. The switching mode means that the switching device is used substantially only in two operating states, namely either in the off-state or in the on-state. In the off-state, the transition resistance of the switching device is at a maximum, so that substantially no current flows through the switching device. In the on state, the transition resistance of the switching device is minimal and thus a maximum current can flow. The time the switching device is in the off-state is also referred to as the off-time. The time the switching device is in the conducting state is also referred to as the on-time. The off-time of the switching device is controlled in accordance with a timer signal.

In case the converter circuit comprises a buck converter, the buck converter may be operated in a so-called intermittent operation mode, also referred to as discontinuous operation mode or Discontinuous Current Mode (DCM). In the discontinuous operating mode, the following three buck converter states can be distinguished:

(1) during the on-time of the switching device, the electrical storage device is charged,

(2) during the off-time of the switching device, the electrical storage device is discharged,

(3) the off time is followed by an inactive time during which the switching device remains in the locked state and the electrical storage device does not continue to output electrical energy.

The dead time is controlled in accordance with a timer signal. This dead time can be reliably achieved by the locking means described above.

The timer means may be designed as part of an integrated control means. The integrated control device may further comprise a comparator for comparing the actual output voltage at the output of the converter circuit with the nominal output voltage and further timer means for limiting the on-time of the switching means. The switching means may be switched on, for example after the expiry of the dead time, while the further timer means is started. The switched-on switching device causes the electrical storage device to charge and the voltage at the output of the converter circuit to rise. When the voltage at the output of the converter circuit has reached the predetermined rated output voltage, the switching device may be turned off and the off-time started as long as the electrical storage device is discharged. For the case that the voltage at the output of the converter circuit does not reach the predetermined nominal output voltage within the time predetermined by the further timer means, the switching means may also be switched off before the nominal output voltage is reached. Thereby, for example, an overload state can be avoided. By forming the two timer devices in one integrated circuit, the circuit arrangement can be constructed compactly and inexpensively. In particular, a conventional integrated circuit may be used, for example, which contains the timer device, the further timer device and the comparator.

The latch means may be formed outside the integrated circuit. For example, the locking means may comprise a diode which supplies the voltage level of the timer signal to an input of the timer means. As soon as the above-mentioned level change controls the timer means to start the dead time, a timer means signal associated with the dead time can be supplied to the input of the timer means via the diode. The signal may keep the input of the timer means at a defined level during the inactive time, so that the level change of the zero crossing signal remains unresponsive and in particular the timer means is not retriggered to restart the inactive time. The locking device can thus be realized reliably in a simple and inexpensive manner.

Another embodiment relates to a dimming circuit for a light emitting diode. The dimming circuit comprises the aforementioned circuit arrangement. In particular in the case of dimming circuits for light-emitting diodes, it can be advantageous to use a buck converter in discontinuous operation to supply a correspondingly small current and/or voltage over a correspondingly long dead time for controlling the light-emitting diodes. By means of the aforementioned circuit arrangement, occasional variations caused by disturbances and in particular an extension of the dead time can be avoided, so that flicker-free operation of the light-emitting diode is achieved.

Drawings

The invention is described below with reference to the accompanying drawings in conjunction with embodiments. In the drawings, like numbering represents like elements.

Fig. 1 schematically shows a circuit arrangement according to an embodiment of the invention.

Fig. 2 schematically shows a timer device and a locking device according to an embodiment of the invention.

Fig. 3 schematically shows various signal curves in a circuit arrangement according to an embodiment of the invention.

Fig. 4 schematically shows another circuit arrangement according to an embodiment of the invention.

Detailed Description

The above features, characteristics and advantages of the present invention and their implementation are described in detail below with reference to the accompanying drawings in conjunction with the embodiments.

Like reference numerals in the following drawings denote substantially identical components.

The embodiments described below relate to a circuit arrangement for operating an LED luminaire, but are not limited thereto, but may also be used for other types of luminaires, such as halogen luminaires.

Fig. 1 shows a circuit arrangement 100 for powering an LED luminaire 200. The circuit arrangement 100 comprises an input 101 for receiving a supply voltage V +. The supply voltage V + may be a voltage potential related to the ground potential, which is provided to the circuit arrangement 100 through the ground terminal 102. The circuit arrangement 100 also has output terminals 103 (X2-a) and 104(X2-b) at which an output voltage is provided for powering the LED light fixture to which it is connected. By means of the circuit arrangement 100, an output voltage suitable for the LED luminaire 200 and an output current suitable for the LED luminaire 200 can be generated at the

output terminals

103 and 104 from this supply voltage V +.

The supply voltage V + supplied to the circuit arrangement 100 may for example comprise a direct voltage in the range of about 10 volts to several hundred volts, for example 12V, 24V or 60V. The supply voltage V + can be generated, for example, by means of an input stage, not shown, from a mains voltage having a national typical root value of 230V or 120V. The output voltage for powering the LED light fixture 200 may be, for example, a few volts (e.g., 2V) or in the range of 10-50 volts.

In order to generate an output voltage from the supply voltage V + at the

output terminals

103, 104, the circuit arrangement 100 may comprise, for example, a buck converter. The buck converter is also referred to as a buck converter or buck regulator. The Buck Converter is known in english as Step-down Converter or Buck Converter.

The circuit arrangement 100 comprises a switch 105, such as a transistor, which is normally switched on and off by the control means 106. Typically hundreds to millions of switching cycles per second may be performed. Thereby, electric power is transmitted from the input terminal 101 to the

output terminals

103, 104. To this end, the circuit arrangement 100 further comprises an inductive accumulator 107 (e.g. a coil), a capacitive accumulator 108 (e.g. a capacitor) and a diode 109, which is also referred to as a freewheeling diode. Both the energy storage coil 107 and the capacitor 108 enable the lamp 200 to be powered in the open phase of the switch 105. The inductance of the coil 107 keeps the higher supply voltage V + away from the lamp 200. The output voltage or output current at the

output terminals

103, 104 can be regulated by controlling the on and off time of the switch 105.

During the on-time when switch 105 is closed, current flows through coil 107 and LED fixture 200. During the off time when the switch 105 is open, the electrical energy accumulated in the coil 107 is dissipated and current still flows through the LED lamp. Diode 109 is conductive and thus completes the circuit. In addition, current flows from capacitor 108 through LED fixture 200 during the off-time.

When the circuit arrangement 100 operates as a buck converter, two different operating modes can be distinguished: intermittent operation and non-intermittent operation.

In non-discontinuous operation, also referred to as Continuous operation or Continuous Current Mode (CCM) in english, Current flows through the coil 107 throughout the entire cycle. This is achieved in that the switch 105 has been re-closed before the accumulated energy from the coil 107 has completely disappeared.

In intermittent operation, also referred to as intermittent operation or Discontinuous Current Mode (DCM) in english, the Current flowing through the coil 107 drops to zero. There is thus a third phase in the switching cycle: in addition to the charging phase when the switch 105 is closed and the phase when the switch 105 is open, which also occur in the non-interrupted operation, there is also a so-called intermittent phase in which no current flows through the coil 107 and the LED lamp is supplied with electrical energy only from the capacitor 108. The time of the intermittent phase is also referred to as the dead time.

In order to adjust the dead time accurately, it is necessary to detect the moment when the current flowing through the coil 107 drops to zero. Such Detection is also called Zero-Crossing Detection (ZCD in english). The circuit arrangement 100 comprises a zero crossing detection device comprising a diode 110 and three

resistors

111 and 113 and coupled to a reference voltage 114 Vref. The reference voltage 114 may be, for example, a few volts (e.g., a voltage of 3.3V). The zero-crossing detection means generates a zero-crossing signal 115(ZCD signal). The zero-crossing detection device measures the voltage potential Vmid at the wiring between the coil 107 and the freewheeling diode 109. When the voltage potential Vmid is higher than the potential at the anode of the diode 110 (approximately Vref), the diode 110 is not conducting and the zero crossing signal 115 is at the level of the reference voltage 114 Vref. This is the case, for example, during the on-time of switch 105. During the off-time of the switch 105, the voltage potential Vmid decreases to approximately zero, and thus the diode 110 is turned on. This results in the zero crossing signal 115 also having a level of approximately 0V and the total voltage Vref of the reference voltage 114 falling via the

resistors

112, 113. The dead time starts when the coil 107 has output its full energy after the switch 105 is turned off. During the dead time, the voltage potential Vmid rises again and oscillates around the output voltage of the buck converter due to inductances and capacitances in the circuit. If the potential Vmid exceeds the reference voltage Vref, the voltage on the zero-crossing signal 115 increases. Thus, the rising edge of the zero crossing signal 115 may be used as a trigger for a timer means for the dead time. Based on the dead time, the Control device 106 can Control the switch 105 via a Control output 116 (Control).

Fig. 2 shows the control device 106 in detail. The control means 106 comprises a timer means 150, a further timer means 151 and a comparator 152. The control device 106 may be designed as part of an Integrated Circuit (IC) 190. The comparator is specified via a line 153 for a setpoint value (soll) of the voltage to be output by the circuit arrangement 100 or of the current to be output by the circuit arrangement 100. The actual value (ist) of the voltage output by circuit arrangement 100 or the current output by circuit arrangement 100 is provided to comparator 152 via conductor 154. The actual value of the current output by the circuit arrangement 100 may be provided as a corresponding voltage value, for example, by means of a so-called shunt resistor. The comparator 152 generates a comparison signal as a function of the comparison of the setpoint value and the actual value and supplies this comparison signal via a connection 155 to a further timer device 151. The timer means 150 generates an inactive time signal having a predetermined duration which is supplied via a connection 156 to the further timer means 151. The timer means 150 is triggered by a zero crossing signal 115 provided to the timer means 150. A further timer device 151 generates a control for the switch 105 at the control output 116 depending on the comparison signal and the dead time signal.

With reference to fig. 1 to 3, the time course thereof is as followsThe operation of the circuit arrangement 100 is illustrated. Fig. 3 schematically shows a plurality of signal curves. The first signal curve (Timer 1) shows the output signal of a further Timer device 151 at the control output 116 from top to bottom. The second signal curve (IL) schematically represents the circuit flowing through the coil 107. The third signal curve (Comp1 out) shows the comparison signal of the comparator 152 on the connection 155. Fourth Signal Curve (Vmid)₎The voltage potential between freewheeling diode 109 and coil 107 is schematically represented. The fifth signal curve (VZCD) schematically represents the zero crossing signal 115 as generated by the zero crossing detection apparatus described above. A sixth signal curve (Timer 2) schematically represents the signal curve of the dead time signal at the connection 156.

At time t1, the expiration time predetermined by timer device 150 ends. By means of the falling edge of the signal on the connection 156, the timer device 150 indicates the end of the dead time to the further timer device 151. The further timer means 151 outputs a signal at the control output 116 to the switch 105 to close the switch, i.e. the switch 105 is on. This increases the current IL flowing through the coil 107. At time t2, the voltage or current at the output of the circuit arrangement 100 reaches a predetermined nominal value, whereupon the comparator 152 outputs a corresponding comparison signal (Timer1 Break) to the further Timer device 151 via connection 155. The further timer means 151 then outputs a signal at the control output 116 to the switch 105 to switch off, i.e. the switch is no longer on. The further timer device 151 additionally ensures a maximum on-time (t) of the switch 105_on,max) Such that the switch 105 is turned off at the latest after the maximum on-time even if no corresponding comparison signal is received from the comparator 152. By opening the switch 105, the current IL flowing through the coil 107 continuously decreases. Further, as described above, by opening the switch 105, the voltage potential Vmid is reduced to substantially zero. At time t3, coil 107 outputs its full energy and current IL through coil 107 drops to substantially zero. This is detected by the above-mentioned zero crossing detection means and signaled to the timer means 150 by the rising edge of the zero crossing signal 115 (see ZCD in fig. 3). The timer means 150 is started by the rising edge to generate an inactive time signal(t_dead). The dead time signal is transmitted from the timer device 150 via a connection 156 to a further timer device 151, which only switches on the switch 105 again at a time t4 after the dead time has elapsed. The preceding cycle is restarted at time t 4.

When negative voltage peaks, voltage disturbances or oscillations act on the voltage potential Vmid during the dead time, further rising edges on the zero crossing signal 115 may be erroneously generated by the zero crossing detection means, as illustrated in fig. 3 by the oscillation signal curve of the zero crossing signal 115. Thus, the timer device 150 may be triggered multiple times afterwards, such that the dead time may be significantly extended. To avoid this, a diode 180 is provided as a latching device in the circuit arrangement of fig. 2. The diode 180 feeds the output signal from the timer means 150 back to the input of the timer means 150, where the zero crossing signal 115 is received. After the initial detection of the zero crossing, the timer means 150 is started and the input of the timer means 150 is kept at a constant level throughout the dead time by means of the diode 180, irrespective of whether the level of the zero crossing signal 115 changes (see the dashed part ZCD latch of the fifth signal curve in fig. 3). This prevents the timer device 150 from being triggered afterwards, so that a dead time signal with a desired dead time can be reliably generated.

Fig. 4 shows another embodiment of a circuit arrangement 300 for operating an LED luminaire. The circuit arrangement 300 comprises the components of the buck converter and the zero crossing detection arrangement described in relation to fig. 1. The switch 105 is designed as a MOSFET in the embodiment of fig. 4. The operation of the circuit arrangement 300 substantially corresponds to the operation of the circuit arrangement 100 of fig. 1. For clarity, the control device 106 is not explicitly depicted in fig. 4. However, a control device 106, for example as shown in fig. 2, may be used in the same way in combination with the circuit arrangement 300 as described earlier with reference to fig. 1 to 3. For this purpose, the Control device 106 will, for example, be connected to the zero-crossing signal 115 and the Control output 116 to the corresponding input (Control) of fig. 4. The additional components shown in fig. 4 serve essentially to reliably control the switch 105 by means of the integrated circuit U200 and to generate the required auxiliary voltage after the supply voltage has been applied and a defined high-load operation of the overall circuit.

It will be apparent that various modifications can be made in the foregoing examples. For example, a plurality of individual light-emitting diodes connected in series and/or in parallel can be used as an LED lamp. In addition, the aforementioned circuit arrangement may also be used in combination with a plurality of different types of other electrical loads, for example in combination with a motor or a fan for moving the LED luminaire. The combination of the zero crossing detection device with the latching device (diode 180) serves to reliably detect zero crossings, which can be used not only in buck converters but also in other converter circuits, in particular in dc converters. In addition, the buck converter embodiments described in connection with fig. 1 and 2 are obviously shown simplified for illustration and may be supplemented or modified in various ways in a practical implementation, as is shown, for example, in fig. 4. Furthermore, the circuit arrangement may be at least partially integrated into the LED luminaire to be powered.

Claims

1. A circuit arrangement for operating a luminaire, characterized in that the circuit arrangement comprises:

-a converter circuit designed to transfer electrical energy from an input (101) of the converter circuit to an output (103, 104) of the converter circuit that can be coupled to the luminaire, wherein the converter circuit comprises an electrical storage device (107);

-zero-crossing detection means (110-113), said zero-crossing detection means (110-113) being designed to generate a zero-crossing signal (115, ZCD) depending on the current output by said storage means (107);

-a timer device (150) having an input, wherein the zero crossing signal (115, ZCD) is provided to the input of the timer device (150), wherein the timer device (150) is designed to generate a timer signal depending on level variations in the zero crossing signal (115, ZCD) at the input of the timer device (150); and

-a locking means (180), said locking means (180) being designed to prevent a level change at the input of said timer means (150) depending on said timer signal.

2. The circuit arrangement according to claim 1, characterized in that the converter circuit further comprises a diode (109), the diode (109) being coupled with the electrical storage device (107) by a wiring,

wherein the zero-cross detection means (110-113) generates the zero-cross signal (115, ZCD) based on a potential comparison between a potential (Vmid) at a wiring between the diode (109) and the electrical storage device (107) and a reference potential (114, Vref).

3. The circuit arrangement according to claim 1 or 2, characterized in that the zero-crossing detection device (110) has a further diode (110) for generating the zero-crossing signal (115, ZCD).

4. The circuit arrangement according to claim 1, characterized in that the electrical storage device (107) comprises a coil.

5. The circuit arrangement according to claim 1, characterized in that the converter circuit comprises a buck converter.

6. The circuit arrangement according to claim 1, characterized in that the converter circuit comprises a switching device (105), wherein the switching device (105) is controlled in dependence of the timer signal.

7. The circuit arrangement according to claim 6, characterized in that the switching device (105) is controlled in a switching operation mode, wherein the off-time of the switching device (105) is controlled in dependence of the timer signal.

8. The circuit arrangement according to claim 6 or 7, characterized in that the timer device (150) is designed as part of an integrated circuit (190), wherein the integrated circuit (190) further comprises a comparator (152) and a further timer device (151), the comparator (152) being configured to compare an actual output voltage (ist) at the output of the converter circuit with a nominal output voltage (soll), the further timer device (151) being configured to limit the on-time of the switching device (105).

9. The circuit arrangement according to claim 8, characterized in that the locking means (180) is formed outside the integrated circuit (190).

10. The circuit arrangement according to claim 1, characterized in that the converter circuit is operated in a discontinuous operation mode, wherein the inactive time of the discontinuous operation mode is controlled in dependence of the timer signal.

11. A circuit arrangement as claimed in claim 1, characterized in that the locking means (180) comprises a diode providing the voltage level of the timer signal to an input of the timer means (150).

12. The circuit arrangement according to claim 1, characterized in that the circuit arrangement (100, 300) is designed to operate at least one light emitting diode.

13. A dimming circuit for a light emitting diode, the dimming circuit comprising the circuit arrangement (100, 300) according to any one of the preceding claims.