AT18197U1 - Low-voltage supply in control gear for lamps - Google Patents

Abstract

The present invention relates to a circuit for low-voltage power supply of an integrated circuit of an operating device for lighting means, comprising: a storage capacitor; and wherein the circuit is supplied with a supply voltage derived from an AC voltage, and the circuit is designed to provide a regulated output voltage at the storage capacitor. The circuit is further designed to provide a higher output voltage in a first temperature range in which a temperature of the circuit and in particular of the storage capacitor is less than a threshold value than in a second temperature range which is higher than the first temperature range.

Description

Description

LOW-VOLTAGE SUPPLY IN OPERATING DEVICES FOR LAMPS

1. FIELD OF THE INVENTION

[0001] The present invention relates to the field of so-called low-voltage supplies, also called low-voltage power supplies, in particular for lighting control devices, such as electronic ballasts for drivers of LED modules (LEDs, OLEDs).

2. BACKGROUND

[0002] A low-voltage supply is a circuit arrangement by means of which a DC voltage supply can be generated in an operating device in a voltage range that is suitable for the supply voltage of (active) electronic components (integrated circuits, microcontrollers, ASICs, etc.). Typically, these DC supply voltages are in a range of less than 15 volts DC.

[0003] LED drivers are often required to start at temperatures of around -25°C for indoor applications and around -40°C for outdoor applications. One of the critical components at these temperatures is the low-voltage supply. In the low-voltage supply, energy is usually stored in an electrolytic capacitor at the output of the circuit. However, this has the property that its equivalent series resistance (ESR), also known as equivalent resistance, increases sharply at low temperatures. As a result, a ripple on the low-voltage voltage applied to the capacitor increases. This voltage ripple can become so large that the low-voltage voltage falls below the threshold value of the components to be supplied. To prevent this, several capacitors can be connected in parallel. However, connecting capacitors in parallel increases the component complexity. The capacity actually required to keep the voltage ripple low at room temperature can be selected to be relatively small. If the low-voltage voltage is increased, the losses in the consumers to be supplied also increase.

[0004] Therefore, a storage capacitor is typically provided in the low-voltage supply, the temperature properties of which are such that a ripple to be filtered by it may no longer be able to be filtered sufficiently at very low temperatures. If the low-voltage supply now outputs a supply voltage with or just above a nominal value of, for example, 12 volts to a microcontroller or ASIC (as an example of a controller), the problem can arise that in certain valleys of the voltage ripple, a minimum value of the supply voltage of the controller is undershot, as a result of which the controller is no longer sufficiently supplied and can therefore enter a defined or "shutdown/lockdown state".

[0005] It is therefore an object of the present invention to improve the low-temperature behavior of a low-voltage supply.

[0006] These and other objects, which will be mentioned upon reading the following description or which can be recognized by the person skilled in the art, are solved by the subject matter of the independent claims. The dependent claims develop the central idea of the present invention in a particularly advantageous manner.

3. DETAILED DESCRIPTION OF THE INVENTION

[0007] According to a first aspect, the invention relates to a circuit for low-voltage power supply of an integrated circuit of an operating device for lighting devices. The circuit comprises a storage capacitor and a supply voltage derived from an AC voltage is supplied to the circuit. Furthermore, the circuit is designed to provide a feedback-controlled output voltage at the storage capacitor and in a

first temperature range, in which a temperature of the circuit and in particular of the storage capacitor is less than a threshold value, to provide a higher output voltage than in a second temperature range which is higher than the first temperature range.

[0008] This has the advantage that even at very low temperatures of, for example, below -20 degrees Celsius, it can be ensured that the valleys of the ripple do not fall below the minimum value for the supply voltage, thus preventing the controller from switching off.

[0009] According to one embodiment, the circuit further comprises a temperature-dependent resistor arranged in a return path for a signal representing the output voltage to the low voltage supply.

[0010] This has the advantage that an increase in the low voltage can be achieved by means of a temperature-dependent resistor and thus a higher ripple can be compensated for by a temporary increase in the low voltage. This also has the advantage that during a start-up phase of the operation of the converter, the setpoint value for the supply voltage, which is regulated by a control loop, is selectively set high.

[0011] According to one embodiment, the resistor is a PTC thermistor or a thermistor and the resistor is arranged such that it experiences substantially the same temperature as the storage capacitor.

[0012] This has the advantage that an increase in the low voltage can be realized by a temperature-dependent resistance and thus a higher ripple can be compensated by a temporary increase in the low voltage.

[0013] According to one embodiment, the circuit is designed to increase the output voltage as a function of time, for example in a period of between 10 seconds and one minute, preferably between 20 seconds and 50 seconds, after starting operation of the circuit.

[0014] According to one embodiment, the circuit further comprises a clamping diode, wherein the clamping diode is designed to prevent an exceeding of a threshold value of the output voltage.

[0015] This has the advantage that the circuit is protected against overvoltage.

[0016] According to one embodiment, the circuit comprises a resistor arranged in series with the storage capacitor.

[0017] According to one embodiment, the storage capacitor is an electrolytic capacitor.

[0018] This has the advantage that electrolytic capacitors offer a higher capacitance for a given volume than other capacitor technologies. Furthermore, properly specified electrolytic capacitors can achieve a lifetime of more than 20 years in demanding industrial applications.

[0019] According to a second aspect, the invention relates to an operating device for lighting means, comprising a circuit according to the first aspect and at least one control unit supplied by the latter.

[0020] According to one embodiment, the control unit is a microcontroller or an ASIC.

[0021] According to one embodiment, the operating device has an actively clocked PFC circuit, wherein the output voltage of the PFC circuit represents the supply voltage of the circuit for the low-voltage power supply of an integrated circuit.

[0022] According to one embodiment, the operating device has a primary-side clocked isolated or non-isolated DC/DC converter supplied by the output voltage of the PFC circuit for supplying a light source.

[0023] This has the advantage of increasing the power factor and improving harmonic distortion.

[0024] According to one embodiment, in the operating device, the circuit for the low-voltage power supply of an integrated circuit is arranged on the primary side of the isolated converter.

[0025] According to one embodiment of the operating device, the circuit for the low-voltage power supply of an integrated circuit is arranged on the secondary side of the isolated converter.

[0026] According to one embodiment of the operating device, the control unit is a control unit for clocking a switch and/or the control unit is designed for communication with an interface of the operating device.

[0027] According to a third aspect, the invention relates to a method for low-voltage power supply of an integrated circuit of an operating device for lighting means by means of a circuit, comprising: supplying a supply voltage derived from an AC or DC voltage to a circuit; providing a regulated output voltage at a storage capacitor; wherein the circuit is designed to provide a higher output voltage in a first temperature range in which a temperature of the circuit and in particular of the storage capacitor is less than a threshold value than in a second temperature range which is higher than the first temperature range.

4. BRIEF DESCRIPTION OF THE FIGURES [0028] A brief description of the figures is given below. It shows:

[0029] Figure 1 is a schematic representation of a circuit for low-voltage power supply of an integrated circuit of an operating device for lamps according to a preferred embodiment; and

[0030] Figure 2 shows a schematic representation of a method for low-voltage power supply of an integrated circuit of an operating device for lamps by means of a circuit according to an embodiment.

5. DETAILED DESCRIPTION

[0031] Figure 1 shows a schematic representation of a circuit 101 for the low-voltage power supply of an integrated circuit of an operating device 100 for lighting means 116 according to a preferred embodiment.

[0032] According to this embodiment, the circuit 101 shown is fed from the output voltage of a PFC circuit. This output voltage typically has a ripple, for example the frequency of a rectified mains voltage.

[0033] The circuit 101 can, however, also be derived from other DC voltages in an operating device for lamps, in particular those that are subject to ripple. The circuit 101 is preferably supplied from a voltage on the primary side of an isolated or non-isolated DC/DC converter for supplying a lamp.

[0034] The circuit 101 comprises a storage capacitor 106, wherein the circuit 101 is supplied with a supply voltage derived from an AC voltage, and the circuit 101 is designed to provide a regulated output voltage at the storage capacitor 106. Furthermore, the circuit 101 is designed to provide a higher output voltage in a first temperature range in which a temperature of the circuit 101 and in particular of the storage capacitor 106 is less than a threshold value than in a second temperature range which is higher than the first temperature range.

[0035] In one embodiment, during a start-up phase of the operation of the converter, the setpoint value for the supply voltage, which is regulated by a control loop, is selectively set high. This can be done, for example, by a temperature-dependent resistor 110 setting the setpoint value or the feedback value of the control loop of the low-voltage supply 109

changed.

[0036] Preferably, the temperature-dependent resistor 110 is arranged such that it experiences substantially the same temperature as the aforementioned storage capacitor 106.

[0037] With increasing operation, for example a period of between 10 seconds and 1 minute, the ripple on the storage capacitor 106 will decrease.

[0038] As the capacitor heats up, the series resistance 105 decreases and the ripple decreases again. It can therefore be provided that the increase in the supply voltage is limited to a time range between 10 seconds and one minute, preferably between 20 seconds and 50 seconds. Preferably, this increase in the supply voltage for a cold start is designed in such a way that it is only active until the temperature on the storage capacitor has increased by 20 degrees relative or above a temperature of, for example, -20 degrees (absolute).

[0039] In the circuit 101, so-called clamping diodes 107 can also be provided, which ensure that the supply voltage does not inadvertently exceed a predetermined range. If this is exceeded, these clamping diodes 107 draw an additional current from the storage capacitor 106, which contributes to the heating of the storage capacitor 106.

[0040] The higher ripple can be compensated by temporarily increasing the low voltage. This increase in the low voltage can be achieved, for example, by the temperature-dependent resistor 110. Once the device has warmed up, the temperature rises due to the losses in the device and the low voltage can then drop again.

[0041] Preferably, the low-voltage power supply 109 is an LVPS ("Low-Voltage Power Supply") and normally supplies e.g. 12V. At low temperatures, a feedback 113 can be manipulated so that the low-voltage power supply 109 supplies a slightly increased voltage (e.g. 15V). Many components can have an undervoltage lockout. To prevent this from being reached at low temperatures, the capacity of the storage capacitor 106 can be chosen to be correspondingly large, or an electrolytic capacitor (Elko) with a low equivalent serial resistance 105 (ESR, hybrid Elko) can be selected.

[0042] Preferably, for 15V operation, some clamping diodes 107 are provided to protect against overvoltage. If the clamping becomes active/conducts, a small part of the LVPS 15V voltage can be short-circuited by the clamping and the critical electrolytic capacitor has a larger load for a short time. This causes the electrolytic capacitor to heat up and the problem of the excessive ESR is solved automatically.

[0043] The operating device 100 for lighting means 116 has the circuit 101 and at least one control unit 112 supplied by it. The control unit 112 can be a microcontroller or an ASIC.

[0044] Furthermore, the operating device 100 can have an actively clocked PFC circuit 103, wherein the output voltage of the PFC circuit 103 represents the supply voltage of the circuit 101 for the low-voltage power supply of the integrated circuit.

[0045] For example, the circuit 100 for low-voltage power supply of the integrated circuit is arranged on the primary side of the isolated converter 104.

[0046] Alternatively, the circuit for supplying the low-voltage power to the integrated circuit can also be arranged on the secondary side of the isolated converter 104.

[0047] The operating device 100 may further comprise an interface 111, wherein the control unit 112 is designed to clock a switch and/or to communicate with the interface 111 of the operating device 100.

[0048] The operating device 100 may further include an electromagnetic interference (EMI) filter and a rectifier 102.

[0049] Furthermore, a unit for sampling and rectifying the current 114 and a filter unit 115 can be arranged on the secondary side of the operating device 100.

[0050] Figure 2 shows a schematic representation of a method 200 for low-voltage power supply of an integrated circuit of an operating device 100 for lighting means 116 by means of a circuit 101 according to an embodiment.

[0051] The low voltage power supply method 200 includes the following steps:

- supplying 201 a supply voltage derived from an AC or DC voltage to a circuit 101;

- Providing 202 a regulated output voltage at a storage capacitor 106, wherein the circuit 101 is designed to provide a higher output voltage in a first temperature range in which a temperature of the circuit and in particular of the storage capacitor 106 is less than a threshold value than in a second temperature range which is higher than the first temperature range.

Claims (10)

Expectations 1. Circuit (101) for low-voltage power supply of an integrated circuit of an operating device (100) for lamps (116), comprising: - a storage capacitor (106); - wherein the circuit (101) is supplied with a supply voltage derived from an AC voltage, and the circuit (101) is designed to provide a feedback-controlled output voltage at the storage capacitor (106) characterized in that the circuit (101) is designed in a first temperature range in which a Temperature of the circuit (101) and in particular of the storage capacitor (106), less than a threshold value to provide a higher output voltage than in a second Temperature range that is higher than the first temperature range. 2. Circuit (101) according to claim 1, characterized in that the circuit (101) further comprises a temperature-dependent resistor (110) which is arranged in a return path for a signal representing the output voltage to the low voltage supply (109). 3. Circuit (101) according to claim 2, characterized in that the resistor (110) is a PTC thermistor or a thermistor and wherein the resistor (110) is arranged such that it experiences substantially the same temperature as the storage capacitor (106). 4. Circuit (101) according to claim 2 or 3, characterized in that the low-voltage supply (109) is designed to increase the output voltage as a function of time, for example in a period of between 10 seconds and one minute, preferably between 20 seconds and 50 seconds, after the start of operation of the circuit (101). 5. Circuit (101) according to one of the preceding claims, characterized in that the circuit further comprises a clamping diode (107), wherein the clamping diode (107) is designed to prevent an exceeding of a threshold value of the output voltage. 6. Operating device (100) for lighting means (106), comprising a circuit (101) according to one of the preceding claims and at least one control unit (112) supplied by the latter. 7. Operating device (100) according to claim 6, comprising an actively clocked PFC circuit (103), characterized in that the output voltage of the PFC circuit (103) represents the supply voltage of the circuit (101) for the low-voltage power supply of an integrated circuit. 8. Operating device (100) according to claim 7, characterized in that the circuit (101) for the low-voltage power supply of an integrated circuit is arranged on the primary side of an isolated converter. 9. Operating device (100) according to one of claims 6 to 8, characterized in that the control unit (112) is a control unit for clocking a switch and/or is designed for communication with an interface (111) of the operating device (100). 10. Method (200) for low-voltage power supply of an integrated circuit of an operating device (100) for lamps (116) by means of a circuit (101), comprising: - supplying (201) a supply voltage derived from an AC or DC voltage to the circuit (101); - providing (202) a regulated output voltage to a storage capacitor (106); characterized in that the circuit (101) is designed in a first temperature range in which a Temperature of the circuit (101) and in particular of the storage capacitor (106), less than a threshold value to provide a higher output voltage than in a second Temperature range that is higher than the first temperature range. 2 sheets of drawings