AT16238U1 - Method for operating bulbs at low outside temperatures - Google Patents

Abstract

The invention relates to a method for operating at least one light-emitting means (3) having a temperature-dependent characteristic current / voltage characteristic U (I) with an LED converter (2), wherein a control circuit (14) of the LED converter (2 ) as the manipulated variable controls the operating frequency of the primary-side circuit (11) of the LED converter (2), wherein a predetermined maximum value of the operating frequency is set to avoid an unstable operating point as a manipulated variable when low outside temperatures are present.

Description

description

METHOD FOR OPERATING LUMINAIRES AT LOW OUTDOOR TEMPERATURES The present invention relates to a method for operating lamps, in particular at low outside temperatures according to claim 1, a control circuit according to claim 8, an operating device according to claim 9 and a lamp according to claim 10 ,

It is known that at low ambient temperatures, the operation of lamps can become unstable, especially at low dimming levels, i.e. it is difficult to keep the operating point on the U / I characteristic curve of the lamp by controlling or regulating.

The instability can lead to fluctuations in brightness or even to the extinction of the lamp.

It is also known that the light efficiency of the illuminant decreases sharply at low temperatures, so that the light output is greatly reduced.

To avoid these problems, countermeasures can be taken, which, however, presupposes that a control circuit detects that low ambient temperatures are present on the illuminant.

However, a direct temperature measurement is only possible with great difficulty, since usually a temperature measurement can take place in the area of an operating device rather than in the actually relevant area of the illuminant itself.

It is known from the prior art that, to stabilize the unstable operating points, regulations are used which are intended to maintain a predetermined operating point.

However, extremely high lamp voltages occur at extremely low temperatures. This makes it impossible to maintain the operating point, and it also violates various standards. For example, a certain maximum permissible terminal voltage can be exceeded based on the dielectric strengths of the terminal connections or the leads.

The invention has therefore set itself the task of providing a solution to the problems mentioned above.

[0010] The basic idea of the invention is the measurement of a variable which is correlated to low temperatures.

The invention thus proposes a method for operating lamps that have a temperature-dependent characteristic current / voltage characteristic U (l). To avoid an unstable operating point at low outside temperatures, a predetermined maximum value of the operating frequency thereof is prevented by increasing the lamp current.

The predetermined maximum value of the operating frequency or its gradient amount is preferably current-dependent.

[0013] The predetermined maximum value can therefore be defined by a limit characteristic G '(l).

The limit characteristic G '(l) preferably represents an adaptive threshold as a function of the current, taking into account the lamp characteristic. This can be designed such that a characteristic characteristic U (l) of a lamp at room temperature is not restricted by this.

[0015] The threshold of the maximum value of the operating frequency can be changed. The threshold can be set in a changeable manner via an interface of an operating device.

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AT16 238U1 2019-05-15 Austrian

Patent Office [0016] In addition, a measurement can be carried out which can at least decide whether there are very high outside temperatures, for example 35 ° C., or very low outside temperatures, for example -10 ° C.

Preferably, the lamp current is increased or the maximum operating frequency is limited only when there are no very high outside temperatures, for example outside temperatures of <10 ° C.

In a further aspect, the invention relates to a control circuit, preferably an integrated circuit, which is designed to carry out one of the methods according to the invention.

The invention also relates to an operating device for lamps that has such a control circuit.

Finally, the invention relates to a lamp which has the operating device described above and at least one connected lamp.

In the following, the invention will be explained in more detail with reference to the attached figures. Show it:

Figure 1 a current-voltage diagram with characteristic curves of a gas discharge lamp at different outside temperatures, Figure 2 a current-voltage diagram with characteristic curves of an LED at different outside temperatures,

[0024] FIG. 3 shows a schematic illustration of a lighting system with an LED converter according to an exemplary embodiment.

Fig. 1 shows a current-voltage diagram with characteristic curves of a gas discharge lamp at different outside temperatures, more precisely at 22 ° C, at 10 ° C and at -15 ° C. Outside temperature is understood to mean the ambient temperature of the gas discharge lamp.

22 ° C represents approximately the usual temperature in a room. 10 ° C and 15 ° C, however, are temperatures that can occur when used outdoors.

It can be seen from the diagram that all the characteristic curves intersect at a point P _s . This means that this working point P _A = P _s (ls, U _s ) applies to the gas discharge lamp at all temperatures.

[0028] In addition,. 1 that the voltage decreases with increasing current for current values I> l _s . The characteristics are falling in this area. The voltage at very low temperatures, for example at -15 ° C, is lower than at higher temperatures, such as 10 ° C.

On the other hand, a non-uniform picture results for current values I <1 _s . For an outside temperature of 22 ° C, the voltage initially increases with increasing current and then decreases again slightly near the intersection P _s . For smaller outside temperatures, however, the characteristic curve drops continuously in this area. The negative slope, ie the negative gradient, is particularly large at particularly low outside temperatures. At the same time, the voltage of the gas discharge lamp is particularly high at low temperatures when the lamp current is low. Here, voltage is understood to mean lamp lamp voltage. This means that an inadmissibly high lamp operating voltage results, in particular for very low temperatures with a small lamp current.

[0030] The gas discharge lamp is dimmed by adjusting the lamp current. The lamp current is reduced for a low dimming level and the lamp current is increased for a high one. This means that a low dimming level is further to the left on a characteristic curve in FIG. 1, while a high one is further to the right.

[0031] According to the invention, an impermissibly high operating frequency can now be avoided by increasing the dimming level. Alternatively, the operating frequency

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Patent office can be limited to a maximum value.

As a result, the operating point P _A is also shifted further to the right on a characteristic curve. Basically, an operating point can reach an inadmissible range by setting the dimming to a level that is too low, especially at low outside temperatures. However, it is also possible for an operating point to reach an impermissible range if the outside temperature drops while the dimming level remains constant.

To compensate, a regulation comes into effect which drives higher dimming levels until the operating frequency falls below the maximum value again. This up-regulation of the dimming level has priority, for example, via an external dimming level command. In the course of regulation, the operating frequency is thus always kept below the maximum permissible operating frequency. This means that low dimming levels are not avoided in principle, but only at impermissibly high operating frequencies.

In the simplest version, the maximum permissible operating frequency can be a constant value, for example 120 kHz.

2 further shows a current-voltage diagram with characteristic curves of a light-emitting diode at different outside temperatures T1, T2, T3, T4, T5, the highest temperature being T1 and the lowest temperature T 5. It can be seen from this that the characteristic curves have a higher forward voltage U _F at low temperatures than at high temperatures.

The limit characteristic G '(I) can have a current-dependent maximum value of the operating frequency which is defined by a limit characteristic G' (I). An upper value of the limit characteristic G 'limits the maximum permissible operating frequency to approximately 100-120 kHz (limit characteristic G2). In this exemplary embodiment, this threshold is only active at small dimming ranges <30%, i.e. it has a limiting effect only in this area. Alternatively, this threshold can also apply to the entire dimming range, i.e. to be independent of the current value.

Furthermore, the values of the limit characteristic G '(I) can vary over the dimming range, for example with higher dimming values a different operating frequency can be used as the maximum value, for example 90 kHz than with low dimming values (limit characteristic G1).

The course of the limit characteristic G '(I) can be a step function, a falling linear function, etc.

The course of the limit characteristic G '(I) or the maximum value of the operating frequency can be adjustable via an interface of an operating device 2.

At very low temperatures, however, it should be noted that the efficiency of the illuminant decreases sharply, so that the light output actually emitted is lower at an identical operating point than at higher temperatures. However, this too low light output is compensated for by the method according to the invention.

Advantageously, the limit characteristics G '(I) has a shape that is adapted to the shape of the lamp characteristic. In addition, if possible, they are designed so that a characteristic characteristic U (l) of the illuminant at room temperature is not restricted by them.

Accordingly, a temperature measurement is preferably carried out accordingly in the method according to the invention. However, this only has to determine whether the outside temperature is a very high or very low temperature. The temperature measurement can be carried out with a temperature sensor 8 which is arranged outside the operating device 2 and is connected to the control circuit 14. Alternatively, the temperature sensor 8 can also be arranged integrated in the control circuit 14.

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Patent Office [0043] It is thus possible to make the activation of the maximum value of the operating frequency flexible. The limit should be deactivated at very high temperatures, for example> = 30 ° C, but should be active at very low temperatures, for example <10 ° C.

As a result, the operating frequency can only be limited at an outside temperature of <10 ° C.

Thanks to the method, it can be freely determined from which temperature which dimming levels are to be permitted.

As stated above, the above-mentioned procedure can avoid unstable operation at low temperatures and low dimming levels.

Alternatively, there can also be temperature ranges which have operating frequencies which are above the maximum values defined by the limit characteristic G '(I) and thus have an impermissible limit violation in this range. These temperature ranges could, for example, be in the range of 25 ° C. Since a limitation in this temperature range is not necessary, a limit violation can be permitted.

A limit characteristic G '(I) can also be defined, at which a minimum current I _{F is} kept constant. The minimum current value l _F which is defined via the limit characteristic G '(I) can be a constant value or dependent on the dimming level value. The limit characteristic G '(I) can also be a step function or have a semicircular shape. The limit characteristic G '(I) can also only be activated from a minimum temperature.

[0049] FIG. 3 shows a lighting system 1 in which an operating device 2 supplies LEDs 3 according to one exemplary embodiment with energy. The operating device 2 can be designed as an LED converter or as a ballast for gas discharge lamps. The LED converter 2 can be designed as a constant current source. The LED converter 2 can be configured in such a way that the brightness of the LEDs 3 can be set via commands that are transmitted, for example, via a bus 4 or wirelessly. The LED converter 2 can comprise a suitable interface for communication with a central control device and can be set up to receive dimming commands via the interface and to output information about the operating state of the LED converter 2 and / or the LEDs 3 via the interface.

The LED converter 2 can be designed as a SELV device in which a primary-side circuit (for example a non-SELV side) and a secondary-side circuit (for example a SELV side) are electrically isolated. The LED converter 2 can comprise an AC / DC converter 10. The AC / DC converter 10 can be set up to be coupled on the input side to a mains voltage. The AC / DC converter 10 can be designed as a so-called smoothing circuit or circuit for power factor correction (PFC). The AC / DC converter 10 provides a bus voltage Vbus to a converter that has an input or. primary circuit 11 and a galvanically isolated output or secondary circuit 13.

Electrical isolation is achieved by means of a transformer 12 or another converter.

The LED converter 2 is designed such that a current strength provided by the LED converter 2 to the LEDs is regulated to a setpoint. The control is based on a control variable recorded in the primary-side circuit 11, which can be, in particular, a peak current through a resistor or a variable proportional to this peak current. In addition to the output current, an output power can also be set. In order to regulate the output current depending on the controlled variable detected in the primary-side circuit, the control circuit 14 is correspondingly coupled to the primary-side circuit 11 in order to receive the controlled variable or information about a comparison of the controlled variable with a reference. The control circuit 14, which can be designed in particular as an integrated circuit, controls a half-bridge circuit of the primary-side circuit 11 depending on the comparison of the controlled variable with the reference. The control circuit 14 can

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Patent office in particular change a frequency with which two switches of the half-bridge circuit are switched, depending on the comparison of the controlled variable with the reference. The control circuit 14 can additionally perform further functions, such as adapting the reference as a function of a dimming command, detecting the load connected to the LED converter 2, in particular for detecting a number of LEDs or the output power, and / or detecting error states. The control circuit 14 can also be coupled to the AC / DC converter, for example in order to adapt the bus voltage.

As shown in FIG. 3 is shown schematically, in the LED converter 2 the output current which is provided to the LEDs 3 can be regulated without a measurement having to be carried out on the SELV side and / or without a corresponding measurement result using the SELV -Barrier must be returned. The control circuit 14 is set up in such a way that it controls at least one component of the primary-side circuit 11 as a function of a peak current measured on the primary side in order to regulate the output current, which is provided by the operating device 2 to the LEDs 3, to a desired value.

Optionally, the LED converter 2 can also have a temperature sensor 8. This can be used for the process described above. The temperature sensor 8 is preferably also connected to the control circuit 14.

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Claims (10)

Expectations 1. A method for operating at least one lamp (3) which has a temperature-dependent characteristic current / voltage characteristic U (l) with an LED converter (2), a control circuit (14) of the LED converter (2) being the control variable Controls the operating frequency of the primary-side circuit (11) of the LED converter (2), characterized in that, in order to avoid an unstable operating point, a predetermined maximum value of the operating frequency is set when the outside temperatures are low. 2. The method according to claim 1, characterized in that the predetermined maximum value of the operating frequency is current-dependent and the predetermined maximum value is defined by a limit characteristic G '(I). 3. The method according to claim 2, characterized in that the maximum value of the operating frequency represents a variable threshold. 4. The method according to claim 3, characterized in that the threshold of the maximum value of the operating frequency as a function of the current can be changed taking into account the lamp characteristic and this maximum value of the operating frequency is designed such that a characteristic curve U (l) of a lamp (3) Room temperature is not restricted by this. 5. The method according to claim 4, characterized in that the threshold of the maximum value of the operating frequency via an interface of an operating device (2) for the at least one lamp (3) can be changed. 6. The method according to the preceding claim, characterized in that a measurement, preferably with a temperature sensor (8), takes place, which can at least decide whether very high outside temperatures, for example 35 ° C, or very low outside temperatures, for example -10 ° C, available. 7. The method according to claim 6, characterized in that the operating frequency is only limited when an outside temperature of <10 ° C is present. 8. control circuit, preferably an integrated circuit, which is designed to carry out a method according to any one of the preceding claims. 9. Operating device for at least one lamp (3), comprising a control circuit (14) according to claim 8. 10. lamp, having an operating device (2) according to claim 9 and at least one lamp (3). Two sheets of drawings 6.8 AT16 238U1 2019-05-15 Austrian Patent Office Fig. 1 Fig. 2 ^U F 7.8 AT16 238U1 2019-05-15 Austrian Patent Office Fig. 3 8.8