DE29622825U1 - Radiation device - Google Patents

Description

TER MEER - MÜLLER - STEINMEISTER & R^aTKlER .".I ·"· "*LoHP01/96/G

DESCRIPTION

The invention relates to an irradiation device with several fluorescent lamps and associated electronic ballasts. In particular, the invention relates to irradiation devices that are used as so-called tanning beds for irradiating the human body with ultraviolet radiation for cosmetic or therapeutic purposes.

In conventional irradiation devices of this type, the radiation source is formed by a large number of fluorescent lamps in which light with a relatively high ultraviolet content (UV A and UV B) is generated by gas discharge. A ballast is required to ignite the gas discharge and to limit the current during operation of the lamp. Usually, the ballast is formed by a choke with a relatively high inductance, which generates the necessary ignition voltage by induction when switched on and then limits the current during continuous operation of the lamp with mains alternating current (50 Hz).

Electronic ballasts have been developed in conjunction with so-called energy-saving lamps, which are based on a similar principle to the UV radiation lamps considered here. Such an electronic ballast has a rectifier for rectifying the AC mains voltage. The rectified voltage is then converted into a pulsed voltage with a relatively high frequency in the order of 30 - 40 kHz using a power unit formed, for example, by power transistors. Because of the high operating frequency, the choke only needs to have a very low inductance. It is therefore possible to use a small choke with lower-loss core materials. The choke forms an oscillating circuit with a capacitor connected in parallel to the lamp with a resonance frequency that is slightly above the operating frequency of the lamp. To ignite the lamp, the frequency of the pulsed voltage is gradually reduced from a high initial value to the operating frequency, so that the resonance frequency of the oscillating circuit is passed through and the necessary ignition voltage is temporarily generated by resonance.

The conventional ballasts are each designed for a lamp with a

TER MEER - MÜLLER - STEINMEISTER & RARSTER .". &Idigr; ·'"· "'eOHPOI/96/G

designed for a specific power. The power of the ballasts available on the market is usually in the order of around 20 W, but ballasts with lamp powers of up to 100 W are also available on the market.

DE 43 12 547 A describes a tanning device according to the preamble of claim 1, in which an electronic ballast of the type described above is provided for each individual lamp, which has a power of approximately 100 W. The ballasts can be controlled by a central controller, for example a microcontroller, and it is possible to regulate the power of the lamps individually in order to adapt the irradiation intensity to the respective therapeutic purpose or to the user's skin type. The power regulation is achieved by varying the frequency of the pulsed voltage of the ballast.

However, the irradiation device proposed in the above-mentioned publication proves to be relatively expensive, since an expensive ballast with the corresponding power is required for each individual lamp.

The object of the invention is to create an irradiation device of the type specified in the preamble of claim 1, which can be implemented more cost-effectively.

This object is achieved according to the invention in that the power units of the ballasts for several fluorescent lamps are fed by a common direct voltage source.

According to the invention, on the one hand, the functions previously integrated in a single device: "converting the mains voltage into direct current" and "converting the direct current into high-frequency voltage" are divided into separate components, and on the other hand, several ballasts for a corresponding number of fluorescent lamps are combined into a group. Within such a group, only a single direct current source is provided for converting the mains voltage into direct current, which supplies all the power units in the group. In this way, the total number of components required and thus also the amount of work required for wiring can be considerably reduced.

TER MEER - MÜLLER - STEINMEISTER & l?AR."fftER .**· I ·"*· ***fX>HP01/96/G

This results in considerable cost savings compared to the use of conventional ballasts.

Depending on the type of device, fluorescent lamps with an output of 160 W, an output of 100 W or a lower output are usually used for irradiation devices. However, electronic ballasts were not previously available for devices equipped with 160 W lamps. In the irradiation device according to the invention, the power units are preferably designed for an output of 160 W or more, so that the 160 W lamps can also be operated with electronic ballasts. However, the same ballasts can also be used for lamps with an output of 100 W or less. To adapt to the respective output of the lamps, the chokes and the associated capacitors may need to be replaced. All of the other electronics can be kept unchanged. This enables the ballast groups to be produced efficiently in large series, thus achieving further cost savings. The chokes designed for the respective lamp power are relatively small and are preferably combined with the corresponding capacitors to form a replaceable module. When manufacturing or converting the electronic control for a specific type of irradiation device, only low storage and labor costs arise.

According to a further development of the inventive concept, it is also possible to operate all the fluorescent lamps in the group with just one single power unit. This achieves a much further reduction in the number of components required and the wiring effort.

If irradiation devices that have a large number of closely arranged fluorescent lamps are to be equipped with electronic ballasts, there is generally the problem that the high-frequency signals occurring in the individual ballasts and lamps become noticeable as interference signals in the neighboring units. It is therefore extremely difficult to maintain stable operation of the entire device.

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This problem is solved according to the invention in that the power units of the ballasts for a group of neighboring fluorescent lamps are controlled with clock signals of the same frequency and phase. Since the high-frequency, pulsed voltages for all lamps in the group are "synchronized" from the outset, mutual interference is largely eliminated. This solution principle can also be used if, contrary to the subject matter of claim 1, a separate DC voltage source is provided for each power unit.

According to the invention, the power control or dimming of the fluorescent lamps is achieved by varying the duty cycle of the pulsed high-frequency signals. If the lamps are only to be dimmed in groups, all power units in the group can be controlled with identical pulse signals.

If the power of each lamp is to be controlled individually, the rising and/or falling edges of the control pulses for the individual lamps are not exactly synchronized. However, even in this case, mutual interference can be largely suppressed if the control signals have the same frequency and phase. In this case, phase equality means that either the rising edges or the falling edges or the pulse centers of the control pulses are synchronized.

As the power of the direct current sources increases, it becomes increasingly difficult to ensure the electromagnetic compatibility of the device. In view of this problem, the invention provides that a low-pass filter is connected upstream of the rectifier of the direct current source, the cut-off frequency of which is in the order of three times the mains frequency. Since a power supply unit under load primarily loads the mains with harmonics of an odd order, the load on the mains caused by harmonics can be effectively reduced by damping the third and higher harmonics with the help of the low-pass filter. The use of an LC filter connected as a second-order low-pass filter is particularly useful. In this case, a higher direct voltage can be obtained for a given mains voltage by increasing the resonance, which enables more stable operation of the fluorescent lamps and greater tolerance of the ballasts to differences between different lamp makes. By using suitable

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By carefully selecting the inductance and capacitance, it is possible to achieve an approximate phase equality of current and voltage while effectively suppressing harmonics, so that the power supply behaves almost like an ohmic load.
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In the following, preferred embodiments of the invention are explained in more detail with reference to the drawing.

Show it:
10

Fig. 1 is a block diagram of the irradiation device;

Fig. 2 a schematic circuit diagram of a power unit

a ballast with associated fluorescent lamp;
15

Fig. 3 Waveforms of various signals in the circuit according to

Figure 2;

Fig. 4 is a schematic circuit diagram of a DC voltage

source;

Fig. 5 shows the waveforms of the mains load for a DC voltage source according to Figure 4 and a corresponding DC voltage source without filter;
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Fig. 6 shows the frequency spectrum of the waveform of Figure 5 for the

DC voltage source without filter and the transfer curve of the filter; and

Fig. 7 and 8 a block diagram and a circuit diagram analogous to Figures

1 and 2 for another embodiment.

The irradiation device shown in Figure 1 as a block diagram has a group of fluorescent lamps 10 which are arranged in a relatively dense pack parallel to one another in the irradiation device.

TER MEER - MÜLLER - STEINMEISTER & PARIER ·"· · . :**; *"tOHP01/96/G

and are controlled by a ballast unit 12. The ballast unit 12 comprises a control unit 14, which is formed, for example, by a microcontroller, a power unit 16, a DC voltage source 18 and a low-voltage power supply 20. An optical sensor 22 and an operating console 24 are also connected to the control unit 14.

Each of the fluorescent lamps 10 has an output of 160 W and is controlled by an associated power unit 26. The power units 26 for all fluorescent lamps 10 in the group are arranged on a common circuit board and together form the power section 16. The direct current source 18 converts the mains voltage, for example a 50 Hz alternating current of 230 V, into a direct current of approximately 340 V and supplies all power units 26 with this direct current.

The control unit 14 is supplied with operating voltage by the low-voltage power supply 20 and generates control signals A and B for the power units 26 based on a program stored in the control unit and on signals that it receives from the optical sensor 22 and the operating console 24. In the example shown, all power units 26 receive the same control signals A and B during normal operation of the irradiation device, so that all fluorescent lamps 10 in the group are controlled synchronously. The total brightness generated by the group of irradiation lamps 10 is detected by the optical sensor 22, which then reports a brightness signal back to the control unit 14. Based on this signal, the brightness of the fluorescent lamps 10 is regulated to a setpoint that can be entered via the operating console 24. For example, the control panel is designed so that different skin types can be selected or entered and then the target value to which the irradiation intensity is regulated is calculated electronically based on the skin type. The lamp output is preferably regulated continuously or quasi-continuously (e.g. in steps of 2.5%, range from 25% to 100% of the maximum output).

In practice, the irradiation device will usually have several groups of fluorescent lamps 10, each of which is assigned a separate ballast unit 12. In this case, preferably a single

TER MEER - MÜLLER - STEiMElSTER &PARTNER;**· · , :**; *"loHP01/96/G

A control unit 14 is provided for all ballast units. Each group of fluorescent lamps is assigned its own optical sensor 22, and the control unit 14 generates a separate set of control signals A and B for each of the power units 16.

Figure 2 shows the basic structure of a single power unit 26. The power unit receives the direct voltage of +340 V from the central direct voltage source 18. Two power transistors Tl and T2 (FETs) are connected in series between the voltage input and ground.

Two capacitors C1 and C2 are connected in series in parallel to the transistors. The center C between the two transistors Tl and T2 is connected to an electrode 28 of the fluorescent lamp 10 via a choke Ll. The other electrode 30 of the fluorescent lamp is connected to the center between the two capacitors Cl and C2. A capacitor C3 and a resistor Rl are connected in parallel to the electrodes 28, 30 of the fluorescent lamp.

The gate electrodes of the transistors T1 and T2 are controlled in push-pull by the control signals A and B received from the control unit 14, as illustrated by the curves A and B in Figure 3. The control signals A and B have the same frequency and pulse width and are phase-shifted by half a period. In a known manner, electronic safety measures ensure that the pulses during which the transistors T1 and T2 are conductive do not overlap. When both transistors are blocking, an average potential of approximately 170 V is established at the point connected to the electrode 30 between the capacitors C1 and C2. When the transistors T1 and T2 open and close in push-pull, the potential at point C in Figure 2 takes on alternating positive and negative values with respect to the average potential, as illustrated by the curve C in Figure 3. This potential reaches the electrode 28 via the choke L1 and maintains the gas discharge in the fluorescent lamp 10.

The clock frequency of the control signals A and B and thus also the frequency of the pulsed voltage at point C is between about 30 kHz and 40 kHz during operation of the lamp. The capacitor C3 and the resistor Rl form an oscillating circuit with the choke Ll, the resonance frequency of which

TER MEER-MÜLLER-STEINMEISTER &rAr5T^ER ·**;·. *,'*, .tOHPOl/96/G

is slightly above the operating frequency of the lamp. Due to the excitation of this oscillating circuit, a certain heating current flows through the electrodes 28 and 30 of the fluorescent lamp 10 even in the pulse pauses in which both transistors T1 and T2 are blocked. This ensures that there are always enough charge carriers in the fluorescent lamp so that the gas discharge does not break off.

For a given clock frequency of the control signals A and B and a given inductance of the choke Ll, the strength of the current flowing through the fluorescent lamp depends on the duty cycle of the control signals A and B. The control unit 14 regulates the brightness of the fluorescent lamps 10 via the duty cycle of the control signals A and B. Curve C in Figure 3 illustrates the voltage curve with a larger duty cycle and correspondingly larger lamp power. Since all fluorescent lamps 10 in the group shown in Figure 1 are controlled with the same control signals A and B, mutual influence of the fluorescent lamps and the associated power units by interference signals is avoided.

Deviating from the described embodiment, it is also conceivable that each power unit 26 is controlled by the control unit 14 using individual control signals A and B. In this case, however, the signals supplied to the various power units should have the same frequency and a fixed phase relationship, preferably the same phase, and should only differ in the duty cycle. In this way, individual power control of each individual lamp can be achieved while largely suppressing mutual interference.

The circuit is designed so that the heating current through the electrodes 28 and 30 increases as the duty cycle decreases. In this way, stable lamp operation can be maintained even when the lamp is dimmed relatively strongly.

When the fluorescent lamp 10 is switched on, a sufficient ignition voltage must first be provided. For this purpose, the control unit 14 is designed so that the clock frequency of the control signals A and B when switched on gradually decreases from a high initial value of about 80 KHz to the operating frequency and in doing so reaches the resonance point of the voltage generated by the throttle.

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be Ll and the capacitor C3. The necessary ignition voltage is then provided by resonance oscillations of this oscillation circuit.

If the fluorescent lamp 10 is replaced by a lamp with a different power, for example a lamp with 100 W instead of 160 W, only the choke L1 and the capacitor C3 need to be replaced. By using a choke with a higher inductance, the power of the fluorescent lamp is reduced while the circuit and mode of operation remain otherwise unchanged. The capacitor C3 is adjusted so that the resonance point of the oscillating circuit is again in the correct frequency range.

In a preferred embodiment of the invention, the choke L1 and the capacitor C3 of each power unit 26 are combined to form an easily replaceable module 32 (plug-in module on the circuit board). Optionally, the module 32 and, if necessary, the resistor R1 can also be integrated into the base of the respective fluorescent lamp 10. If the irradiation device is to be converted to a lower lamp power, only the fluorescent lamps and, if necessary, the modules 32 need to be replaced. Lamps with different power can also be combined in a group and controlled by the same ballast unit 12.

In order to avoid overloading the network when switching on the irradiation device, it is advisable to switch on the lamps at different times. If the irradiation device has several lamp groups 10 with associated ballast units 12, the individual groups can be switched on at different times simply by programming the control unit 14 accordingly. If the individual lamps 10 of each group are also to be switched on at different times, the individual power units 26 must be able to be addressed independently of one another by the control unit 14. The control unit 14 then carries out the ignition procedures for the individual lamps one after the other by supplying the relevant power unit 26 with control signals at a clock frequency that decreases from 80 kHz to 30 kHz. When the lamps have ignited, however, all power units 26 are again controlled by the control signals A and B at the same frequency and the same phase in order to avoid mutual interference.

TER MEER-MÜLLER-STEINMEISTER & BARJ^ER .";·. ·"*· .IjOHPOI/96/G

To avoid interference during operation of the lamps.

In order to ensure stable, trouble-free operation of the fluorescent lamps 10 even when lamps of different makes are used in the same irradiation device or combined with one another in the same group, it is advisable to operate the power units 26 with a relatively high operating voltage and to limit the power by means of a correspondingly high inductance of the choke L1. From this point of view, an operating voltage of 340 V has proven to be particularly suitable. However, by rectifying the alternating mains voltage of 230 V that is usual in Germany with a conventional rectifier, only a direct voltage of around 310 V can be achieved.

Figure 4 shows a schematic diagram of the direct current source 18, with which the mains voltage of 230 V can be converted into the desired direct current voltage of 340 V and at the same time the electromagnetic compatibility of the irradiation device can be ensured.

According to Figure 4, the DC voltage source 18 has, in the usual way, a rectifier formed by four diodes D1-D4 and a downstream smoothing capacitor C4.

According to the invention, a choke L2 and a capacitor C5 are connected upstream of the rectifier, which are connected as a second-order low-pass filter. The operation of this circuit will be explained below using Figures 5 and 6.

Without the low-pass filter, the capacitor C4 would charge up to a voltage of about 310 V in the unloaded state. However, if a load - in this case the power unit 16 - is connected, a certain discharge of the capacitor C4 occurs during each half-wave of the AC mains voltage until either the diode pair D1, D3 or the diode pair D2, D4 becomes conductive and the capacitor is suddenly recharged. The load on the mains in this case corresponds to a waveform that is qualitatively represented by the curve 34 in Figure 5. It can be seen that this load is characterized by relatively sharp excursions with alternating opposite polarity and is strongly influenced by a sinusoidal waveform.

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The frequency spectrum according to Figure 6 therefore shows, in addition to a maximum at the fundamental frequency of 50 Hz, relatively pronounced maxima at the odd-numbered harmonics, i.e. at 150 Hz, 250 Hz, etc. The increasing use of consumers, especially those with high power, which burden the network with such harmonics, is making it increasingly difficult for electricity supply companies to guarantee a stable sinusoidal AC mains voltage of 50 Hz. For this reason, the harmonic load on the network should be kept within limits for consumers with high power.

In Figure 6, the transmission curve of the low-pass filter L2, C5 according to Figure 4 is shown at 36. This low-pass filter is designed so that the cut-off frequency is in the order of three times the mains frequency, i.e. around 150 Hz, and preferably somewhat lower. This relatively simple measure makes it possible to effectively suppress the harmonics and to give the mains load an approximately sinusoidal shape, as indicated by curve 38 in Figure 5.

The use of a second order low-pass filter also results in a certain resonance increase of the curve 36 below the cut-off frequency, with the result that this curve has a higher value at the mains frequency of 50 Hz than at the frequency 0. Due to this resonance increase, the voltage available at the output of the DC voltage source has the value of 340 V, which is optimal for the stable operation of the fluorescent lamps 10 and is slightly above the theoretically achievable value of 310 V - without the low-pass filter. In addition, for a given cut-off frequency of the low-pass filter, the inductance of the choke L2 and the capacitance of the capacitor C5 can be adjusted so that the current curve and the voltage curve are almost in phase, so that the DC voltage source 18 and thus the entire irradiation device on the mains behaves essentially like an ohmic load (cos φ = 1).

Figures 7 and 8 show a modified embodiment in which only a single power unit 26 ^' is provided for a group of several fluorescent lamps 10 (for example two to twelve fluorescent lamps). As can be seen from Figure 8, the power unit 26' in this case essentially comprises only the two power transistors T1 and T2. Each single

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A module 32 is assigned to each individual fluorescent lamp 10, which in this case in addition to the choke Ll and the capacitor C3, also contains the resistor Rl and the two capacitors Cl and C2. The individual modules 32 are connected in parallel to one another to the voltage of +340 V, to point C of the power unit 26' and to ground.

In this embodiment, the power transistors Tl and T2 are designed for the total power of the fluorescent lamps 10 in the group. The choke Ll and the capacitor C3 and, if applicable, the resistor Rl are, as in the first embodiment, adapted to the power of the respective fluorescent lamp 10. The capacitors Cl and C2 normally do not need to be specially adapted to the respective fluorescent lamp. The reason why a separate pair of capacitors Cl and C2 is provided for each module 32 is essentially that in this way, a sufficient capacitance can be achieved with commercially available capacitor components, which corresponds to the larger total power of the power unit 26'.

The advantage of the solution according to Figures 7 and 8 is that only two power transistors and therefore only two control lines are required for the control signals A and B. In addition, the wiring within the irradiation device is considerably simplified. The voltage of +340 V and the output signal C of the power unit 26' as well as the ground potential can be fed directly to the lamp group in the irradiation device via just three lines and only then branch off to the individual modules 32.

Claims (9)

TER MEER - MÜLLER - STEINMEISTER & BARKER .**· I ;**· ILoHPOl/96/G PROTECTION CLAIMS 1. Irradiation device with several fluorescent lamps (10) and associated electronic ballasts, characterized in that the power units (26; 26') of the ballasts for several fluorescent lamps (10) are fed by a common DC voltage source (18). 2. Irradiation device with several fluorescent lamps (10) and associated electronic ballasts, in particular according to claim 1 , characterized by a control unit (14) which controls the power units (26) of the ballasts for several fluorescent lamps (10), which are arranged immediately adjacent to one another in the irradiation device, with control signals (A, B) with the same frequency and fixed phase relationship. 3. Irradiation device according to claim 2, characterized in that the control signals (A ₁ B) supplied to the power units (26) are in phase. 4. Irradiation device according to one of the preceding claims, characterized in that the power units (26) are controlled by control signals (A, B) with variable useful pulse width. 5. Irradiation device according to one of the preceding claims, characterized in that the power units (26) of the ballasts are equipped with power switching elements (Tl, T2) which are designed for a power of at least 160 W per fluorescent lamp, that each fluorescent lamp (10) is assigned a choke (Ll) connected in series with the discharge path of the fluorescent lamp and a capacitor (C3) connected in parallel with the discharge path, and that the choke (Ll) and the capacitor (C3) form an exchangeable module (32) which is adapted to the actual power of the irradiation lamp (10). 6. Irradiation device according to one of the preceding claims, with a rectifier (Dl- D4) for converting the AC mains voltage into a DC voltage to be supplied to the power units (26), characterized in that a low-pass filter (L2, C5) is connected upstream of the rectifier, the cut-off frequency of which is in the order of three times the mains frequency TER MEER -MÜLLER- STEINMEISTER & E&RtfNER ·**· * . «· &Igr;&idigr;&Lgr;&EEgr;&Rgr;&Ogr;&Igr;/96/G - 14 - lies. 7. Irradiation device according to claim 6, characterized in that the low-pass filter has a choke (L2) and a capacitor (C5) and is connected as a second-order low-pass filter whose transmission curve (36) has a resonance peak at the mains frequency. 8. Irradiation device according to one of the preceding claims, characterized in that the ballasts are formed by a power unit (26') and by several modules (32), each of which is assigned to an individual fluorescent lamp (10) and contains a choke (L1) and a capacitor (C3) connected in parallel to the fluorescent lamp and is connected in parallel to one another to the same power unit (26'). 9. Irradiation device according to claim 8, characterized in that the power unit (26') contains two push-pull controlled power transistors (T1, T2) connected between the voltage of the direct voltage source (18) and ground, and that each module (32) contains two capacitors (C1, C2) connected in series between the voltage of the direct voltage source and ground, the connection point of which is connected to an electrode (30) of the fluorescent lamp (10).