AN ELECTRICAL PRESWITCHING DEVICE FOR FLUORESCENT TUBES WHICH PROVIDES A DISTORTION FREE LOAD OF THE NET

Abstract: A switching device for driving of gas discharge tubes using a high frequency alternating voltage from a low frequency alternating voltage source (Um), where the current of the latter becomes distortion free, comprising a low-pass filter (L1, C5), a bridge rectifier (D1-D4), a flattening condenser (C1), a switching means (SW1), and an oscillating circuit (L2, C6), and where the low frequency voltage (Um) is filtered and rectified, where a circuit is formed by the flattening condenser (C1), the inductance of the oscillating circuit (L2), and the switching means (SW1), and where closing high frequency and alternating (Usw1, Ueg) is generated by the switching means (SW1), where a discharge tube (La) is connected to the high frequency voltage source (Usw1) via a condenser (C7), whereby the filtered and rectified voltage is arranged to be added to the flattening condenser (C1), whereby the condenser (C2) is charged from the low frequency voltage source (Um) via the low-pass filter (L1, C5), the rectifying bridge (D1-D4) and one outlet from the high frequency voltage source (e) during one part of the period (moment 2-3) of the high frequency voltage (Ueg) and where the condenser (C2) is charged in opposite direction from the high frequency voltage source (e), the diode (D5), and the flattening condenser (C1) during another part of the period (moment 3-2).

Description: AN ELECTRICAL PRESWITCHING DEVICE FOR FLUOROSCENT TUBES WHICH PROVIDES A DISTORSION FREE LOAD OF THE NET. DESCRIPTION Techni cal ield The present invention discloses a switching device for the driving of gas discharge tubes (f luoroscent tubes) using a high frequency alternating voltage (about 30 kHz). The switching device is intended to be connected to a normal distribution net for alternating voltages (about 50 kHz). The invention also encompasses switching devices to pro¬ vide such a load of the alternating voltage source that the load current becomes substantially uniform with the alternating voltage i.e. the form factor becomes h gh, and the amount of overtones of the load current becomes low. Prior art It is since long known that gas discharge tubes give a higher light yield if the are driven with an alternating voltage, which has a higher frequency than the normal net voltage. In practise the best light yield is obtained at 30 kHz. To obtain this high frequency alternating voltage it s suitable first to rectify the net voltage and to flatten it with a condenser. The direct voltage obtained is then chopped to an alternating voltage of suitable amplitude and frequency. When rectifying followed by a flattening n apparatuses of above, the load current on the net will be highly dis¬ torted. This means a number of serious drawbacks. Other electrical equipment on the net can be disturbed. It means as well that the efficiency of the electrical distribution is lowered, and that the transmission capacity of the dis- tribution net is lowered. To reduce the above mentioned distorsion several methods are used today. Often the apparatus is connected in series SUBSTITUTE with an inductance. This becomes relatively large and ex¬ pensive, the efficiency of the apparatus is reduced, and increases heating. According to another method the net is connected in series with a relatively small inductance, and a switching device, which using a high frequency pul¬ sation technique, gives a distorsion free load of the net.(Cf EP-A1-0 013 866). The ingoing components will, however, become relatively expensive. According to a third method the high frequency alternating voltage which is normally created in the above mentioned apparatuses, is used, together with a condenser, and a diode, to obtain a distorsion reduced load of the net. Solutions of this principle are described in the two Ger- man DAS DE-A1-3 222 534, and DE-A1-3 319 739. The present invention make use of this method but needs a smaller num¬ ber of components than the devices according to the above mentioned published patent applications, and give a comp¬ letely distorsion free net load, in comparison with the first mentioned publication. FIRGURE 1. Circuit description In the description below an example of suitable values of the components used when a standard fluoroscent tube (La) of 36W shall be driven from a net of 220V, 50Hz is given. List of components: C1 10 ,uF, L1 40 mH C2 25 nF, L2, winding S1 1 H C5 500 nF, ratio S1:S2 C6 10 nF 2:1 A sinusoidal alternating voltage (Um, about 50Hz) from a distribution net is fed in between points a, and b. The net voltage passes a conventional lowpass filter compris- ing an inductance L1 and a condenser C5. The net voltage is full wave rectified by the rectifying diodes D1-D4. Via the diode D5 the flattening condenser C1 is charged by the rectified current. The inductance L2 forms together with SUBSTITUTE SHEET the diode D6, and SW1 a series circuit connected over C1. Parallel to the winding S1 on the inductance L2 is a con¬ denser C6. S1 is also loaded by the gas discharge tube La in series with the condenser C7. From the negative pole on C1 a series circuit is formed by the winding S2 and the condenser C2 to the cathode of D5. SW1 is a switching means, suitable of semi-conductor type, transistor, thyristor, or the like. SW1 is controlled in a manner known to be alternating conducting with a fre¬ quency of abotu 30 kHz. The ratio between the windings S1 and S2 is such that the top-to-top value of the alternating voltage Ueg is as high as the voltage over C1 (when the tube has lightened, and the driving conditions has been stabilized). In the Exam¬ ple the rati o i s 2: 1. FIGURE 2 Figure 2 corresponds to the following Examples. Here the curve forms of different voltage and currents are shown along a time axis. Uswl shows the high frequency voltage over SW1. Ueg shows the voltage between the points e, and g, and Ueg shows the voltage between points c, and g of Fig. 1. The point g of Fig. 1 has per definition the pon- tential zero. Um is the instantaneous net voltage and Uc1 is the voltage over C1. Ic2 shows the alternat ng current through C2, and Im the net current (unfiltered) according to the respective arrows in Fig.1. Fig. 2 shows the time lapse in a moment when the net vol¬ tage Um has its top value. In Fig. 2b the net voltage has half its top va lue. FIGURE 1. Functional description An oscillating circuit is formed by the inductance L2 and the capacitance C6. A conventional controlling circuit SUBSTITUTE SHEET brings SW1 to a conducting mode between moments 0, and 1 of Fig. 2. Thereby a current moves from the plus pole of the condenser C1 through S1, D6 and SW1, to the negative pole of the condenser. Thereby energy is stored in the os- cillating circuit (L2/C6). When SW1 disconnects this cur¬ rent (in moment 1) an oscillation will begin. The oscilla¬ tion obtains its energy from C1, each time SW1 conducts. To simplify the explanation we disregard for a moment the influence of C2, and S2 on the circuit. Lightening of the tube As we saw earlier, energy is provided to the oscillation circuit S1/C6 during each high frequency period. Prior to the gas discharge tube has lightened only an inconsider¬ able amount of the energy added is consumed, whereby the amplitude of the oscillation continously increases. The gas discharge tube La is, via the condenser C7 connected in parallel to the oscillating circuit. When the amplitude over the oscillating circuit has become high enough the tube lightens. When the tube has lightened, as much energy is consumed, as is added, and the amplitude of the oscil¬ lation is stabilized. As evident from Fig. 2 the voltage over * SW1 is sometimes negative (moment 3). The diode D6 prevents that negative current flows through SW1 during these moments, which could be the case if SW1 has no ability either to suppress in the back direction. A negative current through SW1 should restrict the amplitude of the oscillation previous¬ ly mentioned, which should render it more difficult to lighten the tube. The diode D6 is, however, not necessary for the function of the switching device, and can thus be deleted (short-circuited). Load of the net The high frequency alternating voltage Ueg has a frequency which is about 600 times higher than the net frequency. SUBSTITUTE SHEET During a period of the high frequency alternating voltage the net voltage thus does not manage to change consider¬ ably, but can be seen as a stable direct voltage. This view simplifies the understanding of the funct on of the invention. We presume, for the sake of simplicity, that the condenser C1 is very large (1F), so that its voltage is substantially constant during a 50 Hz-periode. EXAMPLE A We shall now study what happens during a period of the high frequency alternating voltage. In the first study we presume that the net voltage Um just is at its positive top value (se Fig. 2a) . As the filter L1/C5 is a low-pass fi lter the voltage over C5 follows substantially the low frequency voltage Um. We start the study in moment 2 according to Fig. 2a, when the voltage Ueg has its positive top value. Up to this mo¬ ment the diode D5 has been conducting. The end of the con- denser C2 denoted c(C2c) has thus in this moment a poten¬ tial as high as the plus pole on the condenser C1. Just as the voltage Ueg starts to fall the potential thus falls on the end of the condenser C2 denoted e (C2e) . Due to the influence of the condenser C2 the potential on C2c wi ll thereby also fall. D5 becomes preloaded in the back direc¬ tion, and thus suppresses. The net voltage Um of the brid¬ ge D1-D4 is, up to moment 2a, lower than Ueg, whereby even the diodes of the bridge suppress. The end C2c is thus in this moment electrically disconnected and falls at the same rate as the end C2e falls. In the moment 2a the voltage Ueg has, however, fallen so far that it becomes as high as the instantaneous net vol- « • tage Um. Thereby the diodes D1 and D4 of the bridge are preloaded in the forward direction (we study a positive half period of the net voltage), and C2 wi ll in the future be charged from the net, up unti l Ueg reaches its minimum value, in moment 3. Whi le C2 is being charged, moment 2a SUBSTITUTE SHEEI to 3, thus a positive current Ic2 flows through the con¬ denser C2, from the net, which also is evident from the curves Ic2, and Im of Fig. 2. The potential in the point c is kept at the same level as the net voltage as the di- odes D1 and D6 conduct. This is evident from the curve Ueg, as well. In moment 3 the voltage Ueg starts to raise due to the LC-osci I lation between S1 och C6. As the end e of C2 (C2e) raises the end C2c will also raise. Thereby D1 and D4 sup¬ press in the bridge. Even D5 is preloaded in the back di¬ rection, and suppresses, whereby the voltage Ueg will raise in the same way as Ueg. Ueg and Ueg will thus be uniform up to the moment 1a, when Ueg becomes as high as Uc1. (The flat part of the curve Ueg, moment 0-1, depends on that SW1 then is conducting) . Thereby D5 becomes pre- Uc1. The flat part of the curve Ueg, moment 0-1, depends on that SW1 then is conducting). Thereby D5 becomes pre¬ loaded in the forward direction, and will conduct, as long as Oeg raises, up to moment 2. From moment 3 through mo¬ ment 0 and up to moment 2 a current Ic2 will thus flow from the point g through S2, C2 and D5 up to the positive end of C1. This current thus charges C1. During the high frequency period studied C2 has thus been charged from the net (moment 2a-3) in order then to be discharged to C1 (moment 1a-2). This means that energy has been transferred from the net to the condenser C1. EXAMPLE B In this example we will study a high frequency period du¬ ring which the net voltage Um is on its half top value (see Fig. 2b). The curves Uswl and Ueg are identical with their corresponding units in the first Example, Fig. 2a)T The course of events is in principle the same as in the aforegoing Example. However, moment 2a now occurs later in the high frequency period. The voltage Um is, as said. SUBSTITUTE SHEET in this case lower, and first after the Ueg has fallen all the way down to this low level the diodes D1, and D4 still open, and the charging of C2 will start. C2 will thus re¬ ceive a lower amount of charge in this period, which is also evident from the curve Ic2. As the voltage Ueg in this Example has a lower starting level in moment 3, it will also take a longer time before Ueg reaches up to the voltage Uc1 in moment 1a. The nega- tive charging pulse through C2 will thereby be smaller as well, which is evident from the curve Ic2. Negative net periods In the example above, we have presumed that the net vol- tage has been in a positive half period. During the nega¬ tive half period the course of events will be the same, however, with the difference that instead the diodes D2, and D3 will be open between moments 1a and 2, and that the current pulse Im will be negative. The zero point passage of the net voltage We will now study a high frequency period which occurs du¬ ring the moment when the instantaneous value of the net voltage is zero. In moment 2 of Fig. 2 (a and b) the voltage Ueg is on its positive top value. Ueg falls between moments 2 and 3 to its negative top value. The ratio between the w ndings SI and S2 are, according to the above, so done that the top- to-top voltage of Ueg is as high as the voltage Uc1. Bet¬ ween the moments 2, and 3 the end e of the condenser C2 (C2e) thus falls Uc1 volts. Following this the end C2c also tends to fall Uc1 volts. As the starting potential of Ueg (in moment 2) was Uc1 volts, Ueg thus tends to fall down to zero. In the situation now studied Ueg will fall all the way down to zero (in moment 3 of Fig. 3). As the net voltage SUBSTITUTE SHEET is zero the diodes D1-D4 will never become preloaded in the forward direction and open. The condenser C2 will thus not receive any charge from the net during this high fre¬ quency period. Sinusoidal net current We have seen in the aforegoing discussion that the voltage Ueg in moment 3 of Fig. 2 strive to reach the potential zero. In Examples A and B above, we have, however, seen that the net voltage instead charges the end c of the con¬ denser C2 receives thus in ea.ch high frequency period a charge from the net, which charge is proportional to the instantaneous net voltage. The mean value of the current with which C2 loads the net during a high frequency period will thus be proportional to the instantaneous value of the net voltage. If one should disregard the high frequency pulses of the net current Im, which is created by the device, and only regard the mean value of the net current calculated over each high frequency period one will find that the net cur¬ rent always is proportional to the instantaneous net vol¬ tage Um. As the net voltage is sinusoidal the net current will also become sinusoidal and. in phase with the net vol- tage. The high frequency component which the net current Im will comprise i " s filtered off in a known way by means of the low-pass filter L1/C5. Thus we have obtained the distor- sion free net current, which is one of the objects of the invention. Other curve shape. Using the knowledge of above about the function of the switching device one realizes as well, that the distorsion free net voltage wanted is obtained independent of the curve shape of the voltage Ueg. The only demand one has to have on this voltage is that its top-to-top amplitude SUBSTITUTE SHEEI is as high as the voltage Uc1, and that its frequency is constant. As the voltage Ueg is transferred to Ueg via a condenser C2 it does not matter either around which direct voltage level (mean level) the voltage Ueg alternates. The condenser C1 is charged, as we have seen above by cur¬ rent pulses from C2. The larger the condenser C2 is, the larger will this charging current to C1 become. C1 is dis¬ charged by the current, which the components to the right of C1 in Fig. 1 consume. The consumption of current in¬ creases, the higher the voltage Uc1 is. By increasing or decreasing the capacitance of the condenser C2, the cur¬ rent, which s led to C1, can be increased or decreased, respectively. Thereby the voltage level Uc1 can thus be increased or decreased, respectively, and be brought to a requested value. If the load should not be constant the ingoing current can be regulated in different ways according to the following description. In the above functional description we have presumed that the capacitance of C1 is very large. The capacitance valu¬ es which one uses in practise (10 ,uF in the Example above) means that the voltage Uc1 will vary somewhat, and with a frequency corresponding to the double net frequen¬ cy. As the voltage Uc1 decreases the ampl tude of the vol¬ tage Ueg will also decrease, as this is generated by means of Uc1. The demands which, as above, is put on the voltage Ueg (see heading "Other curve shape") will thus sti ll be met . coupling for interference compensation. In switching devices for gas discharge tubes at a high frequency, radio interferences are generated. These are generally caused by a capacitive circuit between parts in the device, which parts lead high frequency voltage, and the casing of the device. FIGURE 3 List of components: C1 10 ,uF, L1 40 mH C2 25 nF, L2, winding S1 0.25 mH C5 500 nF, winding S1b 0.25 mH C6 20 nF, ratio Sl :Slb.S2 C6b 20 nF, 1:1:1 C7 10 nF C7b 10 nF According to this invention a very large part of these in¬ terfering voltages can be eliminated using a circuit of Fig. 3. Here the winding S1 has been di ided into two parts, compared ith the circuit of F g. 1. Also the con¬ denser C6 has been split into two, C6, and C6b. The switching means SW1 has been moved and been connected into the circuit midway between the two partial windings S1, and S1b. The gas discharge tube La has here been connected parallel to the switching means SW1 via C7, and C7b. The switching device of F g. 3 functions by principle n the same way as the device of Fig. 1. Also the curves of Fig. 2 are aplli cable to Fig. 3. The gas discharge tube is still connected in parallel to the LC-circuit S1 +S1 b/C6+C6b, seen from an alternating voltage view, as Ci, seen from an alternating voltage view, connects the upper end of S1 with the lower end of S1b. The points h, and j of Fig. 3, will lead high frequency alternating voltages which can cause radio interferences. The voltages in the respective points, are, however, uni¬ form but counterd rected. According to the invention the switching de ice is mechanically bui lt in such a way that the two points have the same capacitance to the casing of the device. Thereby the two interfering voltages will eli¬ minate each other, so that the radio interferences will SUBSTITUTE SHEEI be practically eli inated. Also the voltages appearing at both ends of the gas dis¬ charge tube can normally generate radio interferences. In the circuit of Fig. 3 these two interfering voltages wi ll eliminate each other as well. The low radio interference level means most often that any additional radio interferences filter does not need to be used. This makes the switching device cheap and reliable in running, simultaneously with an increase in efficiency. The end e of the condenser C2 is in Fig. 3 connected to the upper end of the winding S2. The ratio between the winding S1b (half of S1) and S2 is normally 1 :1. This means that the voltage in point h is the same as in point e. The end e of C2 can thus be connected to the point h and the winding S2 be eliminated. This makes of course the devi ce cheaper. In accordance with what has been explained under the head¬ ing "Other curve shape" above, the end e of the condenser C2 can equally well be connected to the point j of Fig. 3. When the winding S2 has been eliminated in accordance ith the above and C2 is connected to h, a complete symmetry is not at hand between the voltages in the points j, and h, respectively. The asymmetry is created due to the fact that the windings S1, and S1b are differently loaded and the fact that the magnetic connection between these two never can be perfect. FIGURE 4 List of components: C1 10 .uF, L1 40 mH C2 12.5 nf, L2, winding S1 0.25 H C2b 12.5 nF, winding Sib 0.25 mH C5 500 nF, ratio Sl :S1b 1 :1 SUBSTITUTE SHEET C6 20 nF C6b 20 nF C7 10 nF C7b 10 nF Using a switching device of Fig. 4 this problem has, how¬ ever, been solved. Here the condenser C2 has been split into two equal condensers C2, and C2b. In order to achieve full symmetry the diode D5 has also been replaced by two diodes D5, and D5b. The complex S1, C2 and D5 functions in this switching de¬ vice in the same way as the corresponding components of the previously described switching devices. The complex S1b, C2b and D5b functions analogously, but with opposite polarity on voltages and currents. Regulation According to the invention the effect that can be drawn from the net can be regulated in several ways. Varying the frequency The effect which is drawn from the net is proportional to the frequency of the high frequency alte-rnating voltage. By varying the frequency in accordance with known methods (cf. e.g. EP 0 065 794), the net effect drawn can thus be varied. Varying the capacitance The net voltage drawn is also proportional to the capaci¬ tance of the condenser C2. By replacing C2 with condensers ha ing different capacitances, the net effect can thus be varied. The switching between different condensers can be made by means of mechanical switches, relays, or switching means of semi-conductable type. Switch control SUBSTITUTE SHEET . In accordance with the invention the diode D5 can be re¬ placed by a thyristor or be connected in series with an¬ other suitable switching means (e.g. a transistor) . By controlling this switching means to be open during some of the high frequency period only, one can regulate the effect drawn. Even the two diodes D5, and D5b of Fig. 4 can be replaced and controlled in accordance with the above given princip- Les - In accordance with the present invention several gas dis¬ charge tubes (La) with connected condenser /condensers (C7/C7+C7b) can be connected in parallel with each other in accordance with the dotted part of Figs. 1, 3, or 4. The method is not restricted to two tubes only but can be used for an unli ited amount of tubes. In accordance with the invention the gas discharge tube (-s ) can be connected via one or more additional windings of the inductance L2. This can be suitable if one should like to use tubes with a high ignition voltage. The addi¬ tional windings can also be connected in series with the ordinary windings. Comparison with known construct ons. Below a comparison with the prior art technique is made in order to show the advantages of the present invention. EP 0 013 866 The switching device of EP 0 013 866 request five switch¬ ing components (S1,S2, S2, S4, S7) to obtain the same technical performance as the present invention gives using only one switching component of a comparative type. Com- pared with the present invention the prior art device is thus considerably more expensive, and has a worse reliabi¬ lity in runni ng . SUBSTITUTE SHEET DE-A1-3 319 739 two switching components (9,10 of Fig. 1) are required compared to one of a comparative type. The advantageous interference compensation obtained using the present invention can not be obtained in accordance with DE-A1-3 319 739. DE-A1-3 222 534 In accordance with DE-A1-3 222 534 two switching devices are also required (T1, T2 of Fig. 1) compared to one of a comparative type. The advantageous interference compen¬ sation obtained in accordance with the present invention can not be obtained using DE-A1-3 222 534. SUBSTITUTE SHEE

Claims: CLAIMS . 1. A switching device for driving gas discharge tubes using a high frequency (about 3D kHz) alternating voltage (Uswl) from an alternating voltage source (Um) having a considerably lower frequency (about 50 Hz) where the cur- rent of the low frequency alternating voltage source be¬ comes substantially distorsion free comprising a low-pass fi lter (c1,C5), a bridge rectifier (D1-D4), a flattening condenser (CD, a switching means (SW1), and a osci llating circuit (L2, C6), and whereby the low frequency alternating voltage (Um) is fi ltered and where the low frequency alternating voltage (Um) is fi ltered by said low-pass fi lter (L1, C5) and rec- tified by the rectifying bridge (D1-D4), where a current circuit is formed by at least the flatten¬ ing condenser (C1), the inductance of the osci llating cir¬ cuit (L2), and the switching means (SW1), and where a high frequency and alternating voltage (Uswl, Ueg) is generated by periodically closing and opening of the switching means (SW1), whereby energy is transferred from the flattening condenser (C1) to the osci llating cir¬ cuit (C2, C6), and where a gas discharge tube (La) is intended to be con- nected to one of the outlets of the high frequency alter¬ nating voltage source (Usw1 ) via at least one condenser (C7), characteri zed i n that the fi ltered and rectified voltage, via a connection in which at least one diode (D5) is present, is arranged to be fed to the flattening condenser (C1); that a condenser (C2) is in its one end (C2c) connected to the connection between the rectifying bridge (D1-D4) and the diode (D5), and in its other end (C2e) is connec- ted to an outlet (e) from the source of the high frequency alternating voltage, whereby the condenser (C2) is charged from the source of the low frequency alternating voltage SUBSTITUTE SHEET (Um) via at Least the Low-pass filter (L1, C5), the recti¬ fying bridge (D1-D4), and one outlet of the source of the high frequency alternating voltage (e) during one part of the period (moment 2-3) of the high frequency alternating voltage (Ueg), and where the c.ondenser (C2) is charged in opposite direction via at least one outlet from the source (e) of the high frequency alternating voltage, the diode (D5), and the flattening condenser (C1) during another part of the period (moment 3-2) of the high frequency al- ternating voltage (Ueg). 2. A switching device according to claim 1, characterized in that the inductance of the oscillating circuit (L2) has two partial windings (S1 , Sib), whereby one end of each partial winding (j, and h, respectively) wi ll generate one high frequency alternating voltage each, where these two alternating voltages are substantially uniform but oppo¬ site directed to each other. 3. A switching device according to claim 2, characterized in that an additional diode (D5b) is present in that con¬ nection which provides the fi ltered and rectified voltage to the flattening condenser (C1), that an additional con¬ denser (C2b) is in its one end connected to the connection between the rectifying bridge (D1-D4) and the diode (D5b) and in its other end is connected to an outlet (h) from the source of the high frequency alternating voltage, whereby the condenser (C2b) is charged from the source of the low frequency alternating voltage Um via at least the low-pass fi lter (C1, C5), the rectifying bridge (D1-D4) and one outlet of the source (h) of the high frequency al¬ ternating voltage during one part (moment 2-3) of the pe¬ riod of the high frequency alternating voltage (Ueg), and where the condenser (C2b) is charged in the opposite di- rection, via at least one outlet of the source (h) of the high frequency alternating voltage, the diode (D5b) and the flattening condenser (C1) during another part (moment 3-2) of the period of the high frequency alternating vol- BSTITUTE SHEE t a g e U e g ) . 4.A switching device according to claims 2, or 3, charac¬ ter zed in that the source of the igh frequency alternat- ing voltage has two outlets (j,h) the voltages of which are in anti-phase, whereby a gas discharge tube (La) is intended to be connected to said outlets via at least two condensers (c7, C7b) having substantially the same capaci¬ tance, where one condenser (C7, C7b) is intended to be connected to each end of the gas discharge tube (La) whe¬ reby capacitively connected interfering currents from the both ends of the gas discharge tube to the casing of the device eliminate each other. 5. A switching device according to claims 1, 2, or 3, characterized in that the gas discharge tube (La), and the condenser (C7) being in series with the tube are connected in parallel to one or more additional tubes, each being connected in series with one additional condenser. 6. A switching device according to claim 4, characterized in that the gas discharge tube (La) and the condensers (C7, C7b) in series with said tube (La) are connected in parallel to one or more additional tubes, each of the them being connected in series with two additional condensers each. SUBSTITUTE SHEEC

Inventors: LINNMAN SVEN NILS JOHANNES, LINNMAN, SVEN, NILS, JOHANNES
Applicants: INNOCAP AB, INNOCAP AKTIEBOLAG
Application year: 1986
Main classification: H05B41
IPC codes: H05B41