FI81943B - Electronic ballast system for vapour discharge tube - Google Patents

Description

81943

Electronic current limiting system for gas discharge pipes (Separated from patent application 83 0324)

The present invention relates to a current limiting system for gas discharge pipes.

Current limiting systems for gas discharge tubes and fluorescent light bulbs are known per se and comprise current limiting systems for a plurality of flue-resonant light bulbs as well as for individual flue-resonant light bulbs. However, many of the previously known electronic current limiting systems require a relatively large number of components, which has led to a high space requirement for current limiting systems. The large space requirement is partly due to the number of components included in the circuit, but also to the need for additional components to remove the heat generated by the electronic components.

Other types of current limiting systems are also known which operate at relatively low frequencies but have very low operating efficiencies.

It is an object of the present invention to provide electronic current limiting systems for fluorescent light sources which are highly efficient at converting electrical energy into electromagnetic energy in the visible range of the electromagnetic spectrum and which require as few electronic components as possible, minimizing heat generation and allowing installation in small spaces. Other objects and advantages of the system according to the invention will become apparent from the description below.

It is an object of the invention to provide an electronic current limiting system for lighting systems comprising 2 81943 a gas discharge tube having first and second glow electrodes, the current limiting system comprising: a) a first capacitor (C2) electrically connectable to the first glow electrode (30) of said gas discharge tube (12); ) a transistor (Tr) having a collector (38) connected to the first capacitor on a different side from the first glow electrode (30), c) a transformer (T) having a primary winding (22) connected from one terminal (B) of said transistor (Tr) and a connection point of said capacitor (C2) and connectable to a pulsating DC source from one terminal (A), and having a secondary winding (24) connected at one terminal (C) to the base (44) of said transistor and from the other terminal to the emitter (42) of said transistor to form a positive feedback past the transistor (Tr) , and d) means for generating and conducting a pulsating voltage to a second glow electrode (32) of said gas discharge tube, comprising a second capacitor (C3) connected in series between a secondary winding (24, terminal D) and one electrode of said second glow electrode (32), said second the second electrode of the glow electrode (32) being capable of closing the positive feedback to the emitter (42) of the transistor (Tr).

The invention is further elucidated with reference to the following:. to a drawing showing a circuit diagram of an electronic current limiting system according to the invention for use in connection with a single gas discharge pipe.

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The figure shows an electronic current limiting system 10 according to the invention for one gas discharge tube 12, which is also of the conventional fluorescent type. As will be explained below, the gas discharge pipe 12 is an integral part of the circuit forming the electronic current limiting system 10. System 10 operates at a very high frequency compared to previously known fluorescent lighting systems. Known fluorescent lighting systems operate at approximately twice the mains frequency, or at approximately 120 Hz. The electronic current limiting system in question, on the other hand, operates at a frequency of about 20,000 hertz, which has the advantage of minimizing all kinds of flicker effects. Furthermore, at a high operating frequency, the average light output of the gas discharge tube 12 is substantially higher than that provided by previously known fluorescent lighting systems at a given power source output. Further, as will be apparent from the following paragraphs, the operating period of the system 10 will be at a minimum, so that the reliability will be improved for the electronic components included in the system. Furthermore, with the low operating period of the electronic current limiter system 10 in question, it is achieved that the temperature gradients and temperature rises of the electronic components will be at a minimum compared to the previously known current limiter systems. Minimizing the temperature effects increases the overall reliability of the current limiting system 10 while minimizing overheating problems.

As shown in the figure, the AC power supply 14 is electrically connected to the switch W by the power cord 18. The AC power supply 14 may be a standard 120 N or 200 V AC power supply, as is the case in most households, although other power supplies may be used. The values given below require 120 V AC 4 81943 tocurrent. The switch is a standard on / off switch designed to connect the circuit and connect the current conductor 16 to the conductor 18 in its connected position. The diode input line 16 is connected to the anode side of the diode Dj, which may be a conventional, commercially available diode of the type designation 1N4004. Diode Dj operates like a conventional half-wave rectifier, providing half-wave rectification of the AC pulse coming from conductor 16, such half-wave rectification pulse being present in the output conductor 20 on the cathode side of diode Dj.

The capacitor Cj is connected from its opposite poles to the output of the diode Dj and to the return current conductor 34, respectively. Thus, the capacitor Cj is connected in parallel with the diode Dj and the alternating current source 14, as is clear from the circuit diagram. In this application, the capacitor Cj has a value of about 100 microfarads and acts as a filter during charging during the half-cycle, during which the diode Dj drops current through and discharges during the rest of the cycle. The voltage applied to the transformer T in the conductor 36 is thus a direct current with a small waviness corresponding to the frequency of the network.

The pulsating DC current is applied to the transformer T, its primary winding conductor 36. The transformer T is a ferrite core type transformer and is characterized in that it allows the core to saturate at a relatively early stage during the voltage rise period and voltage drop phase with each pulse acting on the primary. The amplitude of the secondary voltage pulse is limited to a certain value by the ratio of the number of winding turns 22 and 24 of the primary and secondary windings. However, it is to be understood that the energy applied to the base 44 of the transistor Tr is a function of both the voltage ratio and the derivative provided by the resistor C3 and the resistance of the second glow electrode 32. The primary winding 22 has natl 5 81943 terminals A and B and the secondary winding 24 has corresponding terminals C and D. The transformer T is of conventional construction and in the embodiment shown herein may suitably comprise a primary winding with 160 turns of AWG 28 wire wound around a ferrite core . The secondary winding 24 of the transformer T is made of about 18 turns of AWG No. 28 wire. As can be seen from the diagram, the transformer T is phased so that when a voltage impulse occurs at terminal B with respect to terminal A in the primary winding 22, a proportional voltage change between terminals C and D in transformer T's secondary winding 24 is obtained. between. Thus, when an ascending voltage is applied to the collector of the transistor Tr, the opposite pole voltage is applied to the base 44 of the transistor Tr.

The output of the primary winding 22 from terminal B in conductor 40 is connected to collector 38 of transistor Tr by conductor 60. Primary winding 22 is also similarly connected to capacitor C2 by conductors 40 and 50. This type of connection thus provides parallel paths to the current exiting primary winding 22.

Transistor Tr is a conventional, commercially available NPN type. Transistor Tr includes collector 38, base 44, and emitter 42. One transistor Tr that can be used successfully is the commercial transistor MJE13002, manufactured by Motorola Semiconductor, Inc. Transistor Tr acts as a switch in current limiting systems 10 and current passes through transistor Tr when the voltage at base 44 relative to emitter 42 is above a certain value, which is 0.7 V for a given transistor Tr referred to above. the drop between the base 44 and the emitter junction 42 is typical of this type of silicon transistor Tr.

Current also flows from terminal B of the primary winding 22 through the second conductor 50 to the first capacitor C2. The first capacitor C2 is a commercial capacitor with a value of about 0.050 microfarads. In the normal situation, when the current passes through the primary winding 22 of the transformer T, the first capacitor C2 is charged with the voltage prevailing at the terminal B. The output of the first capacitor C2 is supplied through the conductor 70 to the other end of the first glow electrode 30 of the gas discharge tube. When this glow electrode is positive with respect to the second glow electrode 32, the electrons are attached to the glow electrode 30; correspondingly, when the glow electrode 30 is negative, electrons are removed and the negative glow electrode 30 is heated by electron bombardment. When the transistor Tr is in the "on" state, the first and second glow electrodes 30, respectively. 32 are the cathode and the anode, respectively, when the transistor Tr is in the "off" state, the first glow electrode 30 is the anode and the second glow electrode 32 is the cathode. Initially, as base 44 becomes more positive, electrons flow from emitter 42 to collector 38. This causes output conductor 40 to become more negative than terminal A. Simultaneously, an electron current flows from the first glow electrode 30 through the tube 12, the second glow electrode 32, the conductor 80, the emitter 42 and the collector 38 to the conductor 60 and 50 and finally to the capacitor C2. Thus, the first glow electrode 30 acts as a cathode connection during this period of the cycle.

The gas discharge tube 12 may be a standard type of commercially available fluorescent tube, for example a 20 W tube labeled F20T12 / CW. As can be seen, the gas discharge tube 12 is an integral part of the electronic flow.

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7,81943 in the limiter system circuit 10. The second glow electrode 32 is connected to the return conductor 34 of the AC power source 14 by a conductor 80. During this phase of the illumination cycle, the second glow electrode thus acts as an anode to the discharge tube 12. . In particular, the gas discharge tube 12 of the above-mentioned type has a resistance of approximately 1100 ohms.

The second glow electrode 32, in contrast to the first glow electrode 30, has a measurable through current used to heat the glow electrode 32 with the Joule effect and contributes to the inonization of the gas in the fluorescent tube 12 in the gas discharge. The current flowing through the second glow electrode 32 is provided by the secondary winding 24 of the transformer T. In the transformer T used, the secondary winding 24 is formed of 18 turns of a wire 28 wrapped around a ferrite core, as explained above. The terminal D of the secondary winding 24 is connected to the second capacitor C3 by a conductor 46. The current present in the conductor 46 is separated by a capacitor C3 and exits through a conductor 48 which is directly connected; to the second glow electrode 32, as shown in the figure.

The second capacitor C3 also operates to provide the desired operating cycle at the resonant frequency of the inductance of the secondary winding 24, which winding is connected to the capacitor C3.

With respect to the secondary winding 24 of the transformer T, it should be noted that it is phased with respect to the primary winding 22 so that a voltage rise across the primary winding 22 from terminal A to terminal B causes a voltage rise in the secondary winding 24 such that terminal C rises to terminal D; · 'Den.

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The current flowing through the second glow electrode 32 is returned to the secondary winding terminal C of the secondary winding 24 via a second glow electrode output conductor 80, and, either a diode element D2 or a base emitter junction defined by transistor Tr elements 42 and 44, and then back to terminal 24 C. Diode D2 is a commercially available diode element, such as that sold under Model No. IN4001.

Determining whether current flows through diode D2 or transistor Tr is provided by the polarity of the secondary voltages of the secondary winding 24. Thus, the system has a complete current cycle with each half cycle of the secondary voltage produced.

For possible facilitation of understanding of the electronic current limiting system 10, the overall system may be thought of comprising a primary circuit and a secondary circuit. The primary circuit operates to provide a discharge current through the gas-discharge tube 12 between the first and second glow electrodes 30 and 32. The primary circuit includes a primary winding 22 of a transformer T, the primary winding 22 being electrically connected at its opposite terminals to a first glow electrode 30 and an AC power supply 14. A detailed view of the primary circuit The current path from the first capacitor C2 further passes to the first glow electrode 30 through the resistor of the tube 12 to the glow electrode 32, further to the output conductor 80 and finally to the return conductor 34 and the AC power supply 14. The primary circuit provides positive and negative switching voltage pulses with When a positive pulse is applied to the base 44 of the transistor Tr from the secondary circuit, the transistor Tr enters its "on" state. The collector 38 quickly acquires the potential of emitter 42 and conductor 34 because there is essentially no resistance between emitter and conductor 34. In this case, current flows from conductor 36 through transistor Tr and primary winding 22 to conductor 34. This induces a voltage drop across primary winding 22 as opposed to voltage A from terminal A with terminal B more negative than terminal A. The magnetic lines of the current flow outward from the transformer T core.

The voltage drop across the primary winding 22 is substantially the same as the potential difference between the conductors 36 and 34 because the collector 38 is substantially at the voltage of the emitter 42.

When the transistor Tr no longer conducts due to the application of a negative potential to the base 44, the direct current drops to substantially zero and the negative lines of the force are directed back toward the coil, which induces a voltage. The direction of the voltage is such that it tends to maintain the aforementioned direction of the current flow, as explained above, because the induced voltage causes the primary winding 22 to act as a source, in which case-; sa current flows from negative to positive within source V.

Thus, terminal B now becomes more positive than terminal A. Normally, the induced voltage value L di / dt would make this voltage higher than the voltage source in the conductors 34, 34; however, the gas discharge in the tube 12 between the first and second glow electrodes 30 and 31 becomes, in a very significant manner, a bidirectional voltage limiter. Thus, the tube 12 works · as if it were constructed of two Zener diodes connected to each other, thus preventing the detrimental effects of large voltage peaks on the transistor 10 81 943

Tr. The tube 12 thus produces light with energy that would otherwise escape as heat.

When transistor Tr is in its "off" state, there is only one current path in the circuit. Transistor Tr does not draw current from capacitor C2 from the voltage pulse L di / dt or from voltage source conductor 36. When conductor 50 is more positive than conductor 70, the first glow electrode 30 acts as an anode and the second glow electrode 32 acts as a cathode when transistor Tr is again "on" C2 discharges current to pipe 12.

The secondary circuit, for influencing the primary circuit and the transistor Tr and for controlling the gas discharge in the gas discharge tube 12, comprises a secondary winding 24 of the transformer T connected to the second capacitor C3 and the second glow electrode 32. The current path of the secondary circuit to conductor 51 and then to terminal C of secondary winding 24.

In overall operation, the electronic current limiting system 10 provides sufficient electrical discharge in the gas discharge tube 12 to convert electrical energy from the power source 14 to visible light. Prior to the first connection of the switch W, there is of course no voltage drop across any part of the current limiting system 10, thus, as in all other parts of the overall circuit, the potential difference across the transistor Tr and between the conductors 40 and 70 is substantially zero.

When the switch W is first closed, the AC power supply 14 causes current to flow in the electronic current limiter system 10, which is the half-wave rectified current of the diode connected to the conductors 16 and 20, as shown in Fig. 2. A capacitor or filter is connected between the conductor 20 and the return supply conductor 34 in parallel with the AC power supply 14. The filter or capacitor Cj charges during the half cycle during which the diode releases current, i.e. during the positive current cycle in conductor 16, and discharges during the second half cycle, preventing discharge back to power supply 14. Thus, in conductor 36, .

During this time, the transistor Tr does not receive a control voltage, and there is not enough potential difference in the circuit to cause a discharge in the gas discharge tube 12. The resistance between the collector 38 and the emitter 42 of the transistor Tr is very high, practically infinite. Transistor Tr has virtually no voltage at base 44 and emitter 42, and thus transistor Tr is in its "off" state and no current flows from emitter 42 to collector 38. The only current flowing is the current that charges capacitor C2 through conductors 40 and 50. The current flows from the conductor 36 to the conductor 70 and through the primary winding 22 and the capacitor C2 and is small and insufficient to induce a voltage in the secondary winding 24 of the transformer T.

Transformer T is a ferrite core type transformer and is used because in this type of transformer the core becomes rapidly saturated using less than one tenth of the current required to operate the tube 12. Thus, the core transmits the maximum magnetic flux to the secondary winding 24 before a peak voltage occurs in the primary winding 22. Before saturation, a difference of 12 81 943 in the secondary voltage is provided because the primary voltage is constantly increasing. Capacitor C2 is charged in an amount that depends on the value of the capacitance and the resistance value of the gas-tube tube 12, which for the above-described F20T12 / CW 20 W tube is about 1100 ohms during the gas discharge and higher before the gas discharge.

When the switch W is then opened, and closed a second time, a pulse or secondary pulse is provided through the primary winding 22. The pulse causes a current change in the primary winding 22, which is large, and the secondary winding 24 provides a current sufficient for the immediate passage of current through the circuit 10 to turn the transistor Tr into an "on" state. When the transistor Tr is in the "on" state, the voltage drop between the collector 38 and the emitter 42 is very small and the capacitor C2 in the conductor 50 is connected to the supply conductor 34 through the conductor 60 and the transistor Tr.

Capacitor C2 is positively charged in conductor 50 and negatively charged in conductor 70 at this point. The output now has a negative current because the capacitor C2 is connected to the return conductor 34 by a conductor 60 and a transistor Tr. Since a negative output occurs in the conductor 70, the glow electrode 30 becomes a cathode. Another hehkuelektrodi 32, wherein there is a return side of the power supply voltage 14, will thus be the anode. At this point, the capacitor C2 becomes a power source for the gas discharge tube 12 because the other terminal of the capacitor C2 is connected to the return line 34 through conductors 50 and 60 and the transistor Tr and the opposite end of the capacitor C2 is connected to the .

The pole of the capacitor C2 connected to the conductor 50 was positively charged and is at this point i3 81 943 connected to the return conductor 34. A negative voltage is applied to the discharge tube 12 from the conductor 70 and the voltage obtained is greater than approximately 85.0 V, which is the ignition voltage of that tube 12. , providing conventional light development. As will be appreciated, the plasma in the gas discharge tube 12 effectively acts as an electrical resistor. The temperature of the glow electrodes 30 and 32 of the gas discharge tube 12 is kept high enough to ensure the emission of electrons as long as the voltage pulses are conducted from the capacitor C2. For the 20.0 W tube referred to above, the time constant of capacitor C2 in series with tube 12 is about 50.0 microseconds.

The secondary winding 24 of the transformer T provides a difference signal through the capacitor C3 to the base 44 of the transistor Tr. Thus, a narrow pulse is applied to the transistor Tr and when the transistor Tr is switched to the "on" state, the current in the secondary winding 24 will be substantially zero. The cycle is thus repetitive and the capacitor C2 is recharged as explained above.

Furthermore, for the cycle, since the body of the transformer T is saturated, a potential is provided across the diode D2, which is a positive pulse whose voltage also prevails over the boundary between the base of the transistor Tr and the emitter. This positive pulse is a consequence of the fact that the conductor 40 leading to the transformer T has a lower potential than the conductor 36.

Thus, a positive pulse occurs in the conductor 51 caused by the secondary winding 24.

Due to the fact that diode D2 has a blocking forward voltage, it does not conduct when conductor 51 is positive.

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The base-emitter interface has a pass-ahead voltage and conducts current and limits the voltage drop between conductors 51 and 62, which is approximately 1.0 v for current limiter system 10. Transistor Tr then changes to its "on" state and transistor Tr "is in its" state ", induces a voltage in the secondary winding 24 40 with approximately zero potential.

When the transistor Tr loses its saturation, the conductor 51 will be negative. This provides a pass-through voltage to diode D2 and a blocking benefit voltage to the base-emitter interface of transistor Tr. The secondary current passes through diode D2 and the voltage across diode D2 settles at minus 1.5 V in conductor 51 compared to conductor 62. Conductor 40 settles substantially from zero to a positive level. Thus, current flows once again between conductors 40 and 36 and a positive polarity pulse is conducted to conductor 70 over capacitor C2. A positive polarity pulse is applied to the first glow electrode 30 of the gas discharge tube 12 and the plasma continues to burn.

It is to be understood that an additional resistor may be installed between conductors 40 and 51. By installing such a resistor, the necessary pulse in the secondary winding 24 is obtained by simply closing the switch W. Thus, by installing a resistor between the conductors 40 and 51, immediately after saturation has occurred in the transformer T, a pulse is provided to provide a total duty cycle in the current limiting system 10.

These and other variations will be apparent to those skilled in the art without departing from the spirit of the invention as defined in the claims.

Claims (2)

An electronic current limiting system for lighting systems comprising a gas discharge tube having first and second glow electrodes, characterized in that the current limiting system comprises: a) a first capacitor (C2) electrically connectable to the first glow electrode (30) of said gas discharge tube (12); a transistor (Tr) having a collector (38) connected to the first capacitor on a different side from the first glow electrode (30), c) a transformer (T) having a primary winding (22) connected from one terminal (B) of said transistor (Tr), and to a junction of said capacitor (C2) and connectable to a pulsating DC source from one terminal (A), and having a secondary winding (24) connected from one terminal (C) to the base (44) of said transistor and from the other terminal to the emitter (42) of said transistor to form a positive feedback past the transistor (Tr), and d) the devices pulsating to provide and conduct voltage to a second glow electrode (32) of said gas discharge tube comprising a second capacitor (C3) connected in series between a secondary winding (24, terminal D) and one electrode of said second glow electrode (32), a second glow electrode (32) the electrode being capable of closing the positive feedback to the emitter (42) of the transistor (Tr). Electronic current limiting system according to claim 1, characterized in that it comprises elements (80) for connecting the second glow electrode (32) 16 81 943 of the gas discharge tube (12) to the return conductor of the alternating current source and to the emitter (42) of the transistor (Tr) when the gas discharge tube is connected to the system.