AU638068B2 - Preheater circuit for fluorescent lamps - Google Patents

Description

PREHEATER CIRCUIT FOR FLUORESCENT LIGHTS The present invention relates to an electronic circuit for preheating the electrodes of fluorescent lights according to the disclosure part of Patent Claim I for the purpose of completely effective and low-abrasion ignition of the fluorescent light.

Electronic main connecting apparatuses for fluorescent lights are known, since without increase of the power supply voltage from the traditional 110 or 220 volts to an ignition voltage of approximately 1000 volts and the increase of the traditional line frequency of or 60 hertz to approximately 30 kHz, a fluorescent light cannot be ignited and operated. As oppo:ed to conventional electricalmechanical main connectin, Aipparatuses having capacitor and temperature switch, known electronic main connecting apparatuses have the advantage that they are connected with a preheating circuit which in addition to the increase of the lighting voltage makes it possible to attain the ignition point of the electrodes or to heat filaments/incadescent coils of fluorescent lights in such a manner that the electron discharge for the conventional luminous current discharge occurs for ignition of the lights, which protects the fluorescent light and thus allows it a longer life, in other words a greater number of on-off switching cycles.

To be sure, the known preheating circuits have the drawback that they consume current in the range of a half watt during the entire lighting tIime of the fluorescent light. In the case of fluorescent lights of normal efficiencies of 40, 60 or more watts an increased consumption of this sort relative to electricity consumption does not fall at all or practically does not fall in the individual lights.

Also, the additional heating of the directly adjacent environment around the light which occurs thereby is irrelevant in the case of conventional fluorescent lights. Within the framework of the current by-passes intended for reasons of economy and in use today, and with use of so-called low-power-consumption lights with normal efficiencies of only inconsiderably fewer watts, for instance 7, 10 or watts, but still having light yields comparable to the conventional fluorescent lights, however, both drawbacks are still to be considered, because on the one hand the approximately 0.5 watts lost efficiency of the preheating circuit mean an unnecessary waste of current and on the other hand the additional heating of the electronic mechanism occuring in this case, which electronic mechanism is often built into the light socket in current-saving lights, lead to problems.

Therefore the object of the present invention is to disclose an electronic circuit for preheating the electrodes in a fluorescent light, by means of which effective ignition of the light can be attained and following ignition of the light there is no unnecessary waste of current.

This object is attained according to the invention by a circuit as defined in Claim 1.

One advantageous exemplary embodiment of a circuit of this sort is described hereinafter relative to the drawing, in which this novel device is shown in comparison with a circuit of a conventional electronic main connecting apparatus. In the drawing Fig. 1 is a circuit of a conventional electronic main connecting apparatus and Fig. 2 is a circuit according to the invention.

A conventional circuit is to be seen in Fig. 1, a circuit of an electronic main connecting apparatus EVG,, of which the input voltage according to the power supply of 110 or 220 volts is at or 60 hertz. A square-wave voltage of approximately 300 V 40 kHz and a series resonant circuit, consisting of a winding L 1 and two capacitors C 2 and C 3 connected in series, are typically found at the "out" output point from the main connecting apparatus EVG A fluorescent light FL is connected with one terminal for each of two electrodes with incadescent coils WI and W 2 in the output circuit of the main connecting apparatus EVG 1 The other two connections of incadescent coils W I and W 2 are connected with one another over two capacitors C 2 and C 3 as well as a temperature- dependent resistance PTC.

With connection of the main connecting apparatus EVG 1 the resistance PTC 1 is generally cold and therefore of low ohmic resistance. Capacitor C 2 is therefore practically short-circuited. In this switching state, in order to prevent the voltage between f I i' incadescent coils WI and W 2 from becoming sufficiently high to allow luminous current discharge to occur in fluorescent light FL, capacitor C3 must incorporate a corresponding capacity, typically 6 nF. A current of typically 100 mA is flowing through the output circuit of electronic main connecting apparatus EVG I when in this switching state, which heats the two incadescent coils W 1 and W 2 as well as the resistance PTC 1 to approximately 9000 C in a very short time, typically less than I second. As a result of this heating the resistance PTC 1 is highly resistant, which leads to the rise of the voltage between incadescent coils W 1 and W 2 to approximately 1000 V, so that fluorescent light FL is lighted without luminous current discharge. As soon as this has happened and consequently current can flow through the inert gas found in fluorescent light FL between incadescent coils W 1 and W2, the voltage between incadescent coils

W

1 and W 2 collapes to a constant glow of typically approximately 100 V. The two capacitors C (TN sic) and C 3 as well as the resistance PTC 1 are thus indeed not separated from the output circuit of the main connecting apparatus EVG,, or respectively from the incadescent coil circuit, so that the resistance PTC 1 thereafter consumes current in the range of approximately 0.5 W, which heats it and keeps it highly resistant. This leads to the other aforementioned drawbacks of this known circuit.

In order to avoid further unnecessary consumption of current following the ignition of fluorescent light FL in the output circuit of an electronic main connecting apparatus EVG 1 it is suggested according to the invention to configure the output circuit of the main connecting apparatus EVG11 as in Fig. 2. Thus it is required that the main connecting apparatus EVGI,, as opposed to the known electronic main connecting apparatus of Fig. I, in addition to the 300 V 40 kHz "out" output or discharge, also have a 300 V high voltage output Following series-connection of the main connecting apparatus EVGI 1 fluorescent light FL in turn is placed under voltage through the multiple resonant circuit and is supplied with current. As the result of the lack of an incadescent coiligniting current, which in the case of ignited fluorescent lamp FL flows in the inert gas of the lamp between incadescent coils W I and W2, the voltage rises between incadescent coils WI and W 2 because of the fact that the cold thermoresistance PTC22 at this time point has low ohmic resistance, on the voltage present at the high voltage output of the main connecting apparatus EVG 1 1 and current flows simultaneously reciprocally over the two diodes D I and D 2 through the resistance PTC 2 2 and during the entire duration of incadescent burning of the fluorescent light through a pote'tialbalancing capacitor C 3 2 Therefore, thermoresistance PTC 2 2 exactly the same as incadescent coils W I and W 2 in fluorescent light FL, is heated and becomes increasingly resistant. As soon as thermoresistance PTC 2 2 has become sufficiently heated, which with suitable selection of the circuit components is the case in less thin one second, this resistance becomes resistant, which leads to the situation in which the voltage between the two incadescent coils W i and W 2 can rise above the high voltage output of main connecting apparatus EVG 1 1 as far as the ignition voltage of fluorescent lamp FL which is approximately 1000 V. At this moment the voltage between incadescent coils W 1 and W 2 falls to the operational voltage of fluorescent light FL of typically 100 V, which leads to the situation in which no more current can flow through thermoresistance PTC22 and capacitor C32 from the output of main connecting apparatus EVGII. In the case of the fluorescent light FL to be ignited, then, this portion of the circuit is dead and thus consumes no more current.

It has been shown that for the circuit according, to the nhvcntion, starting from an electronic main connecting apparatus EVG 1 1 with the circuit cdonponents according to the output characteristics shown in Fig. 2, the following features are suitable in order to guarantee'a cle.n and effective ignition of fluorescent light FL C,1 68 nF L1 3 mH C2 3 nF C32 =47 nF D IN4007

D

2 1N4007 PTC2 Siemens PTC C890 265V The person skilled in the art recognizes that with a minimum structural cost as compared with conventional main connecting circuitry on the one hand any continuous and superfluous current use can be avoided in the circuit and on the other hand the preheating of i-adescent coils W1 and W 2 of fluorescent light FL occurs under a voltage which is maintained more or less constant. This delivers not only the advantage of an overall lower use of current in a suitably fitted fluorescent light, but also additionally increases the number of possible on-and-off cycles of the ligh*.

Of course the circuit according to the invention can be adapted to special requirements and conditions and laip characteristics, and the components being used can be different from those used until this time. Under certain conditions, for the purpose of comparison of the currents flowing through incadescent coils W1 and W 2 it is possible to connect a capacitor parallel through incadescent coil W 2 which typically can be 47 nF. Also the electronic main connecting apparatus EVG 11 can be adapted corresponding to the power supply voltage and frequency as well as the voltage and current characteristics required for operation of the light associated with it, and this lies completely within the framework of what an average electronics expert can do without further inventive contribution.

Claims (1)

1. Electronic circuit for the preheating of the electrodes (W 1 W 2 of fluorescent lights (FL) for their ignition, which circuit is connected with the outputs "out" and of an electronic main connecting apparatus (EVG. and the terminals of the electrodes (WI, W 2 of the fluorescent light (FL) and to at least one series resonant circuit Consisting of a winding (L. 1 and a first capacitor (C22) as well as a temperature-dependent resistance (PTC 2 2 and a second capacitor (C 32 characterized in that the resistance (PTC 2 2 together with the second capacitor (C32) and a first diode (D is connected parallel to the first capacitor (C22) and is connected through a second diode (D 2 with a high voltage output of the main connecting apparatus (EVGI).