Direct voltage supplied circuit for generating voltages and/or currents with different curve form and/or different frequency and/or different polarity.

(42) Date of commencement of the patent: 15. 8.1990 (45) Date of issue: 25. 3.1991

<td>(56) Documents:</td><td>(73) Patent owner:</td>

<td>DE-0S2710331 DE-0S3107061 GB-0S2071949 FR-0S2344171</td><td>ZUMTOBEL AKTIENGESELLSCHAFT A-6850 DORNBIRN, VORARLBERG (AT).</td>

<td></td><td>(72) Inventor:</td>

<td></td><td>JAGSCHITZ OTTO DIPL.ING. GOTZIS, VORARLBERG (AT).</td>

(54) BALLAST FOR OPERATING GAS DISCHARGE LAMPS WITH DC

CQ

AT 392 384 (57) The ballast for the operation of direct discharge gas discharge lamps (L) has two controlled semiconductor switches (T, T ₂ ), which concerning the

Gas discharge lamp (L) and a choke coil (D) in each case in series, but in different conduction paths (1, 2) and these conduction paths (1, 2) are connected to different potentials of the supply voltage. In operation, one switch (T) is open, the other switch (T₂ ) opened and closed in alternating sequence. After expiration of an adjustable period of time until now in alternating sequence (clock frequency) operated switch (T₂ ), whereas the previously open switch (T j) is opened and closed in alternating sequence. This switch operation is repeated continuously and the ratio of Umpolfrequenz to Schaltfreqenz (clock frequency) is about 1: 1000. By reversing the

Switch T and T ₂ It is achieved that the lamp is traversed in alternating sequence, depending on the Umpolfrequenz the switch, the current in alternating directions.

<img file="AT392384B_D0001.tif" />

MR 0073518

AT392 384 Β

The invention relates to a ballast for operating gas discharge lamps with direct current with at least one gas discharge lamp as a load and with a, choke coil connected in series with the gas discharge lamp and with at least two controlled semiconductor switches, which in each case in series connection with respect to the gas discharge lamp and the choke coil, However, lie in different conduction paths and these conduction paths are connected to different potentials of the supply voltage.

The operation of a gas discharge lamp with DC voltage is preferable to that with AC voltage, since the gas discharge lamp in this case flickers less and shows a higher light output The only disadvantage is that the continuous operation of DC voltage in the electrode region of the gas discharge lamp accumulate deposits, caused by the always in same direction flowing ion flux. In order to avoid these deposits, therefore, the lamp is repeatedly reversed, for which purpose mechanical switches have been used. Although the polarity reversal of the operating voltage reduces the mentioned electrode wear, the equipment necessary for the operation of the lamp are in this case very complex and dimensionally very large, apart from the fact that a series resistor is needed here, so that the lamp burns stable, yes one represents a permanent source of loss

From DE-OS 27 10 331 and FR-OS 23 44 171 a chopper is known with which an AC voltage can be generated whose envelope corresponds to a given pilot signal Such a chopper is completely unsuitable for the operation of gas discharge lamps, because the current Voltage characteristic of a gas discharge lamp is negative and for this reason special control devices for stable operation are necessary.

Also known are circuits for gas discharge lamps (DE-OS 31 07 061 and GB-OS 20 71 949), which are operated with a low supply voltage. At low line voltages, the usual half-bridge inverter circuit provides too low a voltage, which is twice as high when using a full bridge (110 volt operation). In this prior art circuit, the switches are alternately operated thereby the voltage is increased to the desired extent.

The invention now aims to form the ballast for the gas discharge lamps so that the respective positive or negative DC voltage is superimposed on a high-frequency voltage, so that not only AC switching elements can be used for the ballast, but also still those that are purely spatial, can be sized very small. According to the invention, this is achieved by the fact that during normal use of a switch (Tj) is open, while the other switch (T₂) is opened and closed in alternating sequence and after the expiration of an adjustable or controllable period of time so far in alternating sequence (clock frequency) actuated switch (T₂), whereas the hitherto open switch (Tj) is opened and closed in alternating sequence and this alternation of the switch operation (Umpolfrequenz) is constantly repeated and the ratio of Umpolfrequenz to switching frequency of the switch (clock frequency) is about 1: 1000, preferably more , The size of the ratio of Umpolfrequenz to the clock frequency determines the control quality of the circuit; the larger this ratio, the smaller the throttle can be made.

A particularly simple circuit of this kind is characterized by a feature of the invention characterized in that the gas discharge lamp and throttle connected in series circuit path is connected to an average value of the supply voltage. With such a circuit currents and voltages even low frequency (less than 20 Hertz) can be obtained without the need for a special circuit complexity, however, the controllable power of this circuit is limited

Another circuit of this kind, also suitable for low power and low frequencies, is characterized according to a further feature of the invention characterized in that the gas discharge lamp and the choke comprise a series-connected line path via at least two capacitors, which in each case in series connection with respect to the gas discharge lamp and the choke coil, however, lie in different conduction paths, connected to different potentials of the supply voltage, the capacitors being connected to the same potentials of the supply voltage, like the controlled semiconductor switch.

Another circuit, which, however, meets the highest requirements in terms of performance and variation possibilities, is characterized according to a further feature of the invention characterized in that the gas discharge lamp and the choke comprise a series-connected line path via at least two further controllable semiconductor switches, which in each case in series connection with respect to the gas discharge lamp and the choke coil, however, lie in different conduction paths, are connected to different potentials of the supply voltage, wherein these semiconductor switches in the period of Umpolfrequenz the other semiconductor switches open or are closed and so in each case form a closed circuit in conjunction with the gas discharge lamp and choke coil, in which the direction of the current flow Umpolfrequenz changes accordingly

If a capacitor is connected in parallel to the gas discharge lamp, this should smooth current and / or voltage. A similar effect is achieved if between the throttle and the gas discharge lamp, a capacitor is connected, whose other electrode is connected to that connection point for the supply voltage of the two Anschlußpünkten for this supply voltage

-2AT392384B lower potentialL

There are semiconductor switches in which freewheeling diodes are integrated; However, if semiconductor switches are used for the circuit according to the invention, which have no such integrated freewheeling diodes, it is provided according to a further feature of the invention that at least one in alternating sequence (clock frequency) periodically actuated Halbleiterschaltem freewheeling diodes are connected in parallel. By this measure it is prevented that the load current is interrupted when reversing the cyclically actuated, arranged in pairs semiconductor switch.

Reference to the drawings, the invention is described in detail. Show it:

Fig. 1 to 3 three different circuits for ballasts for gas discharge lamps; 4 and 5 are voltage and current flow diagrams; Fig. 6 is a timing chart for the clocking control of the semiconductor switches; Fig. 7 shows a detail from the current flow diagram of Fig. 5 in a considerably enlarged scale.

Fig. 1 illustrates a first embodiment of a circuit according to the invention. The voltage source used here is a battery (B) with a center tap and with the terminal voltage (U). The line branch (3) connected in series with the choke (D) and the gas discharge lamp (L) (FIG. XXX) is connected on the one hand to the center tap of the battery (B), on the other hand between the two controlled semiconductor switches (Tj) and (T₂), each of which by itself via a line (1) or (2) is connected to a terminal of the battery (B) so that each is connected in series with the reactor (D) and the gas discharge lamp (L). The control of the semiconductor will be explained in more detail below. Here, for the time being, it should be noted only once that during a first period of time the semiconductor switch (Tj) is opened and closed in a pulsed manner (clock frequency) and during this time the other semiconductor switch (T₂) is open. This continuous opening and closing of one switch, while the other switch is open, is here and hereinafter referred to as the clock frequency. After this first period of time, the switch (Tj) is now kept open, whereas now the other switch (T₂) is opened and closed, so is actuated in a clock. This change in the operation of the switches (Tj) and (T₂) is called here and in the following Umpolfrequenz. This process can now be repeated as often as you like. While one semiconductor switch (Tj) is clocked, the current flows in one direction (arrow (4)) through the gas discharge lamp (L). While the semiconductor switch (T₂) is clocked, the current flows in the reverse direction through the gas discharge lamp. The height of the lamp current now depends on the one hand on the inductance of the inductor and the clock frequency of the switch (T j) and (T₂); the time duration of the current flow in each case in one direction from the polarity reversal frequency can be controlled by various variables, which will be discussed below.

A further circuit with which low-frequency voltages or currents can also be obtained, starting from a DC voltage, is shown in FIG. 2. At the terminals (XY) of the circuit is the voltage (U), parallel to the semiconductor switches (Tj) and (T₂), freewheeling diodes (Dj) and (D₂) intended. In series with the gas discharge lamp (L) and the throttle (D) is arranged in each case a capacitor (C) in different circuits, such that the gas discharge lamp and the choke comprise a series-connected line path via two capacitors, which in each case in series connection with respect to the gas discharge lamp and the choke, however, lie in different conduction paths, connected to different potentials of the supply voltage, wherein the capacitors (C) are connected to the same potentials of the supply voltage (U) as the controlled semiconductor switches (Tp and (T₂). Also in this circuit, the controlled semiconductor switches (Tp and (T₂The frequency of the voltage applied to the gas discharge lamp (L) is dependent, inter alia, on the capacitance and the time constants of the capacitors.

A circuit which is capable of satisfying all requirements, and which represents a direct development of the circuits explained above, is now shown in FIG.

This DC-powered circuit is designed as a bridge circuit in each outer branch of this bridge circuit is a transistor (Tp to (T₄) arranged. Two of these transistors, namely the transistors (Tp and (T₂), which are located between the connection points (X) and (Y) for the supply voltage (U), parallel freewheeling diodes (Dp and (D₂) on. Also the other two transistors (Tj) and (T₄) are diodes (Dp and (D₄) connected in parallel for protection purposes. The bases (B p to (B₄) of the transistors (Tp and (T₂) are connected, for example, with integrated circuits, which are not shown here. In the diagonal branch of the bridge circuit, the gas discharge lamp (L) is connected to terminals (A) and (E). Between the terminal (A) and the connection point (F) between the two serving as a semiconductor switch transistors (Tj) and (T₂), the throttle (D) is connected. Furthermore, here, a capacitor (C) is provided in parallel to the gas discharge lamp. Instead of this to the gas discharge lamp (L) parallel capacitor, another capacitor (C) may be provided, whose

-3AT392 384 B is one electrode between the gas discharge lamp (L) and the choke (D) and the other electrode is at the connection point (Y) for the supply voltage (U), which has the lower potential. This is indicated in Fig. 3 by a dashed line. In the operational use of the circuit serving as semiconductor switches transistors (Tj) and (T₂) operated in the sense of the above-described clock frequency and Umpolfrequenz. On the other hand, serving as semiconductor switches transistors (Tj) and (T₄) Only the Umpolfrequenz switched accordingly.

Fig. 6 illustrates a pulse train with which the bases of the transistors (Tj) and (T₂) can be controlled. Where (PD) means the period; (ED) the duty cycle (pulse length) and (TL) the tactile gap. The ratio between duty cycle (ED) and period duration (PD) is called the duty cycle. This duty cycle is adjustable and changeable on the integrated circuit, not shown, for example, mentioned.

By means of the described circuit according to FIG. 3, the operation of the gas discharge lamp proceeds essentially as follows:

The DC voltage (U) applied to the terminals (X), (Y) can either be taken directly from a DC voltage network, but it can also be provided via a converter (AC / DC current). The transistors (Tj) to (T₄) serve as electronic switches and their bases are controlled by the magnitude of the operating current via pulse sequences of FIG. In the first phase of operation, the transistors (T j) and (T₄), the transistors (T₂) and (T.₃) open. The transistor (Tj) or its base (Bj) is driven by a pulse sequence shown in FIG. During the duty cycle (ED) of a pulse, the transistor (T j) is closed and DC current flows from the terminal (X) via the transistor (Tj), the choke (D) and the gas discharge lamp (L) over the closed during this phase of operation Transistor (T.₄) to the clamp (Y). Before the nominal size of the lamp operating current is reached - this is in terms of time - at the end of the duty cycle (ED) of the control pulse, the transistor opens (T j), the flow of current from the network is interrupted and the magnetic energy built up in the choke (D) by the flow of current is now converted into electrical energy and provides a countervoltage, until the switch-on time of the next control pulse, ie during the keyping (TL), maintains the flow of current through the gas discharge lamp (L) in the same direction, wherein the energy stored in the throttle is dissipated. Now on the next following control pulse to the base (B j) of the transistor (Tj) this in turn turned on, and thus again energy and power supplied from the network in the manner described the circuit until just before reaching the nominal size of the lamp operating current again , whereupon the mentioned switching process is initiated and carried out again. During this time, the gas discharge lamp (L) is always traversed by the current in the same direction. The described control operations are very short and take place in fractions of seconds. During this first phase, during which the transistor (T j) is cyclically opened and closed cyclically, the transistor (T₄) always closed. In order to avoid the above-mentioned harmful deposits due to the DC operation of the gas discharge lamp, the gas discharge lamp (L) is now reversed after some time. This happens now that the transistors (T j) and (T₄), the transistor (T₃) is closed and the transistor (T₂) becomes in such a way over its basis (B₂) is clocked as described in connection with the transistor (Tj). The current flow in the gas discharge lamp (L) is thereby reversed.

If the period duration (PD) of the control pulses (clock frequency) depends on the time constant of the inductor (D), the polarity reversal frequency can be derived and controlled, for example, from the mains frequency, if the DC voltage at the terminals (X), (Y) of the circuit is obtained via an AC - DC converter, not shown here. Other control frequencies for the polarity reversal can be used successfully. The period of the Umpolfrequenz is always greater than the period of the control pulses (clock frequency). Serve in parallel with the transistors (Tj) and (T₂) connected diodes (Dj) and (D₂) as freewheeling diodes which maintain the current flow when the transistors (Tj) and (T₂) open and close in a pulse-controlled manner, the diodes (D₃) and (D₄) parallel to the transistors (T₃) and (T.₄) Protection function.

The current flow through the gas discharge lamp (L) according to the circuit of FIG. 3 and the above-described operation is shown schematically in FIG. 5 On the whole, it is a trapezoidal curve with a different sign. The period (P) of this sequence depends on the Umpolfrequenz. If the current waveform shown in the diagram with a straight line is enlarged, so to speak, then a line results, which in FIG. 7 is shown and the in Fig. 5 circled section (G) so to speak on an enlarged scale represents this line jagged, their rise or their drop is determined by the resistance behavior of choke (D) and gas discharge lamp (L), their reversal points are dependent

4AT392 384B from the clock frequency and its smoothness (hatched areas) is determined by the smoothing capacitors (C) after the circuit in FIG. 3.

Instead of a current waveform, as shown in FIG. 5, it is also possible, for example, to force a voltage curve, as shown in FIG. 4

To control the clock frequency or Umpolfrequenz circuit-inherent electrical variables can be used, so these are sizes that can be measured, for example, on the gas discharge lamp (L), such as voltage, voltage rise, current, current increase, active or apparent load. In the embodiment explained above in connection with FIG. 3, the load current for controlling the clock frequency for the semiconductor switches (Tj) and (T₄), d. h "the semiconductor switches (Tj) and (T₄) were opened in cycles each time before the load current has reached the lamp current and turned on again as soon as it has fallen slightly. The current values ​​at which has been switched off, are in the graph of FIG. 7 with (IE) resp. (IA). The Umpolfrequenz ((P) - Fig. 5) was derived from the frequency of a standard 50 Hertz AC power supply. A control of or about a circuit-independent size, as here the network frequency of an AC power supply network, is referred to as external excitation.

In the circuit of FIG. 2 on the other hand, the polarity reversal frequency can be controlled by the voltage rise at the capacitors (C) (natural frequency). Further control possibilities for the clock frequency result from the choice of the ratio of the duty cycle (ED) to the switch-off duration (TL) or else by the change of the pulse duration (PD) (pulse width modulation). To control the clock frequency thereby expediently programmable processors are used, with which control curves and cams of any shape can be achieved.

By reversing the polarity of the switches (T j) and (T₂) or (Tj) and (T₄) It is achieved that the lamp is traversed in alternating sequence, depending on the Umpolfrequenz the switch, the current in alternating directions, so that the unwanted deposits on the electrodes can be avoided. With the mentioned circuit but also the brightness of these lamps can be controlled in a simple manner that, for example, the duty cycle (ED) of the control pulse for the cyclic control of the semiconductor switch is shortened.