SWITCHING ARRANGEMENT

Abstract: The invention relates to a switching arrangement for ignition of a high-pressure discharge lamp. The switching arrangement is provided with means for suppressing the production of ignition pulses in case the lamp has ignited. According to the invention, the switching arrangement comprises a pushpull circuit which is supplied on the one hand by the supply voltage and on the other hand by the voltage across the lamp and of which an output terminal is connected to the means for suppressing the production of ignition pulses. Thus, it is achieved in a simple manner that the lamp voltage influences the blocking and activation of the production of ignition pulses.

Description: The invention relates to a switching arrangement suitable for the ignition of at least one high-pressure discharge lamp by means of production of ignition pulses, which is provided with at least three connection terminals, of which a first connection terminal is intended to be connected to a first terminal of the lamp and a second and a third connection terminal are suitable for connection on either side of an impedance connected in series with a second terminal of the lamp, and which is further provided with means for suppressing the production of ignition pulses if the lamp has ignited. Such a switching arrangement known under the type designation Philips SN 61 is frequently used in practice, for example in combination with a high-pressure sodium discharge lamp. The known starting arrangement is provided with an electronic circuit comprising a logic circuit, by means of which the production of pulses is blocked as soon as the voltage at an input of the logic circuit falls below an adjusted voltage level, which occurs as soon as the lamp ignites. In order to prevent that in case of a defective lamp the production of ignition pulses is continued without interruption, the known switching arrangement is further provided with a counter circuit, which blocks the production of ignition pulses after a preadjusted period of time. The production of ignition pulses is not activated until the supply voltage at which the switching arrangement is operated has been interrupted for some time. The electronic circuit comprising the logic circuit together with the counter circuit forms part of the means for suppressing the production of ignition pulses if the lamp has ignited. A property of this known switching arrangement is that the production of ignition pulses remains blocked even if the lamp extinguishes without the supply voltage being interrupted. This means that when a lamp becomes defective during operation, the switching arrangement is not activated, which is a favourable aspect of the known switching arrangement. In general a high-pressure lamp will already extinguish during operation when the applied supply voltage decreases in value for a short time without being interrupted, however. A decrease of 10 % may already lead to extinguishing. With the known switching arrangement, the lamp is not restarted under such conditions. The invention has for its object to provide a means for obtaining in an efficacious and simple manner a switching arrangement which is suitable to be activated if the lamp extinguishes due to a transient decrease of the supply voltage, whilst maintaining the favourable aspect of the known switching arrangement. For this purpose, a switching arrangement of the kind mentioned in the opening paragraph is characterized in that a pushpull circuit is connected between first, second and third connection terminals, and is responsive to a voltage between said first and second terminals to produce at an output terminal a control signal for the means for suppressing the production of ignition pulses. An advantage of the switching arrangement according to the invention is that the pushpull circuit permits of comparing the supply voltage with the voltage across the connected lamp so that the voltage across the lamp can influence the production of ignition pulses. It is known of high-pressure discharge lamps, especially of high-pressure sodium discharge lamps, that during the life of the lamp the voltage across the lamp increases, as a result of which the lamp is more liable to extinguish upon variation of the supply voltage. By means of the push-pull circuit the voltage across the lamp influences the activation and the blocking of the switching arrangement so that a distinction can be made between a lamp having a nominal lamp voltage and a lamp having an increased lamp voltage. In an advantageous embodiment of a switching arrangement according to the invention, which is suitable to be supplied with alternating voltage, the pushpull circuit comprises a voltage division circuit between the first and the third connection terminal, which is formed from the series circuit of a first resistor, a first diode and a capacitor, while the second connection terminal is connected through a series-combination of a second resistor and a second diode on the one hand to the capacitor and on the other hand to the series circuit of the first diode and the first resistor and an anode of the first diode is connected to a cathode of the second diode. By means of this configuration, it is achieved in a simple manner that during each period of the voltage across the lamp the capacitor is subjected for a half cycle to a charge variation, which is related to the voltage across the lamp, and is subjected during each period of the alternating voltage supply for a half cycle to a charge variation which is related to the supply voltage. The polarities of the voltage across the lamp and of the supply voltage are opposite to each other during the charge variation. The charge at the capacitor averaged over a period and therefore the voltage across the capacitor is thus proportional to the voltage across the lamp and is at least in part compensated for the influence of supply voltage variations. Preferably, the switching arrangement according to the invention is suitable for supply with alternating voltage and the impedance in series with the connected lamp forms part of a stabilization ballast of the lamp. Since it is common practice to operate high-pressure discharge lamps at alternating voltage, it is advantageous if the switching arrangement can also be operated at alternating voltage. When also at least a part of the stabilization ballast of the lamp is utilized, the switching arrangement can be combined in a simple manner with the stabilization ballast to form a single arrangement. With a view to cost of installation, this is advantageous. An embodiment of a switching arrangement according to the invention will be explained more fully with reference to a drawing. In the drawing, A and B designated input terminals intended to be connected to an alternating voltage supply source of a lamp circuit provided with a switching arrangement 1 according to the invention. The terminal A is connected through a stabilization ballast 2 to a second terminal 3b of a discharge lamp 3. A first terminal 3a of the lamp 3 is connected to the terminal B. The switching arrangement is provided with three connection terminals 11,12,13. A first connection terminal 11 is connected to the first terminal 3a of the lamp 3. A third connection terminal 13 is connected to a centre tapping of the stabilization ballast 2 and a second connection terminal 12 is directly connected to the second terminal 3b of the lamp. The third and first connection terminals 13,11 are interconnected through a series-combination of a capacitor C₁ and a triac TR, which serve to produce ignition pulses. The third connection terminal 13 is further connected through a series circuit comprising a diode D₁, a resistor R₁ and a capacitor C₈ shunted by a Zener diode D₂ to the connection terminal 11. The voltage across the capacitor C₈ serves as a direct voltage source for a transistor T₁, which is connected in series with a resistor R₁₂ to a control electrode TRS of the triac TR. The control electrode TRS is connected via a diode D₁₁ to a junction point between the capacitor C₁ and the triac TR. The connection terminals 11,12,13 are interconnected through a pushpull circuit 4 provided with an output terminal 44 and with input terminals 41,42,43, which are connected to the connection terminals 11,12 and 13, respectively. The input terminals 41 and 43 are connected interconnected through a voltage division circuit constituted by a first resistor R₂, a first diode D₅ and a capacitor C₇. The connection terminal 42 is connected through a series-combination of a second resistor R₃ and a second diode D₆ on the one hand to the capacitor C₇ and on the other hand to the series circuit of the first diode D₅ and the first resistor R₂. An anode of the diode D₅ is connected to a cathode of the diode D₆. The capacitor C₇ shunted by a resistor R₅ is directly connected to the output terminal 44. The input terminal 41 is connected through a diode D₇ to the resistor R₃ and through a Zener diode D₃ to the resistor R₂. During a half cycle of the voltage across the lamp, the capacitor C₇ will be charged via the connection terminal 12, the input terminal 42, the resistor R₃ and the diode D₆ and will be partly discharged during a half cycle of the alternating voltage supply source via the diode D₅, the resistor R₂, the input terminal 43 and the connection terminal 13. Thus, a voltage is obtained at the output terminal 44, which voltage, averaged in time, is proportional to the voltage across the lamp 3 and is compensated at least in part for the influence of supply voltage variations. The output terminal 44 is connected through a resistor R₇ to a first input of a NAND gate G₁. A capacitor C₄ connects the first input of the NAND gate G₁ to the connection terminal 11. The combination R₇-C₄ ensures that to the first input of the NAND gate G₁ is applied a direct voltage, which is proportional to the voltage across the capacitor C₇ and therefore depends upon the voltage across the lamp. A second input of the NAND gate G₁ is connected to a direct voltage source constituted by the voltage division circuit of the resistor R₁ and the capacitor C₈ (indicated in the drawing by + for the sake of simplicity). An output of the NAND gate G₁ is connected to a pin MR of an integrated counter circuit IC₁. The output terminal 44 of the pushpull circuit 4 is also connected to a Zener diode D₄, which is connected on the one hand to a first input of a NAND gate G₄ and on the other hand via a parallel-combination of a resistor R₆ and a capacitor C₉ to the connection terminal 11. A second input of the NAND gate G₄ is connected via a resistor R₈ to the connection terminal 11 and via a capacitor C₃ to a pin R TC of IC₁. A pin RS of IC₁ is connected to an output of a NAND gate G₂, of which a first input is connected via a voltage division circuit C₆,R₄ to the connection terminal 11 on the one hand and to the connection terminal 13 on the other hand. A second input of the NAND gate G₂ is connected to an output of a NAND gate G₃, of which a first input is connected to the junction point between R₁ and C₈ and of which a second input is connected on the one hand via a diode D₉ to the pin 160S of IC₁ and on the other hand via a diode D₈ and a resistor R₁₀ to the pin 5S of IC₁. Further, the pin 5S is connected via the resistor R₁₀ to a junction point of a diode D₁₀ and a capacitor C₂. The capacitor C₂ is connected to the connection terminal 11 and the diode D₁₀ is connected to an output of the NAND gate G₄. Immediately after the supply voltage source has been connected, the capacitor C₄ is still uncharged so that the output of the NAND gate G₁ conveys a high voltage for a short time, as a result of which the counters of IC₁ are set to zero via the pin MR of IC₁. As long as the lamp is extinguished, the voltage between the connection terminals 11 and 12 and between 11 and 13, respectively, is substantially equal to the supply voltage. The capacitor C₇ of the pushpull circuit 4 and hence also the capacitor C₉ and C₄ are thus charged to a high voltage, as a result of which a comparabively high voltage is applied to the first input of the NAND gate G₄, as well as to the first input of the NAND gate G₁. Consequently, the output of the NAND gate G₁ has a low voltage and the counter circuit IC₁ is released and the counters of IC₁ start counting. Short rectangular voltage pulses having a frequency equal to the frequency of the supply source are generated at the pin R TC of IC₁. By differentiation in the circuit C₃,R₈, needle pulses are thus obtained at the second input of G₄. These pulses are amplified via G₄ and the resistor R₁₁ by the transistor T₁ and are supplied to the control electrode TRS of the triac TR. The triac TR will become conducting at each pulse and will produce ignition pulses in known manner via A, 2, C₁ and B. The rectangular voltage pulses at the pin R TC are formed in IC₁ by means of pulses originating from the NAND gate G₂. The frequency of the pulses supplied by G₂ is derived from the supply source via the series circuit R₄,C₆. The pin 160S is a counter output which between 0 and 160S has a low voltage and has a high voltage from 160S. Due to the high voltage at the pin 160S, the output of the NAND gate G₃ becomes low and hence the NAND gate G₂ is blocked so that the production of ignition pulses is also blocked. The pin 5S of IC₁ is a counter output which supplies rectangular voltage pulses having a pulse width of 5 s and a repetition frequency of 0.1 Hz. Due to the fact that on the one hand the pin 5S is connected to the output terminal 11 via the resistor R₁₀ and the capacitor C₂ and on the other hand the capacitor C₂ is connected to the output of the NAND gate G₄ via the diode D₁₀, it is ensured that the capacitor C₂ is not charged via the voltage originating from the pin 5S as long as pulses are supplied by the NAND gate G₄. As soon as the lamp ignites, the voltage between the connection terminals 11 and 12 will decrease, as a result of which the voltage across C₇ decreases, just like the voltage at the first input of the NAND gate G₄. The voltage at the output of the NAND gate G₄ then becomes high, as a result of which the transistor T₁ is cut off so that the production of ignition pulses is suppressed. At the same time, a high voltage is also applied to the output of the NAND gate G₁, as a result of which the counters of IC₁ are set to zero. If due to a transient decrease of the supply voltage the lamp extinguishes, the voltage at the connection terminal 12 will become substantially equal to that at the connection terminal 13. As a result, the voltage across C₇ increases and G₄ is opened again, just like G₁ and hence the counter circuit IC1. This results in that the production of ignition pulses is activated again. In case the lamp voltage is comparatively high, the average voltage across the capacitor C₇ becomes so high that, although a low voltage is applied to the output of the NAND gate G₁, the voltage at the input of G₄ remains low because the threshold of the Zener diode D₄ is then not reached. Due to the low voltage at the output of the NAND gate G₁, the pin 5S of IC₁ will have a low voltage for 5 seconds. After 5 s, the voltage of the pin 5S becomes high. Since the voltage at the output of the NAND gate G₄ has remained high, the capacitor C₂ will be charged and the counter circuit IC₁ is stopped via the NAND gates G₃ and G₂. Since the voltage at the input of the NAND gate G₁ remains high, the voltage at the output of the NAND gate G₁ remains low and the counters are not set to zero. If the lamp extinguishes as yet, this will not change the state of the NAND gate G₁ so that IC₁ remains blocked. Thus, the possibility of production of ignition pulses remains blocked. The NAND gates G₁, G₂, G₃, G₄, just like the integrated circuit IC₁, are supplied with the voltage across the capacitor C₈. For the sake of clarity, this is not shown in the drawing. As to clearly define the voltage at the second input of NAND gate G₃ in case both diodes D₈ and D₉ are non-conducting, it can be advantageous to connect the second input of G₃ via a resistor to terminal 11. In a practical embodiment, the switching arrangement is connected to a supply voltage of 220 V, 50 Hz. The most important components of the arrangement are then proportioned as follows: G1, G2, G3, G4 = HEF 4093 BP IC1 = HEF 4060 BP C7 470 nF R2 1,5 M Ω R3 1 M Ω R5 1,5 M Ω T1 BC 557 C TR BT 138/800 D3 BZX 79 C20 D4 BZX 79 7.5 V D5 BAW 62 D6 BAW 62 D7 BAW 62 By means of the switching arrangement described, a large number of high-pressure sodium discharge lamps are operated at a supply voltage of 220 V, 50 Hz. The nominal power of the operated lamps varied from 150 W to 1000 W. The threshold value of the lamp voltage at which, after the lamp has extinguished due to a decrease of the supply voltage, the production of ignition pulses remains blocked, lies at 130 V. By variation of the value of the resistor R₂, this threshold value can be adjusted to a different value.

Claims: A switching arrangement (1) suitable for ignition of at least one high-pressure discharge lamp (3) by means of production of ignition pulses, which is provided with at least three connection terminals (11,12,13), of which a first connection terminal (11) is intended to be connected to a first terminal (3a) of the lamp and a second (12) and a third (13) connection terminal are suitable for connection on either side of an impedance (2) connected in series with a second terminal (3b) of the lamp, and which is further provided with means for suppressing the production of ignition pulses if the lamp has ignited, characterized in that a pushpull circuit (4) is connected between first, second and third connection terminals, and is responsive to a voltage between said first and second terminals to produce at an output terminal (44) a control signal for the means for suppressing the production of ignition pulses. A switching arrangement as claimed in Claim 1, characterized in that the switching arrangement is suitable to be supplied with alternating voltage (AB), in that the pushpull circuit (4) comprises a voltage division circuit between the first (11) and the third (13) connection terminal, which is formed from the series circuit of a first resistor (R2), a first diode (D5) and a capacitor (C7), and in that the second connection terminal is connected through a series-combination of a second resistor (R3) and a second diode (D6) on the one hand to the capacitor and on the other hand to the series circuit of the first diode and the first resistor, while an anode of the first diode (D5) is connected to a cathode of the second diode (D6). A switching arrangement as claimed iN Claim 1 or 2, characterized in that the switching arrangement is suitable to be supplied with alternating voltage (AB) and the impedance (2) in series with the connected lamp forms part of a stabilization ballast of the lamp.

Inventors: ALMERING, FRANCISCUS JOSEPH
Applicants: N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1987
Main classification: H05B41
IPC codes: H05B41