CH680968A5 - - Google Patents

Abstract

The ballast comprises a repetition circuit (C2, T1, T2, T3, Z1) which discharges a timing element (C1) of the ballast in the event of the lamp (1) failing to start, in order to operate the lamp (1) once again with the preheating current and to start it. The repetition circuit is deactivated by a temperature sensor (6) when the ballast reaches a predetermined limiting temperature as a result of frequent repetition. The ballast permits reliable lamp starting, to the extent that the lamp can be started, without any risk of overheating the appliance. <IMAGE>

Description

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CH 680 968 A5

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The invention relates to an electronic ballast according to the preamble of claim 1. Such a ballast is e.g. known from European Patent Application No. 118 309.

The problem arises of simply preheating and igniting the lamp again in such a ballast if the lamp has not previously ignited. This is achieved in an electronic ballast of the type mentioned with the characterizing features of claim 1.

A circuit is preferably also provided which deactivates the repetition circuit when a predetermined temperature is reached, which is determined by means of a temperature sensor. This prevents possible damage to the ballast due to constant repetition of the starting process.

In a particularly preferred embodiment, the temperature sensor is arranged on a common substrate together with the semiconductor switches and / or diodes and / or high-voltage resistors carrying the preheating current.

Exemplary embodiments of the invention are explained below with reference to the figures. It shows

Figure 1 shows a first embodiment of the electronic ballast.

2 a to 2 d schematically show voltage curves in the circuit according to FIG. 1 from preheating to ignition;

3 a to 3 d schematically show voltage curves in the circuit of FIG. 1 for repetition operation;

4 shows a further exemplary embodiment of the ballast, and FIG. 5 shows the switching thresholds of the embodiment according to FIG. 4.

1 shows a lamp circuit with a fluorescent lamp connected to AC voltage (as a rule mains voltage). The connection is made in a known manner via a choke L and at most with a capacitor C. Furthermore, an electronic ballast with a fluorine actor 3 is shown, as is known in principle from European Patent Application No. 118 309. Its function can be explained on the basis of the voltage profiles according to FIGS. 2a to 2d. When the AC voltage is applied, the Fluoractor 3 is controlled via its control input and goes into the conductive state. The preheating current II flows through the hot cathodes of the lamp 1. During the preheating operation, the capacitor C1 is charged; the corresponding voltage U2 is ramped with a superimposed ripple. In the region of the maximum of such a ripple, the voltage U2 present at the gate of the thyristor 4 reaches a level which causes the thyristor 4 to be switched through. This means that the control of the fluorine actuator 3 is omitted. However, this only goes into the blocking state when the current II flowing through it has fallen below a current value (holding current) determined by the fluorine actuator. When the fluorine actuator is blocked, the ignition voltage (FIG. 2 d) is induced in the inductor L.

If, however, the lamp does not ignite, the task is to achieve a simple repetition of the preheating time and the ignition pulse. An embodiment of the repetition circuit according to the invention is shown in FIG. 1 with the transistors T1, T2 and T3. The circuit responds to the voltage U4 across the lamp, which is much lower when the lamp is on than when the lamp is not on (not successfully ignited). For a 58 watt lamp, the burning voltage is e.g. approx. 120 volts, the voltage when the lamp is not on the contrary 230 volts. The repeater circuit responds to this difference in order to initiate a repetition when the lamp is not lit. The criterion used here is the voltage U5 across a capacitor C2 which is connected to the lamp voltage U4 via a resistor. When the lamp is not lit, the ramp-shaped voltage U5 (FIG. 3b) reaches the value of the Zener voltage Uz of the Zener diode Z1. This leads to the switching of the transistors T1 to T3. On the one hand, capacitor C2 is discharged. On the other hand, the transistor T3 is connected to the time-determining capacitor C1 of the starter circuit. The transistor T3 discharges this capacitor C1 or sets the voltage U2 to a low value. This means that the thyristor 4 blocks again at the next zero point of the voltage U4. The transistor T3 also goes into the off state due to the discharge of C2 or the drop in U5. This means that the switching state prevails again in which the lamp is preheated: Thyristor 4 blocks and the high potential of U3 allows the fluorine actuator to conduct. The voltage U2 across the capacitor C1 rises in a ramp until the thyristor 4 switches through. When the holding current is reached by the fluorine actuator 3, it blocks and a renewed ignition pulse is generated. If the lamp ignites, the voltage U4 drops to the lower operating voltage, e.g. to 120 volts, which means that the voltage U5 does not reach the value UZ. The repeater circuit remains inactive. If the lamp does not ignite again, the repetition process begins again. The high voltage U4 causes the voltage U5 to rise up to the value Uz, the transistors T1 to T3 switch through briefly, T3 discharges C1 and the fluorine actuator 3 returns to the conducting state for preheating operation.

In the case of a defective lamp which does not come on even in the case of several repetition cycles, the problem also arises of avoiding frequent repetition which could damage the ballast. In the present case, this is achieved by a temperature sensor, which interrupts the repetition at the higher temperatures in the ballast that arise due to repeated repetition. In a first embodiment shown in FIG. 1

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rungsart, an NTC resistor 6 is connected in parallel with the capacitor C2 as a temperature sensor. At a preselected temperature, the resistance of the parallel circuit NTC 6 and R9 drops to a value that prevents the capacitor C2 from charging up to the level Uz; the repetition circuit is thus deactivated as long as the temperature at the temperature sensor is higher than the predetermined value, e.g. Is 90 degrees Celsius.

4 shows a further embodiment of the temperature-dependent repetition circuit. The temperature sensor 6 triggers the switching of a thyristor 7 as soon as the temperature at the sensor exceeds a predetermined value. Fig. 5 shows the different course of the switching thresholds for T1, Z1 and NTC 6, thyristor 7. At temperatures of e.g. below 90 degrees Celsius, U5 first reaches the switching threshold Uz of the repeater circuit, which is thus activated. At temperatures above 90 degrees Celsius, the temperature-dependent threshold voltage Us is reached first, at which the thyristor 7 switches on. The repeater circuit is not active.

The temperature sensor 6 is preferably in heat flow connection with at least one element carrying the preheating current, e.g. with the Fluoractor, the rectifier diodes, the high voltage resistors.

Preferably, several of these elements and the temperature sensor are on a common, thermally conductive substrate, e.g. an AI2 O3 substrate arranged.

Claims (7)

Claims 1.Electronic ballast for fluorescent lamps, in which a semiconductor switching element and voltage limiting element lying parallel to the lamp can be controlled after a preheating time which is dependent on a timing element, in order to interrupt the current flowing through a choke coil and the lamp cathodes and, with the help of the choke, one to generate voltage-limited lamp ignition voltage, characterized by a repetition circuit (C2, T1 - T3, Z1) for repeating the lamp start when the lamp is not ignited, with a switch arrangement (T1 -T3) which responds to the voltage level across the non-ignited lamp controlled semiconductor switching and voltage limiting element (3) and connected to the timing element (C1) in order to interrupt the activation of the semiconductor switching element when the switch arrangement responds and to allow the preheating time to run again, and in that the repetition circuit has a resistance and having the capacitor (C2) connected to the rectified lamp voltage, and in that the switch arrangement comprises a threshold switch with a zener diode (Z1) and a first transistor (T1), which respond to the voltage across the capacitor (C2), and a second and has third transistor (T2, T3), which turn on when the threshold switch responds, the third transistor being connected to the time-determining capacitor of the timing element such that it can be discharged when the transistor is turned on. 2. Electronic ballast according to claim 1, characterized by a circuit with a temperature sensor (6) which activates or deactivates the repetition circuit depending on the temperature. 3. Electronic ballast according to claim 2, characterized in that the circuit comprises a temperature-dependent resistor connected in parallel with the capacitor of the repetition circuit. 4. Electronic ballast according to claim 2, characterized in that the circuit has a thyristor (7) connected in parallel to the capacitor, the gate input of which is connected to a temperature-dependent resistor. 5. Electronic ballast according to claim 3 or 4, characterized in that the temperature-dependent resistor with the lamp preheating current leading semiconductor switches and / or diodes and / or high-voltage resistors is in heat flow connection. 6. Electronic ballast according to claim 5, characterized in that the semiconductor switch and / or the high-voltage resistors and the temperature-dependent resistor are arranged on a common substrate. 7. Electronic ballast according to one of claims 2 to 6, characterized in that the repetition circuit can be deactivated at a temperature of approximately 90 degrees Celsius. 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 3rd