GB2154342A

GB2154342A - Discharge lamp control circuit

Info

Publication number: GB2154342A
Application number: GB08503979A
Authority: GB
Inventors: Martti Sairanen
Original assignee: Helvar Oy AB
Current assignee: Helvar Oy AB
Priority date: 1984-02-17
Filing date: 1985-02-15
Publication date: 1985-09-04
Also published as: GB2154342B; SE8500634D0; DE3504428A1; GB8503979D0; FI840650A0; FI68747C; FI68747B; SE8500634L

Abstract

A light controller for a discharge lamp (1) with an electronic ballast (2) is separate from the ballast, and is connected to control the mains voltage (4) supplied to the ballast. The controller has an output stage (5) connected in the mains voltage line and regulates the input power. A comparator (7) is connected to a control unit (6), the input of the comparator being provided with a control voltage (Uc) and a voltage depending on a phase angle controlled voltage (3). A device (9) regulates the control voltage (Uc) as well as a starting circuit (8) for switching on control voltage (Uc) in order to maintain constant the power taken up by the load despite mains voltage variations, the voltage depending on controlled voltage (3) is connected to comparator (7) through a circuit (10) simulating the electronic ballast (2). Initially, the starting circuit (8) supplies only a low voltage to the comparator (7). <IMAGE>

Description

SPECIFICATION Light controller for a luminous discharge lamp fitted with an electronic ballast The present invention relates to a light controller for a luminous discharge lamp fitted with an electronic ballast, said controller being designed as a controller unit separate from the ballast, which unit is connected to a mains voltage line supplying the ballast for controlling the mains voltage supplied to the ballast, said controller comprising an output stage connected to a mains voltage line and regulating the input power, an output stage control unit for controlling the power regulating components, a comparator connected to the control unit, the input of said comparator being provided with a control voltage and a voltage depending on the controlled voltage, a control device for regulating the control voltage as well as a starting circuit for switching on the control voltage.

Finnish Patent publications 64487 and 63849 disclose a circuit arrangement for supplying power through a separate mains voltage controller to an electronic ballast. By means of this arrangement, the luminosity of lamps can be controlled within a wide range with no malfunctions when employing luminous discharge lamps whose tubes have a thickness of 38 mum. Howadays, so-called thin discharge lamps having, tubes of thickness 26mm are becoming more and more popular.

An advantage gained by these thin discharge lamps is that there is approximately a 10% lower energy consumption as compared to one with a thick tube, with equal luminosity.

However, thin fluoresent tubes are not controllable using traditional methods employed in 38mm tubes. By employing a certain type of electronic ballast (see Finnish Patent publication 64487) it is, however, possible to regulate even thin fluorescent tubes within -a substantially wide range of adjustment. However, the use of an electronic ballast serving as a controller involves the following special requirements.

1. The power taken up by a controller load should be maintained at a constant value by means of the controller despite the mains voltage variations.

2. The maximum output voltage of a controller must be artificially restricted.

3. As the controller is started up, the output voltage of said controller must be made to change according to a certain starting sequence before the output voltage reaches a value set up by a control voltage.

According to the invention there is provided a light dcontroller for a luminous discharge lamp fitted with an electronic ballast, said controller being designed as a controller unit separate from the ballast, which unit is connected to mains voltage line supplying the ballast for controlling the mains voltage supplied to the ballast, said controller comprising an output stage connected to a mains voltage line and regulating the input power, an output stage control unit for controlling the power regulating components, a summing unit comparator connected to said control unit, the input of said comparator being provided with a control voltage (Uc) and a voltage depending on a controlled voltage, a control device for regulating control voltage (Uc) as well as a starting circuit for switching on said control voltage (Uc), wherein the said voltage depending on controlled voltage is connected to said comparator through a circuit simulating said electronic ballast.

One of the advantages gained by objective 1 is that, after setting up a certain minumum level of illumination at which th lamps do not blink, this established minumum level remains unchanged, and a decrease in the mains voltage does not lead to the blinking of lamps.

Similarly, a preset level of illumination, intended e.g. for viewing slides, remains constant.

An advantage gained by ovjective 2 is to avoid burning the lamps on excessive power.

The input stage and thyristor controller of an electronic ballast make up an oscillating circuit, in which the internal direct-current voltage of the electronic ballast may rise higher than the value obtained by supplying a sinusoidal input directly from the mains. This increase in direct-current voltage causes the lamps to burn on excessive power, cutting back the service life of both the lamps and the electronic ballast. Thus, this can be avoided by fulfilling objective 2.

An advantage gained by combining objectives 1. and 2. is e.g. that the increase of the mains voltage higher than a nominal value does not lead to increased power consumption of the lamps, which in turn would result in a shorter service life for the lamps.

An advantage gained by fulfilling objective 3 is that, at the moment of switching on a light, it is always possible to guarantee a sufficient voltage for lighting the lamps. Moreover, by performing the lighting "softly" by first supplying to the lamp cathodes plenty of filament current, the service life of lamps can be increased as a function of lighting times.

One embodiment of the invention will now be described in more detail, by example only, with reference to the accompanying drawings, in which Figure 1 is a block diagram for a conrtroller of the invention and Figure 2 is a circuit diagram for block element corresponding to a simulator circuit.

Figure 3 shows a curve for the controlled voltage during start-up.

Figure 4 is a circuit diagram for several of the blocks in the block diagram shown in Fig.

1.

Electric power is supplied to luminous discharge lamps 1 through electronic ballasts 2.

Ballast 2 may for example be of the type disclosed in Finnish Patent Publication 64487. Connected to one ballast 2 may be one or more discharge lamps. Electric power is delivered to one or a plurality of ballasts 2 through a separate mains voltage controller, the power-regulating output stage 5 of said controller being connected to a mains voltage line. The output stage 5 is provided with thyristors which pass a portion defined by their trigger control from the half-waves of mains voltage 4, the controller output having therein a phase-angle controlled voltage 3.

Reference numeral 6 designates a block which contains the trigger control circuits for thyristors. A control device 9 is fitted with a potentiometer 9 for regulating a control voltage Uc, connected to a summing unit 7 under the control of a starting circuit 8. On the other hand, said controlled voltage 3 is fed back to the controller through a circuit 10 simulating the electronic ballast 2. The voltage Us received from simulator circuit 10 and control voltage Uc are added to each other inopposite signs.If control voltage Uc is sufficiently higher than the absolute value of the voltage Us received from simulator circuit 10, said comparator 7 controls the trigger control unit 6 of thyristors in a manner such the thyristors in output unit 5 pass an increasing portion of the mains voltage half-waves and, accordingly, when control voltage Uc is lower than the voltage corresponding to the state of equilibrium the thyristors pass a decreasing portion of the mains voltage half-waves.

When control voltage Uc remains constant, the thyristors are controlled so as to pass a portion of the mains voltage half-waves such that said control voltage Uc, subtracted with an offset voltage corresponding to the state of equilibrium, and the absolute value of a voltage Us received from simulator circuit 10 are equal.

Fig. 2 illustrates more clearly the simulator circuit 10 of an electronic ballast. It is separated from the main circuit by means of a transformer 11. The circuit, made up by a choke 12, a capacitor 13, a rectifier 1 4 and an electrolyte capacitor 15; corresponds in its connection to the input stage of an electronic ballast. A resistance 1 6 is the simulator of a ballast load. The ballast-simulating components 12-15 react to the controlled voltage 3 exactly the same way as the ballasts 2 themselves, so this type of simulating scale model serves best to find out what kind of directcurrent voltage prevails inside the electronic ballast 2.Another advantage gained by a simulating scale model is that, if one of the controllable electronic ballasts 2 is damaged and causes a change in the voltage level of other ballasts 2, will be immediately discovered and on the basis of this information the controller output voltage will be automatically directed the right way.

In this embodiment said starting circuit 8 is provided with a start voltage circuit which does not connect the control voltage Uc set by a control device 9 to a comparator until after a constant start voltage Us, providing approximately a 10% level of illumination, has been on for a certain period of time. In Fig. 3, the vertical axis shows controlled voltage 3 and the horizontal axis shows time. The mains voltage is switched on at a moment to and, after a waiting time to-ti, then for a certain period of time t,-t2 there acts a start voltage Us on which the incandescence of the lamp cathodes occurs at approximately a 10% level of illumination.During the interval t2-t3, said controlled voltage is set in the state corresponding to control voltage Uc the voltage level "a" being reached with a high control voltage and the voltage level "b" being reached with a low control voltage.

A starting circuit 8 shown in Fig. 4 operates in a manner such that, as the mains voltage is switched on, the capacitor C 3 is empty so as to bring a transistor T into conducting state.

When the transistor is conducting, voltage Uc does not have any effect on the operational amplifier IC 1 and thus also the output of the operational amplifier IC 2 remains low. However, the voltage to be passed to the comparator 7 should not be zero and, therefore, through a diode D 3 is passed a voltage which is set to correspond to 1 0% level of illumination. When C3 is sufficiently charged, transistor T ceases to conduct and also the passage of current through diode D 3 finishes.

Thus, said control voltage Uc will have an effect on the output of operational amplifier IC 2 which is set equal to Uc. Accordingly, the output voltage of the entire controller changes towards the output voltage value corresponding to Uc.

Claims

1. A light controller for a luminous discharge lamp fitted with an electronic ballast, said controller being designed as a controller unit separate from the ballast, which unit is connected to a mains voltage line supplying the ballast for controlling the mains voltage supplied to the ballast, said controller comprising an output stage connected to a mains voltage line and regulating the input power, an output stage control unit for controlling the power regulating components, a summing unit (comparator) connected to said control unit, the input of said comparator being provided with a control voltage (Uc) and a voltage depending on a controlled voltage, a control device for regulating control voltage (Uc) as well as a starting circuit for switching on said control voltage (Uc), wherein the said voltage depending on controlled voltage is connected to said comparator through a circuit simulat ing said electronic ballast.

2. A light controller as set forth in claim 1, wherein a starting circuit, connected between control device and comparator, is provided with a start voltage circuit which does not connect a control voltage set by control device to the comparator until after a constant voltage causing substantially a 10% level of illumination, has been on for a certain period of time (t1-t2).

3. A light controller as set forth in claim 1, wherein the said electronic ballast simulating circuit is connected by means of a differential transformer to the controller output voltage.

4. A light controller for a luminous discharge lamp fitted with an electronic ballast substantially as herein described with reference to the accompanying drawings.