DK171604B1 - Ballast for a discharge lamp - Google Patents

Abstract

A ballast for a discharge lamp (L) contains, in the normal manner, an invertor (C) supplied from a DC voltage source (B), which invertor generates the alternating voltage for the discharge lamp (L). The discharge lamp (L) is located in parallel with the capacitor (C10) of a series-resonant circuit (L6/C10). A variable frequency AC voltage is supplied from a variable frequency generator (6, 7, 8, 9, 15, 16) to the invertor (C). The frequency of the variable frequency generator can be controlled by a control unit (10). Control signals are supplied to the control unit, which signals correspond to various parameters of the ballast. These parameters are the lamp voltage, the lamp current, the DC power, the DC voltage, a low-voltage DC voltage and the phase angle of the load circuit (E) for the invertor (C). The reaction of the control unit (10) to changes in the parameters mentioned is to change the frequency of the frequency generator or to switch off the frequency generator or the invertor (C). <IMAGE>

Description

in DK 171604 B1

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a discharge lamp for a discharge lamp coupled in parallel with a series resonant circuit capacitor in an inverter load circuit / which is connected to a DC voltage source and controlled by a 5 frequency generator. above this idle frequency, and a voltage measuring unit connected to the control unit, which measures the lamp voltage and produces a corresponding signal.

From DE patent specification 30 14 419 it is known to measure the lamp current. When too high, a bistable switching device is activated which short-circuits the inverter transformer.

From DE patent specification 31 52 951 it is known that when the ballast is switched on, a monostable multivibrator is brought into the unstable state in which it short-circuits an extra winding in the inverter transformer so that it operates at a high frequency. At this high frequency there is a reduced voltage above the lamp where ignition cannot take place. However, until the monostable multivibrator returns to the stable state, the filament filament can be heated and emitted. After the multivibrator has returned to the steady state, the short circuit is canceled by the extra winding, whereby the inverter operates at a lower frequency that is close to the resonant frequency of a series resonant circuit. The lamp is connected in parallel with the series resonant capacitor. At the lower frequency, the capacitor and the lamp, due to the resonance, produce an increased voltage sufficient for ignition.

35 DK 171604 B1 2

For control of the inverter, it is known from DE publication no. 32 08 607 to use two frequency generators, one of which generates the working frequency and the other an idling frequency. Instead of two generators, an adjustable generator can also be used. First, the high idle frequency is switched on, where no ignition can occur. Thereby the lamp electrodes are preheated. Due to the large positive temperature coefficient of the electrode resistance, it can be recognized by appropriate selection of the reaction threshold for a threshold value switch whether the electrodes are already sufficiently preheated. If this is the case, then the threshold switch reacts and the low frequency generator is switched on, or - if an adjustable generator is used - the frequency is lowered in the direction of the working frequency so that ignition can occur.

From WO-A 82/01276 a drive circuit is known which has an overcurrent detector for the inverter thyristors. The detector 20 must be alerted when both thyristors are simultaneously in the conductive state and in this case the thyristors are switched off.

Furthermore, it is known from DE-A-3 432 266 to connect a measuring winding to the lamp coil of the lamp, from which a signal can be derived, which shows the ignition state and is fed to a monitoring circuit. The monitoring circuit determines from this signal whether the series resonant circuit containing the throttle coil oscillates at the ignition frequency through the lamp without appreciable attenuation, as is the case with an unlit lamp, or whether the series resonant circuit is attenuated by a lit lamp. The corresponding message from the monitoring circuit is queried by a control circuit for an oscillator operating the inverter. This control circuit controls the oscillator in such a way that it alternates for a specified period first with a high starting frequency, then with a lower heating frequency, then with the further lowered resonant frequency of the series resonant circuit, and finally with the even lower operating frequency. . When the query of the ignition circuit on the ignition frequency shows that the lamp has not switched on, the control circuit resets the oscillator back to the start frequency and the method is repeated.

The object of the invention is to provide a ballast apparatus whose reliability is increased by monitoring and evaluating various parameters, whereby the requirement for increased reliability is particularly due to the realization of most components within the framework of an integrated semiconductor chip.

15

This object is achieved with the features of claim 1.

In the accompanying drawing, FIG. 1 is a block diagram of the ballast apparatus and FIG. 2 shows the timing of the drive voltage of the inverter compared to the total current of the lamp.

25

The block diagram of FIG. 1 consists of several modules which are explained in succession.

Module A is connected to the AC network and serves as a 30 HF harmonic filter to reduce the harmonic harmonics of the grid frequency and for radio noise cancellation. It is constructed in a traditional manner and contains the chokes coils L1 and L2 as well as the capacitors C1, C2, C3 and C4.

DK 171604 B1 4

Module A is connected to Module B. This consists of a schematically indicated rectifier bridge with smoothing circuit.

At module B's terminal 16, a + DC voltage of approx. 250 V available.

5

With module B there is connected a module K which serves to generate a voltage UEG corresponding to the direct current taken from module B. The module K consists of a resistor R1, to which a series connection 10 of a throttle coil L2 is connected in parallel. capacitor C5. From the connection point between L2 and C5 the voltage UiG can be decreased.

An additional module M serves to produce an actual voltage UG corresponding to the DC voltage produced by module B. The module M is connected to the terminal 16 of module B and consists of a resistance voltage divider R2 / R3, whereby the resistor R3 is connected in parallel with a capacitor C6. The voltage UG, which can be taken from the voltage divider point, is proportional to the voltage from module B's terminal 16 but lower than this one.

Module C is an inverter which produces a variable alternating voltage based on the DC voltage from module B. For module C, an alternating voltage is applied from a later explained module E 25 to a winding L3 of a receiver transformer TI. The secondary transformer TI has two windings L4 and L5 on the secondary side. The voltage generated on the winding L4 is fed to the gate terminal of a field power transient FETI via a resistor R4 coupled in parallel with a diode D1. Between the gate terminal and the source terminal of FETI, two series connected, opposite oriented zener diodes Z1 and Z2 are connected. The voltage generated on the winding L5 of the receive transformer T1 is fed to the gate terminal of a field power transistor FET2 via a resistor R5 coupled in parallel with a diode D2. Between DK 171604 B1 5 the gate terminal of FET2 and the source terminal are connected two series connected, opposite oriented zener diodes Z3 and Z4. Resisting R4 and R5 have high resistance values and serve to delay the engagement of the FETs. Diodes 5 D1 and D2 are intended to ensure a rapid interruption of the FETs. In this way, it must be achieved that the two FETs are never fully conductive at the same time, as this would result in a short circuit. The zener diodes Z1, Z2, Z3 and Z4 are intended to protect the gate terminals of the FETs against voltage. Incidentally, the inverter of module C is constructed conventionally and its function is known, so that further explanation can be given here.

To the output of the inverter in module C, a load circuit comprising a gas discharge lamp L and shown as module E. is connected. This contains, in addition to the gas discharge lamp L, a series resonant circuit formed by a choke coil L6 and a capacitor C10. Capacitor C9 pivots for decoupling. The oscillator circuit capacitor C10 is located parallel to the gas discharge lamp L. The use of the series resonant circuit has several known advantages. Before switching on the gas discharge lamp L, the alternating current flows through the filament filaments above the parallel capacitor C10. Thereby the filaments are heated for emission. When the frequency of the voltage transmitted from module C to module E is in the vicinity of the resonant frequency of the series resonant circuit L6 / C10, a voltage increase occurs on the parallel capacitor C10 which is used to switch on the lamp L. After ignition, the lamp L attenuates the good of the series resonant circuit. -30 and the voltage across the lamp decreases as the lamp L is conductive. Now the choke coil L6 acts as a lamp flow limiter. In order to extend the life of lamp L, it is sought to preheat the filament filaments sufficiently long before ignition. To achieve this, module E first introduces a voltage with a frequency so far above the resonant frequency of the series resonant circuit L6 / C10 that the filament L's filament wires are heated, but no ignition of lamp L since the voltage across the parallel capacitor C10 due to its high frequency is too low. Then the frequency is lowered in the direction of the resonant frequency of the series resonant circuit L6 / C10, until the said voltage rise occurs on the parallel capacitor C10 and an ignition can take place. How the said frequency change of voltage applied to module E is effected is explained later.

A module G serves to produce a voltage U1, which is a measure of the total current of lamp L. The module G consists of a resistor R8 connected to one lamp electrode and through which the total lamp current flows.

A module H serves to produce a low supply DC voltage UNV of approx. 10-12 V to the components of module D, which preferably consists of semiconductor chip modules, which will be explained later. For this, module H is connected to the output of module G which, as mentioned, produces a voltage UiL corresponding to the total current of the lamp. This voltage is also derived from the total current of the lamp. It is fed to a diode D3 in module H which rectifies the voltage UiL, which is an alternating voltage. The resistor R9 and the two series-connected zener diodes Z5 and Z6 provide a voltage stabilization. The resistor R10 and the associated capacitor C11 as well as the capacitor C12 provide a smoothing of the unidirectional voltage Uf4V. However, the voltage Umv could also be extracted by the DC voltage (250 V) at module B's terminal 16, even by voltage sharing; in this case, the voltage difference between 250 V and 10-12 V had to be destroyed, which would be associated with a corresponding, undesirable heat loss and unnecessary energy consumption.

35 DK 171604 B1 7

The core of the ballast is module D. This essentially serves to produce a variable frequency for the inverter module C, and this in dependence on several parameters of the ballast. With the variable 5 frequency it is possible to change the voltage of the connections of the lamp L (module E). With an idle frequency substantially higher than the resonant frequency of the series resonant circuit L6 / C10, the load circuit, module E is inductive, and the voltage of the lamp L's connections 10 is effectively no more than 250 V. This relatively low voltage is prescribed by relevant norms (e.g. German VDE 0712) in order to allow a relatively harmless replacement of lamp L. At the ignition frequency, respectively, near the resonant frequency of the series resonant circuit 15 L6 / C10, the alternating voltage of the connections of lamp L amounts to approx. 500 V.

Module D contains a quartz fixed frequency generator 6 which e.g. generates a frequency of 8 MHz.

This frequency is fed to a frequency controller 10 which may contain, for example, a suitably programmed microprocessor (CPU). The frequency controller converts the frequency of 8 MHz from the fixed frequency generator 6 to a block 7 which supplies an 8-bit counter 9 corresponding to counting pulses 25 (clock) and at the same time causes the 8-bit counter 9 to count up or down. The latter occurs in dependence on the state of the parameters of the ballast which is passed to the frequency controller 10. The counter state of the 8-bit counter 9 is transmitted to a 7-bit comparator 16. The latter is also connected to one of the two via a 7-bit bus line. In the counter logic 8, the flip-flop chain is fed to the flip-flop chain 6's 8 MHz frequency for counting, whereby each flip-flop FF in divides the frequency by the factor 2. When the flip-flop chain state 35 equals 8-bit counter 9's, the logic portion DK 171604 B1 8 resets in the counter logic 8 connected to the 7-bit comparator 16, the flip-flop chain via line R. At the same time, the logic portion of the counter logic 8 outputs the correspondingly divided frequency to a driver circuit 15, the output of which is connected to the winding L3 of the receiving transformer T1 in the inverter module C.

The controller 10, which contains the programmed microprocessor, processes the signals fed to it in parallel and / or in series, corresponding to the individual measured parameters. The microprocessor is programmed to execute a specific program for processing these signals. The operation is described below.

A first parameter is the lamp voltage UL produced by block F, which is an alternating voltage. This is fed to one input of a comparator and regulator 12. The comparator and controller 12 are additionally connected to a unit 11 for the output of nominal values for the three three voltages UK, UH and Uz. At these three nominal voltages, these are DC voltages. The comparator and controller 12, respectively, compare the respective threshold value of the lamp alternating voltage UL with the respective nominal voltage.

25

After switching on the ballast, the lamp voltage UL usually increases. Only when the circuit is a short-circuit does it become below the rated short-circuit voltage UK. The control unit 10 now investigates, for a certain period of time, for example a period of the mains voltage, whether the lamp voltage UL remains below the nominal short-circuit voltage UK. If this is the case, the control unit 10 switches off the driver 15. Furthermore, the control unit 10 switches the entire module D in the high impedance state. This means that the blocks and components of module D may well be in standby mode in DK 171604 B1 9 but only take up very little power. Since, when the driver 15 is switched off, AC voltage is no longer applied to module E and thus also to modules G and H, the blocks and components 5 of module D are supplied with voltage from module B. As mentioned, at module B's terminal 16 there is only one high DC voltage available; however, the loss effect arising from the voltage difference to the supply voltage of components or blocks of module D designed as a semiconductor chip is low, however, since also the energy consumption of module D due to its high impedance state is low. When module D is again switched from the high impedance state to the working state, the power supply is effected through the low DC voltage Uijv, which is located at the output of module H. The switching 15 between the two power supply options is effected by the control unit 10 at block 17 for module supply voltage D.

As the lamp voltage UL falls sharply immediately after switching on the lamp 20 L and even below the nominal short-circuit voltage UK, it is necessary to interrupt the examination of lamp voltage Ui at the comparator or regulator 12 immediately after the start (ignition) of lamp L. The switch is programmed in the program. for the microprocessor in the controller 10.

The switching off of the driver 15 and the transmission of module D to the high impedance state by a detected short circuit can only be canceled by switching off and reconnecting the mains voltage. When there is no short-circuit in the coupling, the lamp voltage UL exceeds the nominal short-circuit voltage UK and increases until it reaches the nominal pre-heating voltage UH. This amounts to approx. 1.4 V. This corresponds roughly to a voltage of 200 V on the connections of the lamb-35 pin L. When the comparator and re 1717604 B1, respectively, the controller informs the control unit that the lamp voltage UL is equal to the nominal preheating voltage UH, then the control unit 10 regulates the frequency supplied to module C so that the lamp voltage UL for a certain preheating period 5 remains equal to the nominal preheating voltage Uh-During this time, in the module E the lamp filament L is heated and begins to emit. The idle frequency applied to module C (inverter) in this case is approx.

123 kHz. The preheating time is contained in the microprocessor of the controller 10 (CPU).

After the preheating time, the controller according to the program causes the frequency that is fed to module C to be lowered in the direction of the operating frequency, which is approximately 62 kHz.

15 Lowering the frequency of the inverter (module C) causes an increase in the AC voltage of lamp L's (module E) connections to about 500 V. By comparison in the regulator 12 of the lamp voltage UL with the third nominal voltage, the ignition voltage Uz, from the unit 11, the control unit 20 provides 10 when evaluating the output of the controller 12 so that the lamp voltage UL is kept equal to the nominal ignition voltage Uz. The nominal ignition voltage Uz is approx. 3.5 V. The lamp L should now turn on. When ignition occurs, the lamp voltage UL falls sharply. This is detected by the control unit 10 via the comparator and regulator 12. The ballast apparatus with lamp L is then in operation.

When the lamp voltage UL does not fall below the nominal ignition voltage Uz for a certain period of time, this means that no ignition occurred. The reason for the lack of ignition may be, for example, a gas defect in the lamp L, or the emission capability of the lamp L of the filament lamp may have ceased. If the lamp L does not start, for these or other reasons 35 in spite of obtaining the starting voltage, there is a danger that the circuit will be damaged when the relatively high starting voltage is maintained for a longer period. For this reason, the controller (CPU) 10 is programmed to interrupt a failed start attempt after a specified time. This is done by the control unit 10 increasing the frequency supplied to the inverter (module C) in the direction of the idle frequency, with the result that the voltage on the lamp connections decreases again. The control unit 10 is further programmed such that after a first failed start-10 attempt, a certain number of similar start-up attempts can be made. Also, after this particular number of additional start attempts, if the lamp L is switched on, the frequency of the inverter is set to the highest possible value, ie. idle frequency, and remains there, either until the lamp L is replaced or the AC power is switched off and on again.

Another parameter that is monitored is the lamp current. The lamp current corresponds to the actual voltage UiL, which is emitted by module G. This is fed to a comparator 13 in module D, which also receives from a reference voltage source 1 a reference voltage Uiui / which corresponds to a minimum lamp current. The comparator 13 compares the voltage UiL with the voltage UILM and reports the result to the control unit 25 10. When the voltage corresponding to the lamp current UiL is below the reference voltage, the reason for this may be, for example, a broken filament in the lamp L or the fact that the lamp L does not fit properly in its socket or is removed. In this case, the control unit 10 again controls the frequency fed to the inverter (module C) to the highest possible value, i.e. the idle frequency. Thereby, there is a relatively low and thus harmless voltage on the lamp connections (socket), which is especially important when the lamp L is removed.

35 DK 171604 B1 12

Another parameter monitored is the low DC voltage generated by module H to supply the blocks and elements of module D. This voltage UfJV is fed to a comparator 2, to which a reference voltage equal to the minimum DC voltage to be produced by module H. is also fed from the reference voltage source 15. The comparator 2's result of the comparison is again fed to the control unit 10. generated low DC voltage Unv falls below the reference voltage Unvm »10 the control unit 10 again controls the frequency of the inverter to the idle frequency and brings module D into the high impedance state.

The DC voltage generated by module B is also a monitored parameter. A voltage corresponding to this DC voltage is the voltage UG which can be taken out of module M. It is fed to a comparator 3. In addition, to the comparator 3, a reference voltage UGM corresponding to the minimum DC voltage is also supplied from the reference voltage source 1.

20 The result of the comparator 3 is compared to the control unit 10. When the voltage UG falls below the reference voltage UGM, this means, for example, that the DC voltage generated by module B has fallen below 150 V.

At this DC voltage, the inverter can no longer generate the energy to light the lamp. Initial attempts may then result in premature damage to the lamp. The control unit now checks, for at least half a grid period, whether the DC voltage supplied by module M at least once falls below the minimum DC voltage Unvm · If this is the case, then the driver will be stopped 15. This means that no further start attempts are made.

Also, the DC power is a parameter that must be monitored. The actual DC power is calculated by multiplying the DC voltage UG supplied by Module M with the DC voltage UiG delivered by Module 17 DK1 16060 B1 13. This DC voltage Uig corresponds to the direct current received by the circuit. One of the multiplier 5 produced voltage UPG corresponding to the DC power is fed to the controller 4. In addition, to the controller 5 a nominal value for the power corresponding to the reference voltage UPS is supplied. The output of the comparator 4 operating as a comparator is fed to the control unit 10. This now regulates the frequency of the inverter (module C) so that the DC power 10 recorded remains constant. In this way, the light output of lamp L is also constant. In this context, it should be mentioned that there is the possibility that the reference voltage UpS on the reference voltage source 1 can be made adjustable from the outside in order to equalize component tolerances 15 and adapt the power received by the lamp L to these tolerances by setting a (not shown) resistance clay.

When the frequency generator circuit is to be changed from the operating frequency to the idle frequency, the entire frequency range does not have to be traversed continuously, but this can be done by the control unit 10 transmitting a reset pulse to the 8-bit counter 9 via the line R.

A final parameter to be monitored is the load impedance of the field effect transistors FETI and FET2 in the inverter (module C). When the DC voltage from module B to the inverter drops, e.g. in case of a sharp drop in mains voltage or - if the DC supply to the inverter is taken from a central battery system - by a decrease in its voltage, then the field effect transistors load becomes capacitive due to the parallel capacity CIO which lies parallel to the lamp L. A capacitive load for the field power transistors. in particular, the up-35 may occur with the aforementioned decrease in the DC voltage supply DK 171604 B1 14 to the inverter / when the control frequency applied to the inverter approaches its lower limit value. With capacitive load, there is a risk of destruction of the field-effect transistors. Therefore, to avoid a capacitive load 5, the nature of the load impedance of the field effect transistors is investigated. This is done by taking out the voltage UT from the output of the driver 15 and comparing it in a phase comparator 14 with the voltage UiL corresponding to the lamp current. The rear flank of the voltage UT, which is a square voltage, thus defines the time of comparison TV. As the field effect transistors load becomes inductive, the voltage UiL, which is approximately sinusoidal waves, is shifted to the right in FIG. 2, since the current in the inductive case is after the voltage. In the capacitive case, it is the other way around. The output of the phase comparator 14 is applied to the control unit 10. As the field effect transistors load approaches the capacitive case, the control unit 10 causes an increase in the frequency applied to the inverter with the result that the load becomes inductive again.

Numerous variations can be envisaged in the ballast described above. Thus, it is not necessary that all parameters are measured and taken into account. The parameters can be measured constantly or periodically.

The controller does not have to be a microprocessor (CPU), but it can be made up of a number of single control block stores or the like. The measurement times, the times between the measurements and other times such as the preheating time can be determined by the counter logic (Flip-Flop chain) or by a separate time counter coupling. Of course, the above embodiments also apply to a ballast apparatus having more than one lamp. For example, DK 171604 B1 15 can thus be coupled two lamps in a conventional tandem coupling.

Claims (4)

1. Ballast for a discharge lamp coupled in parallel with a series resonant circuit capacitor in an inverter load circuit connected to a DC source and controlled by a frequency generator whose frequency can be changed by means of a control portion placed between a resonant frequency resonant -10 nuance frequency and an idle frequency above it, and a voltage measuring unit connected to the control unit, which measures the lamp voltage and produces a corresponding signal, and a regulator (12), characterized in that the signal (UL) corresponding to the lamp voltage is supplied to the controller (12) comparing this (UL) to a reference signal (UH) corresponding to a preheating voltage and giving the comparison result to the control unit (10) and the control unit (10) setting the frequency of the frequency generator (6, 7, 8, 9). 15, 16) in the vicinity of the idle frequency and controls said frequency such that the while the preheating period is kept equal to the preheating voltage, and after the end of the preheating time the control unit (10) controls the frequency of the frequency generator (6, 7, 8, 9, 15, 16) so that it is lowered in the direction of the operating frequency. Ballast according to claim 1, characterized in that the measurement signal (UL) corresponding to the lamp voltage in a comparator contained in the controller unit 30 (12) is compared with a reference signal (U2) (corresponding to the ignition voltage of the lamp and the comparison result is applied to the control unit (10), that the control unit (10) regulates the frequency of the frequency generator (6, 7, 8, 9, 15, 16) depending on the comparator result of a comparator in a closed control circuit such that the lamp voltage is 17 of a particular ignition time does not exceed the reference voltage and, after the ignition time, the control unit (10) increases the frequency of the frequency generator in the direction of the idle frequency if the lamp voltage during the ignition time is not greatly reduced due to the ignition. Ballast apparatus according to claim 2, characterized in that the control unit (10) in turn lowers the frequency of the frequency generator (6, 7, 8, 9, 15, 16) towards the operating frequency, the control unit (10) repeating the ignition attempts a predetermined number times if no ignition is obtained in the meantime and the control unit (10) sets the frequency of the frequency generator (6, 7, 8, 9, 15, 16) to a constant frequency at idle frequency if no ignition occurs after the predetermined number. ignition attempts. Ballast apparatus according to one of the preceding claims, characterized in that the control unit (12) or the comparator compares the measurement signal (UL) corresponding to the lamp voltage with a stored reference signal (UK) corresponding to a short circuit over the lamp, and announces the interconnection result to the control unit (10) and the control unit (10) switches off the frequency generator (6, 7, 8, 9, 15, 16) or the inverter (C) when the signal connection shows that the lamp voltage does not during the a certain amount of time exceeds the short-circuit voltage. 30