Method and control circuit for regulation of the operational cha

Details Method and control circuit for regulation of the operational cha Method and control circuit for regulation of the operational cha

1998-07-14

2000-05-09

Wong, Don

Electric lamp and discharge devices: systems

Current and/or voltage regulation

315307, 315194, 315224, G05F 100

Patent

active

060608439

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a method and an electronic control circuit, such as for example an electronic control gear, for regulating the operating behaviour, in particular the brightness, of gas discharge lamps.
2. Description of the Related Art
FIG. 5 shows, for example, the construction of a known electronic control gear for controlling a gas discharge lamp 3 as disclosed in EP-A1-0 490 329. EP-A1-0 338 109 has disclosed an electronic control gear similar to the circuit arrangement shown in FIG. 5 in which however, in place of heating transformers T1 and T2 illustrated in FIG. 5, an ignition or heating capacitor connected in parallel to the lamp coils is used.
In accordance with FIG. 5, a rectifier 1, comprising diodes D1-D4 connected to form a bridge circuit, is connected via capacitors C1 and C2 to an a.c. voltage source u.sub.E. The capacitors C1 and C2 are part of a radio interference suppression arrangement. The input a.c. voltage u.sub.E rectified by the rectifier 1 is fed to an inverter 2 which generally comprises two alternately switched semiconductor switches. The inverter 2 converts the line voltage rectified by the rectifier 1 into an output a.c. voltage. Here the output frequency and/or duty factor between the switch-on times of the semiconductor switches of the inverter 2 is/are variable. The output voltage of the inverter is fed to a load circuit comprising a series-resonance circuit consisting of a coil Li and a capacitor C8, a coupling capacitor C4, heating transformers T1 and T2 for the lamp coils, and the gas discharge lamp 3. The gas discharge lamp 3 is connected via wire conductors to heating transformers T1 and T2. The lamp current i.sub.L flowing across the gas discharge path of the gas discharge lamp 3 is tapped across a shunt resistor R1 and is normally used as regulating variable for the brightness of the gas discharge lamp 3, i.e. the frequency and/or duty factor of the inverter 2 is regulated as a function of the actual value of the lamp current i.sub.L in order to dim the brightness of the gas discharge lamp 3. The gas discharge lamp 3 is dimmed in that the output frequency f of the inverter 2 is increased. The initial ignition of the gas discharge lamp 3 takes place in that the output frequency of the inverter 2 is adapted to the resonance frequency of the series-resonance circuit comprising the coil L1 and the capacitor C8.
If, however, the lamp current i.sub.L is used as regulating variable, operating disturbances can occur due to excessively long connection lines between the terminals of the electronic control gear and the gas discharge lamp. This manifests in particular in the case of strong dimming, i.e. with low brightness of the gas discharge lamp. These operating disturbances are caused by capacitive influences of the wiring as parasitic capacitances C5 and C6 occur between the lines and earth and a parasitic capacitance C7 occurs between the lines. It can be seen from FIG. 5 that the capacitances C5 and C6 between the lines and earth only slightly in fluence the lamp current i.sub.L measured via the resistor R1 as the capacitive currents flowing across these capacitances C5 and C6 are conducted past the resistor R1 and the capacitance C6 of the line 2 is balanced to earth by the dimming c apacitor C3 relative to R1.
On the other hand, the capacitive current produced by the parasitic capacitance C7 between the lines is superimposed upon the lamp current i.sub.L measured via the shunt resistor R1. The resistance equivalent circuit diagram, shown in FIG. 6, of the lines with the gas discharge lamp 3 and the parasitic capacitance C7 shows that the shunt resistor R1 is supplied via the line 2 with the lamp current i.sub.L flowing across the lamp resistor R.sub.Lampe and the capacitive current i.sub.C7 flowing across the parasitic capacitance C7. Thus not a purely ohmic current, but a current i.sub.L +i.sub.C7, shifted in phase relative to the lamp voltage as a function of the parasitic capacitance C7, flows acr

REFERENCES:
patent: 5495405 (1996-02-01), Fujimura et al.
patent: 5563477 (1996-10-01), Ribarich
patent: 5583402 (1996-12-01), Moisin et al.
patent: 5589742 (1996-12-01), Ueda
patent: 5600211 (1997-02-01), Luger
patent: 5717295 (1998-02-01), Nerone
patent: 5739643 (1998-04-01), Usui

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