Electric lamp and discharge devices: systems – Current and/or voltage regulation – Automatic regulation
Patent
1979-10-11
1982-03-16
LaRoche, Eugene R.
Electric lamp and discharge devices: systems
Current and/or voltage regulation
Automatic regulation
315199, 315291, 315308, 315DIG4, H05B 41392
Patent
active
043203264
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an electronic device for controlling the brightness of an electrical gas-discharge lamp, without an incandescent cathode, fed from an a.c. network, comprising a circuit arrangement for controlling the electrical energy, fed to the lamp, by varying the ignition angle within each alternating-voltage half-wave, as a function of an adjustable d.c. control voltage.
Many designs of electronic devices for controlling the brightness of incandescent filament lamps are known and in use. They operate on the basis of so-called phase-shift control in which the ignition angle, as measured beginning with the zero axis crossing of the current, is controlled within each alternating-voltage half-wave. Among known circuit arrangements for phase-shift control are those in which the ignition angle is variable as a function of an adjustable d.c. control voltage.
Whenever use is made of a circuit arrangement for phase-shift control, of the type described, for controlling the brightness of a gas-discharge lamp without an incandescent cathode, e.g. a mercury-vapour lamp or a sodium-vapour high-pressure lamp, it is found that when reducing the brightness that there is a danger of the lamp being completely extinguished, especially if voltage fluctuations, or brief voltage interruptions occur whenever the lamp is in the state of reduced brightness. Once the gas-discharge lamp has been extinguished, it cannot be ignited again, and thus switched on, until it has cooled down to ambient temperature.
Now it is the task of the present invention to create a relatively simple electronic device for controlling the brightness of an electrical gas-discharge lamp, with which device an unwanted extinction of the lamp is reliably avoided whenever its brightness is reduced.
According to the invention, this task is achieved by means of a device of the initially mentioned type, which has an additional circuit arrangement for producing a regulating voltage, dependent on the intensity of the current flowing through the gas-discharge lamp, for ensuring a given minimal intensity of the current flowing through the lamp automatically, regardless of the level of the d.c. control voltage.
The d.c. control voltage is preferably fed to a voltage divider consisting of a fixed resistor and a variable resistor controlled electronically by the regulating voltage, whereby a connecting point between said fixed and variable resistors is connected to an ignition-angle-control input of the first-mentioned circuit arrangement.
The device is a bipole and may therefore be simply arranged like a conventional on-off switch in one of the leads for the supply current to the gas-discharge lamp, and for this reason no additional installations are necessary.
The device comprising the above-mentioned characteristics of the invention is particularly suitable for controlling the brightness of a mercury-vapour lamp, thereby the brightness of the lamp may be reduced to about 3% of the brightness at full rated power, without any danger of inadvertently extinguishing the lamp completely.
It has been found that in case of controlling the brightness of a sodium-vapour high-pressure lamp, additional problems occur. The reason for this is to be found in the great difference between the characteristics of a mercury-vapour lamp and of a sodium-vapour high-pressure lamp. In the case of a sodium-vapour high-pressure lamp, the minimal admissible current intensity is largely dependent on the pertinent temperature of the lamp. At the normal operating temperature of the lamp, the minimal current intensity is relatively high, and decreases as the lamp temperature drops. In case the intensity of the lamp current is altered by varying the ignition angle by means of the d.c. control voltage, a change in the lamp temperature occurs only after a considerable delay in time, because of the thermal inertia of the lamp. Whenever the regulating voltage ensuring the minimal current is made dependent solely on the intensity of the current flowing through the lamp, and whenever
REFERENCES:
patent: 3989976 (1976-11-01), Tabor
patent: 3991344 (1976-11-01), Tabor
Banziger Walter
Coufal Hanspeter
Elstrom Electronic AG
LaRoche Eugene R.
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