Electric lamp and discharge devices: systems – Current and/or voltage regulation – Automatic regulation
Patent
1997-11-06
1999-08-31
Wong, Don
Electric lamp and discharge devices: systems
Current and/or voltage regulation
Automatic regulation
315291, 315224, 315DIG2, 315DIG7, G05F 100
Patent
active
059457872
DESCRIPTION:
BRIEF SUMMARY
STATE OF THE TECHNOLOGY
The invention is based on a power control of an AC-operated, high-pressure gas discharge lamp, particularly for motor vehicles, of the generic type defined in the preamble to claim 1.
DE 37 29 383 A1 discloses a circuit arrangement for operating a high-pressure gas discharge lamp that includes a bridge circuit, in which two controlled switching transistors are disposed in at least one branch, and in which the high-pressure gas discharge lamp is supplied with ignition and burning energy by way of the bridge branch of the bridge circuit.
In this known circuit arrangement, the high-pressure gas discharge lamp is disposed directly in the bridge branch of a bridge circuit configured as a capacitive half-bridge, with a throttle coil further being disposed in series with the lamp. Moreover, the secondary winding of an ignition transformer is provided in series with this arrangement. The supply current of the lamp, and thus the power control, is regulated by changes in the duty cycle of the switching transistors. At the start, the duty cycle is changed in a specific manner. The pulse-sequence frequency of the AC-type, bi-polar supply-current pulses is about 300 Hz in sodium discharge lamps, for example, and is superposed with a higher-frequency voltage between 30 and 70 kHz. The starting duty cycle is set at about 0.7, and the operating duty cycle is set at about 0.5.
It cannot be inferred from this known circuit arrangement whether, on the one hand, it is or can be used for starting and operating high-pressure gas discharge lamps such as those that can be installed into motor vehicles and are supplied with low voltage values, e.g. 6 or 12 Volts, from the onboard DC-voltage electrical system. On the other hand, the power control of this known circuit arrangement operates according to a different principle, and is not as low-loss as is necessary.
Applicant markets high-pressure gas discharge lamps under the name "Litronic." These lamps, which are used in motor vehicles, operate according to two different principles. According to the one principle, both start and operation are executed in so-called resonance operation. The starting frequency, that is, the frequency during lamp ignition, is about 80 kHz, and the burning frequency is about 8 to 16 kHz. According to the other principle, the lamp is operated in so-called free-wheeling DC operation, that is, the direct current changes poles again and again. The pole-reversal frequency is about 400 Hz. The lamp is ignited by way of a separate pulse igniter. The lamps used here are so-called xenon lamps or metal-halogenide lamps whose high pressure is about 80 bar. To ignite the light arc, a high voltage of 24 kV is necessary with regard to the poorest tolerance conditions. In burning operation, the necessary voltage is about 85 Volts.
Fundamental disadvantages associated with these two principles are that relatively numerous components and a special ignition device are necessary and, furthermore, that the components are rather large and must be resistant to high voltages. The disadvantages of this include relatively high costs, fairly high power losses and a considerable space requirement.
ADVANTAGES OF THE INVENTION
In contrast, the power control of the invention for an AC-operated, high-pressure gas discharge lamp, particularly for motor vehicles, having the characterizing features of claim 1, has the advantage of simple and economical power control that is loss-free up to the internal switching losses in the switching transistors. This is particularly essential for avoiding operation-stipulated switching losses in high-frequency operation of the switching transistors, as well as with respect to use in motor vehicles for preserving the battery capacity.
In accordance with the invention, this is basically achieved in that the switching transistors switch the current in the form of pulse packets, with the individual pulse packets respectively containing a specific number of high-frequency pulses; that switching is effected with the lowest possi
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patent: 5481162 (1996-01-01), Boenigk et al.
patent: 5677602 (1997-10-01), Paul et al.
Gorille Ingo
Mueller Bernd
Philogene Haissa
Robert & Bosch GmbH
Spencer George H.
Wong Don
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