Electric lamp and discharge devices: systems – Current and/or voltage regulation – Automatic regulation
Reexamination Certificate
2000-08-23
2001-09-18
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
Automatic regulation
C315S224000, C315S283000, C315S287000, C315SDIG002, C315SDIG005
Reexamination Certificate
active
06291947
ABSTRACT:
I. PRIOR ART
Such a circuit arrangement is disclosed, for example, in German Laid-Open Specification DE 196 19 580. This document describes a safety disconnection device for a half-bridge inverter, said safety disconnection device detecting the occurrence of a rectifying action in the discharge lamp and disconnecting the half-bridge inverter in this case. The safety disconnection device is designed such that it responds to a DC voltage across the half-bridge capacitor which is caused by a DC component of the lamp current. This is because the occurrence of a pronounced rectifying action in the discharge lamp marks the end of the useful life of the discharge lamp and causes a voltage drop across the half-bridge capacitor which is different from the nominal value—that is to say from half the intermediate circuit voltage. This comparatively complex safety disconnection device comprises a threshold switch and a bistable multivibrator which can be used to remove the drive signal from a half-bridge inverter transistor.
II. ILLUSTRATION OF THE INVENTION
The object of the invention is to provide, for a circuit arrangement of this generic type, an improved apparatus for detecting a rectifying action occurring in the at least one discharge lamp.
The invention achieves this object by means of the characterizing features of Patent claim
1
. Particularly advantageous embodiments of the invention are described in the dependent claims.
To monitor the voltage drop across the half-bridge capacitor, the circuit arrangement according to the invention has a first and a second RC element, which are connected to one another by a threshold switch, and means for detecting the switching state of the threshold switch. The first RC element is connected to the center tap of the half-bridge inverter, and the second RC element is connected to the half-bridge capacitor. This means that a DC voltage develops across the capacitor in the first RC element, said DC voltage being equivalent to half the intermediate circuit voltage, that is to say to half the supply voltage of the half-bridge inverter, while a DC voltage develops across the capacitor in the second RC element which is equivalent to the voltage drop across the half-bridge capacitor. The high-frequency voltage components are filtered out of the half-bridge capacitor voltage by the second RC element. During fault-free lamp operation, the aforementioned DC voltages are of approximately the same size, so that there is no significant potential difference between the two RC elements. If a rectifying action occurs in the at least one discharge lamp, then the voltage drop across the half-bridge capacitor changes, as does the DC voltage across the capacitor in the second RC element, accordingly. If the potential difference between the capacitors in the two RC elements reaches the threshold voltage of the threshold switch, then said threshold switch is switched to the conductive state and a current flows between the two aforementioned capacitors in order to equalize their different charge state. The switching state of the threshold switch or the flow of current between the capacitors in the two RC elements is detected by the drive apparatus in the half-bridge inverter using suitable means, so that the half-bridge inverter can be disconnected in a fault situation.
The circuit arrangement according to the invention advantageously has a nonreactive resistor which is arranged in parallel with the threshold switch and forms a voltage divider with the resistors in the first and second RC elements. Using this additional resistor, the switching threshold of the monitoring circuit according to the invention can, with suitable dimensioning of the aforementioned resistors, be set to any desired voltage value above the threshold voltage of the threshold switch. In addition, the circuit arrangement according to the invention advantageously has a capacitor which is arranged in parallel with the threshold switch and holds the threshold switch, once it has been switched on, in the conductive state sufficiently long to ensure that the charges in the capacitors in the first and second RC elements are equalized. The threshold switch used is advantageously a diac, since this reacts both to positive and to negative voltages. To detect the switching state of the threshold switch, the monitoring circuit according to the invention advantageously has a further nonreactive resistor, through which the current equalizing the different charges in the capacitors in the two RC elements flows. A rectifier is advantageously connected upstream of this resistor, so that the aforementioned equalization current between the capacitors in the RC elements produces unipolar voltage pulses across the resistor whose polarity is independent of the direction of flow of the equalization current. These unipolar voltage pulses can be used by the monitor input of an integrated circuit in order to disconnect the half-bridge inverter.
The monitoring circuit according to the invention may advantageously be used for separately controlled half-bridge inverters. It is also distinguished by the fact that it is not susceptible to faults, because, with the exception of the resistor through which the equalization current flows, all the components of the monitoring circuit according to the invention are arranged in the high-voltage part of the circuit arrangement, and the signal line from the rectifier to the resistor through which the equalization current flows is terminated at low resistance by said resistor.
REFERENCES:
patent: 5493182 (1996-02-01), Sowa et al.
patent: 5677602 (1997-10-01), Paul et al.
patent: 5770925 (1998-06-01), Konopka et al.
patent: 5869937 (1999-02-01), Konopka
patent: 5994847 (1999-11-01), Konopka
patent: 6177768 (2001-01-01), Kamata et al.
patent: 196 19 580 (1997-11-01), None
Busse Olaf
Grabner Martin
Koeppl Richard
Bessone Carlos S.
Patent-Treuhand-Gelsellschaft fuer elektrische Gluehlampen mbH
Tran Thuy Vinh
Wong Don
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