Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Periodic switch cut-out
Reexamination Certificate
1999-12-22
2001-03-06
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Periodic switch cut-out
C315S119000, C315S2090SC, C315S291000, C315SDIG007
Reexamination Certificate
active
06198231
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a circuit arrangement for operating at least one discharge lamp.
I. BACKGROUND OF THE INVENTION
A known circuit arrangement is disclosed, for example, in the Laid-Open Patent Specification EP 0 753 987 A1. This circuit arrangement has a half-bridge inverter with a switch-off device which switches off the half-bridge inverter in the case of an anomalous operating state—for example in the case of a lamp which refuses to start or is defective. The switch-off device has a field effect transistor whose drain-source path is arranged in the control circuit of a half-bridge inverter transistor and switches the control circuit between a low-resistance and a high-resistance state. Upon the occurrence of an anomalous operating state, the switch off is performed synchronously with the blocking phase of that half-bridge inverter transistor in whose control circuit the field effect transistor is arranged. The switch-off device of this circuit arrangement certainly switches the half-bridge inverter off reliably in the case of a lamp which refuses to start, but it reacts in general too insensitively to the occurrence of the so-called rectifying effect of the discharge lamp, which will be explained in more detail below.
A possible cause of failure of discharge lamps, in particular of low-pressure discharge lamps, is occasioned by a reduction over the lifetime of the lamp in the ability of the lamp electrodes to emit. Since the loss of the ability to emit generally proceeds with varying intensity in the two lamp electrodes over the lifetime of the lamp, at the end of the lifetime of a discharge lamp operated with alternating current a preferred direction has been formed for the discharge current through the discharge lamp. The discharge lamp develops a current-rectifying effect in this case. This effect is designated as a rectifying effect of the discharge lamp. Owing to the occurrence of the rectifying effect in the discharge lamp, the lamp electrode incapable of emission is heated extremely, with the result that impermissibly high temperatures can occur which can even cause melting of the lamp bulb glass.
Moreover, in the case of discharge lamps which are operated on a half-bridge inverter, the rectifying effect of the discharge lamp causes a substantial deviation in the voltage drop across the coupling capacitor or the coupling capacitors from the normal value, which is usually half as large as the value of the input voltage of the half-bridge inverter. In the case of self-oscillating half-bridge inverters, this deviation in the voltage drop across the coupling capacitor or the coupling capacitors leads to stopping the oscillation of the half-bridge inverter, because the supply voltage of one of the two half-bridge branches is in this case too low to maintain the feedback. However, immediately after being interrupted the oscillation of the half-bridge inverter is set going again by the starting circuit of the half-bridge inverter if the switch-off device is not triggered. As a result, the discharge lamp affected by the rectifying effect is not reliably switched off, but flickers instead.
II. SUMMARY OF THE INVENTION
It is the object of the invention to provide a circuit arrangement for operating at least one discharge lamp with an improved switch-off device which does not have the disadvantages of the prior art. In particular, the aim is for the switch-off device to detect the occurrence of the rectifying effect of the at least one discharge lamp and to switch off the half-bridge inverter permanently in this case.
The circuit arrangement according to the invention, which has a half-bridge inverter with a downstream load circuit, at least one coupling capacitor connected to the load circuit and the half-bridge inverter, as well as terminals for at least one discharge lamp and a switch-off device for switching off the half-bridge inverter upon the occurrence of an anomalous operating state, has, according to the invention, means for monitoring the voltage drop across the at least one coupling capacitor and for activating the switch-off device as a function of the voltage drop detected across the at least one coupling capacitor.
As already explained further above, the occurrence of the rectifying effect of the at least one discharge lamp causes a substantial deviation in the voltage drop across the at least one coupling capacitor from its normal value, which is half as large as the input voltage of the half-bridge inverter. With the aid of the above named means according to the invention, the occurrence of the rectifying effect of the at least one discharge lamp is detected by using these means to monitor the voltage drop across the at least one coupling capacitor, and activating the switch-off device when the voltage drop across the at least one coupling capacitor deviates substantially from its normal value.
The above named means according to the invention advantageously have a first device for activating the switch-off device upon a predetermined upper limiting value of the voltage drop across the at least one coupling capacitor being reached, and a second device for activating the switch-off device upon a predetermined lower limiting value of the voltage drop across the at least one coupling capacitor being reached. The upper and the lower limiting values must be preset so that a slight asymmetry in the case of the lamp electrodes does not already lead to activation of the switch-off device. For this reason, the upper limiting value is advantageously not less than 75 percent of the input or supply voltage of the half-bridge inverter, and the lower limiting value is advantageously at most 25 percent of the input or supply voltage of the half-bridge inverter.
The first and/or second device advantageously have at least one electric component with a nonlinear current-voltage characteristic which is connected to the at least one coupling capacitor and to the at least one control input of the switch-off device. With the aid of such an electric component with a nonlinear current-voltage characteristic, the upper or lower limiting value of the voltage drop across the at least one coupling capacitor for which the switch-off device is activated by the first or second device can be preset to the desired level. Components from the group of diode, Zener diode, suppressor diode and varistor are advantageously suitable as electric components with a non-linear current-voltage characteristic. Furthermore, the switch-off device of the circuit arrangement according to the invention advantageously has at least two control or regulating inputs, specifically one each for the first device and the second device. A control input is advantageously additionally connected in parallel in terms of alternating current with the at least one discharge lamp, in order to monitor the voltage drop across the terminals for the at least one discharge lamp. In order to ensure that the half-bridge inverter is switched off as reliably and permanently as possible during a malfunction or upon the occurrence of the rectifying effect of the at least one discharge lamp, the switch-off device of the circuit arrangement according to the invention advantageously has a bistable switching device. A thyristor equivalent circuit constructed from two transistors is particularly well suited as bistable switching device, since said circuit already has available two separate control inputs which can be used by the first and the second device to activate the switch-off device. The first device advantageously comprises an electric component with a nonlinear current-voltage characteristic, and a diode connected in series therewith, the anode of the diode being connected to a lamp terminal and to the at least one coupling capacitor, while the cathode of this diode is connected to the electric component with the nonlinear current-voltage characteristic, this electric component being connected to the first control input of the switch-off device. The second device advantageously comprises the series circui
Rudolph Bernd
Schemmel Bernhard
Weirich Michael
Bessone Carlo S.
Patent-Treuhand-Gesellschaft Fuer Elektrische Gluehlampen MBH
Philogene Haissa
LandOfFree
Circuit configuration for operating at least one discharge lamp does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Circuit configuration for operating at least one discharge lamp, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Circuit configuration for operating at least one discharge lamp will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2494270