Abstract: An abnormal or unbalanced load operating condition is detected in a single lamp ballast circuit or in either lamp of a two-lamp ballast circuit by feedback voltage signals that are proportional to the flow of current through the cathodes of each lamp. The analog feedback signals are combined algebraically by a summing circuit that produces a null (zero) value corresponding with normal lamp operation, and produces a non-zero value in response to abnormal cathode current flow. The non-zero value is compared with the reference value to generate a shut-down signal. In one embodiment, the cathode currents are sensed by primary windings of a toroid transformer, and the feedback signals are the magnetic flux components that are generated in response to cathode current flow through the current sensing windings.

Abstract: An improved ballast circuit for controlling the power delivered to a fluorescent lamp. The present invention uses a complex resonating circuit to dynamically adjust the power being delivered to the load. The present invention also operates in burst mode allowing an increased voltage to be applied across the lamp load without overstressing the circuit. The increased voltage will light both lamps nearing the end-of-life and lamps in cold weather.

Abstract: An electronic ballast circuit for igniting, supplying and dimming a gas discharge lamp which comprises an oscillation control circuit, an IR2155 self-oscillating half-bridge driver, a dimming control circuit, a load circuit including at least one gas discharge lamp and an over-current protection circuit, wherein the oscillation control circuit controls a current through the lamp by pulse width modulation of a drive signal during a pre-heating stage and the normal operation to control the dimming of the gas discharge lamp.

Abstract: A lighting circuit for a discharge lamp includes lighting control circuit for controlling the lighting of a discharge lamp, ignition means for supplying a trigger pulse to the discharge lamp and a socket. Power is supplied to the discharge lamp via terminals of the socket and terminals of a connector section of the discharge lamp. The socket and the connector section are respectively provided with connection terminals which are to be connected together while the discharge lamp is connected to the connecting member. When those connection terminals are not connected together, the supply of power and the supply of the trigger pulse to the discharge lamp are inhibited. This prevents problems (damaging insulation, an electric shock and the like) from arising when the lighting circuit is activated while the discharge lamp is not connected to the lighting circuit.

Abstract: A ballast system for at least one dimmable fluorescent lamp includes a resonant switching inverter and a controller which controls the inverter to operate above resonance during starting and normal running operation. After a start delay timer allows time for the lamp filaments to heat up, the controller provides control signals to a gate driver to drive the switching devices of the switching inverter initially at a relatively high frequency and then reduces the frequency until a sufficiently high voltage is reached to start the lamp. Once the lamp is started, the inverter is operated in its normal feedback mode. The ballast system further includes an overvoltage shutdown mechanism. During lamp starting, if either the output of the start delay timer is high or the output voltage is greater than a first overvoltage shutdown threshold, then an overvoltage shutdown timer is activated to shut down operation of the inverter for a predetermined overvoltage shutdown period.

Abstract: A discharge lamp driver is configured so that it can be operationally tested using a substitute impedance instead of a discharge lamp. The time required to functionally test the driver circuit with such a substituted non-discharge lamp load is considerably less than if an actual discharge lamp is used for such testing.

Abstract: A daytime running lights adapter kit (10) which is designed to be installed in a vehicle to allow the vehicle to be equipped with daytime running lights. The kit (10) is enclosed within a single enclosure (12) that encloses an electronic unit (14). From the unit (14) extends a set of cable assemblies (40-46) that have attached a set of connectors (30-36). Each connector is keyed to fit into an existing vehicle receptacle (56, 58, 62, 64) that are each connected to the particular vehicle light that is to function as a daytime running light. The daytime running lights adapter kit (120) is enabled and turns on the particular lights only when the vehicle engine (50) is operating and the manual frontlight switch (54) is off. When the vehicle engine (50) is turned off or the frontlight switch (54) is placed in the on position, the kit (10) is disabled.

Abstract: The invention concerns a circuit for operating a discharge lamp with a habridge generator (T1, T2) wherein a turn-off transistor (T3) can stop the half-bridge generator The energy source for the base current of the turn-off transistor (T3) is formed by starter capacitor (C3) which starts the half-bridge generator (T1, T2), In addition, the collector-emitter section of the turn-off transistor (T3) is directly between the base of the lower transistor (T2) of the half-bridge generator and earth.

Abstract: An electronic ballast (10) comprising an AC-to-DC converter (100), an inverter (200), an output circuit (400), a high-voltage detection circuit (500), and a no-load detection suit (600). The inverter (200) includes an inverter control circuit (300) that monitors the lamp(s) via the high-voltage detection circuit (500) and the no-load detection circuit (600), and that terminates inverter switching in response to various lamp-fault conditions such as "diode-mode" behavior. Inverter control circuit (300) also provides for automatic ignition of a replaced lamp and may be economically implemented as a single integrated circuit.

Abstract: When a discharge lamp repeatedly flickers out after illuminating for a long period of time because the same discharge lamp is nearing the end of its usage lifetime, a stored voltage of a capacitor rises gradually every time the discharge lamp flickers out. When the stored voltage of the same capacitor becomes no less than a predetermined voltage, a comparator generates a high level voltage which actuates a transistor. The transistor then terminates the operations of a PWM circuit to deactuate the discharge lamp.

Abstract: An electronic ballast (10) for powering at least one gas discharge lamp (20) comprising an AC-to-DC converter (100), an inverter (200), an output circuit (300), and an inverter protection circuit (400). Inverter protection circuit (400) includes a high voltage detection circuit (500), a no-load detection circuit (600), and a latch circuit (700), and is operable to turn off the inverter (200) in response to removal or failure of the gas discharge lamps. Inverter protection circuit (400) is well-suited for use in ballasts that power multiple, parallel-connected lamps and maintains operation of inverter (200) under a partially-loaded condition in which at least one operational lamp is present and each of the failed lamps has at least one open filament.

Abstract: An electronic ballast (100) for powering at least one gas discharge lamp (10) comprises an inverter (300), an output circuit (400), and a switching circuit (500). Output circuit (400) includes a resonant inductor (440) and a resonant capacitor (460). Switching circuit (500) is coupled between the resonant capacitor (460) and an AC ground node such as circuit ground node (60), and is operable to effectively disconnect the resonant capacitor (460) after the lamp (10) ignites, thereby eliminating circulating current and significantly enhancing ballast energy efficiency. Switching circuit preferably comprises an electronic switch (600) and a pulse circuit (700), and optionally includes a diode matrix for use in ballasts for powering two or more lamps. In one embodiment, pulse circuit (800) monitors for lamp replacement and provides automatic ignition of a replaced lamp.

Abstract: An electric discharge machine is equipped with a current detector 410 for causing an auxiliary discharge circuit 200 to be operated and for detecting that a value of an auxiliary current exceeds a predetermined value; a timer 401 having first setting time longer than time defined until flowing of charge current into the auxiliary current is ended; a timer 403 having second setting time defined after a detection is made that the value of the auxiliary current exceeds the predetermined value until the discharge operation is brought into a stable condition after the first setting time; an operation means 470 for stopping the auxiliary discharge circuit 200 after the second setting time has passed, and for causing the main discharge circuit 300 to be operated during preselected time; and a timer 440 having a setting time longer than such time that after the operation means causes the main discharge circuit to be operated during the preselected time, the current value of the main discharge circuit 300 becomes lowe

Abstract: A circuit arrangement for operating electrical incandescent bulbs, particrly low-volt halogen incandescent bulbs, comprises an inverter in the half-bridge circuit and an overload detector circuit, which comprises a current-voltage transformer, e.g., a resistance (R4), which is serially connected between first half-bridge capacitor (C3) and ground potential. The current-voltage transformer controls a signal-conditioning and cutoff circuit (R5-R7, C4, C5, D4, T3), which disconnects the inverter at least temporarily in the case of overload or short circuit. Preferably, current-voltage transformer (R4) of the overload detector circuit is a component of a frequency adaptation circuit (L1, R4), which opposes a decrease in the frequency of the inverter in the upper power connection range. This variant is particularly cost-favorable, since in this case, no additional component is required for detector circuit (R4).

Abstract: A circuit arrangement for igniting and supplying a discharge lamp by means of a substantially square-wave voltage at a frequency f1. It is possible to dim the lamp by adjusting the frequency of the substantially square-wave voltage to a value f2 which is different from f1. A protection circuit prevents damage to the lamp and to the circuit arrangement if the lamp current does not flow any more at the frequency f2.

Abstract: A circuit arrangement for operating a discharge lamp comprising input terminals for connection to a supply voltage source. A load branch B has terminals for holding the discharge lamp and includes an inductive ballast. A device I is coupled to ends of the load branch and to the input terminals to generate a high-frequency voltage from the supply voltage furnished by the supply voltage source. A device II is coupled to the device I to adjust the power consumed by the discharge lamp, the frequency of the high-frequency voltage being dependent upon the adjusted value of the power consumption. A transformer having a primary winding and secondary windings with each secondary winding shunted by an electrode branch during lamp operation, which electrode branch includes an electrode of the discharge lamp. The primary winding forms part of a branch C which also includes a frequency-dependent impedance and which shunts the load branch.

Abstract: A circuit arrangement for operating a discharge lamp (LA), provided with input terminals (K1, K2) for connection to a supply voltage source. A rectifier (D1-D4) is coupled to the input terminals for rectifying a supply voltage delivered by the supply voltage source. A capacitor (C2) is coupled to the rectifier and a DC-AC converter (III) is coupled to the capacitor and is provided with terminals for accommodating a discharge lamp. The circuit arrangement is also provided with a circuit I (R1-R6. T1, T2, C1, V, VI, VII) for detecting periodic current pulses having an amplitude greater than a given value W1 and with a circuit II (IIa, S1) coupled to the circuit I for changing the operational state of the circuit arrangement. As a result, damage to the circuit arrangement is prevented when the circuit arrangement is used in combination with a dimmer unsuitable for the circuit arrangement.

Abstract: Disclosed is a ballast circuit for a gas discharge lamp comprising a resonant load circuit incorporating the gas discharge lamp, a resonant inductance, and a resonant capacitance. A d.c.-to-a.c. converter circuit induces an a.c. current in the load circuit, and comprises first and second converter switches serially connected in the foregoing order between a bus conductor at a d.c. voltage and a reference conductor. The switches are connected together at a common node through which the a.c. load current flows. The switches each have a control node and a reference node, the voltage between such nodes determining the conduction state of the associated switch. The respective control nodes of the switches are interconnected, and the respective reference nodes of the switches are connected together at the common node.

Abstract: A power supply device for a gas filled arc-type lamp having a transformer with a core with a primary coil and a secondary coil, a power source coupled to the primary coil of the transformer core and providing a generally sinusoidal signal, a connector for joining the secondary coil of the transformer to the gas-filled arch-type lamp, and an unbalanced capacitance for introducing even-order harmonic distortion on the generally sinusoidal signal on the primary coil of the transformer and generating a generally sinusoidal signal on the secondary coil of the transformer such that a flow of ionized gas is created within the gas-filled arch-type lamp for dispersing any bubbles and standing waves in the lamp and so as to avoid adjustment of the power supply. The distorted signal has one-half cycle longer with a lower peak voltage than the other half-cycle.

Abstract: A circuit arrangement for operating electrical lamps has a temperature sensor (NTC) as component part of an overtemperature protection circuit and at least one additional thermal component, which has flowing through it in the event of an overload a current which is increased compared with normal operation, and is thereby heated. The thermal component, for example one or more heating resistors (R5-R8), is coupled in a thermal manner to the temperature sensor (NTC), as a result of which the overtemperature protection circuit is consequently also triggered in the event of an overload.

Abstract: Start and operation of high pressure discharge lamps, in which a high-frequency starting voltage U.sub.HF and an operating voltage U.sub.B are furnished to the lamp electrodes includes the steps of: 1) turning on the high-frequency starting voltage U.sub.HF at a starting time t.sub.0 to ionize the lamp filling and preheat the electrodes; 2) turning on the operating voltage U.sub.B after a preheating interval .DELTA.t.sub.H, that is, at time t.sub.1 =t.sub.0 +.DELTA.t.sub.H ; and 3) turning off the starting voltage U.sub.HF at time t.sub.2 .gtoreq.t.sub.1, as a result of which the lamp is then operated solely by means of the operating voltage U.sub.B. As a result, the transfer phase for the development of the arc is shortened. Advantageously, the frequency of the starting voltage is selected such that the product of the frequency f of the starting voltage U.sub.HF and the spacing d between the electrodes meets the condition f.multidot.d.gtoreq.50 kHz.multidot.cm.

Abstract: A ballast for a gas discharge lamp includes a detection circuit which detects an operating state of the lamp in which the lamp current for the column discharge of one polarity is different from the lamp current for the column discharge of the other polarity by detecting the DC component of the voltage across the discharge lamp. The detection circuit includes (i) a device coupled such that a DC voltage is imposed there across when the lamp current is different for the column discharge according to one polarity verses the other polarity, and (ii) a sensing circuit for sensing the DC voltage across the device. The device may be a capacitive device, and in a particularly inexpensive implementation, is a DC blocking capacitor or a ballast capacitor. The sense circuit senses when the DC voltage across the device exceeds a threshold value, which may corresponds to fully-rectified state of the lamp or more favorably, to a lesser state of imbalance.

Abstract: A ballast circuit for a gas discharge lamp comprises a resonant load circuit incorporating the gas discharge lamp and including a resonant inductance and a resonant capacitance. A d.c.-to-a.c. converter circuit induces an a.c. current in the resonant load circuit. The converter circuit comprises first and second switches serially connected between a bus conductor at a d.c. voltage and a reference conductor, and which are connected together at a common node through which the a.c. load current flows. The first and second switches each comprise a control node and a reference node, the voltage between such nodes determining the conduction state of the associated switch. The respective control nodes of the first and second switches are interconnected. The respective reference nodes of the first and second switches are connected together at the common node.

Abstract: The invention relates to a circuit arrangement for operating electric lam and an operating method for electric lamps. The circuit arrangement has an inverter ((Q1, Q2) with a switch-off device which switches off the inverter (Q1, Q2) in the case of an anomalous operating state. The switch-off device has a field-effect transistor (T1, T1') whose drain-source junction is arranged in the control circuit of an inverter switching transistor (Q2) and switches the control circuit of the inverter transistor (Q2) between a state which is of low resistance in normal operation and a state which is of high resistance in anomalous operation. After the occurrence of an anomalous operating state, it is advantageous to switch off synchronously with the blocking phase of the inverter transistor (Q2) in whose control circuit the field-effect transistor (T1, T1') is arranged.

Abstract: A circuit for protecting fluorescent lamps connected to a high frequency electronic ballast has a detecting bridge connected to the fluorescent lamps, an output of the detecting bridge varying linearly with a difference between a highest and a lowest voltage across the fluorescent lamps. A timer is connected to the detecting bridge output, and a trigger is connected to an output of the timer, the trigger being responsive to an over-voltage condition of a fluorescent lamp operating at failure mode. A controllable switch is connected across the fluorescent lamps, the controllable switch being controlled by an output of the trigger. The controllable switch, when closed, shorts the fluorescent lamps between their terminals, to protect the circuit when one or more fluorescent lamps are operating at failure mode or at the end of their operating life.

Abstract: An electronic ballast (10) for powering at least one gas discharge lamp (20) comprising an AC-to-DC converter (100), an inverter (200), an output circuit (300), a relamping circuit (400), and an inverter protection circuit (500). Protection circuit (500) shuts down the inverter (200) in response to lamp removal or lamp failure. Following replacement of a failed lamp with an operational lamp, relamping circuit (400) provides restarting of the inverter (200) and ignition of the operational lamp by momentarily disabling the inverter protection circuit (500).

Abstract: A device for operating lamps, such as fluorescent lamps includes an input protection circuit, a filter, a DC to DC converter, a power output stage, a lamp connecting circuit and a control circuit. The control circuit includes a pulse width modulator, a multivibrator and a start/stop controller. The pulse width modulator varies the duty cycle of a control signal supplied to the DC to DC converter based on a feedback signal from the DC to DC converter. The multivibrator assists in the control of the DC to DC converter. The start/stop controller initiates the operation of the power output stage when an output of the DC to DC converter reaches a predetermined level and halts the operation of the power output stage if a failure is detected.

Abstract: A ballast includes safety circuitry which senses lamp status through various phases of ballast operation. According to one feature, the ballast is prevented from supplying an output voltage upon initial energization of the ballast when a lamp is not present at the output terminals. The presence of a filament is sensed via a DC path extending through the filament heater windings of an output transformer. When the DC path is not complete, a control input, for example the power supply input of the ballast controller, is not provided with a voltage to start ballast operation. The DC path is also used to restart the ballast if a defective lamp is replaced with a good one. Over-voltage and capacitive mode detection is also disclosed to shut down ballast output upon lamp failure/removal.

Abstract: A monolithic MOS gate driver chip is described for driving high side and low side power MOSFETs in a gas discharge lamp ballast circuit. The chip includes a timer circuit for generating a square output at the natural frequency of resonance of the lamp ballast. Dead time circuits are provided in the chip to prevent the simultaneous conduction of both high side and low side MOSFETs. The chip may be housed in an eight pin DIP package.

Abstract: In order to detect a fault which would result in heating or fuming of a discharge tube lighting circuit and to break the lighting circuit, input voltage and current are measured and multiplied to compute the input power. The discharge tube 3 is extinguished when an input power reaches a predetermined value.

Abstract: An electronic ballast having particular application for driving small diameter fluorescent tubes or lamps (such as the T2, T4 and T5 sizes). The electronic ballast has a shutdown circuit by which to remove power to the oscillator when the tube or lamp is close to the end of its useful life or when an abnormal condition occurs such that a rise in operating voltage is detected. The shutdown circuit detects the rise in the operating voltage of the tube or lamp and energizes a relay through the conduction path of a photoresponsive transistor that is rendered conducting by a light emitting diode. The relay directs power away from the oscillator and towards the control electrode of the photoresponsive transistor to hold the phototransistor on and thereby disable the ballast. The ballast also includes a power factor controller to provide a high power factor and a more efficient operation.

Abstract: A protection method (10) and protection circuit (500) for protecting an inverter (300) in an electronic preheat ballast (100) for powering at least one fluorescent lamp (902). The inverter (300) includes a first inverter switch (306), a second inverter switch (310), an output circuit (800), and an inverter driver circuit (400) having a drive frequency. The protection circuit (500) comprises a frequency shift circuit (600), a latch circuit (700), a current source network (520), a current sensing circuit (510), and a DC supply capacitance (502). The protection method (10) includes the steps of (a) providing a filament preheat period by initially setting the drive frequency at a first frequency, (b) shifting the drive frequency to a second frequency for igniting and operating the lamps, (c) changing the drive frequency back to the first frequency in response to a lamp fault, and (d) providing, upon correction of the lamp fault, a filament preheat period prior to attempting to ignite and operate the lamps.

Abstract: An auxiliary or ballast circuit for high-frequency operation of discharge mps (E), for example sodium high pressure discharge lamps, provides for controlled inrush or "ON current" by including a thyristor (TH1) or pair of thyristors (TH2, TH3) in the current supply path to the discharge lamp (E) integrated into a combination active filter-voltage step-up circuit. The gate of the thyristor (TH1) or a pair of thyristors (TH2, TH3) is, or are, controlled over a resistance (R2, R3, R4) connected to the output capacitor (C2) of the filter-voltage step-up circuit to fire the thyristor when input voltage goes through null, and the output capacitor (C2) has a predetermined voltage level above the input voltage. The output capacitor (C2), before firing, is charged by a charge control resistor (R1) connected in parallel across the anode-cathode path of the thyristor or thyristors.

Abstract: To substantially reduce harmonic distortion and improve the power factor of n operating circuit for a fluorescent lamp, a smoothing circuit (G) is interposed between the outputs from a power rectifier (GL) and an inverter (WR) supplying the fluorescent lamp (L) with high-frequency energy. The smoothing circuit includes a two electrolytic capacitor (C1, C2)--three diode (D1, D2, D3) network, which is so connected, and the diodes so polarized that, during charging of the capacitors, a series circuit is established with one (D2) of the three diodes in series with the two capacitors. For discharge of the capacitors to supply the inverter when the rectified voltage is lower than the capacitor voltage, the two capacitors (C1, C2), through the other two diodes (D1, D3), are connected in parallel to supply the inverter. To substantially reduce harmonic distortion to less than about 30% and improve the power factor of the circuit to above 0.

Abstract: An inverter-type electronic fluorescent lamp ballast has means to disable inverter operation in case of an overvoltage condition and/or in case its internal temperature were to exceed a safe level, thereby to provide automatic protection against damage that might otherwise result from excessive voltage and/or temperatures.

Abstract: The invention relates to a measuring circuit for detecting the amount of deposited electrode material on the wall of a lamp vessel of a discharge lamp by measuring the power of infrared radiation within a specific wavelength range, comprising a detector for generating an electrical signal constituting a measure for the power of the infrared light in said specific wave length range. According to the invention the measuring is done in a time lapse starting after a predetermined time interval following the extinguishing of the discharge lamp. An increased accuracy of the measurement is thereby realized.

Abstract: A lamp protection device includes a circuit to prevent a lamp from being switched on at full line voltage and which provides for the gradual heating of the filament to reduce the expansion rate of the filament. The circuit is connected to a switched alternating current power source and to an incandescent bulb. The circuit includes two silicon controlled rectifiers which are connected in reverse parallel configuration. One of the silicon controlled rectifiers being connected to a capacitor to prevent the full sinusoidal AC current from reaching the lamp until a time delay has expired after the lamp is turned on. A reference switch is connected to the other silicon controlled rectifier to permit the bulb to be turned on only when the AC voltage crosses zero.

Abstract: A lighting circuit supplies an input voltage from a battery to a discharge lamp after the input voltage has been sent via a DC power supply section to a DC-AC converter. This lighting circuit comprises a lighting detector for detecting if the discharge lamp is lighted, an input-voltage monitor circuit for detecting the input voltage to the DC power supply section and checking if the input voltage lies within an allowable range, and a stable power supply circuit and a switch section for supplying power to the discharge lamp or inhibiting the power supply thereto in accordance with a signal from the input-voltage monitor circuit. The input-voltage monitor circuit performs variable control on a reference value to be compared with the input voltage, in accordance with a signal from the lighting detector.

Abstract: There is provided a ballast for at least one gas discharge lamp havingan inverter which has two switches (S1, S2) in series, connected to a d.c. voltage source and switched with complementary timings, and a load circuit connected in parallel with one of the two switches (S1, S2) which load circuit includes a series resonant circuit (L1, C1) and the lamp (LA). Additionally there is provided a heating circuit (T, S3,R1) for current supply of the lamp coils, likewise connected to the inverter, which heating circuit includes a further periodically switchable switch (S3) for control of the heating current, whereby the heating circuit is likewise connected in parallel to one of the two switches of the inverter.

Abstract: A circuit for supplying power to a fluorescent lamp. A control system comprises a buck regulator for supplying a buck current, an inverter circuit for receiving the buck current and for generating a lamp voltage, a circuit for sensing a current in a fluorescent lamp, a circuit for sensing a no lamp condition, and a controller for controlling the buck regulator and the inverter. The circuit for sensing a no lamp condition monitors a voltage level at the inverter transformer. The controller is coupled to the circuit for sensing a no lamp condition. If a no lamp condition is detected, the controller responds by shutting itself down. The controller can be reactivated by toggling an on/off signal to reset a latch.

Abstract: A ballast includes safety circuitry which senses lamp status through various phases of ballast operation. According to one feature, the ballast is prevented from supplying an output voltage upon initial energization of the ballast when a lamp is not present at the output terminals. The presence of a filament is sensed via a DC path extending through the filament heater windings of an output transformer. When the DC path is not complete, a control input, for example the power supply input of the ballast controller, is not provided with a voltage to start ballast operation. The DC path is also used to restart the ballast if a defective lamp is replaced with a good one. Over-voltage and capacitive mode detection is also disclosed to shut down ballast output upon lamp failure/removal.

Abstract: An abnormal or unbalanced load operating condition is detected in a single lamp ballast circuit or in either lamp of a two-lamp ballast circuit by feedback voltage signals that are proportional to the flow of current through the cathodes of each lamp. The analog feedback signals are combined algebraically by a summing circuit that produces a null (zero) value corresponding with normal lamp operation, and produces a non-zero value in response to abnormal cathode current flow. The non-zero value is compared with the reference value to generate a shut-down signal. In one embodiment, the cathode currents are sensed by primary windings of a toroid transformer, and the feedback signals are the magnetic flux components that are generated in response to cathode current flow through the current sensing windings.

Abstract: An electronic ballast has a protection circuit particularly useful for smaller diameter gas discharge lamps including compact fluorescent lamps. The protection circuit prevents lamps from overheating by preventing the ballast from providing sustained output power when the magnitude of the ballast output voltage indicates abnormal lamp operation. The protection circuit has a voltage sensor which develops a voltage that is more negative than the negative DC supply terminal of the inverter so that an inexpensive low-voltage SCR can be used to turn off the inverter. The circuit provides automatic restarting of the ballast after a new lamp has been installed to eliminate the need for toggling the input power to the ballast.

Abstract: A ballast arrangement is disclosed for use in powering fluorescent and other gas discharge lamps. The ballast arrangement controls the arc voltage provide by an arc voltage oscillator independent of the filament voltage provided by a filament voltage oscillator. In this manner, safe maintenance condition during fault and interrupt condition are obtained. The full arc voltage is only applied to the lamp when the lamp filaments are warm or after a time period during which they are warmed. The filament pre-warming time reduces sputtering when an excitation or arc voltage in subsequently applied to induce lamp arcing.

Abstract: An arc detection and cut-out circuit is connected to an electronic ballast to detect when arcing occurs and to disable the ballast when arcing occurs. The arc detection and cut-out circuit is comprised of a current detector and a shunt circuit. The current detector detects the current in the electronic ballast to determine if arcing has occurred. If detected, the current detector causes a shunt circuit to shunt the power inverter of the ballast shutting it down. The arc detection and cut-out circuit prevents the power inverter from starting up until the power to the ballast is cycled off and back on.

Abstract: An automatic illumination intensity control apparatus for a discharge lamp includes a chopper circuit for stepping up D.C. voltage obtained by rectifying commercial A.C. voltage, an invertor circuit for converting D.C. voltage output from the chopper circuit into an A.C. voltage with a higher frequency to drive the discharge lamp, a brightness level sensing portion for sensing the brightness level of the area to be illuminated, a brightness level setting portion for setting brightness level of the area to be illuminated, and a power cut-off portion for stopping the operation of the invertor circuit when the sensed brightness level is greater than the set brightness level. The control apparatus may further include an illumination intensity adjusting portion for varying voltage output from the chopper circuit in proportion to the difference between the set brightness and sensed brightness when the sensed brightness is less than the set brightness.

Abstract: To operate one or more serially connected low-pressure discharge lamps, tcally fluorescent lamps, a preheating circuit is provided to preheat the electrodes of the lamps (E1, E2, E3, E4), which changes from low-impedance to high-impedance state after the lamps have been preheated by controlling a semiconductor switch (Q3) in the heating circuit. In accordance with the invention, to eliminate reliance on the resistances of the lamp filaments themselves, which are subject to variation from lamp-to-lamp due to manufacturing tolerances, and later on, to changes due to aging of the lamp, and to provide for reliable switching of the semiconductor switch, a sensing impedance element (Z), which may be an ohmic resistor or a capacitor (Z', Z"), is serially connected to the switching path of the semiconductor switch (Q3) which, typically, is a field effect transistor (FET).

Abstract: To control preheating current flow through a fluorescent lamp supplied from high-frequency inverter (T1, T2, A) and a series resonance circuit, an electronic switching control circuit (SC) is connected to the preheating circuit of at least one electrode filament (E1, E2, E10, E20, E11, E21, E12, E22) of one or more of the fluorescent lamps. The switching control circuit senses the voltage across the pair of terminals (T1, T1', T2, T2') of the electrode filaments, or across all the electrode filaments. Since fluorescent lamp filaments have a positive temperature coefficient of resistance, the voltage across the filaments will rise as the filament or filaments of the lamp reach electron emission temperature. This rise in voltage is sensed, for example, by a threshold circuit which may include a Zener diode, and is used to break the preheating circuit.

Abstract: A circuit for powering a fluorescent lamp has a direct current power supply (10). An inverter (12) is coupled to the direct current power supply (10) and provides a lamp current to the fluorescent lamp load (14). The inverter(12) is connected to an inverter control circuit (18). A protection circuit (16) for detecting lamp current is coupled to the inverter control circuit (18) such that the inverter control circuit (18) turns off the inverter (12) whenever the protection circuit detects the absence of lamp current.

Abstract: A video projection system having a liquid crystal panel with a video image, a projection lamp with ON/OFF control, a zoom lens with a zoom control mechanism, a focusing lens with a focusing control mechanism, an audio system with a volume control, a projection-lamp light detector, a heat sensor, a variable-speed cooling fan, a control module having a microprocessor and a digital-to-analog converter, a display, a keypad, an alarm/annunciator, a power supply with ON/OFF control, and an infrared based remote control system able to control power ON/OFF, zoom, focus, picture, and sound volume.