Abstract: In the circuit arrangement for the high-frequency operation of a low-power ow-pressure discharge lamp (LP) having a mains rectifier (2) and a half-bridge circuit, a diode (D1) is connected in series and in the DC non-conducting direction in the connecting line between the second electrode (E2) of the lamp (LP) and the positive or negative pole of the rectifier (2). Moreover, the tap (M2) between the diode (D1) and the second electrode (E2) is connected to the other pole of the mains rectifier (2) via a capacitor (C1), and a resistor (R9) is connected in parallel with the diode (D1). The circuit thus created acts as a passive harmonic filter which fulfills for the circuit arrangement the IEC regulations of class D with reference to line current harmonic content.

Abstract: To meet IEC regulations in accordance with IEC publication 555-2 class D, r harmonic content of feedback into power networks upon use of low-power fluorescent lamps, an operating circuit for a lamp, or serially connected lamps is provided which includes a rectifier (2), rectifying a-c input energy, and having a smoothing capacitor (C3) connected across its output (J1, J2), the output of which is inverted in a half-bridge inverter using alternately conductive transistors (T1, T2), a passive filter circuit (5) is connected between an electrode of the lamp, or the last electrode of the lamps and a return connection to the rectifier (2). The passive filter circuit (5) has two serially connected diodes (D1, D2) defining a common junction (M2), connected in d-c blocking direction in a connection line between the second electrode (E2, E4') of a lamp (LP1) or the last of a group of serially connected lamps (LP1', LP2') and one (J1) output terminal of the rectifier (2).

Abstract: To prevent long-time current flow through a positive temperature coeffici resistor (KL) included in the heater circuit of one or more fluorescent lamps (LP, LP1, LP2), a relay is connected in circuit with the PTC resistor (KL), which will respond when the voltage across the capacitor (C4) reaches the level of d-c voltage derived from a relay rectifier (GL) and coupled to the PTC resistor itself. The relay operates a switch contact (S) which interrupts the current flow through the PTC resistor; the flow through the relay is small in comparison with the current flow through the PTC resistor, thereby saving energy and decrease in the heat loading on the circuit structure.

Abstract: To reduce network harmonics upon connecting a fluorescent lamp (LP) with a ower network rectifier (2) and a push-pull frequency generator (3) and a series resonance circuit (4) to the network, a harmonic filter is connected in the circuit with the fluorescent lamp. The harmonic filter includes two diode pairs (D8, D9; D10, D11) connected in forward current passing direction to the power rectifier (2).

Abstract: To provide for automatic disconnect upon failure of a filament of one (E2) f the electrodes of a fluorescent lamp, an output terminal (P1) of a power rectifier is connected through the filament to a supply terminal (P3) of a push-pull frequency generator formed by two transistors (T1, T2). The fluorescent lamp (LP) has its other electrode (E1) connected to a common terminal between two transistors (T1, T2) of the high-frequency generator. A series resonance circuit (L1, C6, C8) is capacitor-coupled (C7) to the lamp. Upon failure of the filament of the first electrode (E2), or removal of the lamp from its lamp sockets, power supply to the transistor oscillator or frequency generator circuit is interrupted, so that the oscillator is deenergized; upon insertion of an operative lamp in the lamp circuit, the circuit is closed so that the fluorescent lamp is automatically started by the push-pull oscillator (3) formed by the two transistors (T1, T2) and associated circuitry.

Abstract: To reduce network harmonics upon connecting a fluorescent lamp (LP1) with a power network rectifier (2) and a push-pull frequency generator (3) and a series resonance circuit (4) to the network, a harmonic filter is connected in the circuit with the fluorescent lamp (LP1) or lamps (LP1, LP2). The harmonic filter includes two diodes (D8, D9), connected in forward current passing direction to the power rectifier (2), and two capacitors (C7, C8) connected, respectively, between the serially connected diodes and a center tap (M1) between the push-pull transistors directly and beyond an inductance forming part of a series resonance circuit (4) for the lamps. In parallel to the two diodes, two further diodes (D10, D11) are provided, having a center tap (M4) which is connected over a capacitor (C9) also to the center tap between the transistors of the push-pull frequency generator (3). Preferably, the capacity value of the further capacitor (C9) is about 0.

Abstract: A circuit for operating low-pressure discharge lamps at elevated frequency comprises a reconnect circuit which disables the disconnect circuit upon exchange of a defective low-pressure discharge lamp (LP1). The disconnect circuit comprises a diode (D10), a resistor (R11) and a thyristor (TH) together with a trigger circuit (5). The reconnect circuit comprises a capacitor (C9) and a resistor (R12). Upon removal of the defective low-pressure discharge lamp (LP1), the capacitor (C9) is charged over the resistor (R12). Upon insertion of a new low-pressure discharge lamp (LP1), the capacitor (C9) is discharged and recharged in opposite direction and the holding current is removed from the thyristor (TH). This causes the thyristor (TH) to block, and enables the push-pull frequency generator (3) to start oscillating again.

Abstract: To insure starting of an oscillatory circuit for fluorescent lamp operation scillating, for example, at about 35 kHz, two transistors are serially connected across the output of a rectifier adapted for connection to an a-c network, and the oscillatory circuit is additionally coupled to one of the a-c terminals of the rectifier, to apply to one of the transistors a triggering voltage which recurs with each undulation of the a-c network. The serially connected transistors each have an emitter resistor, which may be a PTC resistor, to balance currents through the transistors and eliminate unbalancing effects of manufacturing tolerances in the transistors. The PTC resistors additionally have current deviation regulating function.

Abstract: To operate at least one, and preferably a plurality of fluorescent lamps, a elf-oscillating transistor push-pull switching oscillator, using two similar transistors (T1, T2), is connected to respective lamps (3, 3', 3"), with an oscillatory circuit (4, 4', 4") to operate at audio, supersonic or low high frequency, for example in the 20 kHz range. Each lamp operating circuit has an individual series resonance circuit (4, 4', 4") which includes a ballast inductance (L1, L1', L1") and a capacitor (C1, C1', C1"). For multiple operation, the respective lamp operating circuits are connected in parallel. A special starting circuit (10) and a control circuit (9a, 9b; L2, L2', L2"; L3, L3', L3") for the switching transistors insures low-loss operation.

Abstract: A fluorescent lamp control circuit which provides power at high frequency, or example in the order of 35 kHz, includes a push-pull oscillator circuit having two transistors (T1, T2), an inductance element (L1, L1'), and a capacitor (C1, C1') to supply the lamps (3, 3'). To prevent dangerous high voltages upon removal of the lamp load, connected to the oscillatory circuit and to the series resonance circuit, upon removal of failure of a lamp, a protective circuit is provided formed by a thyristor (TH) connected to short-circuit at least one of the transistors (T1) of the oscillatory circuit.