Minimum harmonic distortion operating circuit for at least one

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 0.95, a parallel resistor-capacitor (RC) circuit is connected between two junctions (V1, V2) serially with the series connected diode (D2). The resistor (R1), in combination with the capacitors, reduces, and time-delays, inrush current upon charging of the capacitors (C1, C2). The capacitor (C3) connected in parallel to the resistor (R1) permits backflow of high-frequency current from the inverter to the electrolytic capacitors (C1, C2), thus preventing transfer back to the network supply.