GB645548A - Improvements in or relating to electric circuit arrangements for operating an electric discharge device from an a.c. supply - Google Patents

Abstract

645,548. Control systems for space discharge lamps. GENERAL ELECTRIC CO., Ltd., and WILLIAMS, C. E. Sept. 30, 1948, No. 25516. [Class 38 (iv)] In a circuit for a discharge device (particularly a lamp 1) supplied through a reactive ballast impedance 11 and including power factor correcting means and control means for controlling the intensity of the discharge current, e.g. for dimming, the power factor correcting means is adjusted consequent upon adjustment of the control means to ensure a good power factor with different values of discharge current. Preferably the power factor correcting means is gauged or combined with the control means for adjusting the discharge current to obtain simultaneous adjustment. In the arrangements described, the power factor correcting means comprises a condenser 16 connected in parallel with an adjustable choke 31 across the supply leads and the lamp current control means comprises an adjustable choke 30 in series with the lamp. Adjustment of the chokes may be effected by either tappings or control windings. In the case of tapped chokes (Fig. 1, not shown), the two selector arms are ganged and arranged so that the inductance of one choke is increased when the inductance of the other choke is decreased, to obtain the required compensation. With control windings this may be effected by connecting the two control windings 32, 33 on the respective chokes in series through a resistor having a variable tapping point connected to one pole of a D.C. supply, the other pole of which is connected to the lead between the two windings (Fig. 2, not shown), so that upon adjustment of the tapping point the current in one saturating winding is increased upon decrease in current in the other winding. Alternatively, the two control windings may be supplied in series through a variable series resistor 34, with an opposing biassing winding 36 provided on one choke such that upon increase of current in winding 32 the resulting magnetizing effect is decreased. According to the Provisional Specification variation of the inductance value may also be effected by adjusting the position of the iron cores.