The electronic ballast circuit and low pressure lamps

The well-known half-bridge square wave voltage generator will be used to supply energy to a gas discharge lamp through a ballast circuit comprising an inductor L in series with a resistor R, representing the losses of the circuit. Parallel to the lamp, which is represented by a conductance G, a capacitor C has been connected, for lamp ignition and/or preheating of the electrodes of fluorescent lamps. This LRCG circuit has been used as the model for an exact analysis that presents closed expressions for the lamp current and voltage and the supply current Bs a function of time for one half period of the steady-state operation. Integration provides the power loss in R and the lamp power in G giving easy access to the rms values of lamp current and voltage. The use of the conductance to represent the lamp electrically will also allow calculation of the power control. For this purpose an equation of G as a function of the lamp power is available. The constants of this equation are to be obtained by lamp measurement at different temperatures. The power control by supply voltage modulation (SVM), by frequency modulation (FM) and by pulse width modulation (PWM) has been analysed with a lamp conductance as load. It has been illustrated by P-la-U-la and P-la-frequency curves for one lamp, PLL 55.