Line operated fluorescent lamp inverter ballast

摘要

Applicant has provided a ballast circuit for fluorescent lights made up of the combination of (1) a source of electrical energy, (2) a resonant circuit, (3) a switch means for connecting the source of electricity to the resonant circuit, (4) means to connect the resonant circuit to a load, (5) a resonant current monitor controlling the switch means in synchronism with the resonant current so that the switch means switches the resonant current when the resonant current passes through zero. The resonant current monitor is a current transformer having a primary winding connected in series with the resonant circuit and two secondary windings connected to the bases of the two switching transistors in a two transistor inverter circuit at a polarity that will switch one of the transistors on and the other off at the time current passes through zero. This is the optimum time to switch the transistors since the current flowing through the transistors is passing through zero at that time and therefore the transistors operate at maximum efficiency and there are minimum switching losses and improves the efficiency of the circuit. The circuit will automatically adjust the switching frequency to the changed resonant frequency should the value of the inductor or the capacitor degrade and therefore change, and the switching losses will therefore be maintained at minimum.