Fluorescent lighting control circuit

Abstract

A control circuit for fluorescent lamps having gas filled tubes and a pair of discharge electrodes in the tubes includes a transformer, a gated switching device and a control signal generating circuit. The transformer has a secondary winding connected with the lamp discharge electrodes and a primary winding to which power is applied by the switching device when a gating signal is applied to its gating terminal. The control signal generating circuit normally controls the gating of the switching device by alternatingly applying, and then ceasing to apply, a control signal to the gating terminal. The control circuit is capable of continuing a current between the discharge electrodes once the lamp is conducting. The control circuit is further capable of 'starting' a lamp by applying a high voltage to the discharge electrodes. The high voltage is generated when the gated switching device is not applying power to the primary winding. In order to avoid arcing and corona discharge in the control circuit as a result of misconnected and leaky fluorescent lamps, a voltage responsive device is connected with the gating terminal and responds to the voltage across the primary winding by applying a signal to the gating terminal in order to switch the switching device to apply power to the primary winding and, in this manner, causing the transformer to cease the generation of the damaging high voltage.