Circuit arrangement of a half-bridge invertor

摘要

A multiplicity of variants are known for the circuit construction of electronic ballast devices, which variants in each case require a high outlay in terms of circuitry for the specific area of application. The novel circuit arrangement is to make it possible, with little outlay, to start low-pressure discharge lamps with preheated electrodes. According to the invention the object is achieved in that Darlington transistors (V5/V6; V7/V8) are connected in parallel with the emitter resistors (R1; R2) of the switching transistors (V3; V4) of the half-bridge invertor, the base of one of the Darlington transistors (V7/V8; V5/V6) being connected to a time-delay switch (time switch) (3), the input of a threshold switch (trigger) (4) being connected to a winding of the control transformer (Tr1) and the output of the threshold switch (4) switching the current supply of the other Darlington transistor (V5/V6; V7/V8) (Fig.). The novel circuit arrangement is suitable for driving two electronic switches, which are on different electrical potential, on a time basis by means of a threshold switch and the control transformer, which is necessary anyway for free-running half-bridge invertors for low-pressure discharge lamps, and thus for utilising the advantages of symmetrical operation of the invertor when heating the filament electrodes of the lamp. <IMAGE>