Stopper protection circuit of electronic ballast for fluorescent lamp

A stopper protection circuit of an electronic ballast for fluorescent lamps, wherein the electronic ballast has an inverter to convert a direct current source into a square-wave source, and the square-wave source is provided to a plurality of lamp tubes, the stopper protection circuit comprising:

• a plurality of harmonic oscillating capacitors, with first terminals electrically connected to first terminals of the lamp tubes;
• a sampling transformer, with an output winding and a plurality of detecting windings, wherein first and second terminals of the detecting windings are electrically connected to second terminals of the lamp tubes and second terminals of the harmonic oscillating capacitors, respectively, the sampling transformer generating a normal sampling signal and an error sampling signal with a significant difference in between;
• a protection signal processing circuit, electrically connected to the output winding to receive the normal sampling signal and the error sampling signal,
• and to output an error signal after receiving the error sampling signal;
• and
• a stopper circuit, electrically connected between the protection signal processing circuit and the inverter and outputting a stop signal after receiving the error signal, so as to stop operation of the inverter.