ballast lamp operations application_number US 64989803 A description with reference now to fig3 a self oscillating driver ic 10 drives half bridge power stages with transistors m 1 and m 2 generating an ac voltage across the input of a resonant load ic 10 has a built in oscillator that is or is similar to the u201c 555 u201d timer of the prior art oscillator frequency can be programmed with a timing circuit 12 coupled to pins rt ct and common u201c corn u201d the feedback circuit includes blocks 14 and 16 that couple inverter high voltage output lh to timing circuit 12 block 14 attenuates the output voltage signal and block 16 phase shifts the output voltage signal from 150 u00b0 to 200 u00b0 to compensate for the phase difference between the inverter output voltage and the external synchronization signal timing circuit 12 may include a timing capacitor ct and resistor rt see fig2 and switches when the timing capacitor is charged to u2154 vcc and discharged to u2153 vcc in a standard ic application the timing capacitor voltage waveform is an exponential ramp that is superposed on the dc voltage by mixing in a small phase shifted signal to the ramp the ic oscillator correlates its frequency preferably a source of this signal is coupled between ground and the timing capacitor in an embodiment of the device shown in fig4 which is particularly suited for high frequency application 200 270 khz attenuating block 14 fig3 includes a capacitive divider with capacitors c 4 and c 5 connected to inverter high voltage output lh phase shifting block 16 includes an active signal inverter that includes transistor m.