Self powering technique for integrated switched mode power supply

Abstract

A regulator circuit is connected to a transformer. The transformer has a primary winding connected to a rectified D.C. voltage signal and has a feedback winding. A feedback capacitor is coupled across the feedback winding of the capacitor. The regulator circuit includes a high voltage switching transistor, a pulse width modulator which controls the high voltage switching transistor and a high voltage power up transistor. At power up, the high voltage power up transistor connects the single high voltage pin to the feedback capacitor allowing the feedback capacitor to begin charging. When the feedback capacitor has charged past a first threshold voltage the pulse width modulator alternately turns the high voltage switching transistor on and off. When the high voltage switching transistor is turned on, the high voltage pin is connected to ground and current passes through the primary winding of the transformer, and thus current is generated through the feedback winding into the feedback capacitor. Additionally, when the high voltage power up transistor is on, the gate of the high voltage power up transistor is connected to ground turning the high voltage power up transistor off. Once the feedback capacitor has been charged to a second threshold voltage a transistor connects the gate of the high voltage power up transistor to ground thus permanently switching the high voltage power up transistor off.

Dependencies are inferred from the claim text.