| 摘要 |
<p>A self-oscillating circuit for driving high-side and low-side switching devices, (50, 52) such as MOSFETs connected in a half-bridge configuration. The circuit alternatively turns on the switching devices (50, 52) by providing alternating gate pulses varying in duration or width. The pulses are separated by dead time to prevent cross conduction. At start up, the pulpes increase from a minimum duration of zero to a maximum duration, while dead time duration simultaneously decreases to its minimum duration, to provide soft start. The circuitry includes an oscillator (60) for providing a periodic signal in which each cycle includes a rising portion followed by a falling edge to a low portion. Reference circuitry (90) provides a varying reference signal. A comparator (100) responds to the periodic signal and the varying reference signal, and provides a pulse output signal whose pulse width in proportional to the reference signal. The oscillator (60) also provides a gate pulse during the low portion of alternate periods and the rference circuitry (90) includes circuitry that provides a rising signal that increases at startup to a maximum value; sampling circuitry (102) reponds to each gate pulse by samlping the rising signal's value, and the reference circuitry (90) obtains the varying reference signal from each sampled value until the next gate pulse. The circuit is preferably implememted in an integrated circuit with appropriate pins for external connection.</p> |
