Simplified AC-DC switching converter with output isolation

Details Simplified AC-DC switching converter with output isolation Simplified AC-DC switching converter with output isolation

1997-10-23

1999-06-22

Berhane, Adolf Deneke

Electric power conversion systems

Current conversion

Including d.c.-a.c.-d.c. converter

363 97, 323902, H02M 3335

Patent

active

059148659

ABSTRACT:
An AC-DC switching converter converts AC mains power into regulated DC power into a load. It is desired to electrically isolate the load from the mains, and this requires isolation in both the forward power transfer path and the reverse feedback path. The forward path is isolated by use of a transformer, and the feedback signal is transferred through an optocoupler. In a typical pulsewidth modulation control loop design, it is difficult to achieve good loop dynamics when using low cost optocouplers, because of the wide variation of their transfer function gain. However, in the disclosed invention, the loop is operated as a nonlinear limit cycle ("bang--bang") controller. In this mode, the optocoupler gain variation has an insignificant effect on loop operation. The converter switching signal is provided by an inexpensive 555 timer oscillator, and the optocoupler is connected to the reset pin of this timer to turn it ON and OFF in short bursts, as is characteristic of this type of controller. Since a converter must operate over a mains voltage range of about 3:1, the disclosure also includes a technique for protecting the transformer from possible saturation by narrowing the oscillator pulses as an inverse function of the mains voltage.

REFERENCES:
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patent: 5450304 (1995-09-01), Cox
patent: 5475579 (1995-12-01), John et al.
patent: 5694305 (1997-12-01), King et al.
patent: 5729448 (1998-03-01), Haynie et al.

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