UNINTERRUPTIBLE POWER SUPPLY

摘要

Power supplies are known which normally derive power from commercial AC power mains but, in the event of a power interruption, switch over to battery power. The switch-over is accomplished by a relay which results in a brief interruption in the output of the power supply. This interruption cannot be tolerated in some applications, e.g. computing devices and electronic cash registers. The present invention avoids this problem by providing an inverter which is normally connected to the output of a rectifier connected to the AC mains and also to a battery. During normal operation the battery is charged by a charger circuit. In the event of a mains interruption, the battery continues to power the inverter with no interruption of the AC output of the power supply. If the rectifier voltage drops below a predetermined level, the battery is disconnected so as not to discharge it. If the output of the inverter drops below another predetermined level, the load is connected directly to the AC mains.