In electronic circuit why technically saying for example uc3843 is off line ic what that mean? Where as it uses main voltage i never understand this phenomena !

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In electronic circuit why technically saying for example uc3843 is off line ic what that mean? Where as it uses main voltage i never understand this phenomena !

Refer back to post #2, in the original thread.

An online supply operates directly from the AC mains without a mains transformer which operates at the powerline frequency. The mains are directly rectified to a high DC voltage and then run through a DC-DC conversion process at a much higher switching frequency than the frequency of the mains.

An offline supply operates from a DC source supplied by a battery or by a DC power supply with a mains transformer, rectifier, and filter.

One type has a mains transformer in the conversion path and the other does not. Simple as that.

 

OK, that is a reasonable distinction, but at one time I had thought it applied primarily to standby power systems, where "On-Line" meant that in the event of a mains loss there was not even any disturbance in the output, while "OFF-LINE meant that when the mains failed the backup supply would start up and take over, within some short time period, up to a few minutes.
So the on-line system had the mains power feeding a battery that directly fed an inverter supplying AC power to some critical load. THAT was one definition back in 1968. Those definitions are also reasonable, but not the same.