I can understand how an isolation transformer can establish isolation but since SOME SMPS supplies don't have transformers and they have rectifiers instead I wonder how the AC and DC ends are isolated.
Edit: Here is an SMPS with no galvanic isolation.
Here is the datasheet which says there is no galvanic isolation.
How is that possible?
I'm asking because people here all agreed SMPS has small transformers which isolates the input and output power.
Sure they have transformers: -
The transformer looks different to a regular AC type but it's still the largest single component on the PCB but a whole lot smaller than it would be for 50/60 Hz operation. The transformer is the big yellow taped thing in front of the heat sink at the back/left.
SMPSs also use opto-isolators for feeding back a measure of the output voltage so that it can be regulated. This is another significant isolation feature thus, output and input remain galvanically isolated to several kV and are therefore "safe".
I suppose this is a common misconception, among people who have studied DC-DC converters only. The truth is that transformers are often used in AC-DC SMPS, specifically when isolation is required.
The difference is that the transformer takes the place of the inductor of a regular DC-DC converter, and energy is transferred magnetically to one or many secondary coils.
Feedback is often achieved with an opto-isolator, but there are other methods of feedback as well.
Typically a first stage will be a non-isolated power factor correction stage, which passes the 400V DC to the regulator with transformer isolation.
SMPS do have transformers. They are not quite the same as the 50Hz transformers you find in linear power supplies, because they work at a much higher frequency, (like ~100kHz), but they have one. Look inside a PC power supply:
The transformer is the block with the yellow tape and the writing on it, between the heat sinks.
Any AC-input supply also have rectifiers (usually as a bridge). They are placed before the transformer for SMPS, or after the transformer for a linear supply, but they don't replace the transformer.
To answer your original question, yes, you can have a non-isolated AC-DC SMPS that uses an inductor instead of a transformer. Generally you want isolation for safety, but for some applications isolation isn't required.
Some of the confusion is because the product page linked to in the question is all messed up. Although the page says the product is is a SMPS, the title is wrong. The page shows an inrush current limiter that takes AC input and outputs AC, limited to 10A. It doesn't provide galvanic isolation since it's kind of a surge protector for a SMPS, not a complete SMPS. The page describes the product as a "redundancy module", but that is a totally different product that can be added to an SMPS.
I can understand how an isolation transformer can establish isolation; but since SOME SMPS supplies dont have transformers and they have rectifiers instead; I wonder how the AC and DC ends are isolated.
Simple: they aren't.
