Firstly not all DC-DC converter are galvanic isolated. Most of the small point-of-load DC-DC converters are non-isolated, including the VRM on the PC motherboards. Secondly galvanic isolation is quite important for safety. My company (Pepperl+Fuchs) has a lot of Ex and Non-Ex interface cards to transmit power and signals (from sensors: current, voltage, digital signal, fieldbus signal, etc) for the process automation industry like chemical plants. Most of the telecom power supply with 48V input are also galvanic isolated for safety reasons. All the PC power supply (silver box) should be galvanic isolated as well for safety reasons. Some of them are using simple push-pull converter. Some of them are using much more complicated power supplies. One thing in common is to use transformer, opto-coupler and relays as isolation components. Sometimes there are some safety caps across the primary and secondary side for EMC reasons (better AC ground). But they are governed by the standards and is normally very small. Under what circumstances this could be a problem? Xiaofan >Date: Sat, 25 Dec 2004 23:50:20 +1300 >From: Russell McMahon >... >In its most general sence "Galvanic isolation" means that there is no direct >current path between the input and output*. Galvanic action is usually taken >to mean the setting up of an electrochemical action when a cell is formed by >two dissilar metals and an electrolyte. Often the context is related to >"galvanic corrosion" when a metal object inadvertently becomes part of a >cell and is damaged by the electrochemical action. >... > >> What I am looking at is a bunch of DC/DC converters >> for an industrial control system and they have them labeled as "Galvanic >> Isolators". Why not just call them DC/DC power supplies? Are they more >> than just a DC/DC converter? The circuit is a simple oscillator made >> from discrete components that fires a 1:1 pulse transformer and the >> output is just rectified and unregulated. Nothing fancy about it. > >The fact that thye call them Galvanic isolators suggests that the main task >is electrical isolation of input from output. Whether they are used as DC DC >converters per se depends on the application. They may take a moderate power >input signal and produce an output whose main job is to indictae that input >is present. They may be powerful enough to drive a bulb or relay. In such a >case the isolation is the key thing and the power provided is necessary but >secondary. > >Or they may provide power as their main function where isolation matters. > >* "no direct path" is relative. Isolation may be to a DC potential, and/or >to AC or to sudden voltage changes. Many different isolation techniques are >used. Many provide a degreee of AC coupling (albeit in the picofarad range) >that can cause problem sin some circumstances. Where substantial poweer >transfer is required, high isolation against transient signals can be a >major design task. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist