POWER SUPPLY, GROUND ISOLATING

[mhamini]

In power supply design, using a Switching Regulator. The output voltage supply are isolated from the Input supply but how about the Ground. Is it isolated too?? as it is just direct connection from the input.
Is there any suggestion to have a good Power supply with isolation.

 

[alexz]

Are you using optocouplers?

 

[smxx]

hi mhamini
for dc/dc Switching Regulator not output nor gnd are isolated.
in switch mode power supply if isolating transformer is used its maybe not isolated yet(feeback network).

 

[pisoiu]

Hi,
This book can be helpful , also, search e-books forum with "smps".
If I remember corectly, the ground connection from the secondary circuit is usually connected to earth in the mains outlet (assuming you are talking about isolated SMPS, ex. flyback).

/pisoiu

 

[omore]

You must consider some differences.

Althought I´m a little confused when you said no isolation at GROUND I understand you refer to the zero voltage reference. Well it may or not be isolated, depending of the circuit you use, but if you need isolation, sure it can be isolated. For instance an OFFLINE SMPS, normally has its outputs isolated from the input trough the power inductor ( normally called transformer ). As you need and output reference to feed the input stage to get regulation and wish the output isolated you can do this with an optocopler.

 

[jonw0224]

omore is correct, it depends on the circuit you use as to whether or not the secondary (of a transformer) is grounded. At the very least, the chassis is connected to the ground prong on the power outlet on most equipment. On some power supplies, the secondary is floating. On others, the secondary is grounded at some point. This is good information to know, because it affects whether or not you can put the supplies in series. Generally, I assume the zero volt terminal is grounded and avoid using supplies in series. You can check this using an ohmmeter to check for connection between the ground plug and the zero volt terminal. You can isolate the terminal from ground (sometimes there is a wire from the secondary to the chassis, sometimes its done on the board itself, and sometimes AT THE TERMINAL ITSELF). If you disconnect the ground, you will still have rated voltage between the terminals in circuits that use a transformer with the secondary isolated from the primary, but the zero voltage terminal may not be at ground potential anymore.

Some power supplies do not use a transformer. I don't think you can isolate those.