transformer full-wave rectifier topology 1

[RyreInc]

I have a colleague that professes using the center tap of a transformer as the positive voltage node instead of ground is superior, having "read it somewhere." See attached drawing.

Is there some advantage to using the alternate topology (lower schematic) that I'm missing? As far as I can see there are no advantages and one big disadvantage, which is having double the voltage relative to ground.

 

[VEBill]

The load resistor wouldn't notice any difference. No advantage either way.

The transformer insulation will be happier with the traditional architecture (top).

Considering the final score, it's no wonder that the traditional architecture is the traditional architecture.

 

[OperaHouse]

There are two practical reasons he could have read it. One is it sllows two voltage outputs (one double the other) if an additional two diodes are added. The other is that some diode packages could easily use the case/ground for a heatsink in higher current applications without using any insulators. Electrically there is no difference.

 

[VEBill]

Good point about diode cases.

If we're allowed to add two additional diodes, then the top circuit can become a bipolar power supply.

Float the circuit (delete the ground connection). Then ground whatever node you please.

 

[RyreInc]

Thanks for the responses, just what I was looking for.

As far as the advantages OperaHouse listed, we are utilizing neither... I will try to convince my colleague to switch to the standard.

 

[ScottyUK]

In some telecoms applications, especially ones which have battery backup, the positive pole is grounded to reduces galvanic corrosion of circuits which may have leakage to the mass of earth.


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If we learn from our mistakes I'm getting a great education!

 

[RyreInc]

ScottyUK, are you saying that the system basically runs at a negative voltage in that case? This is something we are doing, and might help explain why. But wouldn't the desired polarity of the voltage depend only on the order of the two dissimilar metals at the junction? And is an electrolyte required?

I've been reading about galvanic corrosion this morning, but have a lot of learning to do! Any suggested resources I might check out?

 

[ScottyUK]

Yes, the system runs at a negative potential with respect to earth. Most corrosion cells are in the order of a volt or so, perhaps less but rarely more. Most common supply voltages are greater in magnitude than this, so the corrosion cell is reverse biased by the supply. I guess you could think of the corrosion cell as being 'recharged' rather than 'discharged' if you want to think in terms of how a normal secondary cell behaves, which prevents the loss of metal ions.

Yes, you need an electrolyte. There's forum338 where you might get some hints, although they're a funny bunch over there.


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If we learn from our mistakes I'm getting a great education!