Rectifier Characteristics

[jasper1963]

Could someone please answer this question for me: If the 2 diodes in a full wave rectifier were accidentally connected in parallel with each other, what would happen to the transformer? Thanks

 

[RCinFLA]

You need to draw a diagram of the configuration.

 

[dougy83]

Could someone please answer this question for me: If the 2 diodes in a full wave rectifier were accidentally connected in parallel with each other, what would happen to the transformer? Thanks

You would be shorting the transformer secondary and it would:
a) heat up (possibly tripping any thermal fuse in the transformer)
b) burn-out one of the windings which would remove the 'short' condition

You need to draw a diagram of the configuration.

A full-wave rectifier with 2 diodes uses a centre-tapped transformer; the diodes conduct on alternating phases of the transformer.

 

[Vizier87]

in my experience, two diodes in parallel behaves just like a single diode with the same forward voltage with double the current rating.

 

[jasper1963]

Thanks for your speedy replies they are greatly appreciated

 

[Sceadwian]

Except they don't Vizier. No matter how close you are forward voltage is never the same, and thermal run away will cause one diode to heavily favor the current flow vs the other unless a series resistance is used. LED's tend to be parellled in cheap flashlights, but this is at nearly their rated forward voltage and a common thing forgotten about LEDs is they have a lot of built in bulk resistance at their rated currents so in many cases the series resistors are either not needed or the device will function just long enough not to notice.

 

[RCinFLA]

You would be shorting the transformer secondary and it would:
a) heat up (possibly tripping any thermal fuse in the transformer)
b) burn-out one of the windings which would remove the 'short' condition


A full-wave rectifier with 2 diodes uses a centre-tapped transformer; the diodes conduct on alternating phases of the transformer.

Or it could be a half wave rectifier with two diodes in parallel on same side, leaving other side of transformer center tap open.

 

[dougy83]

Or it could be a half wave rectifier with two diodes in parallel on same side, leaving other side of transformer center tap open.

The OP clearly stated that it was a fullwave rectifier. True, it could be anything (maybe the "diodes" are actually resistors), but I gave the OP the benefit of the doubt.

 

[Vizier87]

Mmm yeah. I guess you're right. My DMM's diode tester shows the same value of forward voltage for paralleled diodes but I didn't consider the racing conditions of the diode threshold.

 

[Mikebits]

The OP clearly stated that it was a fullwave rectifier. True, it could be anything (maybe the "diodes" are actually resistors), but I gave the OP the benefit of the doubt.

But the diodes in parallel would make it halfwave instead of fullwave, assuming the second half of secondary was left open. Hence a better explanation would be nice.