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What would be the side-effects of placing two bridge rectifiers in series?

The question stems from reading how some devices are manufactured with a bridge at the input to make reverse polarity mistakes impossible for consumers/users with, for example, battery powered devices; coupled onto that is the naïve curiosity I have of whether two rectifiers and filter caps in series after an AC/DC transformer would equate to a smoother DC signal (I somehow doubt that)Double rectifier question. Attached is a schematic of what I'm referring to, the image seems to have come out a tad blurry in places but can be seen. It's only a fun question, but a genuine one nonetheless.

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  • \$\begingroup\$ Did you intend to connect the two 0V nets together? Because that's what the schematic shows. \$\endgroup\$ – Spehro Pefhany Jun 10 '15 at 22:51
  • \$\begingroup\$ Not intentionally. Meant to be AC into first rectifier, then DC into second. \$\endgroup\$ – d123 Jun 10 '15 at 23:19
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The bridge rectifier can be thought of mathematically as taking the absolute value of the input voltage.

Taking the absolute value again does... nothing. The only difference of adding a second bridge is you are out 4 more diodes and the output voltage is 2 diode forward voltage drops lower.

Pros

  1. Make diode manufacturers happy by buying more diodes
  2. Keeps your circuit warm by dissipating heat in the second bridge
  3. Slightly lower output voltage (by 2 diode forward voltage drops, though there are simpler ways to get this)

Cons

  1. More parts in your design (more board space, money, assembly time...)
  2. Consumes more electrical power, lower efficiency, increased heat dissipation requirements...
  3. Slightly lower output voltage (by 2 diode forward voltage drops, though there are simpler ways to get this)

Joking aside, I can think of no practical reason to do this. If you want a smoother DC output, add more/larger smoothing output capacitors, not a second bridge.

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  • \$\begingroup\$ Great answer, thanks. I'm pretty hopeless, but this wasn't an intention to actually carry out, I was just curious. BTW, there's nothing wrong with gratuitous component syndrome - it keeps the global economy moving! \$\endgroup\$ – d123 Jun 10 '15 at 23:22
  • \$\begingroup\$ @d123 until we run out of sand and have to go back to germanium for everything, of course. Ew, germanium windows. \$\endgroup\$ – Asmyldof Jun 11 '15 at 0:58
  • \$\begingroup\$ Hey - maybe you have a good idea: Carbon trading, water trading... Why not add silicon trading, we could publish spurious news about "Peak Silicon", and at the same time corner the germanium market, purporting it's benefits for wholly inappropriate uses and rig both commodity prices?! \$\endgroup\$ – d123 Jun 12 '15 at 14:40
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Another pro, as drawn: Twice the filter capacitors, which actually could make a difference in smoothing the final DC output.

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  • \$\begingroup\$ Hi, that's about the only benefit, though; but I agree about a smoother DC output, which is always welcome. \$\endgroup\$ – d123 Jun 12 '15 at 14:41

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