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Again I Have a question regarding Bridge Rectifier's Made using 4 Diodes

if I use 4 pieces of 1N5408 with rating of 3 amp in Bridge mode what will be current rating or handling capacity of rectifier ,does its rating will increase or will be same as single 1N5408

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  • \$\begingroup\$ There will still be the same amount of current going through each diode, just at different times. \$\endgroup\$ – Ignacio Vazquez-Abrams May 2 '16 at 3:23
  • \$\begingroup\$ Four '3A' diodes makes a '6A' bridge, with the details of the conditions for the current rating the same. \$\endgroup\$ – Spehro Pefhany May 2 '16 at 15:54
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The diode rating is for the part itself. The manufacturer states that the part is rated for 3A for each part, so you shouldn't exceed 3A. There is some judgement in this statement, meaning that you can exceed the rating without damaging the part for short periods, but not for long periods.

A bridge rectifier uses 4 of these, two of which are conducting at a time. This means that if the bridge rectifier is seeing an RMS current of 3A, then each diode is experiencing an RMS current of 1.5A. So to answer your question, yes, your rating could be considered increased over that of the individual components.

Having said that, a 2x safety margin is a good thing in power electronics. If you need 3A continuous output, I would recommend a 5A or higher diode.

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  • \$\begingroup\$ As an addendum to this statement: "meaning that you can exceed the rating without damaging the part for short periods, but not for long periods." Some datasheets specify "continuous" ratings versus "peak repetitive" and "peak non-repetitive", which are self-descriptive and describe how much it can handle for "short periods". They usually specify the short period in question and maybe even shape of the current waveform. The 3A would be the continuous rating. Your duration and shape might differ, but it gives you even more reference points to make a judgement call on it. \$\endgroup\$ – Laogeodritt May 2 '16 at 6:15
  • \$\begingroup\$ One more factor to consider is an operating temperature of the system. If your diodes have a perfect heat sink and it never exceeds 25 C (water cooling or good forced circulation), then you definitely can take 5 A RMS from a bridge rectifier of 3 A diodes. However, if your system operates in hot industrial environment (near a car engine, in hot climate etc) then I suggest never taking more than 3 A RMS of the same rectifier. You can check the datasheet for max junction temperature, junction-to-case thermal resistance, consider your max ambient (case) temperature and power dissipation. \$\endgroup\$ – Master May 2 '16 at 7:06
  • \$\begingroup\$ I agree with both comments, there are many factors that go into the rating of the final assembly. My personal preference is to get a 2x rated component to start out and then check it using a thermal camera under normal operating conditions. \$\endgroup\$ – slightlynybbled May 2 '16 at 13:02
  • \$\begingroup\$ @user3211730 So I see that you changed your title, but this doesn't answer your question? Between my text and the comments, there appears to be an agreeable answer... \$\endgroup\$ – slightlynybbled May 2 '16 at 13:04

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