Bridge rectifier

Discussion in 'General Electronics Chat' started by mhtplsh, Apr 12, 2009.

  1. mhtplsh

    Thread Starter Member

    Jul 29, 2007
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    In full wave rectifier 4 diodes r used. If i use in4001 x 4 , how much current i will get from this rectifier? 2A or 4 amp? The diode is rated 1A each. I understand that bridge will not used for full load in practice. This question is for academic interest.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    You will get the 2 amps a bit longer than you will the 4, but the duration will be no more than a few seconds. Those diodes are rated for 1 amp, and so will fail when passing more than the rated current. Much better to choose a bridge rated for somewhat more than the load output.
     
  3. mhtplsh

    Thread Starter Member

    Jul 29, 2007
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    Thanks beenthere
    So u mean to say that the bridge rectifier will be just useful for 1A in continuous use.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    Even the 1 amp is a bit of a stretch if the diodes are not able to dissipate the heat. Any component is going to be stressed and potentially fail when run right at its rated maximum.
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    You can buy bridge rectifiers as components. The come in many packages, some are designed to be easily heatsinked (metal case, with a hole in the middle). The come in many ratings, you can buy pretty much off the shelf what you want, anywhere.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Actually, the 1N400x series is rated for 1A average current. When used in a rectifier bridge, only 1/2 of the bridge (2 diodes) will be conducting at any given time.

    However, when carrying a constant 1A, the Vf (forward voltage) of the diode is about 1.1v. This means power dissipation is 1.1 Watts. They're rated for 3W maximum. The higher the current flow through the diode, the higher the Vf becomes, until the diode is destroyed due to heat.
     
  7. mhtplsh

    Thread Starter Member

    Jul 29, 2007
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    Thanks SgtWookie,
    U hv explained nicely.
    When two diodes r used in bridge at a time, means 1A current will be shared by 2 diodes. Each will carry current of .5A. it is 50% of the current capacity of 1N400X. Is this ok, as i understand.
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    Uhhh, no, Two diodes each will carry the current, as they are in series with each other.
     
  9. Audioguru

    New Member

    Dec 20, 2007
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    The 1N400x has an absolute max average half-wave rectified current rating of 1A. The diodes on each side of the full-wave bridge are half-wave rectifiers. Two diodes are in series on each side and they can pass an average of 1A. So if the rectified and filtered DC current is 1A or more then the 1N400x diodes are overloaded and are in trouble.
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    That is not correct.
    It has an absolute maximum average rectified forward current of 1A, at 75°C with 0.375" lead length. "Half-wave" would indicate a 50% duty cycle.

    It can also take a single 8.3mS half-sinewave current of 30A (non-repetitive)

    Not correct. Since the rectifiers are running at a 50% duty cycle, they could actually pass 2A and be within the maximum ratings. However, I would not deliberately operate components at their absolute maximum specifications and expect them to last for any amount of time.
     
  11. Audioguru

    New Member

    Dec 20, 2007
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    According to Fairchild (I didn't look at Chinese and Indian datasheets), the 1N400x diode has a max allowed average half-wave rectified current of 1A.
    The temperature is 75 degrees C on the text but is any temperature up to 75 degrees C on the graph.
     
  12. italo

    New Member

    Nov 20, 2005
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    NO you will not get 2 amps if the diodes are rated for 1 amps the diodes conduct two at the time in series so if a manufacture say 1 amp only 1 amp can flow. This is basic guys
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    We were looking at the same datasheet from Fairchild. In your prior post, you said:
    I maintain that this is still an incorrect statement, as the evidence you posted is a combination of the "Absolute Maximum Ratings" (which is as I stated), and the graph is from the "Typical Characteristics" on Page 2 of the same datasheet; the latter of which is not an absolute maximum rating.

    However, we ARE in complete agreement that it would be unwise to operate a 1N400x rectifier at or near it's maximum ratings, which I inferred in my reply.
     
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