Bridge Rectifier HELP !!!!!!!!!

Discussion in 'Homework Help' started by purecilia, Feb 23, 2009.

  1. purecilia

    Thread Starter Member

    Dec 29, 2008
    I have encountered 2 questions in the troubleshooting can someone give me some answers please ?? Check the questions

    1.why the dc output voltage and ripple frequancy drop in half when any diode opens

    2.If any type of diode in a bridge rectifier is shorted for any reason.What will happen to the other diodes when power is applied

  2. b.shahvir

    Active Member

    Jan 6, 2009
    Ans 1) With one diode open, bridge rectifier ckt. will act as a Half Wave Rectifier…… hence all values will drop to half.

    Ans. 2) When any one diode is shorted, then the AC power source sees a direct short-circuit. The Xmer or AC source supplying power to the bridge rectifier will get damaged due to over heating. The other diodes will remain safe as whole of the short circuit amps will circulate within the AC source only (as the current simply takes the low resistance path of the short circuited leg).

    Hope this solves your doubt. :)
  3. ecb123

    New Member

    Mar 6, 2008
    1) In a bridge there are 4 diodes; 2 for the positive peak of the incoming AC source voltage and 2 diodes for the negative peak of the AC source. If a diode opens then there is no current through that path, or no current through both diodes of that path even though only one diode may be open in that path-since they are in series. Therefore only half of the incoming AC source voltage (resulting in half frequency) can pass to the load.
    2)If any one diode shorts then the other diode in the affected series path will now have to carry the full burden or doulbling of the reverse voltage. And the load will see a small voltage increase by the amount of the forward diode voltage that is no longer present across the shorted diode. The other path with the 2 good diodes will not be affected.
  4. dht115

    New Member

    Feb 13, 2009
  5. LesterPhil


    Feb 25, 2009
    ans. 1. it is not stated there if it is fullwave or hafwave rectifier if it is fullwave, the output will the range of the voltage from negative to positive. eqs. a transformer 110VAC to 12VAC the label will be 12 0 12 means -12 0 +12 or +12 0 -12 depending were is your starting point. since the range from -12 to +12 is 24V, 24VDC will be the output so that's why you need to ha a capacitor have 2 times the output of the transformer. The capacitor generates a ripple(so much for that). So if there's is one diode is open, it makes it halfwave and so the voltave will be divided into two...
    --The ripple will also divided into two because that alternate of the halfwave will be neglected. Fullwave form is like this "nnnnnn" and halfwave is like this "n_n_n_n" that is why the capacitor will discharge more.

    If it's normaly halfwave, by opening the diode it will make it an open circuit. it become an incomplete circuit..

    2. It makes the half-cycle of the circuit ok but the other half is not ok. The cycle that is not ok, is making a high current flowing across th diode next to the shorted diode as if no current will flow to the output side and it produces heat and it could even destroy the diode depending the spex. of the diode because there are high current diode. That's why diode can be use as short-circuit protector.......heheheheheheh

    Hope you will understand my explanation because this is my very first day in the forum and I am not a native English speaker, but I understand english the prob. is I am not using it 80% in my daily routine or even 10%.... heheheh
  6. ashokcraze

    New Member

    Oct 27, 2009
    Ans1) if it is full wave ig one diode will not work the average dc output will half.
    Vdc = 2Vm/Pi full wave
    half wave Vm/Pi

    Ans 2) generally at output of full wave is pulsating dc in which 2nd harmonic will dominant means frequency will 100 Hz..if one diode will not work then frequency again will half.....
  7. peranders

    Well-Known Member

    May 21, 2007
    purecilia , a good help to understand things especially "what if" questions is to use the freeware LTSpice. Just draw the circuit and simulate, then you'll know the answer which can be sufficient although it might be good to know "why" also.