rectifier with 220V ac to 200V dc ?

Discussion in 'General Electronics Chat' started by h.d, Dec 16, 2007.

  1. h.d

    Thread Starter Active Member

    Oct 22, 2007
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    hi
    i want to ask if we can get 200V dc output by rectifier circuit
    with 220V ac (50Hz)input?
    sure its full wave,and i need it uncontrolled rectifier.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Without some regulation, you can't rectify Ac and come out with a lower DC voltage. If you use capacitor filters, the output voltage is about 1.4 times the AC input.
     
  3. h.d

    Thread Starter Active Member

    Oct 22, 2007
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    you mean that i can get output dc more than the ac-input?how can i use the capacitor filter to do that?
    sure threr are regulation.
     
  4. cheddy

    Active Member

    Oct 19, 2007
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    He meant to say that DC is ~.707 times the AC
    AC is ~1.4 times the DC
     
  5. h.d

    Thread Starter Active Member

    Oct 22, 2007
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    in that the maximum dc-output is
    220*0.707=155.5V
    ?
     
  6. eeboy

    Active Member

    Sep 27, 2007
    90
    1
    No, he was correct. The rectified DC output is 1.4 times the AC input. 220 is the RMS voltage and is .707 * the peak.
     
  7. Papabravo

    Expert

    Feb 24, 2006
    10,136
    1,786
    With a large capacitor to hold the peaK voltage until the next peak, the estimate of 1.4 times the RMS voltage is correct. The DC output will be in the neighborhood of 308 Volts. Dropping that to 200 volts without dissipating a ton of power will be a challenge. Good Luck.

    It might be easier to get a 220 to 140 transformer then the rectified and filtered voltage will be in the neighborhood of 200 VDC
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    What are you planning on powering with it? Tube plates?
    What will your minimum, maximum, and average expected current be?

    Running off the mains is risky business. When there are failures, the operator can be exposed to the power of the mains. I say when, because sooner or later, something will break.

    A transformer serves not only to isolate from the power mains, but to better match the voltage you need while limiting the maximum current.

    If the amount of current you need is small, you might consider using a moderate voltage transformer, and then voltage doubler/tripler/quadrupler circuit(s) to reach the voltage you need.

    When you're working with high voltage, even small currents can kill you. Be careful.
     
  9. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
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    The 220VAC is the RMS value of the grid voltage. The peak value is 1.414 times greater (Vpeak = sqrt (2) x Vrms) and that is the voltage of the resulting rectified current.

    No. Its the opposite.
     
  10. h.d

    Thread Starter Active Member

    Oct 22, 2007
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    i need it as power supply for dc-motor(Vt=200V,6A,2hp)
    and the average current is 6A,maximum is 7A
     
  11. h.d

    Thread Starter Active Member

    Oct 22, 2007
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    i will try it simulation.
     
  12. Papabravo

    Expert

    Feb 24, 2006
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    At those power levels you won't be wanting to regulate 308 VDC down to 200 VDC.
    Code ( (Unknown Language)):
    1.  
    2. 108 Volts x 7 A = 756 Watts.
    3.  
    Thats about a horsepower worth of wasteed heat. Get thee a transformer and be done with it.
     
  13. h.d

    Thread Starter Active Member

    Oct 22, 2007
    150
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    Hi
    Am back again
    That’s the model which I done
    The input voltage is 220 Vac 60 Hz
    The output voltage is 213 Vdc
    But I know that the output voltage and input acts with the following relation
    Vdc=2^0.5*Vac
    I don’t know if I take the output correctly
    And what is the output which I get is it rms or dc or what????
    If any one can help me.
    And thanks.
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    Your output is DC with ripple. You can reduce the ripple by increasing the size of the filter capacitor, but "real world" capacitors for those kinds of voltages are going to be quite large and expen$ive. However, since your load is inductive, some ripple probably won't matter that much.
     
  15. jamers

    Member

    Jan 24, 2008
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    A sine wave is measured by the rms voltage. Which is the the Peak-Peakvoltage divided by the square root of 2.

    So to get a 200V dc output, you first have to convert your ac voltage to an ac voltage of 141.42VAC, and then when you rectify it you will get a dc voltage of 200V.

    An example of this we can use is your AC wall voltage of 115VAC.
    The RMS value is 115VAC, however if i were to get P-P voltage it would be 163V.

    If you dont want to use a transformer you have to rectify your AC voltage using a SCR bridge, but then you need to worry about adjusting your triggering point to capture exactly the right amount of the ac wave.
     
  16. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    h.d.,

    Your simulation is quite frightening of what can happen when you don't understand the problem accurately. As most people have mentioned, AC outputs are specified as RMS. You are taking them as peak values! Be careful with all of that voltage and power, safety is a priority.

    You should use a transformer to do this, since it is straightforward and safe to do. It is possible to power a high voltage H-bridge, then just PWM the input. This IC is a bit under-rated current-wise, but it might be a good starting point. It is meant for 3-phase operation, but it will be happy with only two half bridges in use.

    http://www.irf.com/product-info/datasheets/data/irams06up60a.pdf

    Steve
     
  17. h.d

    Thread Starter Active Member

    Oct 22, 2007
    150
    0
    for safety i will use circuit braker before the rectifier
    and after the output of rectifier would use MOSFET with PWM controlling
    is it good?
     
  18. h.d

    Thread Starter Active Member

    Oct 22, 2007
    150
    0
    my project is to drive dc motor by PWM so i will use MOSFET in the output of rectifier as a chopper class A
    the motor is 220Vdc so i will limit the duety cycle in 70%.
    i think thats good , isnt it?
     
  19. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    In your model, it appears that you are using an N-channel MOSFET on the high side of your load. You would normally have it between the load and ground. Otherwise, your gate control voltage would have to have a 220v swing!

    Also, your load doesn't have any reverse EMF protection, such as a diode and a capacitor; without it you'll wind up with extremely high voltages across your MOSFET, destroying it. You'll need a diode capable of carrying a fairly large amount of current. I also suggest paralleling the diode with a small capacitor (say 0.1uF) with at least 300V rating. Diodes can take some time to turn on and off; the capacitor will absorb the peak voltage until the diode begins to conduct.
     
  20. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    MOSFETs can and do short when they fail. This would subject your motor to 150% of rated voltage. (225% of rated power.) A standard breaker might not trip quickly enough to protect your motor. A fuse or breaker capable of tripping quickly enough might also open during motor start-up.

    A transformer would solve all of this.
     
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