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Pmax in the given circuit.

  • Engineering
  • Thread starter rama1001
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  • #1
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Hi,
Can any one tell me how to calculate the Pmax for Rs in the attched circuit. where Rs value is 220ohm
 

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  • #2
berkeman
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Hi,
Can any one tell me how to calculate the Pmax for Rs in the attched circuit. where Rs value is 220ohm
What is the context of the question? Is it for schoolwork, or are you building something?

And what do you mean by Pmax? Do you mean the power that will be dissipated by the resistor Rs? That would depend on the value of the load clamp and resistor, no?
 
  • #3
132
1
Hi,
i feel the same and i search throughout the web. That is my course work regarding to laborations. In that task we just calculated the series resistance and we see the stabilized output. I have to answer that question when load(R=1k /4W.) is there and without load case. i dont know how to calculate. the zener we used is BZX85/C30.
 
  • #4
berkeman
Mentor
57,306
7,291
Hi,
i feel the same and i search throughout the web. That is my course work regarding to laborations. In that task we just calculated the series resistance and we see the stabilized output. I have to answer that question when load(R=1k /4W.) is there and without load case. i dont know how to calculate. the zener we used is BZX85/C30.
Please remember to post schoolwork questions in the Homework Help forums. I'll move this thread there now.

What is the voltage that your zener clamps at? What do you think the output DC voltage of your rectifier bridge will be, given that it has a 24Vrms input AC waveform? What will the voltage drop then be across Rs?
 
  • #5
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the resistor Rs must be choosen that maxium powerdessipation shoud not exceed 1.3W of the ZEner. I choosen the Rs as 220ohm and the output is 30V.
 
  • #6
berkeman
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7,291
the resistor Rs must be choosen that maxium powerdessipation shoud not exceed 1.3W of the ZEner. I choosen the Rs as 220ohm and the output is 30V.
Ah, Rs is to limit the current that goes through the Zener diode. Okay, that makes sense.

And you are saying that the Zener diode is a 30V diode? How do you caluculate the voltage out of the diode bridge? Remember that it will not be purely DC.... How did you arrive at the 220 Ohm value for Rs? Can you show us your detailed calculations?
 
  • #7
132
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total information is there in the attachment with my answer. First i made mistake in the report calculation and then again i rectified even though they are not satisfied.

could you help to dig it out.

i want remove this scrap possibly after getting the information. i dont know how to remove this entire post. Could you make a way for that.
Thanks in advance..
 

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  • #8
205
0
total information is there in the attachment with my answer. First i made mistake in the report calculation and then again i rectified even though they are not satisfied.

could you help to dig it out.

i want remove this scrap possibly after getting the information. i dont know how to remove this entire post. Could you make a way for that.
Thanks in advance..
You seem to have an incorrect value for Vs. What voltage would you expect across a capacitor fed by a bridge rectifier from 24V AC? Wouldn't you expect something closer to the peak value minus the bridge drop?

The answer I get is actually a bit low even if we assume a 30V Zener, so I wonder if there could have been a mistake in the original question?

Did it not seem strange to you that the voltage across Rs appeared to be NEGATIVE? That cannot work. You must have Vs greater than Vz.
 
  • #9
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Of course, Vs will not be at its maximum value at all times, but it should not have dropped to anything near 24V unless C was very small, say 47uF. (IT =CV, assuming 8V drop in 10ms at 30mA gives 37.5uF.)
 

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