Half wave rectifier

[charlie b]

Re: Half wave rectifier

It seems that we are talking about apples and carburetors (i.e., different languages). The paper in Dereck?s link described the average value as ?Vdc.? In the language that Steve66 and I are using, the RMS value of any alternating waveform is the DC value that would provide the same heating effect. As Steve said, if you want to calculated power (or heating effect, for that matter), you have to use the RMS values.

By the way, that paper also confirmed the value that I had given earlier. Specifically, it said that the RMS value of the half-wave rectified signal is half the peak value. I had said that the RMS value of the half-wave rectified signal is 70.7% of the original sine wave?s RMS value. Those two statements are the same.

 

[charlie b]

Re: Half wave rectifier

Originally posted by ronaldrc:That?s a good point Charlie, but I'm assuming that the source that generated that positive side of the first half of the sine wave will generate an identical negative half. I assuming they have the same amount of bananas.

Apparently, my analogy was not as clear as I had hoped. My point was that two different things are going to behave differently. The ?RMS Value of a Waveform? is different from the waveform itself. So if you cut the waveform (i.e., the bananas) in half, there is no reason to expect that the RMS value (i.e., the fruit salad) will be cut in half.

 

[ronaldrc]

Re: Half wave rectifier

Hope everyone is having a good evening.

Theres one thing I said 120 VDC pulsating maybe I should have said 120 RMS the actual voltage would be 170 peak just the bottom or negative half has been removed. Eds formula took this into consideration. He gave it both ways.

Doesn't RMS treat each half of the waveform equally its just a way to get the effective value of the varying wave, wouldn't this result be half?

Ronald

[ September 01, 2004, 05:34 PM: Message edited by: ronaldrc ]

 

[Ed MacLaren]

Re: Half wave rectifier

As Steve66 has stated above, one should not use the term RMS when describing the output of a rectifier circuit.
The term RMS should only be applied to an AC voltage or current.
Once that AC voltage has been rectified it is DC and AVE (average) is the term that should be used to describe it.

Ed

 

[ronaldrc]

Re: Half wave rectifier

Ed and Steve

You've confused me which ain't hard to do but I was taught about a hundred years ago that RMS was an average for a sine wave and the constant was .707.

120 Volts=170 Volts X .707

Why would this change if where just using half of it.

Ronald

 

[jimwalker]

Re: Half wave rectifier

with no load and a high impedance meter ,and the wires themself are actually a capacitor, one might very easily read 170 volts DC.
Keep in mind that a clamp on amp meter was designed to work on a full sine wave,so any readings are false if this is DC.
My answer is you have just at 50% of the power if rectified.
We must understand that a rectifier offers high resistance to current in one direction but there still is a very small current flow from the other half,less than 1%

 

[ronaldrc]

Re: Half wave rectifier

Jim I agree

With no load and a meter with high internal impedance that reads peak voltage it should be 170 volts because all we did was clip the negative half off?

Ed
I agree that maybe not refering to it as RMS because RMS is the average of both halfs and we use the constant of .707.

But its still the average and we use the constant you give at .318 is that fair enough?

Ronald

 

[charlie b]

Re: Half wave rectifier

Originally posted by Ed MacLaren: The term RMS should only be applied to an AC voltage or current.

You can calculate the RMS value of anything. If you calculated the RMS of a constant DC value of 12 volts, if you actually went through the math, the result would be, not surprisingly, 12 volts.

 

[hurk27]

Re: Half wave rectifier

Oh never mind

[ September 02, 2004, 01:37 AM: Message edited by: hurk27 ]