Full Wave Rectifer !!

magdyfayad said:

... the value of the voltage as 220 instead of 110 , then we did not need four diodes to make full wave rectifier as two diodes are sufficient !!

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Wrong. The voltage has nothing to do with it. The potential of the neutral with respect to earth has nothing to do with it. Now go study like I told you.

Terminology is important.

A 1/2 wave rectifier produces a DC pulse to the filtering circuit during only 1/2 half of the cycle. The other half is blocked.

A fullwave rectifier produces a DC pulse to the filtering circuit during each half of the cycle. Thus both designs are FULL-WAVE rectifiers.

The supplying of the 2 diode circuit from a center tapped secondary provides a pulse each half cycle but that pulse originates from only 1/2 of the transformer secondary.

Using the 4 diode bridge you get approximately twice the output voltage (though at lower current capability than the 2 diode design if we are using the same transformer) across the bridge. You can opt to use either leg as a reference point and connect it to earth ground if desired. A benefit to using a center-tapped secondary to drive a bridge circuit is that, if the center leg is grounded then, after appropriate filtering, balanced plus and minus DC voltages are available from the bridge.

magdyfayad said:

yes , you are Gil47 right at Egypt

and i think you are right also at Amerca

so if we use at homes or at our factories single phase 220 volts between N and A, or B, or C , how then the full wave rectifer occurs ??

must be also use four diodes ??

or may be two diodes are suffucent ??

thanks

Click to expand...

As Bernie said the Voltages are relative from one lead to the other in your case it is 220 volts
It just so happens that if I test from earth as a reference then the N reads 0 volts and A or B or C will read 220 volts.
Now if I use A as the reference then N is 220 volts and B and C are 380 volts.
The reason for Earthing the mid point N in a 380 volt star transformer is to give no more than 220 vols above earth instead of 380
Earth is a safety Reference point that we chose to make a mid point which just happens to be the Neutral.
And by choice I would not want it to be anywhere else.

Most situations where DC is wanted it is at reduced Voltages of say 24 Volts and to achieve that a transformer is used which effectively seperates the input from output
the output or secondary is then fed to the diodes and any earth reference has to be created by you at your choice.

first i went to links about Switch Mode Power Supplies but the first step for Switch Mode Power Supplies is the rectifer cicuit , so i did not find the solution there

as this figure :




second we have two cases :

CASE 1 :

i have two AC terminals

the first one is 220 VAC relative to the ground like : A , B , C

the second one is the nuteral : N which is connected to the ground

and i apply these two AC terminals to the bridge ( four diodes )

what are the measuring voltages at the DC output ( positive and negative ) at the positive half cycle and at the negative half cycle ?



CASE 2 :

i have two AC terminals

the first one is 110 VAC relative to the ground
the second one is - 110 VAC relative to the ground

and i apply these two AC terminals to the bridge( four diodes )

what are the measuring voltages at the DC output ( positive and negative ) at the positive half cycle and at the negative half cycle ?


is this any difference between these two cases or not ??



i found each book or each link says about full wave rectifer use case 2 , while practically at Egypt or at America or any country either home or factoy use case 1 !!


thanks

No difference. The USA is Case 1 with 120VAC.
The major part to understand is where you connect the black lead of your meter. When you say 110V or 220V or whatever, you must ask the question 'relative to what?'.
On a SMPS, the AC neutral, minus side of bridge, and minus side of output are all different reference points. You must understand the concept of ground first. Study terms are Neutral, common, ground, and reference.

yes , no difference if I measure the voltage between the two terminals of the output as- at both two cases - as the voltage between the two terminals of the output is always fixed around 220 VDC


but if I mesaure each terminal of the output seperatly with respect to the ground , i think there is a difference


as for case 1 i think it must be :

for the positive half cycle : the output of the bridge which is DC is :

the positive DC is 220 V relative to the ground
the negative DC is zero V relative to the ground

which the different between them is 220 V

b - for the negative half cycle : the output of the bridge which is DC is :

the positive DC is zero V relative to the ground
the negative DC is - 220 V relative to the ground

which the different between them is also 220 V



but for case 2 :

i think it must be :

for the positive half cycle : the output of the bridge which is DC is :

the positive DC is 110 V relative to the ground
the negative DC is - 110 V relative to the ground

which the different between them is 220 V

for the negative half cycle : the output of the bridge which is DC is :

the positive DC is 110 V relative to the ground
the negative DC is -110 V relative to the ground

which the different between them is also 220 V



am i correct or not ??

Case 1 and case 2 will give you the same voltage between Positive and Negative being 220 volts RMS or about 300 volts peak. its only if you tried to measure positive or negative to earth that differences would be seen and if you are using DC why are you using anything but the positive or negative.

Just be aware that Earthing should occur at one point, which is at the transformer star earth point, or you will require, transformer isolation, primary to secondary if you wish to earth the DC side either the positive or negetive again your choice.

The centre tap method was very common in the days of valve rectifiers, now days bridge rectifiers would be the more common, but it is really just a matter of choice.

Earth really is only a safety reference point that you or someone else chose.

for case 1 what happen if we remove the two diodes which are connected to the nuteral ??


please apply the voltage on the four diodes and show the result before removing the two diodes and after removing the two diodes for case 1 i.e : there is a neutral terminal , is there any differnce for the output or not ??

thanks

Post 21: Multiply every voltage mentioned by 1.414. You have capacitors. They will charge to the peak.
Post 23: You are wrong in your thinking. How many times do I have to tell you? You cannot use just 2 diodes. It won't work.

Study sine wave, full wave rectification, half wave rectification, voltage doubler.
For AC, study Root-Mean-Square (RMS), Peak, and Peak-to-Peak.

thanks

keithkyll is right

it must be needed four diodes to make full wave rectifer if we have two wires only ( one only is a hot wire and the another is a nuetral wire ) as the same if the two wires are hot

1- but if we use two hot wires , the positive output DC is fixed positve value as 110 VDC with respect to ground at both positive half cycle and negative half cycle , and the negative output DC is fixed negative value as - 110 VDC with respect to ground at both positive half cycle and negative half cycle

while if we use only one hot wire and the second is the nuteral wire , the positive output DC is not fixed with respect to ground at both positive half cycle and negative half cycle as for the positive half cycle its voltage with respect to ground is 220 VDC , and for the negative half cycle its voltage with respect to ground is zero voltage , while the negative output DC is zero voltage with respect to ground at the positive half cycle , and the negative output DC is - 220 VDC with respect to ground at the negative half cycle

is my note correct ??

i know there is no difference if we measure the voltage between the two terminals of the DC output as - at both two cases - as the voltage between the two terminals of the output is always fixed 220 VDC and the cuurent pass into only one direction , while the difference only for measuring with respect to ground , so i repeat is my note for this difference with respect to ground correct or not ??


2- it is very wrong to connect the negative output DC to the ground at both cases ( two wire are hot & only one wire is hot and the another is nuteral ) as it makes short circuit , is not right ?? , the only method to to connect the negative output DC to the ground is to use center tapped transformer , isnot right also ??

3- if we want to grounded the negative output DC without using center tapped transformer , the only method avliable is to use Switch Mode Power Supplies (SMPS) , at this case only we can grounded the negative output DC , is not right or not ??

4- all the discussion about full wave rectifer on electeral books and all links , it consider the two wires are hot and are out of phase as used in USA as the secondry of the transformer is Delta connection and we take the two terminals at the side of winding which makes 240 VAC , as i did not find any electeral book or any link say about if there is only one hot wire as at Egypt or at Europe ,

as this is the main reason for my miss understanding the concept for the full wave rectifer as i considered - which i think it is wrong consideration now - the AC input is output of star transformer i.e : ( only one wire is hot and the another is the nuteral ) , but in fact all the discussions - as i consider now - the AC input is output of delta transformer i. e : ( the two wires are hot ) so i made this forum which is

http://www.plctalk.net/qanda/showthread.php?t=41408


to understand well how the two out of phases is called single phase , as i am trying now to understand it well

so i repeat to be sure for all the discussion about full wave rectifer on electeral books and all links , it consider only the two wires are hot and are out of phase as used in USA as the secondry of the transformer is Delta
not star transformer as it used at Egypt or at Europe , is this note correct or not ??


thanks

Think of pedaling a bicycle. You have 2 pedals and 2 feet. What if you had 3 feet and 3 pedals? Each spaced 120 degrees apart. If you use all 3 pedals to power something, you consider all 3 phases. The end of one is connected to the start of the next.
If you only used one of the pedals to power something, you would only be using a single phase.

thanks , but can you answer me exactly for each note - four notes - i stated it, are it right or wrong for each one ??


thanks

magdyfayad said:

keithkyll is right

it must be needed four diodes to make full wave rectifer if we have two wires only ( one only is a hot wire and the another is a neutral wire ) as the same if the two wires are hot

1- but if we use two hot wires , the positive output DC is fixed positive value as 110 VDC with respect to ground at both positive half cycle and negative half cycle , and the negative output DC is fixed negative value as - 110 VDC with respect to ground at both positive half cycle and negative half cycle

while if we use only one hot wire and the second is the neutral wire , the positive output DC is not fixed with respect to ground at both positive half cycle and negative half cycle as for the positive half cycle its voltage with respect to ground is 220 VDC , and for the negative half cycle its voltage with respect to ground is zero voltage , while the negative output DC is zero voltage with respect to ground at the positive half cycle , and the negative output DC is - 220 VDC with respect to ground at the negative half cycle

is my note correct ??

i know there is no difference if we measure the voltage between the two terminals of the DC output as - at both two cases - as the voltage between the two terminals of the output is always fixed 220 VDC and the current pass into only one direction , while the difference only for measuring with respect to ground , so i repeat is my note for this difference with respect to ground correct or not ??

Click to expand...

No. Positive side is zero to 170VDC (110V using your terms). Negative side is zero to -170VDC. Forget about 2 hots verses hot/neutral. This is single phase.

magdyfayad said:

2- it is very wrong to connect the negative output DC to the ground at both cases ( two wire are hot & only one wire is hot and the another is neutral ) as it makes short circuit , is not right ?? , the only method to to connect the negative output DC to the ground is to use center tapped transformer , is not right also ??

Click to expand...

Right, right.

magdyfayad said:

3- if we want to grounded the negative output DC without using center tapped transformer, the only method avalible is to use Switch Mode Power Supplies (SMPS), at this case only we can grounded the negative output DC, is not right or not ??

Click to expand...

The only method for having grounds at different potentials is to use a transformer. A SMPS has a transformer.

magdyfayad said:

4- all the discussion about full wave rectifier on electrical books and all links, it consider the two wires are hot and are out of phase as used in USA as the secondary of the transformer is Delta connection and we take the two terminals at the side of winding which makes 240 VAC , as i did not find any electrical book or any link say about if there is only one hot wire as at Egypt or at Europe ,

as this is the main reason for my miss understanding the concept for the full wave rectifier as i considered - which i think it is wrong consideration now - the AC input is output of star transformer i.e : ( only one wire is hot and the another is the neutral ), but in fact all the discussions - as i consider now - the AC input is output of delta transformer i. e : ( the two wires are hot ) so i made this forum which is

http://www.plctalk.net/qanda/showthread.php?t=41408


to understand well how the two out of phases is called single phase , as i am trying now to understand it well

so i repeat to be sure for all the discussion about full wave rectifier on electrical books and all links, it consider only the two wires are hot and are out of phase as used in USA as the secondary of the transformer is Delta not star transformer as it used at Egypt or at Europe , is this note correct or not ??

Click to expand...

No. The 2 hots ARE NOT out of phase with respect to each other. The only difference between countries is the voltage. Phases have the same concept worldwide.
The neutrals are at different points. With home AC wiring in the USA, the neutral is a center tap of one phase. This is 120/240.
With Industrial 3 phase(120/208), a single phase to neutral is 120 VAC. One phase to another is single phase 208VAC (120 * square root of 3).

thanks , but i do not understand well the first answer

assume as at USA we applied 120 VAC between the line and the nuteral to the BRIDGE ( FOUR DIODES ) :

1- at the maximum of the positive half cycle , the positive DC output is 170 vdc and the negative DC output is zero voltage , is not right or not ??

2- at the maximum of the negative half cycle , the positive DC output is zero vdc and the negative DC output is - 170 voltage , is not right or not ??

while if we applied the 240 VAC between the two hot wires to the BRIDGE ( FOUR DIODES ) :

3- at the maximum of the positive half cycle , the positive DC output is 170 vdc and the negative DC output is -170 voltage , is not right or not ??

4- at the maximum of the negative half cycle , the positive DC output is 170 vdc and the negative DC output is - 170 voltage , is not right or not ??


THANKS