maxum Posted January 7, 2006 Report Share Posted January 7, 2006 Dear Friends I am doing some small research about power supplies and found this one interesting: www.redcircuits.com/Page36.htmI have some questions if you don't mind:Why is it that a centre tapped transformer is used instead of a normal transformer? Is this only to use two diodes instead of four or because of any other particular reason?What is the difference between linear and non linear power supplies please?Your answer would be greatly appreciated Thanks in advance.Regard,SteveMalta ;) Quote Link to comment Share on other sites More sharing options...
owais Posted January 7, 2006 Report Share Posted January 7, 2006 dear, i have recieved ur question. ans : actually cetre tapped transformers has its own advantages , u can use normal transformer but its depend on application.when there isa requirement for greater amperage at a given voltage,we use discussed transformers,now in ur mentioned supply u can see that there is a variable voltage, also it has limit of 2 A current at given voltage, so schemated transformer provide u desired amperes and voltage , if u use normal then may be it will disturb ur current limitations. Quote Link to comment Share on other sites More sharing options...
maxum Posted January 7, 2006 Author Report Share Posted January 7, 2006 thanks very much friend! any other ideas and suggestions are welcome!!Thanks again Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 7, 2006 Report Share Posted January 7, 2006 Most regulated power supplies use a voltage reference like a zener diode. This project doesn't, so I don't think its output voltage would be stable. It would change with input voltage, output current and temperature. Quote Link to comment Share on other sites More sharing options...
ante Posted January 7, 2006 Report Share Posted January 7, 2006 Hi Steve,Welcome to our forum.For this PSU you don’t need a tapped transformer you can use a standard one. A non linear PSU is a switch mode power supply. There are many characteristics which are different between them. Try Google “linear vs switch” and you get some interesting hits. ;D Quote Link to comment Share on other sites More sharing options...
MP Posted January 8, 2006 Report Share Posted January 8, 2006 The use of a center tapped transformer and two diodes provides less ripple. A needed feature when you regulate the supply in this manner.The circuit in your link with two diodes is a full wave rectifier. Using a non center tapped transformer with one leg to common and the other leg to a rectifier diode is known as half wave rectification. In half wave rectification, you will have less positive swings and more ripple. With full wave rectification, you will have more voltage swings and thus, less ripple. This is because of the smoothing effect of the bypass capacitor.To use a non center tapped transformer, I would not recommend using only one diode for a full wave rectifier. I would recommend using a bridge rectifier instead. However, note that by using a bridge rectifier, the voltage output will be different.MP Quote Link to comment Share on other sites More sharing options...
ante Posted January 8, 2006 Report Share Posted January 8, 2006 Hi MP,Do you think that two diodes on a center tap will provide less ripple than four on a conventional transformer?? I don’t think so.Steve asked :"Why is it that a centre tapped transformer is used instead of a normal transformer? Quote Link to comment Share on other sites More sharing options...
MP Posted January 8, 2006 Report Share Posted January 8, 2006 To use a non center tapped transformer, I would not recommend using only one diode for a full wave rectifier. I would recommend using a bridge rectifier instead. Ante,I was not implying that 2 diodes are better than 4. Only that 2 are better than 1 in regards to ripple. I also recommended that Steve use a bridge rectifier (4 diodes) if he were not going to use a center tapped transformer. Sorry if I was not clear on that.MP Quote Link to comment Share on other sites More sharing options...
ante Posted January 8, 2006 Report Share Posted January 8, 2006 MP,Obviously this is me not interpreting this correctly: “The use of a center tapped transformer and two diodes provides less ripple.” Less ripple than what? And : “A needed feature when you regulate the supply in this manner.” Which manner is this PSU regulated in?Further more I do not distinguish between a bridge rectifier and the configuration of four diodes, they are both the same to me.I assumed by his statement that Steve already knew the different uses four vs two diodes.Sorry for the inconvenience. Quote Link to comment Share on other sites More sharing options...
MP Posted January 8, 2006 Report Share Posted January 8, 2006 ante,Completely written while looking at Steve's link. I did not assume from the post that anyone knew what full wave or half wave rectification is, and thus a little explanation. I think the post is explained pretty well if you look at the terms for rectification type. Something anyone should learn if they are going to be making the various types.My earlier post explains that the two diode setup as in his diagram would be better than deleting the center tap, connecting the other leg to ground and using only one diode (half wave rectification).I have added a diagram in hopes that this makes it easier for anyone who still needs explanation.MP Quote Link to comment Share on other sites More sharing options...
ante Posted January 9, 2006 Report Share Posted January 9, 2006 Ante,I was not implying that 2 diodes are better than 4. Only that 2 are better than 1 in regards to ripple. I also recommended that Steve use a bridge rectifier (4 diodes) if he were not going to use a center tapped transformer. Sorry if I was not clear on that.I must be loosing it, I can’t find where anybody except you have mentioned one diode. And when using one diode I agree, there is more ripple! :-\ Quote Link to comment Share on other sites More sharing options...
MP Posted January 10, 2006 Report Share Posted January 10, 2006 Put it to rest, ante. If Steve needs more information he will ask.I think you have kicked this dog enough. It is no longer moving.MP Quote Link to comment Share on other sites More sharing options...
ante Posted January 10, 2006 Report Share Posted January 10, 2006 No use! I give up!BTW: I never kick dogs I like dogs they are not patronizing! Quote Link to comment Share on other sites More sharing options...
maxum Posted January 10, 2006 Author Report Share Posted January 10, 2006 thanks guys. Yes actualy i know the difference between half wave and fullwave. And for the guy who said it would not work well, i built this circuit and obtained good results.What i wanted to know is that what dirreence in the output one would get when using centre tapped and normal trans.thanks to all of you. 8) Quote Link to comment Share on other sites More sharing options...
ante Posted January 10, 2006 Report Share Posted January 10, 2006 Hi Steve,Well, as I tried to say; as far as I can see they are both the same. ;DI am glad it works well! Quote Link to comment Share on other sites More sharing options...
MP Posted January 11, 2006 Report Share Posted January 11, 2006 Hi Steve,To answer your question: You will see some differences in output, but mostly dependent upon whether you have a capacitor on the output or a resistive load. There is also a difference in the current output for the different types. See below:MP Quote Link to comment Share on other sites More sharing options...
ante Posted January 11, 2006 Report Share Posted January 11, 2006 Hi Steve,If in doubt, the drawings I supplied apply only for capacitive load; C1 in your circuit (which the question was about) is the capacitive load! Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 11, 2006 Report Share Posted January 11, 2006 Hi Guys,I simulated the circuit of the "variable voltage regulator" and it oscillated unless the output capacitor was removed. Its voltage regulation was 50 times worse than an LM317 or LM350 which is much simpler and costs less. Quote Link to comment Share on other sites More sharing options...
ante Posted January 12, 2006 Report Share Posted January 12, 2006 Hi Audioguru,Yes I agree, it’s simpler to use and performs much better with its internal reference and feedback. Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 12, 2006 Report Share Posted January 12, 2006 Yes I agree, it’s simpler to use and performs much better with its internal reference and feedback.Hi Ante,Maybe the circuit was designed before the simple and excellent LM317 was invented.Maybe LM317's weren't available over there.My variable voltage power supply has an LM317 in a simple circuit. Its performance doesn't "just give good results", its performance is perfect. ;DOf course, its current-setting resistor is the proper value of 120 ohms and it has a heatsink. ::) Quote Link to comment Share on other sites More sharing options...
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