chasmith17 Posted September 7, 2005 Report Share Posted September 7, 2005 Is it possible to get a positive and negative voltage from just one power supply? Quote Link to comment Share on other sites More sharing options...
Staigen Posted September 7, 2005 Report Share Posted September 7, 2005 Hi there chasmith17, velcome to this forumAbout your question, no, not easily :(! But if you mean from a transformer, yes, its easy! If you have a transformer with only one secondary you can use halfwave rectifiers, just ground one of the transfomer output wire and connect diodes to the other and if you prefer a fullwave rectifier you must use a transformer with double the voltage and a centertap, just ground the centertap and connect the other two wires to a rectifier bridge. The negative output from the bridge is the negative rail and the positive output from the bridge is the positive rail.//Staigen Quote Link to comment Share on other sites More sharing options...
chasmith17 Posted September 8, 2005 Author Report Share Posted September 8, 2005 Thanks for your reply Staigen,How could I achieve the + and - voltages from just one DC power supply? I could get another power supply to make it easy but I like the challenge. Quote Link to comment Share on other sites More sharing options...
Staigen Posted September 8, 2005 Report Share Posted September 8, 2005 Hi thereIt depends on how much current you have in the "ground" terminal, and how much it can be tolerated to differ from exact center voltage.How much output do you have from the PSU? Voltage?//Staigen Quote Link to comment Share on other sites More sharing options...
chasmith17 Posted September 8, 2005 Author Report Share Posted September 8, 2005 I am just looking for +12v and -12v. It is for an op amp. I know you can cheat and use ground but I would like to have the -12v. Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted September 8, 2005 Report Share Posted September 8, 2005 There are many specialized ICs and modules around that'll do this but here is a way to do it using normal off the shelf componants.Here's another way of doing this but you loose 1.4V in diode drops, and there'll be more ripple on the output tooMake sure the 100uf capacitor is rated at least to twice the maximum supply voltage. Quote Link to comment Share on other sites More sharing options...
Staigen Posted September 8, 2005 Report Share Posted September 8, 2005 Oh, you wanted a +12V to -12V converter! As Alun show you here, this is a simple one, but lack exactly center of the ground, and is not nessarily in many cases. But i would connect the positive terminal of the 100uF cap at ground instead of connecting it to the positive terminal. And use ordinary 555:s, not the cmos type. And, it can't supply much current!//Staigen Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted September 8, 2005 Report Share Posted September 8, 2005 I agree, this circuit was origionally used as a voltage doubler but I'd forgotten to alter the capacitor position. ;D Quote Link to comment Share on other sites More sharing options...
autir Posted September 9, 2005 Report Share Posted September 9, 2005 Why not just use an LM7912? Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 9, 2005 Report Share Posted September 9, 2005 An LM7912 doesn't make a negative supply, it is not a generator. It just regulates a negative supply that is already there. Its input voltage must be at least -15V for it to work perfectly. ::) Quote Link to comment Share on other sites More sharing options...
chasmith17 Posted September 9, 2005 Author Report Share Posted September 9, 2005 Thanks to all that replied, I now have my -12volts. Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted September 9, 2005 Report Share Posted September 9, 2005 How did you do it in the end? Quote Link to comment Share on other sites More sharing options...
chasmith17 Posted September 12, 2005 Author Report Share Posted September 12, 2005 The voltage double with the 100uf cab to ground. Quote Link to comment Share on other sites More sharing options...
autir Posted September 12, 2005 Report Share Posted September 12, 2005 An LM7912 doesn't make a negative supply, it is not a generator. It just regulates a negative supply that is already there. Its input voltage must be at least -15V for it to work perfectly. ::)Darn... you are right... :-\But I am sure I have seen a similar circuit in the LM7800 series datasheet. Producing negative voltage from an LM78xx. Quote Link to comment Share on other sites More sharing options...
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