Making a +12 / -12 split power supply from one 12 v DC supply - Page 1
Forum section: electronics / projects

author: Heevy
author_rank: Newbie
timestamp: February 10, 2016, 09:48:43 pm
content: Hello everyone.first of all this is my first post on this forum, though i've been following the forum and the eevblog on youtube for quite a while now.Im building a system for a project, where i need a split supply for some op amps in two filters i have designed. ( 6 op amps in total )i have found IC's that will provide the neccesary conversion's from 12 v to -12 v,but i was wondering if there is a elegant way to do this with dicrete components, as i would like to understand the process.Im currently taking a degree in electronics engineering, so i am familiar with electronics in general,but i am far from an expert. also english is not my native language so please be lenient with me.I hope someone is willing to give me some pointers.Heevy.

author: ThomasDK
author_rank: Regular Contributor
timestamp: February 10, 2016, 10:54:38 pm
content: You could make a charge pump using a 555 timer.It's a pretty simple circuit to grasp, might be just what you wantDepending on your current requirements, you may need a couple of transistors for buffering.Thomas

author: mariush
author_rank: Super Contributor
timestamp: February 10, 2016, 11:50:03 pm
content: A MC34063 DC-DC switching regulator in inverting mode would be a very cheap solution.If it's a proper solution, it depends on how important the quality of your -12v is for your opamps, if the "noise" of the switching would affect your design.

author: rob77
author_rank: Super Contributor
timestamp: February 10, 2016, 11:51:44 pm
content: 555 is again an ICbut yes , agree - a charge pump made with 555 is a nice circuit to play with for a beginner.if you want to avoid the 555 timer, then you can do it with an astable multivibrator circuit made of discrete components.but for the -12V rail itself... if low current is enough (< 40-50mA) then a charge pump will do, if you need more current then a inverting DC converter (e.g. MC34063 )

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: February 11, 2016, 12:58:03 am
content: Can you get 24V instead and use virtual ground? Switching DC-DC invertors are noisy I would really weary of them if I using Opamps for any kind of measurement or signal conditioning.

author: ejeffrey
author_rank: Super Contributor
timestamp: February 11, 2016, 05:37:48 am
content: Charge pumps are pretty simple and don't have the sharp switching transients and magnetic interference of an inductor based SMPS. However, they have poor regulation and can't provide much output current. You can of course make one with a discrete transistor based oscillator instead of a 555, but the 555 is the simple way to go.An inductor SMPS will give you better regulation and higher load capacity, but is harder to filter the noise if that is something you care about. Not impossible, but you have to be more careful about layout and filtering than with a charge pump.One issue with a charge pump is that the output voltage will be on the order of -11.5 or so due the diode drop. Further, if you need to kill the ripple with a linear regulator you lose a bit more and end up at maybe -11. If you need the full 12V for your circuit, you won't be able to get it. For most opamp circuits it doesn't matter. With a switch mode inverter you can set the output voltage to -14 and then use an LDO to get the right voltage.

author: Heevy
author_rank: Newbie
timestamp: February 11, 2016, 07:03:32 am
content: Wow so many answers already. Awesome. My main concern is noise, since its for audio applications.I will try some of your suggestions and see which will give me the best result.Thanks a lot!Heevy

author: Zero999
author_rank: Super Contributor
timestamp: February 11, 2016, 09:31:00 am
content: Why do you need a dual supply?Can't you bias all DC nodes of the circuit connected to 0V at half the supply voltage using a potential divider?You could also look at using a virtual earth circuit which will give +/-6V.

author: han
author_rank: Frequent Contributor
timestamp: February 11, 2016, 11:02:50 am
content: Where the 12V supply came from?if you using linear regulator and plain transformator + diode, you can get +/- 12V at the same time, even without CT transformer..

author: Heevy
author_rank: Newbie
timestamp: February 11, 2016, 01:22:46 pm
content: The DC supply is a 12 V i took from an old router, since im a student i can't afford to buy anything new, so cant really get another supply at the moment.I have specifications saying that i need a +12 to -12 supply, so im hesitant to go with virtual earth. But i believe i will try with a charge pump made with an astable multivibrator made from discrete components, since i get those for free.

author: Zero999
author_rank: Super Contributor
timestamp: February 13, 2016, 09:33:40 pm
content: Quote from: Heevy on February 11, 2016, 01:22:46 pmNormally in an educational situation, the college provides the power supply. It's unusual for them to expect you to build your own power supply, especially if it involves mains.In any case, you should get extra marks if you can design it to run of a single supply.