Negative Supply Voltage

Question

I am trying to use an TI UA741 opamp and supply it with +12 VDC and -12 VDC. To obtain -12 VDC, i configure the power supply like i have shown below on the picture. Can i get -12 VDC (V2 on Figure 1 that i connected the circuit without any regulator)using this configuration in real life? I am also using a negative voltage regulator L7912CV. I have shown how i intented to design with regulator in Figure 2 that i have roughly shown without peripheral resistors or capacitors. If you share your comments i will be happy. You can advise any other methods to achieve negative voltage. I am just trying to clutch the logic. Thank you.

Figure 1:

Figure 2:

It will be connected to circuit's ground, i just visualized what i want to do roughly. — layout789, Jul 19 '17 at 14:57
I don't recognize the pin out on the 8 pin device shown in yellow on your 2nd circuit. — Andy aka, Jul 19 '17 at 14:59
It is so easy to get some example circuits these days, just google: "dual rail supply circuit" and press the images tab. There are plenty of example circuits. Try to figure out how the simplest of these work. Profit. — Bimpelrekkie, Jul 19 '17 at 15:14
If your design is meant to solve a real problem (not an academic exercise) please read Reasons not to use a 741 op-amp? before you continue. — The Photon, Jul 19 '17 at 16:03

score 1 · Answer 1 · answered Jul 19 '17 at 15:16

Theoretically that will work, but only if V2 is a floating (isolated) supply. Many power supplies are actually referenced to the protective earth AKA 3rd prong. These would not obviously work.

For an easy way to generate -12V from +12V, you can use a buck-boost SMPS circuit. TI SLYT286 shows how to use a common buck-converter in an inverting buck-boost configuration. Do note that this will effectively double the voltage so you need something that's OK with 24VDC input. You can obviously use a dedicated buck-boost converter but for actual product designs it's beneficial to use same parts if you can.

http://www.ti.com/analog/docs/litabsmultiplefilelist.tsp?literatureNumber=slyt286&docCategoryId=1&familyId=751&keyMatch=SLYT286&tisearch=Search-EN-Everything

If you really want to get fancy, you can do +/- output SMPS circuit using a common mode choke but that's a bit beyond the scope here.

Thank you. Is this the circuit that you mean? http://www.circuitdiagramworld.com/uploads/allimg/201411/12-VOLT-DUAL-POWER-SUPPLY-550x299_555154286.jpg I have found an IC for that https://www.maximintegrated.com/en/products/power/switching-regulators/MAX764.html Which one do you suggest, fullwave bridge rectifier one or MAXIM's IC? — layout789, Jul 19 '17 at 18:17
@layout789 mm, not really. Although I suspect the principle is somewhat similar. Dual output configuration uses one coil as usual and the other one is connected via diodes to provide the negative output. I think for you use you just need normal buck converter. Like so https://www.google.co.uk/url?sa=t&source=web&rct=j&url=http://www.ti.com/lit/ml/szzn001/szzn001.pdf&ved=0ahUKEwjS59DvjpbVAhUoB8AKHSXoCTEQFggdMAA&usg=AFQjCNFL3vZqHIfLAEqtMokHk1HFA4zazQ — Barleyman, Jul 19 '17 at 19:50

Negative Supply Voltage

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