Op-Amp Power Supply From 5v

[ParkingLotLust]

Hey guys,

When Im in the lab working, I often find a tracking, +/- power supply is very useful when experimenting with opamps. I have a beastly bench supply that I use, which works with no problems. However, I am investigating something a lot easier.

My goal is this: to implement a step-up converter, from 5v to 32v, so I can split the 32v in half, to get my op-amp supply. This way, I can use the fixed 5v supply that I use in nearly every circuit ANYWAY, to drive my opamps. The output voltage will also be adjustable.

Ive already tested a step-up circuit using the MC34063 which works flawlessly - I have no problems up to this part. Ive also included a resistor + pot for R2, so I can adjust this voltage down to about 3v.

However, my issues come in when I try and split the 32v to +/-16v. This requires me to create a virtual ground, which I dont want to do. Id much prefer using circuit ground, to make life a lot easier. With my current approach, I dont see this as being possible.

What would you guys recommend to overcome my problem? Any ideas Ive had thus far are not permanent, Im just trying to show my thought process.

 

[Reloadron]

Depending on your current requirements I would just use one of these or another DC to DC converter fro another manufacturer like it. I was looking at the ZUW1R50515 part number.

Ron

 

[ParkingLotLust]

Current requirements would be in the order of 30-60mA, fairly small by todays standards. I appreciate the link but I would much rather build my own, for the knowledge gained from doing so. Parts are not a problem, a few friends from school and I do weekly/bi-weekly Mouser orders anyway.

 

[audioguru]

Don't you know that many opamp circuits do not need a dual-polarity supply? Simply use a single supply, bias the input at half the supply voltage and use coupling capacitors. Like this: https://www.electro-tech-online.com/threads/basic-opamp-circuits.35258/

Also, most opamps (except the lousy old 741) work fine from supply voltages less than 30V.
MC33171, MC33172, MC33174, MC34071, MC34072 and MC34074 single, dual and quad opamps work fine from a single supply as low as 3.0V.
A lousy old LM324 and LM358 also work from a single supply as low as 3.0V.

 

[canadaelk]

Audioguru is right. But: I now power a lot of my projects via the USB port and use V-Infinity DC-DC converters (VSD1 and VSD2 series) available from Digi-Key for less than $10 each. So, build one and learn, than buy. E

'

 

[ParkingLotLust]

I understand that most opamps do not NEED dual-polarity supplies, and I even have your little image printed out above my workstation, Audioguru. However, with a single supply comes the requirement of a Vcc/2 bias, which Id just rather not have.

 

[crutschow]

With a single supply you need a virtual ground to have a plus and minus voltage. So it's either a virtual ground and or two supplies, take your pick.

You can create a high current virtual ground using a transistor circuit such as this.

 

[audioguru]

Opamps have very low input bias current. So the Vcc/2 is not a high current virtual ground circuit, instead it is just two 100k resistors in series to make half the supply voltage plus a 10uF filter capacitor to ground, and a 100k resistor from there to the input of an opamp.

 

[crutschow]

An issue I see is that the 32V virtual ground can not be connected to the 5V common since it is generated by a non-isolated converter from the 5V. This means all the op input and output circuits can not be DC coupled.

Now, if the 32V was generated by an isolated converter from the 5V, then the virtual ground could be connected to the 5V ground.

 

[ParkingLotLust]

An issue I see is that the 32V virtual ground can not be connected to the 5V common since it is generated by a non-isolated converter from the 5V.

This. I was having trouble wording this properly but this is what I was trying to get across.

So it seems I need an isolated converter so that my virtual ground can be connected to the 5v ground. What defines an "isolated converter"?