Power supply - unipolar instead bipolar.

[temol]

Is there any simple solution for using unipolar supply (up to 23V) for the following scenario?



I need unipolar 9V and 5V for the BBD and symmetrical for the opamps.

T.

[GibsonGM]

Just for clarification, Temol...where does the higher voltage come into play?  The "up to 23V"....and I see your schematic has + and -  9 to 15v.   

So I take this to mean the opamp wants +/- 15V?

If so, that's a 30v differential.  As long as the opamp is rated for that, fine.    Converting it over to uni with a 23V limit will cause you to lose a bit of headroom, a few volts, which may or may not matter. 

To 'convert' it over to unipolar, you'd need to provide a bias voltage to the input of the opamp (and use input and output caps to keep this DC voltage where you want it), the value of this voltage would be about 1/2 your unipolar voltage, so for 23V of course it would be about 11.5V.      Usual way is by using the 2 equal-value resistor bias setup found in tons of pedals.    This network goes where "C1" is, and their mid-point is that half voltage you want.  An electro cap is used at that point to ground to stabilize this bias voltage.   A fair-value resistor connects this point to your opamp input to cause a current flow.     

The "-Vcc" of the opamp (pin 4) would be grounded, zero volts.    Seeing what this is part of would be helpful as there may be some "gotcha!" in there that I can't see without the whole thing....I hope this steers you in a direction that helps....

[temol]

GibsonGM - I've already tried typical setup with a voltage divider. It's ok (as usual) for powering opamps but no luck with a voltage stabilizers connected to  Vbias and positive voltage. Full schematic.

T.

[sixthfloor]

Temol, would a charge pump with bipolar output qualify as a simple solution ?

http://www.generalguitargadgets.com/effects-projects/power-supplies/charge-pumps/

[temol]

Yes, it does qualify for a simple solution. Tried this too, even with a simpler circuit. +9V / -8.7V and whistling .

T.

[anotherjim]

A resistive voltage divider probably isn't best to handle the ground connection of the regulators. You want at least 12v on the positive side to keep the 9v regulator happy, which in turn needs to output enough for the 5v regulator. Unfortunately, the current draw on the positive side of the resistive divider raises the voltage of the divider reference ground with respect to the supply ground (which is the negative supply). That means the input volts to the regulators falls.

A Hack would be to put resistance across the negative side to equal the current draw the regulators need on the positive side. A better solution is to have a power op-amp buffer "drive" the ground reference from the divider so the divider voltage remains centred despite the unequal load. A "power" op-amp might be a line driver with enough current drive type like 4580 or a small audio power amp that can handle a 30v supply (obvious type like LM380 only handle 22v).

[temol]

So, as I suspected - the voltage divider is not the best solution here. I doubt that I really need bipolar 15V, 10-12V is probably OK too. I think I'll try with opamps you have mentioned about (unfortunately I do not have any of them available now).
Of course I could use bipolar power supply (first I'd need to make one) but for me it's inconvenient. It requires separate power supply, dedicated for this pedal only, with a three pin DC socket. Or a power supply that's built into pedal. I'd like to power it just like my other devices - standard DC jack.

T.

[italianguy63]

Temol, would a charge pump with bipolar output qualify as a simple solution ?

http://www.generalguitargadgets.com/effects-projects/power-supplies/charge-pumps/

+1

MC