Power supply PCB

Question

I made a PCB board (my first one) recently and I ran into some issues with it while troubleshooting. The PCB board is connected to an Arduino and draws 5V and the 3.3V supply from it. Also, the board and the Arduino shares a common ground. Since I need + and - 3.3V and 15V on the board, I used a 5-15V converter (After I get the + and - 15V I divide it to + and -3.3 V). When I assembled the board I ran into a problem which I need help troubleshooting. If I ground the +3.3V terminal and just use the -3.3V, I get -3.3V at both the ICs and vice versa. However, If both +3.3 and -3.3 V are present on the board, the ICs get +1.5V and around -0.92 V. I really do not understand what's going on. Would a buffer fix the problem?

Power supplied to ICs The power supply

Please read: [Rules and guidelines for drawing good schematics](http://electronics.stackexchange.com/q/28251/7036) — Nick Alexeev, Jun 21 '15 at 04:42
@NickAlexeev - Thank you for the guidelines. I am new to drawing schematics on a CAD software. Will keep them in mind — Mathews_M_J, Jun 21 '15 at 17:41

score 1 · Answer 1 · answered Jun 20 '15 at 15:33

Well just as a quick suggestion the AD8130 uses 10.8mA in the quiescent state, or when it's doing nothing. You're trying to power it with a resistive divider that can supply what (15-3.3) / 3300 or about 3.5mA at 3.3V. As @corecode said resistive dividers for power supplies are a poor choice better to use some regulators, they're not going to hold their voltage when your opamp starts to draw power because how could they with no feed back? The voltage divider formula you used to calculate those resistors only holds if there's no load. Once you attach the load the calculations changes, and as you see the output voltage changes as well.

Thanks for the answer. I should have thought of this while I designed the circuit. Since a regulator would be difficult to place I was thinking of using a battery instead for now (or a coin cell battery). Can you suggest how I can go about searching for batteries? — Mathews_M_J, Jun 20 '15 at 21:35

score 1 · Accepted Answer · answered Jun 20 '15 at 15:35

1

You will not achieve a stable regulated voltage with a resistive divider. Instead, you should use a 3.3V regulator at that end. You don't mention current, efficiency or budget requirements, so I'll just suggest a DC/DC Converter like this V7803-500.

You can use two of these regulators to achieve +/- 3.3V from a single 15V rail. enter image description here

answered Jun 20 '15 at 15:35

Saad

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Thank you so much. This with the other answers perfectly answers my question – Mathews_M_J Jun 20 '15 at 21:28

score 0 · Answer 3 · answered Jun 20 '15 at 15:16

0

Using a resistive divider is a bad way to generate a stable voltage: any load you put on it will change the output voltage. If you need a stable voltage, better use a linear regulator, e.g. the LM317 (positive) and LM337 (negative).

answered Jun 20 '15 at 15:16

corecode

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Power supply PCB

3 Answers3