Dual Power Supply Design

[sougata]

Hi,

I fried my LAB power supply and really inspired to one controlled by a PIC. I need the following features:

1. Dual Digital Variable +/- 0 - 30 Volts
2. Display of V/I on the LCD (both arms single PIC)
3. Tracking mode

I plan to use the LM350 for its robustness. PWM controlled voltage reference for the Vref. Input of the regulator (with/without digital feedback correction perhaps)

Where I am confused is the negative part of the supply. Measuring the supply ouput is okay but current....? If the opamps are on the PIC board powered by the positive half then common mode voltage is out of range. Level shifting accuracy is also a concern ?

Any insights would be of great help

[Luciano]

Hi,

See this link:
http://www.linear.com/currentsense/00-intoduction.pdf
(At the bottom of this one page PDF you will see more links).

* * *


Precision Circuit Monitors Negative Supply Current

This current-sensing circuit monitors a negative power supply
and provides a positive output voltage proportional to the load current.

http://www.maxim-ic.com/appnotes.cfm/appnote_number/3855


Best regards,

Luciano

[sougata]

Hi,

Luciano thank you for the links. The reference designs are really handy. However I was thinking of something very simple. Here is what I have in mind.

1. A basic linear regulator with low side current sense amplified by an OP-AMP (LM358)

2. Another block as above connected in series

3. PIC supplied with the lower side so the higher side is refereced to the lower side.

4. Simple resistor dividers to sense voltage. (Lower side first then higher side where higher side actual = higher side measured - lower side measured)

5. Next I would try to implement a switching pre-regulator using one of the HPWM's of the PIC and possibily use the other PWM to generate a reference voltage. In tracking mode use another software PWM to offset main reference.

I hope I would be able to complete it.

[sayzer]

At the link Luciano posted, you can also find LTC2970.
I did not check for 0-30V versions.

Dual I2C Power Supply Monitor and Margining Controller.


Here I attached two sample applications for your ref.

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<img src="http://img10.picsplace.to/18/LTC1.GIF" alt="Image Hosting by PicsPlace.to" >

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<img src="http://img10.picsplace.to/18/LTC2.GIF" alt="Image Hosting by PicsPlace.to" >


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[sougata]

Hi ,

Thank you very much for the info. I didn't know such a chip exists. However my problem is somewhere else. The chip would definately not be available in Kolkata where I live. Even if I get it from somewhere else in my country it will be terribily costly (I suppose). Since this is not a commercial project I am not in a mood of spending much on it. Only fascinated by the idea of using a PIC and PBP in my design. So I will stick to legacy components. I would be using a inverting OP-AMP so that a -2.5V t0 +2.5V gives me a swing of 0 to 5 volts. I know I would be reducing the resolution but okay for this crude design. The other part is that I would not be using rail-to-rail OP-AMPs so for a full scale range of 0 to 30volts I would be generating a reference voltage using the PWM and scale it up. The statedgy is Keep It Simple. Your links were very helpful and I hope you can comeup with something very cheap using general components.