Help with 12 volt battery variable voltage supply please

[acestu]

Hi all,

I have a 12 volt sla battery and I would like to have a pot that when turned increases the voltage output between 0 and 12 and would also tell you what was being output on an lcd screen, I am not sure how to go about this so any info would be greatly appreciated.

Thanks
Stuart

EDIT

I could use an LM317 with pot and a bought voltage display but for learning purposes I would like to use Flowcode and try and calibrate an lcd display to the voltage being output.

[jgu1]

Hi Stuart!

Maybe you Can use something form here:

http://www.matrixtsl.com/mmforums/viewt ... 99&p=20326

It's fc5 projekt, maybe you Can import it, otherwice you Can copy.

Really good voltmeter.

Br

Jorgen

[acestu]

Hi Jorgen,

Thanks for the heads up, I have had a look at the chart but just wondering how it is implemented in hardware ie where do you connect your voltage to be measured ?

Thanks
Stuart

[acestu]

Hi,

I am just thinking out loud here but could I use a multi channel rotary encoder to control A. the voltage output of a LM317 and at the same time B. The on screen display ?

Thanks
Stuart

[Steve001]

Hi Stuart

have a look at these application notes that use digital pots

https://www.maximintegrated.com/en/app- ... mvp/id/183

http://www.onsemi.com/pub_link/Collateral/TND6010-D.PDF

Be aware that no matter how you make a linear regulator, you will be limited to low current loads when the voltage is low, because of the high power dissipation of the series pass element

digital pot experiment here

http://www.matrixtsl.com/mmforums/viewt ... pot#p39000

Steve

[acestu]

Hi Steve,

Thanks for the info will check it out now.

Stuart

[Steve001]

Hi Stuart

What voltage and current you looking for ? a DC DC Convertor with and adjustment pin may be a better way

Steve

[Steve001]

Hi stuart

A couple of products that may be of interest

LM723 this can be configured as an adjustable regulator and switching regulator (bit more complex)

http://www.ti.com/product/LM723

or a tsr-3 traco DCDC converter

Steve

[acestu]

Hi Steve,

Thanks for all this info, basically using a sealed lead acid battery I want to be able to adjust between 1 and 10 volts for testing electric valves, you probably know of the 2 standards used for controlling valves which are the 4-20 ma current loop, and 1-10 volts dc which is only milli amps, because the changing voltage would be frequent the mini screw pots on the buck converters wouldn't really be practical, something with a standard size potentiometer would be better, I have ordered a few power supplies to try but just thought I could do something in Flowcode with on screen LCD voltage for a learning curve.

Thanks
Stuart

[acestu]

Hi Steve,

I have just checked these tsr3 devices but you wouldn't get the 1 - 10 volts range.

Thanks
Stuart

EDIT Also LM723 dosen't go down to 1 volt on output

[Steve001]

not many regulators will go down to 1 volt

this may be an idea I have made a few 0 - 20 and 4 - 20 ma test boxes , started a couple for my self then mates ooo can we have one


http://www.ti.com/lit/ds/symlink/xtr110.pdf

You can configure the output to allsorts you would need a 15 volt supply though

or you could use a power op amp with a simple voltage divider pot on the input pin

http://www.ti.com/lit/ds/sbos264a/sbos264a.pdf

Steve

[acestu]

Hi Steve,

Thanks for this, I have some bits and pieces coming from China so will be about 3 weeks before I know if I have anything that will do the job, I will have a go at making something with one of the xtr110 as well i think because they are readily available in pdip where as the op amp is only soic.

Thanks again
Stuart

[Brendan]

For the record, you might also like to consider a voltage-controlled (active) current sink in a regulator's feedback circuit, where PWM voltage (amplified by an op-amp for stability and offset correction) leaches current from a feedback arrangement. Imagine an N-channel MOSFET with source to ground via a resistor, gate connected to the op-amp o/p, and drain connecting to the regulator feedback terminal (junctioned with a feedback resistor). The op-amp inverting input is coupled to the MOSFET source leg so that the PWM input voltage is accurately reflected across the source resistor to ground, with the non-inverting input driven by RC-filtered PWM signal.

'Leached' (constant) current through the MOSFET therefore determines how high the regulated output must go before the available current through the feedback resistor to the feedback pin attains the regulator reference voltage - and therefore the regulated output potential. The voltage drop across the MOSFET source resistor to ground determines how much current is 'leached' from the feedback resistor.

There are other ways to implement such an arrangement, but PWM control to a conventional regulator yields all the advantages of thermal and overcurrent protection, effectively isolates the voltage-regulated side from the logic and op-amp, and the MOSFET Vds specification dictates how high the voltage you can safely control. If your supply source is limited (2V headroom is often inadequate for a common linear regulator), then you can incorporate a boost switching regulator, or switched-capacitor technique to the regulator input if current demand is limited.

I'll leave others to calculate values appropriate to a given regulator/circuit combination, but a solution some might like to consider

Best regards,

Brendan