Replace a potentiometer by a digital pot

[flotulopex]

Hello,

I'm trying to control a voltage regulator via a Digital-Pot ("DP" hereunder, it's a DS1804-010 / 10k - 100 steps model).
<img src="http://home.citycable.ch/flotulopex/downloads/Adj-VR_Num-pot.jpg">
I replaced the 4k7 pot by the DP and nothing happens (= voltage doesn't vary). Just as if the DP wouldn't increment/decrement anymore.

The DP is working well as long as I don't connect it to the VR.

Any idea what's wrong here?

[Acetronics2]

Bonjour Roger,

Excerpt of the datasheet ...

<< H - High-Terminal Potentiometer. This is the high terminal of the potentiometer. It is not required that
this terminal be connected to a potential greater than the L-terminal. Voltage applied to the H-terminal
cannot exceed the power-supply voltage, VCC, or go below ground.

L - Low-Terminal Potentiometer. This is the low terminal of the potentiometer. It is not required that this
terminal be connected to a potential less than the H-terminal. Voltage applied to the L-terminal cannot
exceed the power-supply voltage, VCC, or go below ground.

W - Wiper of the Potentiometer. This pin is the wiper of the potentiometer. Its position on the resistor
array is controlled by the three-terminal control port. Voltage applied to the wiper cannot exceed the
power-supply voltage, VCC, or go below ground >>

as the max DS1804 supply voltage is ....


Bouhou ,snifffff ... goodbye precious chip ! ... if you insist too much !!!

Try the AD 7376 ...

Alain

[Luciano]

Hi Roger,

PWM controlled LM317, output voltage 0V to 6V. (Yes, really 0V!)
The PWM signal is generated by the microcontroller and the output
voltage is monitored by the ADC of the microcontroller.

Best regards,

Luciano

http://img522.imageshack.us/img522/8532/lm317pwmzw7.th.png (http://img522.imageshack.us/img522/8532/lm317pwmzw7.png)
(Click to enlarge).

[Acetronics2]

Hi, Roger

another excerpt ... from the 317 datasheet ...

Smells the R-2R ladder ... don't you think !

with a full port ... 256 steps : no so bad !

Alain

[flotulopex]

...snif et m.... encore raté!

Thanks Alain, I've seen this info but, unlike in the shema of my first post, the High end is "open" (not connected) and I thought this would be okay this way.

Okay then, so how should I control the voltage regulator if not with my DS1804?

The AD7376 is another option, yes.

And yes, I've tried to control the LM317 with R+Tr already but you fully loose in ouput voltage precision.

Is there a other way to do?

[flotulopex]

Alain,

How would you make a 256 resistors ladder with 8 ports?

Any example?

[Ioannis]

Hope this helps.

http://www.irctt.com/pdf_files/LADDERNETWORKS.pdf

Ioannis

[flotulopex]

Is it correct to say that this is a Digital-To-Analog converter?

[Ioannis]

That is correct. This is exactly what it does.

Ioannis