Digital Voltage Controller

[somf0872]

Hi everybody,

My target is to have different voltage levels like 3V, 4V, 7V, 15V etc etc..

I want to know whether there is any variable voltage regulator that can digitally controlled using this micontroller in order to get varying voltages from +3 to +15 V.

For example in my software routine I give any specific combination of bit to controller and in return it communicates with that voltage regulator and give the desired voltage output. Something like controlling the voltage level thru software.

Any idea??

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[Davood Amerion]

Somf0872,

read this post:


Regards,
Davood.

 

[IanP]

If you are happy with a set of fixed output voltages then quite simple solution can be based on the LM317 voltage regulator (see picture below) ..
The idea is based on a resistor divider pulled down to 0V by a BJT or MOSFET transistor ..
Each resistor is selected in such a way that the output voltage is 3V, 4V, .., 15V ..
(on how to calculate the ouput voltage see the LM's data sheet at https://www.fairchildsemi.com/ds/LM/LM317.pdf )
The LM317 works with currents <1.5A, for currents below 100mA you can employ LM317L and for currents close to 3A the LM350 will be the answer ..
The same priciple can used with other voltage regulators such as, for example, the L200 ..

Regards,
IanP

 

[somf0872]

This is a smart approach ........... Thanks.

Well, in case if I don't want to use all such discrete transistors with LM317, then could we employe the same strategy with some CMOS isolation buffers along with LM317 or any other IC connected with LM317 to just regulate its output voltage depending on digital inputs. I mean instead of transistor ......... some intgrated package.

Any idea?

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[IanP]

These transistors can be replaced by CMOS switches such as CD4066, 74HC4066 .. and similar .. with one side connected to 0V/GND ..
Or, there are so callled "digital transistors" with build-in resistors .. **broken link removed**

Regards,
IanP

 

[sda]

Here's something I have come up for setting voltage output, and also current sensing (current metering and limiting)
I have used a R/2R ladder on a port, with 8 bit resolution.
Works nicely.

Regards
sda

 

[Davood Amerion]

you can use (TTL) 7406 insted of discret transistors.

 

[somf0872]

Hi Davood Amerion and IanP

Thanks for ur suggestions. Now, i am facing one more problem!!!

Initially before having a specific voltage outputs, I need to have 0 volt at outputs. I mean the lowest voltage level I can get with these ICs is 0.5 to 1.2 V.

Is there any other IC which have something like RESET or CLEAR pin by which I can get exact 0V at the outputs? and then by giving specific digital inputs I can have my required digital voltage levels.

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[IanP]

There are adjustable regulators with ON/OFF pin (shutdown) ..
For example, have a look at the LM2941 ..
**broken link removed**

Regards,
IanP

 

[somf0872]

Thanks a lot IanP!!

I studied the datasheet but it never mentioned that what will be the state of output when it is in OFF mode. It mentions that ON voltage threshold is 1.3V or below and OFF voltage threshold will be 1.3V or above, but in OFF mode what will be the output ....................... high impedance, any Vol or Voh???

Have u tried this before??

Sorry to drill u ..............

Thanks

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[IanP]

In the OFF mode the output is put into high-impedance stage ..
As a dummy load, and this should set the floating output voltage to 0V, you can connect, say, 10kΩ resistor between +Vout and -Vout(0V) ..

Regards,
IanP

 

[somf0872]

I need something that could vary right from 0V to 15V digitally. The lower limit of 1.3V in LM317 is a big problem for me.

Any idea????

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[IanP]

In this instance, maybe you can build 0-15V power supply with transistors and opamps and instead of using potentiometer connect DAC ..
Here is an example of an 0-15V regulated power supply in which you can replace V1(- voltage and V2 - current) variable resistor(s) with 0-5V DAC ..

Regards,
IanP

 

[somf0872]

Thanks for this!!

Can this work for -ve variable voltage too?

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