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Digitaly controled power supply

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tjalps

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schematic

Hello!

I'd like to use LM2678( h**p://www.national.com/pf/LM/LM2678.html ) for digitaly controled power supply. But I can't find solution to control the output voltage with microcontroler.

Any good proposal?

Regards!
 

v_c

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current sensing lm358

check out the digital control solutions from Texas Instruments. In particular their UCD series will probably do what you want
 

VSMVDD

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lm2576 proteus

Hi tjalps

also concider using a dual dpot chip like ad8402-100k

this can be used to control current and voltage as part of a bridge network in the regulator stages zener lock section adding a pass transistor as a digital controlled
current shunt also yields current limit





maxim range of digital variable current, voltage shunts and digital audio pots...
http://www.maxim-ic.com/pl_list.cfm/filter/dp
i model proteus vsm models for these parts ask for what you need
 

tjalps

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lm2576 digital

Hello!

Thanks for your help and sugestions. I'm strongly decided that I'll use as base LM2678 because this is well tested in my aplications and is not so demanding.

I need to find the way to see how to replace the R2 resistor on added picture.
Maybe with combination of AD converter?

Any good solution?

Best regards![/img]
 

IanP

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In the attached file you will find schematic of a power supply based on the LM2576ADJ (close relative to the LM2678) ..
The control of this IC is achieved through digital potentiometer (IC6), but the main idea of this excercise was to create 0-5V control of the LM2576 ..
This can be done by feeding 0-5V control voltage to the right-side of R11, what, in your case, can be realized by D/A converter controlled by a microcontroller ..

Maybe this idea will be of any use to you ..

Regards,
IanP
 

tjalps

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Hello!

I think that this is not bad solution. What do you think about temperature stability and tolerances of digital potentiometers?

I' think that with 12 bit A/D I'll achive beter resolution and temperature stability.

Regards!
 

Davood Amerion

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It is very simple:
Just connect DAC output to left terminal of R1.
It is obviuse that, first R1 left terminal must disconnected from ground!
change values of R1 and R2 so you can get desirable value for output voltages.

with this method, also, you can get output voltage less than Vref of chip too.
 

tjalps

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Hello!

The best solution by my opinion is one from IanP. What do you think or anyone else?

Regards!
 

aNdreiBuuu

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...you can also "divide" and compare the output voltage using an R2R DAC; in some words feed the R2Rref with vout and use DAC output as feedback voltage...

hope this helps,
//a
 

IanP

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12-bit D/A converter, in this application, seems to be better option ..
Also, A/D converters usually have their own, internal voltage reference, whereas if you used digital potentiometer you would need to add on ..

Another possible extension of that circuit is current limiting section; in simple words, use another opamp with current sensing resistor on the positive rail and combine the opamp's output with the control voltage at R11 ..

Regards,
IanP
 

    tjalps

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tjalps

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Hello you all and IanP!

I think that this debate goes in right direction. Could you shortly describe functions of your schematics about voltage regulation part around LM2576 and also IC1 opamp.

I would also be hapy if we can countinue with detailed description of current limiting section.

Best regards!
 

dacadc

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I saw good digitally controlled power supply at Circuit Cellar web site contests archive. I can looking for links.
 

tjalps

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Hello!

Did we stop with news? Please continue with this subject.

Regards!
 

IanP

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Attached is an example on how to build D/A-controlled current regulator ..
With some minor modifications this idea can be implemented to previously discussed power supply ..
And again, the output from curent limitter can be combined with signals from R11/R7 ..

Regards,
IanP
 

tjalps

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Any new ideas about digitaly controled Power Supply?

Regards!

Added after 4 minutes:

IanP maybe you can explain a little about your circuit operation especialy part for voltage adjustment?

Regards!
 

IanP

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As I mentioned before, this circuit is a battery charger with programable output current (control voltage fed to FB - feedback - through D2) and voltage limit set around 5.5V (control voltage from this branch is fed to FB through D4) ..
As you can see, both control voltages, one from current control, one from voltage control, "meet" at the FB pin and whichoine is higher takes control over the LM2576 ..
Without anything connected to output terminals, there is no current flowing through Rsense(0.05Ω) so the voltage on the anode of D2 will be low and the LM2576 will "try" to generate as high output voltage as possible .. but, there is another control voltage, generated by voltage divider (R5-9.1k/R8-1k) and this control voltage (fed through D4) will actually set the output voltage level to:
Vout * [1kΩ/(9.1kΩ+1kΩ)] +0.7V(D4) = Vref(1.25V)
Then: Vout ≈ 5.5V

As far as the current control is concerned, current flow is sensed on R=0.05Ω and amplified by 1/2 LM358. The output is fed to 2/2 LM358 and compared with the control voltage from D/A converter: the higher the voltage from the D/A (the lower the FB voltage) and the higher the output voltage (- read: current) supplied to the output ..

Regards,
IanP
 

tjalps

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Hello IanP!

Thanks for this description. maybe if it's not too much you could also describe upper schematic LM2576_DigitalControl.gif !

Best regards!

Danilo
 

tjalps

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Hello IanP!

Can you please describe first circuit(LM2576_DigitalControl). We have tried to build this but it didn't operate correctly. Can you be so kind and provide info?

Regards!
 

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