Problem with LM317 and digital pot

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jvjtech

Joined Jan 26, 2008
23
BTW: Im open for other ways to adjust the voltage from a microcontroller :D
I am sorry I cannot offer more than a concept here but I will try. Many microcontrollers have a PWM output and for those that do not one can create a PWM output with an IO pin that is toggled High or Low in the control loop in a controlled fashion, i.e. to adjust the duty cycle. Integrating the PWM output through an RC will give you a voltage relative to the duty cycle. Taking that voltage as a control voltage to the base of a transistor one can vary the current through the transistor. Bring this transistor into the circuit driving the control pin of the LM317 should give you a circuit that has control of the output of the regulator based on the PWM duty cycle. Regards. JJ
 

Wendy

Joined Mar 24, 2008
23,415
I doubt the OP will ever see this post. You really need to limit responding to about 3 months or less since the last post. All that has happened here is a very old thread has been dragged up.

I was guilty too, for what it's worth.
 

megajc1

Joined Jan 29, 2010
2
I kind of know what you are trying to do, you are trying to control the voltage trough a darlington transistor, if that is the case you may better use an op-amp, you have already the digital potenciometer just amplify the output voltage with the op-amp, and it is easier to add both ofset and amplifying adjust and it is more lineal than a transistor.
 

megajc1

Joined Jan 29, 2010
2
Why dont you use an op-amp to amplify the voltage that comes from the digital potenciometer, in my experience the op-amps are easier to use than transistors, at least for this kind of aplications
 

Wendy

Joined Mar 24, 2008
23,415
Check the dates, except for old hands on this site these folks are gone, long gone.

Welcome to AAC!

Sit back and chat a while while the soldering iron heats!
 

hp1729

Joined Nov 23, 2015
2,304
Hi guys!
I have a problem trying to adjust the LM317 voltage with a digital pot (MCP41050, 50K). I have placed the pot in parallel with a 3,3K(R2) resistor and this makes me adjust the resistance from 3095ohm to about 270ohm+- (measured). The R1 resistor is 220 ohm. After what i have calculated, this will give me a range from bout 20V to 2.80V.

The problem is that im just able to adjust it from 2.80V to bout 7.00V.

Can anyone give me some pointers on what im doing wrong here?

Cheers
Jan

I realize this is am old post but for those who might follow ...
If you want to keep with the same family there is an MCP41HV... that works on resistor voltages outside VDD and VSS.
If you replace the 220 ohm resistor with a 3K you can use the 50K pot directly.
As a thought, if you want the power supply to go all the way down to 0 V return the bottom of the pot to -1.2 V.
 

ScottWang

Joined Aug 23, 2012
7,397
I realize this is am old post but for those who might follow ...
If you want to keep with the same family there is an MCP41HV... that works on resistor voltages outside VDD and VSS.
If you replace the 220 ohm resistor with a 3K you can use the 50K pot directly.
As a thought, if you want the power supply to go all the way down to 0 V return the bottom of the pot to -1.2 V.
Please don't reply to the old thread, specially it had 5 years old, because it may bring the alerts to the members who joined the discussion, but the members maybe already leave this site or don't want to get that alert.
 
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