Dear Team,

I am building an LM317 PWM Circuit. Please see the figure below.


My output is coming properly when VG1 output up to 3V when VG1 goes higher there is no output. Please see the output below.





I am attaching my simulation file along with this. please let me know where I went wrong.

 

The LM317 is a voltage regulator with a low frequency response, designed to generate a DC output voltage.
Why are you using it to try to generate PWM?

 

Can I ask why you are doing this and what you hope to achieve?

 

The LM317 is a voltage regulator with a low frequency response, designed to generate a DC output voltage.
Why are you using it to try to generate PWM?

Hi ,
I need to generate a variable output using LM317.In real board PWM will be coming from a microcontroller board.
Regards
HARI

 

Hi ,
I need to generate a variable output using LM317.In real board PWM will be coming from a microcontroller board.
Regards
HARI

Can I ask why you are doing this and what you hope to achieve?

 

Quite frankly I don't see any change in Vout, V_ADJ, VF1 or AM1 in either graph.

 

Quite frankly I don't see any change in Vout, V_ADJ, VF1 or AM1 in either graph.

Hi,
In the first graph Vout is 2.7V and in the second graph it is 19mV.

Regards
HARI

 

Hi ,
I need to generate a variable output using LM317.In real board PWM will be coming from a microcontroller board.
Regards
HARI

Then LM317 is the wrong device to use. ADJ input is a sample of output voltage for regulation purposes, not a voltage control input.

Now tell us what your requirement is, and maybe we can give a better suggestion.

 

Yes, in the first graph the output is 2.7V but there is no change from 0V in to 3V in.

 

@Irving How do you adjust the output voltage from a LM317?

 

I think what you may be trying to do is use a Voltage Regulator as a Power Amplifier, because the LM741 does not have ANY substantial output Drive capability. If that is the case, I can tell you that it is a profoundly pointless approach to the problem. If you would like to have a suggestion or two on how to create a suitable PWM signal with appropriate voltage and current levels just state the requirement and we can help.

 

@Irving How do you adjust the output voltage from a LM317?

To the TS: You sample the output voltage and use a fixed resistor divider to put the reference voltage of 1.25V ((?) consult datasheet for actual value), below the output voltage, on the adjust pin. What you have done in your misguided attempt to use the part in a way it was not designed for is caused it to detect a severe overvoltage on the output and shut the regulator down. It is doing just exactly what it is supposed to do!!

 

Do you need to use a PWM ?
if you "just" want a variable output from a 317

https://www.electronics-tutorials.ws/blog/variable-voltage-power-supply.html

 

@Irving How do you adjust the output voltage from a LM317?

As @Papabravo says, ADJ is held 1.25v below desired output but that has to be sampled from the output to keep it closed loop for regulation.

Now, there are ways to do this with an LM317 but they aren't straightforward. Also, from the TS setup he/she appears to be confused between PWM as a switching control signal in an SMPS, versus its use as a pseudo analog (DAC) output which is what I think was intended. In which case there are issues with switching noise/ripple to resolve.

 

The TS really needs to clarify his intentions. It is absolutely pointless to speculate about what he is trying to do. We want to help, but can't without more information.

 

Hello,

Have a look at the following article:
https://www.radiolocman.com/shem/schematics.html?di=98904

Bertus

 

Then LM317 is the wrong device to use. ADJ input is a sample of output voltage for regulation purposes, not a voltage control input.

Now tell us what your requirement is, and maybe we can give a better suggestion.

Hi Irving,

My intention is to control LM317 as given like this .EDN ARTICLE .
This is used to make a variable output regulator.Another Article

Regards
HARI

 

Hello,

Have a look at the following article:
https://www.radiolocman.com/shem/schematics.html?di=98904

Bertus

This is exactly why a coherent statement of intention is so crucial to understanding what the TS was trying to do. Notice that in the TS's original circuit there is no DC path to ground for Vout. The circuit in the referenced article has the DC path to ground and is using the PWM signal to adjust the value of the output voltage. This intent was certainly not clear to me from his original post. Had the TS started with this circuit his intent would have been more clear.

I admit that my interpretation of what the TS was trying to do may have been flat out wrong, but we really won't know until he tells us.
EDIT: I posted just after he told us.

 

Hi Irving,

My intention is to control LM317 as given like this .EDN ARTICLE .
This is used to make a variable output regulator.Another Article

Regards
HARI

So why didn't you implement the circuit from the EDN article, which is identical to the one Bertus posted, instead of the one you posted?
The one in the second article uses a different opamp (LM358) and does not show the power connections, and may or may not be operating in single supply mode. The drawback of the second circuit as I see it is the lack of a DC path to ground for Vout.

 

Probably it had too many parts

Bob.