Hi.
I was trying to adjust the output of this LM2596 3 POT to 1.4VDC and 30mA. The voltage potentiometer(left pot)was not a problem to be adjusted to 1.4VDC,but i couldn't adjust the current potentiometer(right pot)to 30mA. The instructions says to connect the output to ammeter(dmm)at 10A option and adjust the current(without load),but even if i am turning counterclockwise the screw until i heard the'click'noise,the current is still above 30mA.(spec. says:0-3A). The only way to get the 30mA was to raise the voltage to minimum 1.6vdc and then the current could decrease to 30mA.And if i want to decrease the current more,i have to increase the voltage.Since that,i can't adjust the current to the voltage that i would like to adjust.I am using this 3 pot for my first time,so i am not sure if it should work like that or is it defective.

 

Any help,please?

 

spec. says:0-3A

Specs of cheap products sold by some online market sites are notoriously exaggerated, incomplete or inaccurate. Maybe "0-3A" is an approximation.
The module presumably has a single current-sense resistor. Expecting the use of that to give accurate current control over a 100:1 range is somewhat optimistic.

 

Specs of cheap products sold by some online market sites are notoriously exaggerated, incomplete or inaccurate. Maybe "0-3A" is an approximation.
The module presumably has a single current-sense resistor. Expecting the use of that to give accurate current control over a 100:1 range is somewhat optimistic.

Yes,i familiar with the exaggerated specification and i take it into account,but my main issue is to understand how a normal module should work.After setting the voltage,In a normal functional module(which the spec. is true 0-3A),can i adjust the current value to any value that i want between 0-3A,without the need of playing again with the voltage poteniometer?
As i mention before,i can adjusted the voltage potentiometer to 1.25v-30v with no issue,but if for example i set the voltage to 1.4v
,then i can only adjust the current to minimum ~40mA.
In order to get lower current value,i need to increase the voltage to 1.6v to get minimum ~30mA or increase the voltage to 1.8v to be able to deecrease the current to 20mA and so on until i get 1mA but at higher voltage than i need.So,what i would like to know is:if this is a normal behavior of adjustment for a normal module?.After setting the voltage,shouldn't the current be able to adjusted to lower current value as 1mA without the need of increasing the value of the voltage?

 

The LM2596 IC in that module is just a switch-mode voltage regulator, so how the current and charge controls operate is unclear. Maybe the current control won't work as you expect down to the small current you want.
For 30mA a 3A-capable regulator seems a tad OTT. Can you source a lower-rated one?

 

The LM2596 IC in that module is just a switch-mode voltage regulator, so how the current and charge controls operate is unclear. Maybe the current control won't work as you expect down to the small current you want.
For 30mA a 3A-capable regulator seems a tad OTT. Can you source a lower-rated one?

The problem is that it is possible to adjust it to small currents values.I can adjust it even to 1mA,but i must increase the voltage in order to do that and this is what i would like to clear-up.
Why must i increase the voltage in order that i be able to lower the current?
For example:if the voltage is adjusted to 1.4V,i can't adjust the current to lower than 40mA,but if i will increase the voltage,then the current can be adjusted to lower than 40mA and so.The current even decrease by itself when i increase the voltage,without touching the current potentiometer.(like when the current potentiometer is all the way closed left).

 

The problem is that it is possible to adjust it to small currents values.I can adjust it even to 1mA,but i must increase the voltage in order to do that and this is what i would like to clear-up.

You will probably have to ask the module manufacturer, or obtain a complete schematic of the module.

 

We are flying blind here. Please post a link to the exact web page and part you have.

ak

 

The LM2596 data sheet states: Adjustable version output voltage range: 1.2-V to 37-V ±4% maximum over line and load conditions so obviously it won't go to 0V.

And there is no example showing how to provide an adjustable current limit, so don't know how it's done here.

If you only need 1.4V @ 30mA, a simple linear regulator may be more appropriate.

Are you trying to drive an LED?
They just need a current limit, not both current and voltage.

 

The LM2596 data sheet states: Adjustable version output voltage range: 1.2-V to 37-V ±4% maximum over line and load conditions so obviously it won't go to 0V.

And there is no example showing how to provide an adjustable current limit, so don't know how it's done here.

If you only need 1.4V @ 30mA, a simple linear regulator may be more appropriate.

Are you trying to drive an LED?
They just need a current limit, not both current and voltage.

I am talking about the current.The voltage is okay,it can be set to minimum 1.25V and that is okay according to spec.
The problem is that i can't set the current to less than 40mA when the voltage is set to 1.4v,but if i increase the voltage higher than 1.4v,the current trimpot let me to lower the current even to 1mA(depends how much i increase the voltage).
The issue here is to understand if this is a normal behavior,since it is my first time to use this 3 pot module and i just study how to use it.So,it doesn't matter for what application i need it,but its behavior.(though i am using a led for testing it,indeed).

You will probably have to ask the module manufacturer, or obtain a complete schematic of the module.

We are flying blind here. Please post a link to the exact web page and part you have.

ak

I would be happy to attach a schematic for this module,but you can only found,around the net,a schematic for LM2596 module type that has only one trimpot(voltage).For this 3 pot module i can't find any schematic.The seller also doesn't have any.
But if you type on google photos:LM2596 module 3 trimpot,you may see alot of photos of this 3 trimpot module,that seems to be the same,the same components,the same number of component.
I believe that some of you have used this type of module,so i am just trying to understand,if the behavior of the module as i described before is normal.For me,it looks like there might be some limits when setting the current value that depended on the voltage value,but i don't have any past experience how it should work,so i am trying to understand that with those that have experience with that kind of module.

 

So,it doesn't matter for what application

If the application doesn't matter than why are you concerned about how low the voltage and current can be adjusted?

 

YES, this is COMPLETELY NORMAL.

A supply of that power level is usually designed to operate in continuous conduction mode CCM. At the very low power level you are attempting to operate it, it must be deeply operating at discontinuous conduction mode, DCM, and the control loop won’t be able to regulate it.
This problem is as old as electronics, for supplies using inductors, and the solution is simple, add a bleeder resistor to provide a minimum load.

 

YES, this is COMPLETELY NORMAL.

A supply of that power level is usually designed to operate in continuous conduction mode CCM. At the very low power level you are attempting to operate it, it must be deeply operating at discontinuous conduction mode, DCM, and the control loop won’t be able to regulate it.
This problem is as old as electronics, for supplies using inductors, and the solution is simple, add a bleeder resistor to provide a minimum load.

Thanks,schmitt trigger.So,you mean that at DCM the control loop can't be regulated to my low required current,but when i increase the voltage,the module turns to CCM and then the control loop can regulate to my required low current,as the power level is increased?

If the application doesn't matter than why are you concerned about how low the voltage and current can be adjusted?

Because my interest is to understand its behavior,if it is normal?if it is defective.That all.

 

Because my interest is to understand its behavior,if it is normal?if it is defective

So it appears to be normal, given the limited information we have on the actual circuit.

 

The LTspice file LM2596 can be found on thread link below post #6 explained by EG
The explanations given are very helpful.
(31) Need LTspice model for LM2596 buck converter .. #2 | All About Circuits

The evaluation board documentation usually shows differences which are not completely correct in the economy board.
The economy board use lower grade parts and not the parts that are called for, a very cheap replication loses much quality
Could you change up the design and send it off to avoid costly OEM eval board, but are you on the right controller, simulation will help.
If we had all the information like the eval shows, it would be possible to simulate it. The missing information is important.
Someone working with it a long time might tell you to change a few parts and that worked but simulation also can test those things.
LM2596S-ADJEVM Evaluation board | TI.com

There are other DC DC controllers like ADP1613 Eval docs are available Ltspice file below
This dc converter eval was used to power a laser for passive fiber optic network at several Gb/sec. Is it any good? I don't know.
The IC costs 95 cents you need breakout adapter board and the other parts that meet specs. Later you find a reasonably fair
populated board for $15 and it is welded gold quality low fever. Desolder most everything after learning the real downside is.
When you figure your time, the completed eval board is fully documented answers the questions and usually working correctly.

 

I would be happy to attach a schematic for this module,

I understand that a schematic for something like this is almost impossible to find. What I asked for was a link to the same product page you used to purchase the module. Buried in it might be something we can use.

Separate from that, I agree with schmitt trigger. There are a half-dozen basic switching supply topologies, and in their standard forms they all have some kind of minimum load current requirement.

ak

 

Thanks alot for all the responses, i guess that,as schmitt trigger explained,it is normal and not a defective one.Also,maybe it is an economy board with lower grade parts,as sparky 1 said,so i can't actually expect from it to function as a quality one,even though it is not a defective one.
Thanks again for all the help.