Hello, I’m designing a simple buck converter using IC LMR14030
Specs:
Vin : 17V
Vout: 1V-12V (adjustable, using pot)
Iout: 3A
The question is: How can I get 3A constant output current for the whole output voltage range: 1V-12V

 

Put a 0.33Ω resistor in the negative supply to your load, and connect the fb pin to there.
Or buy a proper constant current driver IC than is intended for LEDs. It will be more efficient because you won’t have to dissipate 3W in the current sense resistor.

 

Hello, I’m designing a simple buck converter using IC LMR14030
Specs:
Vin : 17V
Vout: 1V-12V (adjustable, using pot)
Iout: 3A
The question is: How can I get 3A constant output current for the whole output voltage range: 1V-12V

A buck converter is designed for constant voltage not constant current.
Use a constant current driver.

 

It does not matter what the components were designed to do as much as it matters what you make them do.

Both approaches are valid.

 

A buck converter is designed for constant voltage not constant current.
Use a constant current driver.

Most constant-current LED drivers are buck regulators.

 

How can I get 3A constant output current for the whole output voltage range: 1V-12V

I think we jumped to the conclusion he wants CC but that is not directly stated. He did not say driving LEDs.
He wants 1 to 12Vout. I think he wants an overcurrent limit of 3A at all voltages.
But I have been in error many times today.

 

My guess is that he wants one of those fantastical Ohm's-law-defying power supplies that can produce a fixed voltage AND a fixed current simultaneously.

 

fixed voltage AND a fixed current simultaneously

I can do it. Put a fixed resistor on the output of a power supply. 1 ohm, 1V and 1A and it never changes.

 

Most constant-current LED drivers are buck regulators.

yes. But buck topology inherently regulates voltage not current. You can add circuitry to do just about anything you want.

 

yes. But buck topology inherently regulates voltage not current. You can add circuitry to do just about anything you want.

I disagree. There are both voltage mode and current mode buck circuits. Each can then be made to regulate the other by an external feedback loop.
The simplest is the hysteretic circuit.

 

I disagree. There are both voltage mode and current mode buck circuits. Each can then be made to regulate the other by an external feedback loop.
The simplest is the hysteretic circuit.

View attachment 323409

I disagree. Both use different methods of utilizing feedback, but the end result is voltage regulation

 

Here are two different LED PWM that are CC.
Here is one I have used many time. 5724 It is a boost. The LED current is measured at Rset.


Here is a buck. 8803 LED current is measured at Rset.