DC/DC buck converter

[Winsu]

Hi All,


I would like to develop an application where I need to convert a constant voltage( the application should be able to deal with a range of voltages from 42V to 57V) to a constant current ( a bit less than 1A). I have though about this one, but not sure:

https://www.ti.com/lit/ds/symlink/lm5085-q1.pdf

Any other suggestion or idea?.

Cheers.

 

[KlausST]

Hi,

It´s not clear to me what is your
* input votage (range)
* output voltage range

As far as I understood you need a constant current at the output.

****
The easiest method with this controller is that you use a shunt (connected to GND) wiith 1.25 Ohms (= 1.0A. Higher value for lower current).
The other side of the shunt is
* connected to the load
* and to the FB input of the controller.
The power dissipation of the shunt is about 1.25W .. use a shunt with a higher power rating. Maybe 3W. Maybe you need a heatsink, because it becomes hot.
Use a low impedance shunt, no "wire wound".

The shunt is in place of R_FB1. don´t use R_FB2. (datasheet, page 1 schematic).
Don´t forget to feed the load current through the shunt.

Klaus

 

[Winsu]

Thanks for the advise. The input voltage range goes from 42V to 57V and the output voltage should be 40V. It must be constant current rather than constant voltage.

Cheers

 

[asdf44]

In general a buck controller IC's suited for these voltage and current ranges can be set-up for constant current.

As Klauss says you'll need a current measurement circuit, probably a shunt with shunt amplifier (possibly 'high side shunt amplifier') and then you'll feed back current instead of voltage to the error amplifier.

I'd start by looking for 'current mode' controllers. They're already regulating current at the modulator level and will therefore be easy to configure current regulation.