reguleted current supply with LM2576

[luckym]

Hello.
I'm building a regulated current supply with LM2576 (pict 1). It works OK but in the boundary positions (max/min current) it behaves badly(pict. 2 and 3)(yellow (A) channel is voltage at the output from IC and blue (B) is the voltage at the FB). It happens at the time the transistor is switched OFF or ON and there are transients on the FB line. I think the problem is caused by the spikes in the FB. The spikes are on the output terminal also (pict 4). I want to use it with inductive load (valve coil). And if I connect inductive load the problem get worse.
I haven't work with switching PS yet so thanks for any advice.

regards
michal

 

[IanP]

- try to remove 10nF from the equation ..
- make sure that "all grounds" are connected in STAR configuration, where the LM2576's GND is the central point ..
- add caps between +14 and -3V and GND and -3V ..

- add 10kΩ between (+) and 0.1Ω ..

Regards,
IanP

 

[luckym]

Thanks for reply. I've made some changes according to your advices, it has improved. But it is still not ok.
Why should I remove the 10n cap? It is in original schematic
**broken link removed**.

 

[IanP]

'Try and Verify" ..
If 10nF doesn't work try other options: 1nF, 100pF or nothing at all ..

Two other things:
- input and output (µF electrolytic) caps should be of very low ESR ..
- if you intend to work with inductive loads you may consider adding Schottky (3-5A) diode in series with output, something like this: output=>diode=>load ..

Regards,
IanP

 

[luckym]

thanks,
the better caps helped.