current source reference design & switching mode power supply designquestions

[[email protected]]

Hi, there, back again.

Anybody could provide some online switch mode adjustable current
source design notes? I prefer buck configuration, > 8A reference
design.

I designed a buck converter, but I saw some ringing and overshoots,
check out the picture here:

http://www.flickr.com/photos/26914086@N05/2669342560/sizes/o/

using a snubber circuits I can minimize the left lower corner's
ringing but I couldn't minimize others, how come?

thanks a lot.

 

[Paul E. Schoen]

Hi, there, back again.

Anybody could provide some online switch mode adjustable current
source design notes? I prefer buck configuration, > 8A reference
design.

I designed a buck converter, but I saw some ringing and overshoots,
check out the picture here:

http://www.flickr.com/photos/26914086@N05/2669342560/sizes/o/

using a snubber circuits I can minimize the left lower corner's
ringing but I couldn't minimize others, how come?

thanks a lot.

It is not always necessary or desirable to eliminate ringing, and a snubber
will only dissipate heat and reduce overall efficiency. The cause of the
ringing and overshoot is very likely due to the characteristics of the
inductor, the free-wheeling diode, and the output capacitor. It may also be
artifacts of the scope probe, or the PCB design. Without more details, such
as frequency, component values, slew rates, and voltages, there is not
enough information to provide any help. This would be an easy circuit to
simulate in LTSpice, where you can add parasitic parameters to duplicate
the waveform observed, and then take steps to eliminate them.

Paul

 

[legg]

Hi, there, back again.

Anybody could provide some online switch mode adjustable current
source design notes? I prefer buck configuration, > 8A reference
design.

I designed a buck converter, but I saw some ringing and overshoots,
check out the picture here:

http://www.flickr.com/photos/26914086@N05/2669342560/sizes/o/

using a snubber circuits I can minimize the left lower corner's
ringing but I couldn't minimize others, how come?

The blue circles enclose noise with the correct timing and polarity to
suggest gate drive to the pfet.

Improve local decoupling from the chip ground to Vin.

RL