Howdy :D

It's my first boost SMPS, actually my first SMPS at all, and it seems to wo=
rk.

However my scope shows some ringing, and I wanted to ask if it's normal.

So, here's what's happening:

1) A nice sinusoid comes from a transformer.

2) It passes through a diodes bridge, so it's rectified now.

3) My PIC32 shorts it through an NPN transistor, effectively exploiting the=
 inductance of the secondary of the transformer. Yes, it can withstand the =
resulting voltage spikes. :)

4) Currents starts to grow, as the shunt between the emitter of that transi=
stor and ground shows.

5) At 600mA of current, before the 1215 mH inductor (secondary of the trans=
former) saturates, the PIC32 turns off the transistor.

6) The energy from the inductor goes through a fast recovery diode, into a =
high tension 3.3 uF capacitor.

7) The energy raises the voltage into the capacitor, until..

until the energy is not enough anymore, of course.

Now, probing the voltage at the transformer, I can see some cycles of dampe=
d ringing between this point and when the voltage returns to follow the inp=
ut from the transformer, i.e. that rectified sinusoid.

Is it normal?

Clearly it has to settle someway from the high voltage spike to the normal =
input waveform, once the energy is vanished.. but where does the (40 KHz by=
 the way) ringing come from? 3.3 uF capacitor and 1215 mH secondary of tran=
sformer? The numbers (resonance of LC circuit) say it's not the cap and the=
 secondary that are resonating, or I would get 80 Hz ringing, not 43 KHz. :=
P
Probably it's the secondary and.. a 11 pf capacitor, which can be only para=
sitic.

Maybe it's even the very 10x oscilloscope probe that is causing it!!

Do I have to live happy with this little and supposedly harmless ringing (w=
hich amplitude is contained within the limits of the waveform, and quickly =
damped in 2-3 cycles), or should I fight it like a brave warrior 'till it d=
ies? :P

Cheers,
Mario

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