On 31 Jan 2017 at 22:13, IVP wrote:

> With the new 10-turn inductor
>=20
> Load =3D 6R8, Vout 5.01
> Load =3D 4R7, Vout =3D 5.01
> Load =3D 3R4, Vout =3D 3.74 :-(
>=20
> Starting to see 50Hz ripple (0.3V) on the supply, so I bumped up
> the filter cap to 20,000uF
>=20
> Gate and drain picture
>=20
> https://www.flickr.com/photos/97814409@N04/31812934043/in/album-721576759=
78832174/=20

At the risk of showing my ignorance, in the scope trace wondering why there=
 is a=20
third distinct voltage level appearing on the FET drain. i.e.

1. FET switches on with g =3D 0V, d goes to supply 9V (can see a little slo=
pe which=20
may be  the supply ripple you mention). Inductor charges.

2. FET switches off with g =3D 9V, d goes to 0V minus diode drop. Inductor=
=20
discharges to keep currnet flowing to load.

3. FET d goes to a mid point, presumably the 3.74V which will be the output=
=20
voltage. Lines up with a small but noticeable glitch in the gate voltage at=
 this point.

My guess is this is the point where the inductor stored energy has diminish=
ed such=20
that it is no longer able to forward bias the diode and supply current to t=
he load.=20
Sound about right? Seems to follow that the M34063 is loosing regulation ar=
ound=20
this point, explaining the discontinuous gate pulses. I haven't played with=
 switchers=20
enough to observe this on scope before, so it's interesting.

So if so then inductor needs more stored energy =3D=3D> lower freq to incre=
ase=20
charging time and/or increase inductance.


--=20
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