Zero current sensor for a power converter
An inductor or transformer for a switching power converter includes a primary coil and a secondary coil inside the air gap of the primary coil. A secondary core of the secondary coil is magnetized to saturation by a small current through the primary coil, such that the secondary coil produces a nonzero output voltage when the current through the primary coil crosses zero. The secondary coil may be used to detect a zero-current state of the primary coil and to actuate a switch to operate the converter in critical conduction mode (CCM) or other zero-current-triggered switching mode.
1 . A switched electrical power converter comprising:
an inductor or transformer comprising:
a primary coil disposed on a ferromagnetic core, the primary coil and core defining an air gap;
a secondary coil disposed in the air gap, the secondary coil configured to generate an output voltage at a secondary coil output; and
a secondary sensor housing disposed in the air gap, wherein the secondary sensor housing defines a receiving space, the secondary coil disposed in the receiving space; and
a switch configured to regulate a current through the primary coil, the switch electrically coupled to the secondary coil output so as to switch in response to the output voltage of the secondary coil.
2 . The electrical power converter of claim 1 , wherein the primary coil defines a primary coil axis and the secondary coil defines a secondary coil axis, wherein the primary coil axis is parallel with the secondary coil axis.
3 . The electrical power converter of claim 2 , wherein the primary coil and the secondary coil are coaxial.
4 . The electrical power converter of claim 2 , wherein the primary coil and the secondary coil are not coaxial.
5 . The electrical power converter of claim 1 , wherein the core is a primary coil core, the inductor or transformer further comprising a ferromagnetic secondary coil core on which the secondary coil is disposed.
6 . The electrical power converter of claim 5 , wherein the primary coil core comprises a different material from the secondary coil core.
7 . The electrical power converter of claim 1 , wherein:
the primary coil defines a primary coil axis;
the air gap has an axial length along the primary coil axis; and
the secondary coil defines a secondary coil axis and has an axial length that is 90% or more of the air gap axial length.
8 . A switched electrical power converter comprising:
an inductor or transformer comprising:
a primary coil disposed on a first ferromagnetic core, the primary coil and first core defining an air gap;
a second ferromagnetic core disposed in the air gap;
a secondary coil disposed on the second core, the secondary coil configured to generate an output voltage at a secondary coil output; and
a secondary sensor housing disposed in the air gap, wherein the secondary sensor housing defines a receiving space, the secondary coil disposed in the receiving space; and
a switch configured to regulate a current through the primary coil, the switch electrically coupled to the secondary coil output so as to switch in response to the output voltage of the secondary coil.
9 . The electrical power converter of claim 8 , wherein the primary coil defines a primary coil axis and the secondary coil defines a secondary coil axis, wherein the primary coil axis is parallel with the secondary coil axis.
10 . The electrical power converter of claim 9 , wherein the primary coil and the secondary coil are coaxial.
11 . The electrical power converter of claim 9 , wherein the primary coil and the secondary coil are not coaxial.
12 . The electrical power converter of claim 8 , wherein the first core comprises a different material from the second core.
13 . The electrical power converter of claim 8 , wherein:
the primary coil defines a primary coil axis;
the air gap has an axial length along the primary coil axis; and
the secondary coil defines a secondary coil axis and has an axial length that is 90% or more of the air gap axial length.