Insulation type step-down converter
An insulation type step-down converter includes first and second step-down transformers each of which includes an input-side coil and an output-side coil. An intermediate portion of the output-side coil of the first step-down transformer and an intermediate portion of the output-side coil of the second step-down transformer are connected to each other. First, second, third, and fourth rectifier elements are connected in series with first, second, third, and fourth output-side coils, respectively. Smoothing coils are connected to the first to fourth output-side coils. The first, second, third, and fourth rectifier elements are connected such that electric currents flow simultaneously in the first output-side coil and the third output-side coil, and electric currents flow simultaneously in the second output-side coil and the fourth output-side coil in a manner alternating with the electric currents in the first output-side coil and the third output-side coil.
1. An insulation type step-down converter comprising first and second step-down transformers aligned with each other,
the first step-down transformer including
a first core including a first middle leg, a first one outer leg spaced from the first middle leg and arranged to extend in a direction identical to the first middle leg, and a first other outer leg spaced from the first middle leg opposite to the first one outer leg,
a first input-side coil wound around the first middle leg of the first core, and
first and second output-side coils wound around the first middle leg of the first core, overlapping at least part of the first input-side coil and spaced from each other,
the second step-down transformer including
a second core including a second middle leg, a second one outer leg spaced from the second middle leg and arranged to extend in a direction identical to the second middle leg, and a second other outer leg spaced from the second middle leg opposite to the second one outer leg,
a second input-side coil wound around the second middle leg of the second core, and
third and fourth output-side coils wound around the second middle leg of the second core, overlapping at least part of the second input-side coil and spaced from each other,
the insulation type step-down converter further comprising:
a first rectifier element connected in series with the first output-side coil;
a second rectifier element connected in series with the second output-side coil;
a third rectifier element connected in series with the third output-side coil;
a fourth rectifier element connected in series with the fourth output-side coil; and
first and second smoothing coils each connected to two of the serial connections between the first to fourth output-side coils and the first to fourth rectifier elements,
the first output-side coil includes a first end connected to a reference potential and a second end located opposite to the first end and connected to the first rectifier element, the second output-side coil includes a first end connected to the reference potential and a second end located opposite to the first end and connected to the second rectifier element, the third output-side coil includes a first end connected to the reference potential and a second end located opposite to the first end and connected to the third rectifier element, the fourth output-side coil includes a first end connected to the reference potential and a second end located opposite to the first end and connected to the fourth rectifier element, and each of the first, second, third and fourth output-side coils has an intermediate portion at a part of a path from the first end toward the second end,
the intermediate portion of the first output-side coil and the intermediate portion of the third output-side coil being connected to each other,
the intermediate portion of the second output-side coil and the intermediate portion of the fourth output-side coil being connected to each other,
the first, second, third, and fourth rectifier elements being connected such that electric currents flow simultaneously in the first output-side coil and the third output-side coil, and electric currents flow simultaneously in the second output-side coil and the fourth output-side coil in a manner alternating with the electric currents in the first output-side coil and the third output-side coil, so as to cancel out magnetic fluxes passing through the middle legs each time when electric current flowing in the first and second input-side coils is changed in direction.
2. The insulation type step-down converter according to claim 1 , wherein
the first output-side coil and the third output-side coil are integrated and partly shared with each other, and the second output-side coil and the fourth output-side coil are integrated and partly shared with each other.
3. The insulation type step-down converter according to claim 1 , wherein
the first output-side coil, the third output-side coil, and a connection portion connecting the intermediate portion of the first output-side coil and the intermediate portion of the third output-side coil are arranged on an identical layer, and
the second output-side coil, the fourth output-side coil, and a connection portion connecting the intermediate portion of the second output-side coil and the intermediate portion of the fourth output-side coil are arranged on an identical layer.
4. The insulation type step-down converter according to claim 1 , further comprising a multilayer printed board having a plurality of patterns stacked therein, wherein
the first, second, third and fourth output-side coils are arranged as the plurality of stacked patterns included in the multilayer printed board,
the first output-side coil and the third output-side coil are arranged on layers different from each other, and the intermediate portion of the first output-side coil and the intermediate portion of the third output-side coil are connected to each other by a via interposed between the different layers, and
the second output-side coil and the fourth output-side coil are arranged on layers different from each other, and the intermediate portion of the second output-side coil and the intermediate portion of the fourth output-side coil are connected to each other by a via interposed between the different layers.
5. The insulation type step-down converter according to claim 1 , further comprising an input-side drive circuit configured to apply voltages to the first and second input-side coils alternately in directions opposite to each other at regular time intervals.
6. The insulation type step-down converter according to claim 1 , further comprising:
a radiator arranged to come into contact with the first and second step-down transformers; and
an insulating component arranged between the radiator and at least one of the first and second input-side coils and at least one of the first, second, third, and fourth output-side coils, wherein
heat generated by at least one of the first and second input-side coils and at least one of the first, second, third, and fourth output-side coils is transferred to the radiator through the insulating component.
7. The insulation type step-down converter according to claim 6 , wherein
at least one of the first, second, third, and fourth output-side coils is arranged between the radiator and at least one of the first and second input-side coils, and
the radiator is arranged as the reference potential of an output-side circuit including the first, second, third, and fourth output-side coils of the first and second step-down transformers.
8. The insulation type step-down converter according to claim 6 , wherein
the radiator comes into contact with an intermediate portion between the first output-side coil and the third output-side coil or an intermediate portion between the second output-side coil and the fourth output-side coil, through the insulating component.
9. The insulation type step-down converter according to claim 1 , wherein
each of the first, second, third, and fourth output-side coils is formed as a flat plate component made of copper.