Forward type dc-dc converter
AssigneeFuji Electric Co., Ltd.
InventorTadahiko Sato
Life of this patent
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Abstract
With the use of a voltage across a secondary winding of a transformer, a DC output voltage and a conduction time width of a current in the DC reactor on the secondary side circuit in an immediately preceding period, the turning-on time width and the turning-off time width of a synchronous rectification MOSFET in the secondary side circuit of the transformer are obtained by calculations, without receiving any signals from a primary side circuit, to thereby carry out control of a synchronous rectification circuit in a forward DC-DC converter with the time in which a current flows in a diode reduced to the minimum.
Claims16
A forward type DC-DC converter that converts a voltage of a DC input power supply to a specified DC output voltage insulated from the voltage of the DC input power supply, the DC-DC converter comprising:
- a series circuit of a primary side semiconductor switch and a primary winding of a transformer, the series circuit being connected in parallel to the DC input power supply;
- a rectifying diode that rectifies a voltage across a secondary winding of the transformer;
- a smoothing filter comprising a DC reactor and a smoothing capacitor, the smoothing filter that smoothes an output voltage of the rectifying diode;
- a freewheeling diode that freewheels a current in the DC reactor;
- a first MOSFET connected in inverse parallel to the rectifying diode;
- and
- a second MOSFET connected in inverse parallel to the freewheeling diode,
- a voltage across the smoothing capacitor being served as a DC output voltage,
- the DC output voltage being controlled by turning-on and-off operations of the first MOSFET and the second MOSFET based on periodical turning-on and-off operations of the primary side semiconductor switch, and
- an arithmetic circuit in which
- a turning-on time width of the first MOSFET is calculated by use of a time width within which a current flows in the DC reactor on a secondary side within a turning-off time width of the primary side semiconductor switch in a previous period, the DC output voltage and the voltage across the secondary winding of the transformer, and
- a turning-on time width of the second MOSFET is calculated by use of a turning-on time width of the primary side semiconductor switch immediately before a turning-on of the second MOSFET, the DC output voltage, and the voltage across the secondary winding of the transformer.
A DC-DC converter device comprising:
- a transformer having a primary side winding and a secondary side winding;
- a primary side switching device coupled to the primary side winding;
- a first switching device coupled to the secondary side winding;
- a second switching device coupled to the first switching device;
- an inductor coupled to the second switching device;
- and
- a control device configured to
- determine an on-time duration of the first switching device based at least partly on a conduction time of the inductor during an off-time of the primary side switching device, and
- determine an on-time duration of the second switching device based at least partly on an on-time duration of the primary side switching device.
Dependencies are inferred from the claim text.