Switching power supply device having main switching element period control circuit
AssigneeMurata Manufacturing Co., Ltd.
InventorTatsuya Hosotani
Life of this patent
Estimating the term…
Abstract
A switching power supply device in which the increase in the switching frequency when the load is light is restrained, whereby the switching loss is reduced, intermittent oscillating operation is prevented, and heat generation in the main switching device at the time of short-circuiting is restrained. In a switching power supply device, the charging/discharging time of a capacitor of a switch circuit comprising a time-constant circuit is controlled so as to make the OFF-period of a main switching element a predetermined period that continues after the completion of the discharge of excitation energy from the secondary coil of a transformer of the power supply device.
Claims7
A switching power supply device comprising:
- a transformer having a primary coil, a secondary coil and a feedback coil;
- a main switching element having a control terminal, the main switching element being connected in series with the primary coil;
- a control circuit connected between the control terminal of the main switching element and the feedback coil to turn the main switching element on and off alternatingly, the main switching element thereby having an ON-period and an OFF-period, the main switching element being turned on and off based on a voltage generated in the feedback coil so that an excitation energy is accumulated in the primary coil during the ON-period of the main switching element, the excitation energy accumulated in the primary coil being discharged from the secondary coil during the OFF-period of the main switching element and converted into electric energy to be supplied to a load, the load having an impedance level that can vary;
- and
- a period control circuit to make the OFF-period of the main switching element a predetermined period which continues after the completion of the discharge of the excitation energy from the secondary coil, regardless of variation of the impedance level of the load.
Dependencies are inferred from the claim text.