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Switching power supply device

  • US 9,787,204 B2
  • Filed: 07/11/2016
  • Issued: 10/10/2017
  • Est. Priority Date: 08/27/2012
  • Status: Active Grant
First Claim
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1. A switching power supply device, comprising:

  • an isolation transformer having a primary winding, a plurality of secondary windings, and a tertiary winding, the primary winding being connected to a direct current voltage source via a capacitor, leakage inductance of the isolation transformer and the capacitor forming a series resonant circuit;

    a first switching element connected in series to the primary winding of the isolation transformer, the first switching element being configured to be driven by a drive control circuit that performs a separately excited oscillation operation, to thereby apply a direct current input voltage from the direct current voltage source to the series resonant circuit;

    a second switching element connected in parallel to the series resonant circuit, the second switching element being configured to be driven upon turning-off of the first switching element, to thereby form a current path of the series resonant circuit;

    an output circuit configured to rectify, smooth, and output power generated on the secondary windings of the isolation transformer; and

    the drive control circuit, includingan output control circuit configured to generate an output control signal with a pulse width corresponding to an output voltage of the output circuit;

    a winding detection circuit configured to compare a voltage generated in the tertiary winding of the isolation transformer with a winding threshold voltage, and to output a winding detection signal;

    a drive circuit configured to generate, in accordance with the winding detection signal and the output control signal, a pulse-width controlled drive signal for driving the first switching element; and

    a threshold setting circuit configured to change the winding threshold voltage in the winding detection circuit in accordance with the direct current input voltage applied to the series resonant circuit, to thereby adjust the timing of turning on the first switching element.

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