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Constant current output control method and constant current output control device for switching power supply circuit

  • US 20040196672A1
  • Filed: 12/29/2003
  • Published: 10/07/2004
  • Est. Priority Date: 02/03/2003
  • Status: Active Grant
First Claim
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1. A constant current output control method for a switching power supply circuit having a transformer provided with a primary winding and a secondary output winding;

  • an oscillating switching device connected in-series with the primary winding to connect the primary winding to an energizing direct current power supply;

    a switching control circuit to execute ON/OFF control of the oscillating switching device; and

    a rectifying smoothing circuit to rectify and smooth an output of the secondary output winding;

    the constant current output control method for changing an ON/OFF time of the oscillating switching device of the switching power supply circuit, and executing a constant current output control of an output current I2o of the rectifying smoothing circuit comprising;

    deriving an OFF adjustment time T3 based on equation (1), T3=T2×

    (Np÷

    Ns×

    Ip
    ref÷

    2÷

    I
    2oset

    1)−

    T1



    (1) where, I2oset represents a set output current of the rectifying smoothing circuit for which the constant current output control is to be executed, Np represents a number of turns of the primary winding, Ns represents a number of turns of the secondary output winding, T1 being a fixed time representing an ON time of the oscillating switching device to excite the primary winding during an oscillation period T, Ipref representing a reference peak current flowing in the primary winding when the ON time T1 completely elapses, and T2 representing an output time during which output is generated in the rectifying smoothing circuit;

    controlling an OFF time of the oscillating switching device during the oscillation period T wherein the OFF time is equal to the sum of the output time T2 and the OFF adjustment time T3; and

    setting the output current I2o of the rectifying smoothing circuit to the set output current I2oset.

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