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    7 - L-22 (DP) (Pe) ( (Ee) Nptel)

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    Chark
    The document discusses the operation of a flyback converter circuit. It describes how the secondary winding current abruptly rises when the switch turns off, charging the output capacitor. The output capacitor voltage builds up over multiple switching cycles until it stabilizes at a steady-state value determined by factors like the input supply, transformer parameters, switching frequency, and load. During the steady state, the secondary current decays linearly as it flows against the constant output voltage. The circuit can operate in either discontinuous or continuous flux mode depending on the length of the switch off period.

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    7 - L-22 (DP) (Pe) ( (Ee) Nptel)

    Uploaded by

    Chark
    10 views1 page
    The document discusses the operation of a flyback converter circuit. It describes how the secondary winding current abruptly rises when the switch turns off, charging the output capacitor. The output capacitor voltage builds up over multiple switching cycles until it stabilizes at a steady-state value determined by factors like the input supply, transformer parameters, switching frequency, and load. During the steady state, the secondary current decays linearly as it flows against the constant output voltage. The circuit can operate in either discontinuous or continuous flux mode depending on the length of the switch off period.

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    Original Title

    7_L-22(DP)(PE) ((EE)NPTEL)

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    The document discusses the operation of a flyback converter circuit. It describes how the secondary winding current abruptly rises when the switch turns off, charging the output capacitor. The output capacitor voltage builds up over multiple switching cycles until it stabilizes at a steady-state value determined by factors like the input supply, transformer parameters, switching frequency, and load. During the steady state, the secondary current decays linearly as it flows against the constant output voltage. The circuit can operate in either discontinuous or continuous flux mode depending on the length of the switch off period.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    10 views1 page

    7 - L-22 (DP) (Pe) ( (Ee) Nptel)

    Uploaded by

    Chark
    The document discusses the operation of a flyback converter circuit. It describes how the secondary winding current abruptly rises when the switch turns off, charging the output capacitor. The output capacitor voltage builds up over multiple switching cycles until it stabilizes at a steady-state value determined by factors like the input supply, transformer parameters, switching frequency, and load. During the steady state, the secondary current decays linearly as it flows against the constant output voltage. The circuit can operate in either discontinuous or continuous flux mode depending on the length of the switch off period.

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    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
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    of 1

    change in the magnetic field energy and this in turn will mean infinite magnitude of

    instantaneous power, some thing that a practical system cannot support.]

    For the idealized circuit considered here, the secondary winding current abruptly rises from zero
    to I P N1 N 2 as soon as the switch ‘S’ turns off. N 1 and N 2 denote the number of turns in the
    primary and secondary windings respectively. The sudden rise of secondary winding current is
    shown in Fig. 22.5(a) and Fig. 22.5(b). The diode connected in the secondary circuit, as shown in
    Fig.22.1, allows only the current that enters through the dotted end. It can be seen that the
    magnitude and current direction in the secondary winding is such that the mmf produced by the
    two windings does not have any abrupt change. The secondary winding current charges the
    output capacitor. The + marked end of the capacitor will have positive voltage. The output
    capacitor is usually sufficiently large such that its voltage doesn’t change appreciably in a single
    switching cycle but over a period of several cycles the capacitor voltage builds up to its steady
    state value.

    The steady-state magnitude of output capacitor voltage depends on various factors, like,
    input dc supply, fly-back transformer parameters, switching frequency, switch duty ratio
    and the load at the output. Capacitor voltage magnitude will stabilize if during each switching
    cycle, the energy output by the secondary winding equals the energy delivered to the load.

    As can be seen from the steady state waveforms of Figs.22.5(a) and 22.5(b), the secondary
    winding current decays linearly as it flows against the constant output voltage (VO). The linear
    d
    decay of the secondary current can be expressed as follows: LSec × iSec = −VO ---------- (22.2),
    dt
    Where, LSec and iSec are secondary winding inductance and current respectively.
    VO is the stabilized magnitude of output voltage.

    Under steady-state and under the assumption of zero on-state voltage drop across diode, the
    secondary winding voltage during this mode equals VO and the primary winding voltage =
    VON1/N2 (dotted ends of both windings being at lower potential). Under this condition, voltage
    stress across switch ‘S’ is the sum total of the induced emf in the primary winding and the dc
    supply voltage (Vswitch = EDC + VON1/N2).

    The secondary winding, while charging the output capacitor (and feeding the load), starts
    transferring energy from the magnetic field of the fly back transformer to the power supply
    output in electrical form. If the off period of the switch is kept large, the secondary current gets
    sufficient time to decay to zero and magnetic field energy is completely transferred to the output
    capacitor and load. Flux linked by the windings remain zero until the next turn-on of the switch,
    and the circuit is under discontinuous flux mode of operation. Alternately, if the off period of the
    switch is small, the next turn on takes place before the secondary current decays to zero. The
    circuit is then under continuous flux mode of operation.

    During discontinuous mode, after complete transfer of the magnetic field energy to the output,
    the secondary winding emf as well as current fall to zero and the diode in series with the winding
    stops conducting. The output capacitor however continues to supply uninterrupted voltage to the
    load. This part of the circuit operation has been referred to as Mode-3 of the circuit operation.

    Version 2 EE IIT, Kharagpur 7

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