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    參數(shù)資料
    型號(hào): MC33260DR2G
    廠商: ON SEMICONDUCTOR
    元件分類: 穩(wěn)壓器
    英文描述: GreenLine TM Compact Power Factor Controller: Innovative Circuit for Cost Effective Solutions
    中文描述: 0.5 A POWER FACTOR CONTROLLER, PDSO8
    封裝: LEAD FREE, SOIC-8
    文件頁數(shù): 10/22頁
    文件大?。?/td> 232K
    代理商: MC33260DR2G
    MC33260
    http://onsemi.com
    10
    Pin Numbers are Relevant to the PDIP8 Version
    Ro
    VoregH
    Vpin1
    IregH
    Consequently:
    In practice, V
    pin1
    is small compared to (V
    o
    )
    regH
    and this
    equation can be simplified as follows (I
    regH
    being also
    replaced by its typical value 200 A
    ):
    Ro
    5
    The regulation block output is connected to the Pin 2
    through a 300 k
    resistor. The Pin 2 voltage (V
    control
    ) is
    compared to the oscillator sawtooth for PWM control.
    An external capacitor must be connected between Pin 2
    and ground, for external loop compensation. The bandwidth
    is typically set below 20 Hz so that the regulation block
    output should be relatively constant over a given ac line
    cycle. This integration that results in a constant ontime over
    the ac line period, prevents the mains frequency output
    ripple from distorting the ac line current.
    VoregH(k )
    OSCILLATOR SECTION
    The oscillator consists of three phases:
    Charge Phase: The oscillator capacitor voltage grows
    up linearly from its bottom value (ground) until it
    exceeds V
    control
    (regulation block output voltage). At
    that moment, the PWM latch output gets low and the
    oscillator discharge sequence is set.
    Discharge Phase: The oscillator capacitor is abruptly
    discharged down to its valley value (0 V).
    Waiting Phase: At the end of the discharge sequence,
    the oscillator voltage is maintained in a low state until
    the PWM latch is set again.
    Figure 26. Oscillator
    I
    charge
    = 2
    I
    o
    I
    o
    / I
    ref
    0
    1
    CT
    3
    15 pF
    0
    1
    Output_Ctrl
    The oscillator charge current is dependent on the feedback
    current (I
    o
    ). In effect
    Icharge
    2
    I2
    o
    Iref
    where:
    I
    charge
    is the oscillator charge current,
    I
    o
    is the feedback current (drawn by Pin 1),
    I
    ref
    is the internal reference current (200 A
    ).
    So, the oscillator charge current is linked to the output
    voltage level as follows:
    Icharge
    2
    Vo
    R2
    Vpin1
    2
    o
    Iref
    where:
    V
    o
    is the output voltage,
    R
    o
    is the feedback resistor,
    V
    pin1
    is the Pin 1 clamp voltage.
    In practice, V
    pin1
    that is in the range of 2.5 V, is very small
    compared to V
    o
    . The equation can then be simplified by
    neglecting V
    pin1
    :
    Icharge
    2
    V2
    o
    R2
    o
    Iref
    It must be noticed that the oscillator terminal (Pin 3) has
    an internal capacitance (C
    int
    ) that varies versus the Pin 3
    voltage. Over the oscillator swing, its average value
    typically equals 15 pF (min 10 pF, max 20 pF).
    The total oscillator capacitor is then the sum of the internal
    and external capacitors.
    Cpin3
    CT
    Cint
    PWM LATCH SECTION
    The MC33260 operates in voltage mode: the regulation
    block output (V
    control
    Pin 2 voltage) is compared to the
    oscillator sawtooth so that the gate drive signal (Pin 7) is
    high until the oscillator ramp exceeds V
    control
    .
    The ontime is then given by the following equation:
    Cpin3
    ton
    Vcontrol
    Ich
    where:
    t
    on
    is the ontime,
    C
    pin3
    is the total oscillator capacitor (sum of the
    internal and external capacitor),
    I
    charge
    is the oscillator charge current (Pin 3 current),
    V
    control
    is the Pin 2 voltage (regulation block output).
    Consequently, replacing I
    charge
    by the expression given in
    the
    Oscillator Section
    :
    R2
    o
    2
    ton
    Iref
    Cpin3
    Vcontrol
    V2
    o
    One can notice that the ontime depends on V
    o
    (preconverter output voltage) and that the ontime is
    maximum when Vcontrol is maximum (1.5 V typically).
    At a given V
    o
    , the maximum ontime is then expressed by
    the following equation:
    tonmax
    Cpin3
    R2
    o
    Iref
    Vcontrolmax
    2
    V2
    o
    This equation can be simplified replacing
    2
    [(Vcontrol)max* Iref]
    by Kosc
    Refer to
    Electrical Characteristics, Oscillator Section
    .
    Then:
    tonmax
    Cpin3
    Kosc
    R2
    o
    V2
    o
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