參數(shù)資料
型號(hào): NCP4326DR2
廠商: ON SEMICONDUCTOR
元件分類: 模擬信號(hào)調(diào)理
英文描述: Secondary Controller for Multi−Output Quasi−Resonant Switchmode Power Supplies
中文描述: SPECIALTY ANALOG CIRCUIT, PDSO16
封裝: SOIC-16
文件頁(yè)數(shù): 20/30頁(yè)
文件大?。?/td> 432K
代理商: NCP4326DR2
NCP4326
http://onsemi.com
20
Detailed SoftStart Behavior
A softstart is proposed to avoid a high peak current
during startup sequences in trailing edge mode control.
Increasing smoothly the secondary duty cycle from zero to
the nominal value in trailing edge mode control does not
limit this current (see Figure 43).
NCP4326 is a voltage mode controller type (i.e. the
secondary peak current is not sensed); the peak current
sensing can not be used to ensure a proper peak current ramp
up on secondary side.
Instead of controlling the peak current ramp up, if the
secondary controller smoothly ramps up the duty cycle then
the result will not yield a smooth ramp up peak current as in
conventional PWM controllers (see Figure 43).
As depicted in Figure 43, when the secondary duty cycle
is increased smoothly the peak current does not ramp up. It
is not possible to have a ramp up peak current because at the
beginning of the OFF time period the flux stored in the
flyback transformer is at the maximum value so the peak
current yields by this flux will be also at a maximum value.
Consequently, the peak current is not linked to the duty cycle
width. The peak current is only linked to the energy stored
in the flyback transformer and the current sharing during the
primary OFF time.
t
0
t
0
0
Verror
VCt
DRV
0
ID2
Vsync
OFF Time
ON Time
0
Transformateur Flux
t
t
t
Figure 43. Increasing Smoothly the Duty Cycle Does Not Yield a Smooth Peak Current Ramp up
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