參數(shù)資料
型號(hào)： NCP1205P2
廠商： ON SEMICONDUCTOR
元件分類： 穩(wěn)壓器
英文描述： Single Ended PWM Controller Featuring QR Operation and Soft Frequency Foldback
中文描述： SWITCHING CONTROLLER, 125 kHz SWITCHING FREQ-MAX, PDIP14
封裝： PLASTIC, DIP-14
文件頁(yè)數(shù)： 11/20頁(yè)
文件大?。?/td> 163K
代理商： NCP1205P2
NCP1205
http://onsemi.com
11
If we now enter this formula into a spreadsheet, we can easily plot the switching frequency versus the output power demand:
Figure 12. A Typical Behavior of Free Running Systems
with a Smooth Frequency Foldback with the NCP1205
150000
0
250000
50000
100000
200000
0
15
10
5
S
Transition
BCM to VFM
OUTPUT POWER (W)
20
Fmax
Fmax
V
CO
Action
The typical above diagram shows how the frequency
moves with the output power demand. The components used
for the simulation were: Vin = 300 V, Lp = 6.5 mH,
Vout = 10 V, Np/Ns = 12.
The red line indicates where the maximum frequency is
clamped. At this time, the VCO takes over and decreases the
switching frequency to the minimum value.
VCO Operation
The VCO is controlled from the Verr voltage. For Verr
levels
above
1.0 V, the VCO frequency remains unchanged
at 125 kHz. As soon as Verr starts to decrease below 1.0 V,
the VCO frequency decreases with a typical
small–signal
slope of –175 kHz/mV @ Verr = 500 mV down to
zero (typically at FB
≈
3.3 V). The demagnetization
synchronization is however kept when the Toff expands.
The maximum switching frequency can be altered by
adjusting the Ct capacitor on pin 5. The 125 kHz maximum
operation ensures that the fundamental component stays
external
from
the
international
specification beginning.
The following drawing explains the philosophy behind
the idea:
EMI
CISPR–22
Figure 13. When the Power Demand goes Low, the Peak Current is Frozen and the Frequency Decreases
3 V
1 V
0.75 V
Peak Current is Fixed
Peak current
can change
V
CO
Frequency
is Fixed at 130 kHz
V
CO
Frequency
can Decrease
Internal V
err
BCM Mode
Zero Crossing Detector
To detect the zero primary current, we make use of an
auxiliary winding. By coupling this winding to the primary,
we have a voltage image of the flux activity in the core.
Figure 13 details the shape of the signal in BCM.
The auxiliary winding for demagnetization needs to
be wired in Forward mode. However, the application
note describes an alternative solution showing how to wire
the winding in Flyback as well. As Figure 13 depicts, when
the MOSFET closes, the auxiliary winding delivers
(Naux/Np
.
Vin). At the switch opening, we couple the
auxiliary winding to the main output power winding and
thus deliver: (–Naux/Ns
.
Vout). When DCM occurs, the
ringing also takes place on the auxiliary winding. As soon
as the level crosses–up the internal reference level
(65 mV), a signal is internally sent to re–start the MOSFET.
Three different conditions can occur:
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
NCP1205P2G 功能描述:電流型 PWM 控制器 Single Ended Quasi Resonant PWM RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14
NCP1205PG 功能描述:電流型 PWM 控制器 Single Ended Quasi Resonant PWM RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14
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