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參數(shù)資料
| 型號： | NCP1205P2G |
| 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： | LEAD FREE, PLASTIC, DIP-14 |
| 文件頁數(shù)： | 10/17頁 |
| 文件大?。?/td> | 277K |
| 代理商： | NCP1205P2G |
NCP1205
http://onsemi.com
10
In order to clarify the device behavior, we can distinguish the
following
simplified
operating phases:
1. The load is at its nominal value. The SMPS operates in
borderline conduction mode and the switching
frequency is imposed by the external elements (Vin,
Lp, Ip, Vout). The MOSFET is turned on at the
minimum drain
source level.
2. The load starts to decrease and the free
running
frequency hits the internal clamp.
3. The frequency can no longer naturally increase
because of the clamp. The frequency is now controlled
by the internal VCO but remains constant. The peak
current finds no other option that diminishing to satisfy
equation (1).
4. The peak current has reached the internal minimum
ceiling level and is now frozen for the remaining
cycles.
5. To further reduce the transmitted power (V
FB
goes up),
the VCO decreases the switching frequency. In case of
output overshoot, the VCO could decrease the
frequency down to zero. When the overshoot has gone,
V
FB
diminishes again and the IC smoothly resumes its
operation.
Advantages of the Method
By implementing the aforementioned control scheme, the
NCP1205 brings the following advantages:
Discontinuous only operation: in DCM, the Flyback is
a first order system (at low frequencies) and thus
naturally eases the feedback loop compensation.
A low
cost secondary rectifier can be used due to
smooth turn
off conditions.
Valley switching ensures minimum switching losses
brought by Coss and all the parasitic capacitances.
By folding back the switching frequency, you turn the
system into Pulse Duration Modulation. This method
prevents from generating
uncontrolled
output ripple as
with hysteretic controllers.
By letting you control the peak current value at which
the frequency goes down, you ensure that this level is
low enough to avoid transformer acoustic noise
generation even at audible frequencies.
Detailed Description
The following sections describe the internal behavior of
the NCP1205.
Free
Running Operation
As previously said, the operating frequency at nominal load
is dictated by the external elements. We can split the different
switching sections in two separated instants. In the following
text we use the internal error voltage, Verr. This level is
elaborated in Figure 13. Verr is linked to VFB (pin 4) by the
following formula:
(eq. 2)
Verr
10
3 · VFB
ON time:
The ON time is given by the time it takes to
reach the peak current setpoint imposed by the level on FB
pin (pin 4). Since this level is internally divided by three, the
peak setpoint is simply:
3 · R1
The rising slope of the peak current is also dependent on
the inductance value and the rectified DC input voltage by:
dIL
dt
By combining both equations, we obtain the ON time
definition:
Lp
VinDC
OFF time:
The time taken by the demagnetization of the
transformer depends on the reset voltage applied at the
switch opening. During the conduction time of the
secondary diode, the primary side of the transformer
undergoes a reflected voltage of: [Np/Ns . (Vf + Vout)]. This
voltage applied on the primary inductance dictates the time
needed to decrease from Ip down to zero:
Ipk
(eq. 3)
VinDC
Lp
(eq. 4)
ton
· Ip
Lp · VERR
VinDC· 3 · Rsense
(eq. 5)
toff
Lp
Np
Ns
· (Vout
Vf)
(eq. 6)
· Ip
Lp · Verr
Np
Ns
· (Vout
Vf) · 3 · Rsense
By adding ton + toff, we obtain the natural switching
frequency of the SMPS operating in Borderline Conduction
Mode (BCM):
(eq. 7)
ton
toff
Verr · Lp
3 · Rsense·
1
VinDC
1
Np
Ns
· (Vout
Vf)
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| NCP1205PG | Single Ended PWM Controller Featuring QR Operation and Soft Frequency Foldback |
| NCP1205P | Single Ended PWM Controller Featuring QR Operation and Soft Frequency Foldback |
| NCP1205P2 | Single Ended PWM Controller Featuring QR Operation and Soft Frequency Foldback |
| NCP1205 | Single Ended PWM Controller Featuring QR Operation and Soft Frequency Foldback |
| NCP1207APG | PWM Current−Mode Controller for Free Running Quasi−Resonant Operation |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| 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 上升時間: 下降時間: 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 |
| NCP1207/D | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:PWM Current-Mode Controller for Quasi-Resonant Operation |
| NCP1207A | 制造商:ONSEMI 制造商全稱:ON Semiconductor 功能描述:PWM Current-Mode Controller for Free Running Quasi-Resonant Operation |
| NCP1207A_06 | 制造商:ONSEMI 制造商全稱:ON Semiconductor 功能描述:PWM Current−Mode Controller for Free Running Quasi−Resonant Operation |
| NCP1207A_07 | 制造商:ONSEMI 制造商全稱:ON Semiconductor 功能描述:PWM Current-Mode Controller for Free Running Quasi-Resonant Operation |
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