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參數(shù)資料
| 型號(hào)： | NCP1239 |
| 廠商： | ON SEMICONDUCTOR |
| 英文描述： | Low−Standby High Performance PWM Controller |
| 文件頁數(shù)： | 33/38頁 |
| 文件大小： | 1145K |
| 代理商： | NCP1239 |
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NCP1239
http://onsemi.com
33
Skipping Cycle Mode
The NCP1239 automatically skips switching cycles when
the output power demand drops below a given level. This is
accomplished by monitoring the FB pin. In normal
operation, Pin 8 imposes a current setpoint accordingly to
the load value. If the load demand decreases, the internal
loop asks for less peak current. When this setpoint reaches
a fixed determined level, the IC prevents the current from
decreasing further down and starts to blank the output
pulses: the IC enters the socalled skipcycle mode, also
named controlled burst operation. The default skipcycle
current is internally frozen to 30% of the maximum peak
current which is 0.5 V/Rsense The power transfer now
depends upon the width of the pulse bunches (Figure 54).
Suppose we have the following component values:
Lp, primary inductance = 350
H
fsw , switching frequency = 65 kHz
Ip skip = 600 mA (or 140 mV/Rsense)
The theoretical power transfer is therefore:
1/2 * Lp * Ip
2
* fsw = 4 W
If this IC enters skipcycle mode with a bunch length of
10 ms over a recurrent period of 100 ms, then the total power
transfer is:
4 W * 10 ms/100 ms = 400 mW
To better understand how this skipcycle mode takes
place, a look at the operation mode versus the FB level
immediately gives the necessary insight:
4.3 V, FB Pin open
2.7 V upper dynamic range
Normal current mode operation
0.43 V
Skipcycle operation
Ip
MIN
= 150 mV/Rsense
FB Pin Voltage
Figure 54.
When FB is below the skipcycle threshold (0.43 V by
default), the circuit skips the switching cycle. When the IC
enters the skipcycle mode, the peak current cannot go
below (0.43 V/3)/Rsense or 140 mV/Rsense. Figure 55
shows different values of pulse widths when the SMPS starts
to skipcycles at different power levels:
Power P1
Power P2
Power P3
Figure 55.
Output pulses at various power levels (X = 5 s/div) P1 < P2 < P3
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| NCP1239FDR2G | Low−Standby High Performance PWM Controller |
| NCP1239VDR2 | Low−Standby High Performance PWM Controller |
| NCP1239VDR2G | Low−Standby High Performance PWM Controller |
| NCP1271 | Soft−Skip Mode Standby PWM Controller with Adjustable Skip Level and External Latch |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| NCP1239D | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Low-Standby High Performance PWM Controller |
| NCP1239F | 制造商:ONSEMI 制造商全稱:ON Semiconductor 功能描述:AC-DC Offline Switching Controllers/Regulators |
| NCP1239FDR2 | 功能描述:電流型 PWM 控制器 Low Standby Power 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 |
| NCP1239FDR2G | 功能描述:電流型 PWM 控制器 Low Standby Power High Performance 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 |
| NCP1239V | 制造商:ONSEMI 制造商全稱:ON Semiconductor 功能描述:AC-DC Offline Switching Controllers/Regulators |
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