参数资料
型号: UCC2891DR
厂商: Texas Instruments
文件页数: 16/41页
文件大小: 0K
描述: IC REG CTRLR FLYBK ISO CM 16SOIC
标准包装: 2,500
PWM 型: 电流模式
输出数: 1
频率 - 最大: 1MHz
占空比: 74%
电源电压: 8.5 V ~ 16 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 125°C
封装/外壳: 16-SOIC(0.154",3.90mm 宽)
包装: 带卷 (TR)
UCC2891, UCC2892
UCC2893, UCC2894
SLUS542F ? OCTOBER 2003 ? REVISED JULY 2009
FUNCTIONAL DESCRIPTION
VOVP
VOVH
VIN
VSS
OUT
AUX
UDG?03150
Figure 4. Line Overvoltage Sequence, P?Channel
Pulse Skipping
During output load current transients or light load conditions most PWM controllers needs to be able to skip
some number of PWM pulses. In an active clamp topology where the clamp switch is driven complementarily
to the main switch, this would apply the clamp voltage across the transformer continuously. Since operating
conditions might require skipping several switching cycles on the main transistor, saturating the transformer is
very likely if the AUX output stays on.
FB
TSW
OUT
AUX
D = 0 Boundary
1.25 V
UDG?03151
Figure 5. Pulse Skipping Operation, P?Channel
To overcome this problem, the UCC2891 family incorporates pulse skipping for both outputs in the controller.
As can be seen above, when a pulse is skipped at the main output (OUT) because the feedback signal demands
zero duty ratio, the corresponding output pulse on the AUX output is omitted as well. This operation allows to
prevent reverse saturation of the power transformer and to preserve the clamp capacitor voltage level during
pulse skipping operation.
16
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