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参数资料
| 型号： | LT3957EUHE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 16/28页 |
| 文件大小： | 0K |
| 描述： | IC REG MULTI CONFIG ADJ 36VQFN |
| 特色产品： | LT?3957/LT?3958 Converters |
| 标准包装： | 61 |
| 类型： | 升压（升压），反相，回扫，Sepic |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 1.6 V ~ 40 V |
| 输入电压： | 3 V ~ 40 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 100kHz ~ 1MHz |
| 电流 - 输出： | 5A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 36-WFQFN 裸露焊盘 |
| 包装： | 管件 |
| 供应商设备封装： | 36-QFN-EP（6x5） |
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LT3957
APPLICATIONS INFORMATION
FLYBACK CONVERTER APPLICATIONS
The LT3957 can be con?gured as a ?yback converter for the
applications where the converters have multiple outputs,
high output voltages or isolated outputs. Due to the 40V
rating of the internal power switch, LT3797 should be used
in low input voltage ?yback converters. Figure 6 shows a
simpli?ed ?yback converter.
The ?yback converter has a very low parts count for mul-
tiple outputs, and with prudent selection of turns ratio, can
have high output/input voltage conversion ratios with a
desirable duty cycle. However, it has low ef?ciency due to
the high peak currents, high peak voltages and consequent
power loss. The ?yback converter is commonly used for
an output power of less than 50W.
The ?yback converter can be designed to operate either
in continuous or discontinuous mode. Compared to con-
tinuous mode, discontinuous mode has the advantage of
smaller transformer inductances and easy loop compen-
Figure 7 shows the waveforms of the ?yback converter
in discontinuous mode operation. During each switching
period T S , three subintervals occur: DT S , D2T S , D3T S .
During DT S , M is on, and D is reverse-biased. During
D2T S , M is off, and L S is conducting current. Both L P and
L S currents are zero during D3T S .
V SW
I SW
I SW(MAX)
I D
I D(MAX)
sation, and the disadvantage of higher peak-to-average
current and lower ef?ciency.
DT S
D2T S
T S
D3T S
t
3957 F07
SUGGESTED
V IN
+
C IN
–
V SN
+
RCD SNUBBER
C SN R SN
D SN
L P
N P :N S
L S
D
I D
C OUT
+
+
–
V OUT
Figure 7. Waveforms of the Flyback Converter
in Discontinuous Mode Operation
The ?yback converter conversion ratio in the discontinu-
ous mode operation is:
= S ?
SW
I SW
V OUT
V IN
N D
N P D2
LT3957
According to Figure 6, the peak SW voltage is:
GND
3957 F06
V SW(PEAK) = V IN(MAX) + V SN
V SN = k ?
Figure 6. A Simpli?ed Flyback Converter
Flyback Converter: Switch Duty Cycle and Turns Ratio
The ?yback converter conversion ratio in the continuous
mode operation is:
where V SN is the snubber capacitor voltage. A smaller V SN
results in a larger snubber loss. A reasonable V SN is 1.5
to 2 times of the re?ected output voltage:
V OUT ? N P
N S
= S ?
V OUT
V IN
N D
N P 1 ? D
k = 1.5 ~ 2
where N S /N P is the second to primary turns ratio. D is
duty cycle.
3957f
16
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3957EUHETRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Boost, Flyback, SEPIC and Inverting Converter with 5A, 40V Switch |
| LT3957IUHE#PBF | 功能描述:IC REG MULTI CONFIG ADJ 36VQFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LT3957IUHE#TRPBF | 功能描述:IC REG MULTI CONFIG ADJ 36VQFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LT3957IUHEPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Boost, Flyback, SEPIC and Inverting Converter with 5A, 40V Switch |
| LT3957IUHETRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Boost, Flyback, SEPIC and Inverting Converter with 5A, 40V Switch |
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