參數(shù)資料
型號(hào)： LT3837IFE#PBF
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： SWITCHING CONTROLLER, 110 kHz SWITCHING FREQ-MAX, PDSO16
封裝： 4.40 MM, LEAD FREE, PLASTIC, TSSOP-16
文件頁(yè)數(shù)： 5/28頁(yè)
文件大?。?/td> 247K
代理商： LT3837IFE#PBF
LT3837
13
3837fc
APPLICATIONS INFORMATION
Primary Winding Feedback
The previous work was developed using a separate wind-
ing for voltage feedback. It is possible to use the primary
winding as the feedback winding as well. This can simplify
the design of the transformer.
When using the primary winding the feedback voltage
will be added to the VIN voltage so:
V
VI
ESR R
N
FLYBK
OUT
DS ON
SP
=
+
()
where NSP is the transformer effective secondary to
primary winding turns ratio. Use the circuit of Figure 2
to get more accurate output regulation. In this case the
regulation equations becomes:
R
V
VI
ESR R
N
V
FB
OUT
DS ON
SP
BE
1
2
=
+
()
()
where VBE is the base emitter drop of the PNP (approxi-
mately 0.7V).
Likewise the load compensation equation needs to be
changed to use NSP instead of NSF so:
RK
RDC
ESR R
RN
CMP
SENSE
DS ON
SF
=
()
+
1
–
()
MS
MP
R2
R1
SECONDARY
PRIMARY
COUT
VIN
VFLYBK
3837 F02
LT3837
FB
PG
Figure 2
Transformer Design
Transformer design/specication is the most critical part
of a successful application of the LT3837. The following
sections provide basic information about designing the
transformer and potential tradeoffs.
If you need help, the LTC Applications group is available to
assist in the choice and/or design of the transformer.
Turns Ratios
The design of the transformer starts with determining
duty cycle (DC). DC impacts the current and voltage stress
on the power switches, input and output capacitor RMS
currents and transformer utilization (size vs power).
The ideal turns ratio is:
N
V
DC
IDEAL
OUT
IN
=
–
1
Avoid extreme duty cycles as they, in general, increase
current stresses. A reasonable target for duty cycle is
50% at nominal input voltage.
For instance, if we wanted a 9V to 3.3V converter at 50%
DC then:
NIDEAL ==
33
9
10 5
05
1
272
.
–.
..
In general, better performance is obtained with a lower
turns ratio. A DC of 52% yields a 1:3 ratio.
Note the use of the external feedback resistive divider
ratio to set output voltage provides the user additional
freedom in selecting a suitable transformer turns ratio.
Turns ratios that are the simple ratios of small integers;
e.g., 1:1, 2:1, 3:2 help facilitate transformer construction
and improve performance.
When building a supply with multiple outputs derived
through a multiple winding transformer, lower duty cycle
can improve cross regulation by keeping the synchronous
rectier on longer, and thus, keep secondary windings
coupled longer.
For a multiple output transformer, the turns ratio between
output windings is critical and affects the accuracy of the
voltages. The ratio between two output voltages is set with
the formula VOUT2 = VOUT1 N21 where N21 is the turns
相關(guān)PDF資料
PDF描述
LT3837IFE#TRPBF SWITCHING CONTROLLER, 110 kHz SWITCHING FREQ-MAX, PDSO16
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LT3845EFE#TR SWITCHING CONTROLLER, 600 kHz SWITCHING FREQ-MAX, PDSO16
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LT3844EFE#PBF 功能描述:IC REG CTRLR BST INV PWM 16TSSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 特色產(chǎn)品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 標(biāo)準(zhǔn)包裝:1 系列:PowerWise® PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1MHz 占空比:81% 電源電壓:4.5 V ~ 18 V 降壓:是 升壓:無(wú) 回掃:無(wú) 反相:無(wú) 倍增器:無(wú) 除法器:無(wú) Cuk:無(wú) 隔離:無(wú) 工作溫度:-5°C ~ 125°C 封裝/外殼:32-WFQFN 裸露焊盤 包裝:Digi-Reel® 產(chǎn)品目錄頁(yè)面:1303 (CN2011-ZH PDF) 其它名稱:LM3754SQDKR
LT3844EFE#TRPBF 功能描述:IC REG CTRLR BST INV PWM 16TSSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無(wú) 升壓:是 回掃:無(wú) 反相:無(wú) 倍增器:無(wú) 除法器:無(wú) Cuk:無(wú) 隔離:無(wú) 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR)
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