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| 型号： | LT1424CN8-9#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 8/16页 |
| 文件大小： | 0K |
| 描述： | IC REG FLYBACK ISOLATED 9V 8DIP |
| 标准包装： | 50 |
| 类型： | 回扫，隔离 |
| 输出类型： | 固定 |
| 输出数： | 1 |
| 输出电压： | 9V |
| 输入电压： | 2.8 V ~ 20 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 285kHz |
| 电流 - 输出： | 200mA |
| 同步整流器： | 无 |
| 工作温度： | 0°C ~ 125°C |
| 安装类型： | 通孔 |
| 封装/外壳： | 8-DIP（0.300"，7.62mm） |
| 包装： | 管件 |
| 供应商设备封装： | 8-PDIP |
LT1424-9
OPERATIO N
The LT1424-9 is a current mode switching regulator IC
that has been designed specifically for the isolated fly-
back topology. The special problem normally encoun-
tered in such circuits is that information relating to the
output voltage on the isolated secondary side of the
transformer must be communicated to the primary side
in order to maintain regulation. Historically, this has been
done with optoisolators or extra transformer windings.
Optoisolator circuits waste output power and the extra
components they require increase the cost and physical
volume of the power supply. Optoisolators can also
exhibit trouble due to limited dynamic response (tempo-
ral), nonlinearity, unit-to-unit variation and aging over
information from the flyback pulse. Due to space con-
straints, this discussion will not reiterate the basics of
current mode switcher/controllers and isolated flyback
converters. A good source of information on these topics
is LTC’s Application Note 19.
ERROR AMPLIFIER—PSEUDO DC THEORY
Please refer to the simplified diagram of the Flyback Error
Amplifier. Operation is as follows: when output switch Q4
turns off, its collector voltage rises above the V IN rail. The
amplitude of this flyback pulse, i.e., the difference between
it and V IN , is given as:
V FLBK = OUT
life. Circuits employing extra transformer windings also
exhibit deficiencies. The extra winding adds to the
transformer’s physical size and cost. Dynamic response
V
+ V F + (I SEC )(ESR)
N SP
α FLBK = or,
) ) ) )
V FLBK = V BG
is often mediocre. There is usually no method for main-
taining load regulation versus load.
The LT1424-9 derives its information about the isolated
output voltage by examining the primary side flyback
pulse waveform. In this manner no optoisolator nor extra
transformer winding is required. This IC is a quantum
improvement over previous approaches because: target
output voltage is directly resistor programmable, regula-
tion is maintained well into discontinuous mode and
optional load compensation is available.
The Block Diagram shows an overall view of the system.
Many of the blocks are similar to those found in tradi-
tional designs including: internal bias regulator, oscilla-
tor, logic, current amplifier and comparator, driver and
output switch. The novel sections include a special
flyback error amplifier and a load compensation mecha-
nism. Also, due to the special dynamic requirements of
flyback control, the logic system contains additional
functionality not found in conventional designs.
The R REF , R RFB and R OCOMP resistors in the Block Diagram
are application-specific thin-film resistors internal to the
LT1424-9. The capacitor connected to the R CCOMP pin is
external.
The LT1424-9 operates much the same as traditional
current mode switchers, the major difference being a
different type of error amplifier which derives its feedback
V F = D1 forward voltage
I SEC = Transformer secondary current
ESR = Total impedance of secondary circuit
N SP = Transformer effective secondary-to-primary
turns ratio
The flyback voltage is then converted to a current by the
action of R FB and Q1. Nearly all of this current flows
through resistor R REF to form a ground-referred voltage.
This is then compared to the internal bandgap reference by
the differential transistor pair Q2/Q3. The collector current
from Q2 is mirrored around and subtracted from fixed
current source I FXD at the V C pin. An external capacitor
integrates this net current to provide the control voltage to
set the current mode trip point.
The relatively high gain in the overall loop will then cause
the voltage at the R REF resistor to be nearly equal to the
bandgap reference V BG . The relationship between V FLBK
and V BG may then be expressed as:
V V BG
R FB R REF
R FB 1
R REF α
α = Ratio of Q1 I C to I E
V BG = Internal bandgap reference
sn14249 14249fs
8
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| LT1424CS8-5#PBF | 功能描述:IC REG FLYBACK ISOLATED 5V 8SOIC 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:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
| LT1424CS8-5#TR | 功能描述:IC REG FLYBACK ISOLATED 5V 8SOIC RoHS:否 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 |
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