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| 型号： | LT1424CN8-9#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/16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
) )
I IN =
V OUT
(V IN )(Eff) OUT
) )
DC OFF
) )
V OUT
) )
R OUT = ESR
)
)
? V OUT = K1( ? I OUT )
R OCOMP
) ) ) )
? V RCCOMP R FB
? I SW
R OCOMP
) ) ) )
? V RCCOMP R FB
? I SW
R OUT
time.Certainparametersofflybackampbehaviorwillthen
be directly affected by the variable enable period. These
include effective transconductance and V C node slew rate.
LOAD COMPENSATION THEORY
The LT1424-9 uses the flyback pulse to obtain information
about the isolated output voltage. A potential error source
is caused by transformer secondary current flow through
the real life nonzero impedances of the output rectifier,
transformer secondary and output capacitor. This has
been represented previously by the expression (I SEC )(ESR).
However, it is generally more useful to convert this expres-
sion to an effective output impedance. Because the sec-
ondary current only flows during the off portion of the duty
cycle, the effective output impedance equals the lumped
secondary impedance times the inverse of the OFF duty
cycle. That is,
1
R OUT = ESR where,
R OUT = Effective supply output impedance
ESR = Lumped secondary impedance
DC OFF = OFF duty cycle
Expressing this in terms of the ON duty cycle, remember-
ing DC OFF = 1 – DC,
1
1 – DC
DC = ON duty cycle
In less critical applications, or if output load current
remains relatively constant, this output impedance error
may be judged acceptable and the external R FB resistor
value adjusted to compensate for nominal expected error.
In more demanding applications, output impedance error
may be minimized by the use of the load compensation
function.
To implement the load compensation function, a voltage is
developed that is proportional to average output switch
current. This voltage is then impressed across the external
R OCOMP resistor and the resulting current is then sub-
tracted from the R FB node. As output loading increases,
average switch current increases to maintain rough output
voltage regulation. This causes an increase in R OCOMP
resistor current subtracted from the R FB node, through
which feedback loop action causes a corresponding
increase in target output voltage.
Assuming a relatively fixed power supply efficiency, Eff
Power Out = (Eff)(Power In)
(V OUT )(I OUT ) = (Eff)(V IN )(I IN )
Average primary side current may be expressed in terms
of output current as follows:
I
combining the efficiency and voltage terms in a single
variable,
I IN = K1(I OUT ) where,
K1 =
(V IN )(Eff)
Switch current is converted to voltage by a sense resistor
and amplified by the current sense amplifier with associ-
ated gain G. This voltage is then impressed across the
external R OCOMP resistor to form a current that is
subtracted from the R FB node. So the effective change in
V OUT target is:
(R SENSE )(G)
R FB
Expressing the product of R SENSE and G as the data sheet
value of ? V RCCOMP / ? I SW ,
R OUT = K1 and,
R OCOMP = K1 where,
K1 = Dimensionless variable related to V IN , V OUT and
efficiency as above
sn14249 14249fs
10
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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 |
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