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参数资料
| 型号： | 750108 |
| 厂商： | Wurth Electronics Inc |
| 文件页数： | 8/30页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL FOR LT3748 |
| 设计资源： | LT3748 Design Schematic/Tips |
| 标准包装： | 1 |
| 主要目的： | DC/DC，步降 |
| 输出及类型： | 1，隔离 |
| 功率 - 输出： | 30W |
| 输出电压： | 12V |
| 电流 - 输出： | 2.5A |
| 输入电压： | 22 ~ 75 V |
| 稳压器拓扑结构： | 回扫 |
| 板类型： | 完全填充 |
| 已供物品： | 板 |
| 已用 IC / 零件： | LT3748 |
| 相关产品： | LT3748HMS#TRPBF-ND - IC REG CTRLR FLYBK ISO CM 16MSOP LT3748HMS#PBF-ND - IC REG CTRLR FLYBK ISO CM 16MSOP LT3748IMS#TRPBF-ND - IC REG CTRLR FLYBK ISO CM 16MSOP LT3748IMS#PBF-ND - IC REG CTRLR FLYBK ISO CM 16MSOP LT3748EMS#TRPBF-ND - IC REG CTRLR FLYBK ISO CM 16MSOP LT3748EMS#PBF-ND - IC REG CTRLR FLYBK ISO CM 16MSOP |
| 其它名称： | 732-3308 |
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LT3748
OPERATION
The LT3748 is a current mode switching regulator con-
troller designed specifically for the isolated flyback topol-
ogy. The special problem normally encountered 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 opto-
isolators or extra transformer windings. Opto-isolator
circuits waste output power and the extra components
increase the cost and physical size of the power supply.
Opto-isolators can also exhibit trouble due to limited
dynamic response, nonlinearity, unit-to-unit variation
and aging over life. Circuits employing extra transformer
windings also exhibit deficiencies. Using an extra wind-
ing adds to the transformer’s physical size and cost, and
dynamic response is often mediocre.
The LT3748 derives its information about the isolated
output voltage by examining the primary-side flyback
pulse waveform. In this manner, no opto-isolator nor
extra transformer winding is required for regulation. The
output voltage is easily programmed with two resistors.
The LT3748 features a boundary mode control method,
(also called critical conduction mode) where the part
operates at the boundary between continuous conduc-
tion mode and discontinuous conduction mode. Due to
the boundary control mode operation, the output voltage
can be calculated from the transformer primary voltage
when the secondary current is almost zero. This method
improves load regulation without external resistors and
capacitors.
The Block Diagram shows an overall view of the system.
Boundary Mode Operation
Boundary mode is a variable frequency, current mode
switching scheme. The external N-channel MOSFET turns
on and the inductor current increases until it reaches the V C
pin-controlled current limit. After the external MOSFET is
turned off, the voltage on the drain of the MOSFET rises to
the output voltage multiplied by the primary-to-secondary
transformer turns ratio plus the input voltage. When the
secondary current through the output diode falls to zero,
the voltage on the drain of the MOSFET falls below V IN . A
boundary mode detection comparator detects this event
and turns the external MOSFET back on.
Boundary mode returns the secondary current to zero
every cycle, so the parasitic resistive voltage drops do not
cause load regulation errors. Boundary mode also allows
the use of a smaller transformer compared to continu-
ous conduction mode and does not exhibit subharmonic
oscillation.
At low output currents the LT3748 delays turning on the
external MOSFET and thus operates in discontinuous mode.
Unlike traditional flyback converters, the external MOSFET
has to turn on to update the output voltage information.
Below 0.6V on the V C pin, the current comparator level
decreases to its minimum value and a variable delay timer
waits to reset before turning on the external MOSFET. With
the addition of delay before turning the MOSFET back
on, the part starts to operate in discontinuous mode. The
average output current is able to decrease while still allow-
ing a minimum off-time for the error amplifier sampling
circuitry. The typical maximum discontinuous off-time
with V C equal to 0V is 24μs.
Many of the blocks are similar to those found in traditional
switching regulators, including current comparators, inter-
nal reference and regulators, logic, timers and an N-channel
MOSFET gate driver. The novel sections include a special
sampling error amplifier and a temperature compensation
circuit.
3748fa
8
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| 750-109 | 功能描述:安装硬件 CIRC-O-GIDE .75in Nylon Black 94V-0 RoHS:否 制造商:Harwin 类型:SMT Cable Clip 材料:Phosphor Bronze 安装孔大小: 长度:5 mm 外径: 内径: 厚度: 电镀:Tin 螺纹大小: |
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| 75010-BK002 | 制造商:Alpha Wire 功能描述: |
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