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| 型号： | 88EM8081XX-SAG2C000-T |
| 厂商： | MARVELL SEMICONDUCTOR INC |
| 元件分类： | 稳压器 |
| 英文描述： | 2 A POWER FACTOR CONTROLLER, 120 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封装： | GREEN, SOIC-8 |
| 文件页数： | 15/64页 |
| 文件大小： | 667K |
| 代理商： | 88EM8081XX-SAG2C000-T |
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88EM8080/88EM8081
Datasheet
Doc. No. MV-S106340-01 Rev. B
Copyright 2010 Marvell
Page 22
Document Classification: Proprietary
August 6, 2010, Preliminary Information
3.6.2
FB – Regulation
3.6.2.1
Output Current Regulation - Isolated Output
The general application for 88EM8080/88EM8081 is for LED current control. The LED current is
passed through a series sense resistor and the voltage across that resistor is proportional to the
LED current. This sense resistor needs to be very small to limit the power dissipation in the resistor.
The sensed voltage is then amplified to have 2.5V at the full load current. It is applied to the TL431
type of device where the error voltage between the amplified voltage and TL431 device reference
(2.5V) is amplified. An optocoupler can be used to pass the error information to the feedback pin FB
on the primary side. In addition the primary current is sensed and the average current is adjusted to
be sinusoidal (in phase with AC input Voltage). The amplitude of the primary current is adjusted to
make the secondary LED current constant at the desired level. Because this is a single stage PFC
there will be second harmonic ripple at the output. Output capacitors are added to reduce the output
second harmonic ripple and also the high frequency switching ripple. The proportional and integral
compensation within the IC make the system stable. The over voltage protection at the output can
be achieved by clamping the output of TL431.
It is well known that CTR of an optocoupler varies with temperature and there is a CTR variation
among different units of the same optocoupler. An NTC circuit can be designed to help reduce the
effect of variation of CTR. The entire circuit design of the NTC circuit is provided in Section 5.3.5.
It is important to note that the IC has internal compensation for the loop stability.
3.6.2.2
Output Current Regulation - Non-isolated Output
The application is similar to the isolated example (Section 3.6.2.1) except there is no optocoupler.
The LED current is passed through a series sense resistor and the voltage across that resistor is
proportional to the LED current. This sense resistor needs to be very small to limit the power
dissipation in the resistor. The sensed voltage is then amplified to be 2.5V at the full load current. To
reduce the number of components the amplifier can be eliminated. In this case, a higher valued
sense resister should be used to get the sense voltage equal to 2.5V at full load. It is to be noted that
this will reduce the over all efficiency of the LED driver.
To have over voltage protection, the output voltage also can be sensed and diode or'ed to the output
of the current sensing circuit. Initially voltage loop takes over because the LED load needs a
minimum voltage to turn on. The voltage from the current sensing side is designed to be higher than
the voltage from voltage sensing diode during normal operation. Also the voltage sensing helps to
limit the output voltage, if one of the LEDs becomes open for any reason. The proportional and
integral compensation within the IC make the system stable.
3.6.2.3
Output Voltage Regulation - Isolated Output
The output voltage is sensed through a divider resistor and a TL431 type of device can be used to
amplify the error voltage from a reference voltage. An optocoupler can be used to pass the error
information to the feedback pin FB on the primary side for isolating the output. In addition, the
primary current is sensed and the average current is adjusted to be sinusoidal (in phase with AC
input Voltage). The amplitude of the primary current is adjusted to make the secondary voltage
constant at the desired level. Because this is a single stage PFC there will be second harmonic
ripple at the output. Output capacitors are added to reduce the output second harmonic ripple and
also the high frequency switching ripple. The proportional and integral compensation within the IC
make the system stable. The over voltage protection at the output can be achieved by clamping the
output of TL431.
It is well known that Current Transfer Ratio (CTR) of an optocoupler varies with temperature and
there is also a CTR variation among different units of the same optocoupler. An NTC circuit can be
designed to help reduce the effect of variation of CTR.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| 88EM8082A1-SAG2C000 | 制造商:Marvell 功能描述:?ACTIVE PFC CONTROLLER FOR AC-DC FLYBACK LED APPLICATIONS - Bulk 制造商:Marvell 功能描述:88EM8082 Series - Single-Stage 120 kHz Fly-back AC/DC LED Driver - SOIC-8 |
| 88EM8182B0-SAE2C000-AL00 | 制造商:Marvell 功能描述:?NON-DIMMABLE, TRIAC AC/DC LED DRIVER, 110V/220V, LOW VOLTAG - Trays |
| 88EM8182B0-SAE2C000TAL00 | 制造商:Marvell 功能描述:?NON-DIMMABLE; TRIAC AC/DC LED DRIVER; 110V/220V; LOW VOLTAG - Tape and Reel 制造商:Marvell 功能描述:88EM8182 Series - Fly-back Non-Dimmable LED Driver 110V/220V - 8-Pin SOIC |
| 88EM8183B0-SAE2C000-AL00 | 制造商:MARVELL 功能描述:0 |
| 88EM8183B0-SAE2C000TAL00 | 制造商:Marvell 功能描述:?DIMMABLE; TRIAC AC/DC LED DRIVER; 110V/220V; LOW VOLTAGE + - Tape and Reel 制造商:Marvell 功能描述:Marvell 88EM8183 Series 19V Universal Triac Dimmable LED Driver - SOIC-8 |
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