UTCUC3843A中文资料

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UC3843AN中文资料

OSCILLATOR SECTION Frequency
TJ = 25°C TA = Tlow to Thigh Frequency Change with Voltage (VCC = 12 V to 25 V) Frequency Change with Temperature TA = Tlow to Thigh
Vref Undervoltage
Lockout
Oscillator
+ − Error Amplifier
Latching PWM
GND 5(9) Pin numbers in parenthesis are for the D suffix SOIC−14 package.
VC
7(11) Output
These devices are available in an 8−pin dual−in−line plastic package as well as the 14−pin plastic surface mount (SOIC−14). The SOIC−14 package has separate power and ground pins for the totem pole output stage.
Operating Junction Temperature
Operating Ambient Temperature UC3842A, UC3843A UC2842A, UC2843A
Vin
− 0.3 to + 5.5 V
IO
10
mA
PD RqJA
PD RqJA
TJ TA
862 145
1.25 100 + 150

uc3843中文资料 (2)

UC3843中文资料简介UC3843是一种高性能固定频率电流模式PWM控制器。

它是专为开关电源和DC-DC转换器设计的，可提供快速且精确的响应。

UC3843在广泛的电源和应用中得到了广泛的应用，具有可靠性高、性能优越等特点。

本文档将详细介绍UC3843的特性、应用领域、电路原理和参数规格等相关信息。

特性1.工作电压范围：8V - 35V2.最大输出频率：500kHz3.可调或固定输出电压4.可调或固定输出电流5.内部电流检测和保护功能6.过温度保护7.低功耗待机模式应用领域UC3843广泛应用于以下领域：1.开关电源2.DC-DC转换器3.逆变器4.电池充电器5.照明系统6.电动机驱动器电路原理UC3843采用了固定频率PWM控制方式，通过周期性的开关MOSFET来控制电源输出。

其基本电路原理如下：UC3843基本电路原理图•Vin为输入电源电压，通常为DC电压•Vref为参考电压，可以通过外部电路调整来控制输出电压或电流•COMP为比较器输入引脚，用于比较反馈信号和参考电压的大小•PWM为PWM信号输出引脚，用于控制开关MOSFET的开关状态•Feedback为反馈信号输入引脚，用于监测输出电压或电流UC3843通过不断比较反馈信号和参考电压的大小，动态调整PWM信号的占空比，以达到稳定输出的目的。

同时，UC3843还具有内部电流检测和保护功能，可以保护电源和负载免受过电流的影响。

参数规格UC3843的主要参数规格如下：参数典型值工作电压范围8V - 35V输出频率范围100kHz - 500kHz输出电压范围0V - 30V输出电流范围0A - 3A参考电压 2.5V最大工作温度125°C待机模式静态功耗（最大）5mA使用注意事项在使用UC3843时，应注意以下事项：1.请严格按照UC3843的电气参数和工作条件进行设计和使用，避免超过其额定数值范围。

2.请注意电路的散热和绝缘设计，确保电路稳定、安全。

uc3843中文资料 (4)

UC3843中文资料1. 简介UC3843是一款集成了PWM控制电路的高性能电源管理芯片。

它能够通过自身的内部反馈环路来实现稳定的输出电压，并且可调节输出电压范围。

这使得UC3843非常适用于开关电源和DC-DC转换应用中。

UC3843具有低启动电流、内部锁死和内部软启动功能，能够有效地降低功耗和延长系统寿命。

此外，它还具有短路保护、过温保护和欠压保护功能，确保了系统的安全性和可靠性。

2. 特点•集成了PWM控制电路，适用于开关电源和DC-DC转换应用。

•可调节的输出电压范围，能够满足不同应用的需求。

•低启动电流，节省功耗，提高系统效率。

•内部锁死和软启动功能，保护系统并延长使用寿命。

•短路保护、过温保护和欠压保护功能，确保系统安全可靠。

3. 参数规格以下是UC3843的主要参数规格：•输入电压范围：5V至25V•输出电压范围：0V至24V•最大输出电流：1A•工作频率：50kHz至500kHz•工作温度范围：-40°C至125°C•封装：DIP-8、SOP-84. 应用示例UC3843广泛应用于各种开关电源和DC-DC转换器设计中。

以下是一些应用示例：4.1 5V至12V降压转换器UC3843可以用于设计一个从5V输入降压到12V输出的DC-DC转换器。

通过调节内部反馈环路，可以使输出电压保持稳定在12V。

此外，UC3843的低启动电流和软启动功能确保了系统的正常启动和运行。

4.2 24V恒流LED驱动器UC3843还可以用于设计一个24V恒流LED驱动器。

通过控制PWM信号的占空比，可以调节LED的亮度，并通过反馈电路实现恒流驱动。

短路保护和过温保护功能能够保护LED和驱动器的安全性。

4.3 太阳能充电控制器由于UC3843具有广泛的输入电压范围和可调节的输出电压范围，因此非常适合用于设计太阳能充电控制器。

通过控制PWM信号，可以实现对充电电流的精确控制，并通过反馈电路实现恒压和恒流充电。

电源控制芯片UC3843介绍

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应用原理1
Adobe Acrobat 7.0 Documentຫໍສະໝຸດ 图 3.4 DC公司交流电源
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应用原理2
Microsoft Word 文档
图 3.5 直流电源
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谢谢！
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应用介绍5
隔离输出应用
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UC3843和UC3844对比
1、工作电压： UC3842和UC3844低压锁定门限：16V通，10断； UC3843和UC3845工作电压更低： 8.5V通，7.6断。 2、最大占空比： UC3842和UC3843最大占空比：96％； UC3844和UC3845最大占空比：50％。
电源控制芯片UC3843介绍
黄子轩 2009-6-26
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UC3843
UC384X是高性能电流模式控制器，专为离线式和DC-DC电源变换器应用而设计。
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内部框图
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管脚功能介绍
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应用介绍1
外部时钟同步
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应用介绍2
外部时钟同步
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应用介绍3
增加RC滤波器消除尖脉冲引起的不稳定
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应用介绍4
串联栅极电阻，防止栅源引线电感引起的寄生振荡

UC3843D中文资料

Description
The UC3842/UC3843/UC3844/UC3845 are fixed frequencycurrent-mode PWM controller. They are specially designed for Off-Line and DC to DC converter applications with minimum external components. These integrated circuits feature a trimmed oscillator for precise duty cycle control, a temperature compensated reference, high gain error amplifier, current sensing comparator and a high current totempole output for driving a Power MOSFET. The UC3842 and UC3844 have UVLO thresholds of 16V (on) and 10V (off). The UC3843 and UC3845 are 8.5V(on) and 7.9V (off). The UC3842 and UC3843 can operate within 100% duty cycle. The UC3844 and UC3845 can operate with 50% duty cycle.
8
VREF
COMP 1
14 VREF
VFB 2
7
VCC
N/C
2
13
N/C
CURRENT SENSE

UC3843开关电源

使用UC3843 组成小功率开关电源(图)开关电源具有工频变压器所不具备的优点，新型、高效、节能的开关电源代表着稳压电源的发展方向，因为开关电源内部工作于高频率状态，本身的功耗很低，电源效率就可做得较高，一般均可做到80%，甚至接近90%。

这样高的效率不是普通工频变压器稳压电源所能比拟的。

开关电源常用的单端或双端输出脉宽调制（PWM），省去了笨重的工频变压器，可制成几瓦至几千瓦的电源。

用于脉宽调制的集成电路很多，我们现在介绍的是UC38 43集成电路的一般特性及由它组成小功率开关电源的方法。

UC3843更详细的资料可参见其数据手册。

(UC3842_UC3843_UC3844_UC3845参考资料)[1].UC3843的主要特性UC3842-UC3845的外形图UC3843是近年来问世的新型脉宽调制集成电路，它具有功能全，工作频率高，引脚少外围元件简单等特点，它的电压调整率可达0.01%V，非常接近线性稳压电源的调整率。

工作频率可达500kHz，启动电流仅需1mA，所以它的启动电路非常简单。

下面是它的主要特性：最优化的离线DC-DC变换器低静态电流(1mA)快速自动补偿电路单步脉冲控制电路增强负载回馈特性断电停滞特性双脉冲抑制大电流标识输出内置能隙参考电压500kHz的工作频率低Ro过零放大器[2].UC3843的工作原理UC3843有4种封装形式，一种是14pin双列直插和SOP-14，另一种是8pin双列直插和SOP-8。

我们以最简的8pin封装简述其工作原理。

[IMG]20072289575883293.gif[/IM G] pin(1)是补偿端，外接电阻电容元件以补偿误差放大器的频率特性。

第(2)脚是反馈端，将取样电压加至误差放大器的反相输入端，再与同相输入端的基准电压进行比较，输出误差控制电压。

第(3)脚接过流检测电阻,组成过流保护电路。

RT/RC为锯齿波振荡器的定时电阻和电容的公共端，内部基准电压为VREF=5V。

UC3843中文资料

UC3843牢固频次电流模式统制器之阳早格格创做型号：UC3843A启拆：DIP8主要应用：开关电源UC3842 、UC3843 是下本能牢固频次电流模式统制器博为离线战曲流至曲流变更器应用而安排，为安排人员提供只需最少中部元件便能赢得成本效率下的办理规划.那些集成电路具备可微调的振荡器、能举止透彻的占空比统制、温度补偿的参照、下删益缺面搁大器.电流与样比较器战大电流图腾柱式输出，是启动功率MOSFET的理念器件.其余的呵护个性包罗输进战参照短压锁定，各有滞后、逐周电流节制、可编程输出静区时间战单个脉冲丈量锁存.UC3842A 有16V（通）战10 伏（断）矮压锁定门限，格中符合于离线变更器.UC3843A是博为矮压应用安排的，矮压锁定门限为8.5伏（通）战7.6V（断）.个性:微调的振荡器搁电电流，可透彻统制占空比.电流模式处事到500KHZ自动前馈补偿锁存脉宽调制，可逐周限流里里微调的参照电压，戴短压锁定大电流图腾柱输出短压锁定，戴滞后矮开用战处事电流曲交与安森好半导体的SENSEFET产品交心引足图下图是一个隐现器的UC3842应用电路图UC3842佳坏的推断鉴别要领正在海内电子设备核心，电源PWM统制电路最时常使用的集成电路型号便是UC3842（或者KA3842）.也便是果为时常逢到，对于它也有一些之得，底下简朴介绍一下UC3842佳坏的推断要领：正在调换完周边益坏的元件后，先不拆开关管(MOSFET)，加电丈量UC3842的7足电压，若电压正在1017V间动摇，其余各足也分别有动摇的电压，则证明电路已起振，UC3842基础平常;若７足电压矮，其余交足无电压或者不动摇，则UC3842已益坏. 正在UC3842的7、5足间中加+17V安排的曲流电压，若测8足有+5V电压，1、2、4、6足也有分歧的电压，则UC3842基础平常，处事电流小，自己阻挡易益坏．它益坏的最罕睹本果是电源开关管(MOSFET)短路后，下电压从G极加到其6足而以致其废弃．而有些机型中省来了G极交天的呵护二极体，则电源开关管(MOSFET)益坏时，UC3842战G极中交的限流电阻必坏．此时曲交调换即可. 需要注意的是，电源开关管源极（S极）常常交１个小阻值、大功率的电阻动做过流呵护检测电阻．此电阻的阻值普遍正在0.20.6之间，大于此值会出现戴不起背载的局里（便是次极电压偏偏矮）. 由于UC3842（KA3842）的处事电压战输出功率均与UC3843（KA3843）出进甚近， 3842系列战3843系列正在开用电压战关关电压圆里也存留着较大的辨别.前者的开用电压为16V，关关电压为10V;后者的开用电压为8.5V，关关电压为7.6V.那二个系列的IC不克不迭曲交代换.如确有需要用后者代换前者时，要对于电路加以变革圆可.果此，那一面正在维建处事中必须要注意。

[VIP专享]uc3843与tl3843中文

TL 3843中文▓優化用於離線和直流到直流轉換器▓低啟動電流（<1 mA ）的▓自動前饋補償▓脈衝通過脈衝電流限制▓增強的負載響應特性▓滯後欠壓閉鎖▓雙脈衝抑制▓大電流圖騰柱輸出▓內部微調帶隙基準▓500-kHz 的工作頻率▓誤差放大器，具有低輸出阻力▓設計為可與UC2842和UC3842系列描述/訂購信息所述TL284x 和TL384x 一系列控制集成電路提供所必需的執行離線或直流到直流固定頻率電流模式控制方案，與外部元件的最小數量的功能。

一些內部實現電路是一個欠壓鎖定（UVLO ），具有小於1 mA 的啟動電流，以及精密基準的誤差放大器的輸入修剪的準確性。

其他的內部電路包括邏輯，以確保鎖存操作中，一個脈衝寬度調製（PWM ）比較器（也提供限流控制），和一個推拉輸出級設計成源或匯的高的峰值電流。

輸出級，適用於驅動N 溝道MOSFET ，為低時，它處於關閉狀態。

這些系列的成員之間的主要區別是UVLO 門限和最大佔空比範圍。

16 V （on ）和10 V （關閉）的TLx842和TLx844器件的典型UVLO 門限使它們非常適用於離線應用。

為TLx843和TLx845設備相應典型閾值是8.4伏（上）和7.6 V （關閉）。

該TLx842和TLx843設備可運行在佔空比接近100％。

由TLx844和TLx845獲得通過加入內部雙穩觸發器，它將消隱輸出關閉所有其他時鐘週期的0至50％的佔空週期的範圍。

在工作自由空氣的溫度範圍內絕對最大額定值（除非另有說明）電源電壓（見注1）（ICC<30 mA ）的自我限制模擬輸入電壓範圍，VI （VFB 和ISENSE ）-0.3 V 至6.3 V 輸出電壓，VO （OUTPUT ）35 V 輸入電壓，VI ，（VC ，D 包只）35 V 電源電流，ICC30毫安輸出電流，IO±1誤差放大器的輸出灌10 mA 電流封裝的熱阻抗，θJA （見注2和3）：D 包86°C / WD-8封裝97°C / W P 封裝85°C/ W虛擬結溫TJ150℃輸出能量（電容性負載）5μJ鉛的溫度，1,6毫米（1/16英寸）的情況下，10秒260℃存儲溫度範圍，TSTG-65°C 至150℃超出“絕對最大額定值”列出的壓力可能會造成永久性損壞設備。

UTCUC3842A中文资料

UTCUC3842A中⽂资料UTC UC3842A / 3843A LINEAR INTEGRATED CIRCUITUTC UNISONIC TECHNOLOGIES CO., LTD.1QW-R103-002,ACURRENT MODE PWM CONTROL CIRCUITSDESCRIPTIONThe UTC UC3842A/3843A provide the necessary functions to implement off-line or DC to DC fixed frequency current mode , controlled switching circuits with a minimal external part countFEATURES*Low external part count. *Low start up current ( Typical 0.12mA ) *Automatic feed forward compensation *Pulse-by-Pulse current limiting*Under-voltage lockout with hysteresis *Double pulse Suppression*High current totem pole output to drive MOSFET directly *Internally trimmed band gap reference *500kHz operation BLOCK DIAGRAMVref VFB COMPRT/CT VccOUTPUTVccABSOLUTE MAXIMUM RATINGS (Ta=25°C)PARAMETER SYMBOL VALUE UNITSupply Voltage(Low Impedance Source) V CC 30 VSupply Voltage(Icc<30mA) Vcc Self Limiting V Output Current ( Peak ) Io +-1 AOutput Energy(capacity Load) 5µJ Analog Inputs(pin 2,3) V I(ANA) -0.3 ~ +6.3 V Error Amplifier Output Sink Current I SINK(EA) 10 mAPower Dissipation PD DIP-8 at T amb <=25°C 1.0 W SOP-8 at T amb <=25°C 0.5 WLead Temperature( Soldering 10 Sec ) Tlead 300 °CUTC UC3842A / 3843A LINEAR INTEGRATED CIRCUITUTC UNISONIC TECHNOLOGIES CO., LTD.2QW-R103-002,A(continued)PARAMETRER SYMBOL VALUE UNITStorage Temperature Tstg -65 ~ +150°C Note 1: Ta>25°C, P D derated with 8mW/°C.ELECTRICAL CHARACTERISTICS (0°C <=Ta<=70°C,V CC =15V,R T =10k ?,C T =3.3nF,unless otherwise specified) PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNITReference SectionOutput Voltage V REF Tj=25°C,Io=1mA 4.9 5 5.1 V Line Regulation ?V REF 12<=V IN <=25V 6 20 mV Load Regulation ?V REF1<=Io =20mA 6 25 mV Temperature Stability (Note 2) 0.2 0.4 mV/°CTotal Output Variation Line, Load, Temp(note 2) 4.82 5.18 V Output Noise Voltage Vosc 10Hz<=f<=10kHz,Tj=25°C (note 2) 50 uVLong Term Stability Ta=25°C,1000Hrs(note 2) 5 25 mV Output Short Circuit I SC -30-100 -180 mAOscillator Section Initial Accuracy f Tj=25°C 47 52 57 kHz Voltage Stability ?f/?Vcc 12<=Vcc<=25V 0.2 1 % Temperature Stability Tmin<=T A <=Tmax(note 2) 5 % Amplitude Vosc Vpin 4 peak to peak 1.7 VError Amplifier SectionInput Voltage V I(EA) Vpin 1=2.5V 2.42 2.50 2.58 V Input Bias Current I BIAS -0.3 -2 µA A VOL 2 <=Vo<=4V 60 90 dB Unity Gain Bandwidth Tj=25°C (note 2) 0.7 1 MHz PSRR I2<=Vcc<=25V 60 70 dB Output Sink Current Isink Vpin 2=2.7V,Vpin 1=1.1V 2 6 mA Output Source Current Isource Vpin 2=2.3V,Vpin 1=5V -0.5-0.8 mA Vout High V OH Vpin 2=2.3V, RL=15k ? to GND 5 6 V Vout Low V OL Vpin 2=2.7V,Vpin 1=1.1V 0.7 1.1 VCurrent Sense sectionGain G V (note 3,4) 2.85 3 3.15 V/V Maximum Input signal V I(MAX)Vpin 1=5V( note 3) 0.9 1 1.1 V PSRR 12<=Vcc<=25V 70 dB Input Bias Current I BIAS -2 -10 µA Delay to Output Vpin 3=0 to 2V 150 300 nsOutput SectionOutput Low Level V OL Isink =20mA 0.1 0.4 VIsink =200mA 1.5 2.2 V Output High Level V OH Isource =20mA 13 13.5 V Isource =200mA 12 13.5 VRise Time t R Tj=25°C,C L =1nF(note 2)50 150 ns Fall Time t F Tj=25°C,C L =1nF(note 2)50 150 ns Under-Voltage Lockout Output SectionStart Threshold V TH(ST)UTC3842A 14.516 17.5 V UTC3843A 7.88.4 9 V Min. Operating Voltage V OPR(min)After Turn On UTC3842A8.510 11.5UTC3843A 7 7.6 8.2 VPWM SectionMaximum Duty Cycle D (MAX) 95 97 100 %UTC UC3842A / 3843A LINEAR INTEGRATED CIRCUITUTC UNISONIC TECHNOLOGIES CO., LTD.3QW-R103-002,APARAMETER SYMBOLTEST CONDITIONS MINTYP MAX UNITMinimum Duty CycleD (MIN)0 % Total Standby CurrentStart-up Current I ST 0.12 0.3 mAOperating Supply Current I CC(opr)Vpin 2=Vpin 3=0V 11 17 mA Vcc Zener Voltage Vz Icc=25mA 34 V note 2:These parameters, although guaranteed ,are not 100% tested in production. note 3:Parameters measured at trip point of latch with Vpin 2=0. note 4:Gain defined as:Vpin 1Vpin 3A=; 0<=Vpin3<=0.8Vnote 5:Adjust Vcc above the start threshold before setting at 15V.OPEN-LOOP LABORATORY TEST FIXTUREVrefVccAdjustHigh peak current associated with capacity loads necessitate careful grounding techniques. Timing and bypass capacitors should be connected close to pin 5 in single point GND. The transistor and 5k ? potentio-meter are used to sample the oscillator waveform and apply an adjustable Ramp to Pin 3.UNDER-VOLTAGE LOCKOUTVonVoffVccDuring Under-Voltage Lockout, the output driver is biased to a high impedance state. Pin 6 should be shunt to GND with a bleeder resistor to prevent activating the power switch with output leakage currents.UTC UC3842A / 3843A LINEAR INTEGRATED CIRCUITUTC UNISONIC TECHNOLOGIES CO. LTD4QW-R103-002,AERROR AMPLIFIER CONFIGURATIONError amplifier can source or sink up to 0.5mACURRENT SENSE CIRCUITPeak current (Is) determined by the formula:Ismax=10V/Rs.A small RC filter be required to suppress switch transients.SLOPE COMPENSATIONA fraction of the oscillator ramp can be resistively summed with the current sense signal to provide slope compensation for converts requiring duty cycles over 50%.Note that capacitor C, forms a filter with R2 to suppress the leading edge switch spikes.UTC UC3842A / 3843A LINEAR INTEGRATED CIRCUITUTC UNISONIC TECHNOLOGIES CO. LTD5QW-R103-002,AOSCILLATOR SECTIONLarge RT Small CTSmall RT Large CTV4V4INTERNAL CLOCKINTERNAL CLOCKDead time VS C T (R T >5k ?) TimingResistance Vs Frequency 1101001101000.1td (µs)CT (nF)110RT (k ?Frequency (Hz)SHUTDOWN TECHNIQUESShutdown UTC UC3842A can be accomplished by two methods; either raise pin 3 above 1V or pull Pin 1 below a voltage two diode drops above ground. Either method caused the output of PWM comparator to be high(refer to block diagram).The PWM latch is reset dominant so that the output will remain low until the next clock cycle after the shutdown condition at pins 1 and/or 3 is removed . In one example, an externally latched shut –down may be accomplished by adding an SCR which be reset by cycling Vcc below the lower UVLO threshold. At this point the reference turns off allowing the SCR to reset.UTC UC3842A / 3843A LINEAR INTEGRATED CIRCUITUTC UNISONIC TECHNOLOGIES CO. LTD6QW-R103-002,ATYPICAL PERFORMANCE CHARACTERISTICS0.010.1101234S a t u r a t i o n V o l t a g e (V )Output Current(Sourse or Sink Current) (A)710310610510410102406010080Frequency (Hz)V o l t a g e G a i n (d B )-180-135-90-45P H A S E (D e g r e e )Output Saturation Characteristics Error Amplifier Open-Loop Frequency Response UTC UC3842A / 3843A LINEAR INTEGRATED CIRCUITUTC UNISONIC TECHNOLOGIES CO. LTD7QW-R103-002,A-50-25255075100125150Vref (V)Temperature (°C)-50-250255075100125150I s t a r t (m A )Temperature (°C)-50-252550751509101112131415Icc (mA) Temperature (°C) Vref Temperature Drift Istart Temperature Drift Icc Temperature Drift。

3843的芯片资料

UC3842A UC3843A 中文资料UC3842A UC3843A 是高性能固定频率电流模式控制器专为离线和直流至直流变换器应用而设计，为设计人员提供只需最少外部元件就能获得成本效益高的解决方案。

这些集成电路具有可微调的振荡器、能进行精确的占空比控制、温度补偿的参考、高增益误差放大器。

电流取样比较器和大电流图腾柱式输出，是驱动功率MOSFET的理想器件。

其它的保护特性包括输入和参考欠压锁定，各有滞后、逐周电流限制、可编程输出静区时间和单个脉冲测量锁存。

这些器件可提供8脚双列直插塑料封装和14脚塑料表面贴装封装（SO-14）。

SO-14封装的图腾柱式输出级有单独的电源和接地管脚。

UC3842A 有16V（通）和10 伏（断）低压锁定门限，十分适合于离线变换器。

UC3843A 是专为低压应用设计的，低压锁定门限为8.5伏（通）和7.6V（断）。

特点:微调的振荡器放电电流，可精确控制占空比.电流模式工作到500KHZ自动前馈补偿锁存脉宽调制，可逐周限流内部微调的参考电压，带欠压锁定大电流图腾柱输出欠压锁定，带滞后低启动和工作电流直接与安森美半导体的SENSEFET产品接口图1图2 引脚图下图是一个显示器的UC3842应用电路图图3UC3842好坏的判断鉴别方法在国内电子设备当中，电源PWM控制电路最常用的集成电路型号就是UC3842（或KA3842）。

也就是因为常常遇到，对它也有一些之得，下面简单介绍一下UC3842好坏的判断方法：在更换完周边损坏的元件后，先不装开关管(MOSFET)，加电测量UC3842的7脚电压，若电压在10-17V间波动，其余各脚也分别有波动的电压，则说明电路已起振，UC3842基本正常;若７脚电压低，其余接脚无电压或不波动，则UC3842已损坏。

在UC3842的7、5脚间外加+17V左右的直流电压，若测8脚有+5V电压，1、2、4、6脚也有不同的电压，则UC3842基本正常，工作电流小，自身不易损坏．它损坏的最常见原因是电源开关管(MOSFET)短路后，高电压从G极加到其6脚而致使其烧毁．而有些机型中省去了G极接地的保护二极体，则电源开关管(MOSFET)损坏时，UC3842和G 极外接的限流电阻必坏．此时直接更换即可。

UC3842AD中文资料

©2000 Fairchild Semiconductor InternationalRev. 5.0Features•Low Start Current 0.2mA (typ)•Operating Range Up To 500KHz•Cycle by Cycle Current Limiting •Under V oltage Lock Out With Hysteresis •Short Shutdown Delay Time: typ.100ns •High Current Totem-pole Output •Output Swing Limiting: 22VDescriptionThe UC3842A/UC3843A are fixed PWM controller for Off-Line and DC to DC converter applications. The internal cir-cuits include UVLO, low start up current circuit, tempera-ture compensated reference, high gain error amplifier, current sensing comparator, and high current totem-pole out-put for driving a POWER MOSFET. Also UC3842A/UC3843A provide low start up current below 0.3mA and short shutdown delay time typ. 100ns. The UC3842A has UVLO threshold of 16V(on) and 10V(off). The UC3843A is 8.4V(on) and 7.6V(off). The UC3842A and UC3843A can operate within 100% duty cycle.8-DIP8-SOP11UC3842A/UC3843ASMPS ControllerUC3842A/UC3843AAbsolute Maximum RatingsParameter Symbol Value UnitSupply Voltage V CC30VOutput Current I O± 1AAnalog Inputs (pin 2, 3)V I(ANA)- 0.3 to 6.3VError Amp. Output Sink Current I SINK(EA)10mAPower Dissipation P D1WElectrical Characteristics(V CC = 15V, R T = 10KΩ, C T = 3.3nF, T A = 0°C to + 70°C ,Unless otherwise specified)Parameter Symbol Conditions Min.Typ.Max.Unit REFERENCE SECTIONOutput Voltage V REF T J = 25°C, I O = 1mA 4.9 5.0 5.1V Line Regulation∆V REF V CC = 12V to 25V-620mV Load Regulation∆V REF I O = 1mA to 20mA-625mV Output Short Circuit I SC T a = 25°C-- 100- 180mA OSILLATOR SECTIONInitial Accuracy F OSC T J = 25°C475257KHz Voltage Stability ST V V CC = 12V to 25V-0.21% Amplitude V OSC V PIN4, Peak to Peak- 1.7-V Discharge Current I DISCHG T J = 25°C, Pin4 = 2V7.88.38.8mA CURRENT SENSE SECTIONGain G V (NOTE 2, 3) 2.853 3.15V/V Maximum Input Signal V I(MAX) V PIN1 = 5V(NOTE 2)0.9 1.0 1.1V PSRR PSRR V CC = 12V to 25V (NOTE 1, 2)-70-dB Input Bias Current I BIAS--- 2-10uA Delay to Output T D V PIN3 = 0 V to 2V (NOTE1)-100200ns2UC3842A/UC3843A3Electrical Characteristics (Continued)(V CC = 15V , R T = 10K Ω, C T = 3.3nF, T A = 0°C to + 70°C, Unless otherwise specified)* Adjust V CC above the start threshold before setting at 15V Notes :1.These parameters, although guaranteed, are not 100% tested in production.2.Parameter measured at trip point of latch with V2 = 0V.3.Gain defined as: G V = ∆V PIN1∆V PIN3(V PIN3 = 0 to 0.8V)ParameterSymbolConditionsMin.Typ.Max.UnitERROR AMPLIFIER SECTION Input Voltage V I T PIN1 = 2.5V2.42 2.50 2.58V Input Bias Current I BIAS ---0.3- 2uA Open Loop Gain G VO V O = 2V to 4V (NOTE 1)6590-dB Unity Gain Bandwidth GBW T J = 25°C (NOTE 1)0.71-MHz PSRRPSRR V CC = 12V to 25V (NOTE 1)6070-dB Output Sink Current I SINK V PIN2 = 2.7V V PIN1 = 1.1V 26-mA Output Source Current I SOURCE V PIN2 = 2.3V V PIN1 = 5.0V -0.5-0.8-mA Output High Voltage V OH V PIN2 = 2.3VR1 = 15K Ω to GND 56-V Output Low Voltage V OLV PIN2 = 2.7VR1 = 15K Ω to Pin8-0.81.1VOUTPUT SECTION Output Low Level V OL I SINK = 20mA -0.10.4V I SINK = 200mA - 1.5 2.2V Output High Level V OH I SOURCE = 20mA 1313.5-V I SOURCE = 200mA1213.5-V Rise Time t R T J = 25°C , C1 = 1nF (NOTE 1)-40100ns Fall Timet F T J = 25°C , C1 = 1nF (NOTE 1)-40100ns Output Voltage Swing LimitV OLIMV CC = 27V, C1 = 1nF -22-V UNDER VOLTAGE LOCKOUT SECTION Start Threshold V TH UC3842A 151617V UC3843A 7.88.49.0V Min. Operating Voltage ( After turn on )V TLUC3842A 91011V UC3843A7.07.68.2V PWM SECTION Maximum Duty Cycle D MAX UC3842A/UC3843A9496100%Minimum Duty CycleD MIN ---0%TOTAL STANDBY CURRENT Start-Up CurrentI ST --0.20.4mA Operating Supply Current I CC V PIN2 = V PIN3 = 0V -1117mA V CC Zener VoltageV Z I CC = 25mA-29-VUC3842A/UC3843AMechanical DimensionsPackage8-DIP4UC3842A/UC3843A Mechanical Dimensions (Continued)Package8-SOP5UC3842A/UC3843A6Ordering InformationProduct Number Package Operating TemperatureUC3842AN 8 DIP 0 ~ + 70°CUC3842AD 8 SOP UC3843AN 8 DIP UC3843AD8 SOPUC3842A/UC3843A7UC3842A/UC3843A7/12/00 0.0m 001Stock#DSxxxxxxxx” 2000 Fairchild Semiconductor InternationalLIFE SUPPORT POLICYFAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR INTERNATIONAL. As used herein:1.Life support devices or systems are devices or systemswhich, (a) are intended for surgical implant into the body, or (b) support or sustain life, and (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can bereasonably expected to result in a significant injury of the user.2. A critical component in any component of a life supportdevice or system whose failure to perform can bereasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness.。

uc3843中文材料运用电路

uc3843中文材料运用电路UC3843A是高功用固定频率电流方法操控器专为离线和直流至直流转换器运用而计划，为计划人员供应只需起码外部元件就能取得本钱效益高的处理计划。

这些集成电路具有可微调的振动器、能进行精确的占空比操控、温度赔偿的参看、高增益过失拓宽器。

电流取样比照器和大电流图腾柱式输出，是驱动功率MOSFET的抱负器材。

其它的维护特性包含输入和参看欠压断定，各有滞后、逐周电流束缚、可编程输出静区时刻和单个脉冲丈量锁存。

这些器材可供应8脚双列直插塑料封装和14脚塑料外表贴装封装（SO-14）。

SO-14封装的图腾柱式输出级有独自的电源和接地管脚。

UC3842A有16V（通）和10伏（断）低压断定门限，非常适宜适离线转换器。

UC3843A是专为低压运用计划的，低压断定门限为8.5伏（通）和7.6V（断）。

特征:微调的振动器放电电流，可精确操控占空比.电流方法作业到500KHZ主动前馈赔偿锁存脉宽调制，可逐周限流内部微调的参看电压，带欠压断定大电流图腾柱输出欠压断定，带滞后低主张和作业电流直接与安森美半导体的SENSEFET商品接口引脚功用引脚功用阐明8管脚14管脚11赔偿该管脚为过失拓宽器输出，并可用于环路赔偿。

23电压反响该管脚是过失拓宽器的反相输入端，通常经过一个电阻分压器连至开关电源输出。

35电流取样一个正比于电感器电流的电压接至此输入，脉宽调制器运用此信息接连输出开关的导通。

47RT/CT经过将电阻RT联接至Vref以及电容CT联接至地，使振动器频率和最大输出占空比可调。

作业频率可达500kHz。

5-地该管脚是操控电路和电源的公共地（仅对8管脚封装如此）610输出该输出直接驱动功率MOSFET的栅极，高达1.OA的峰值电流经此管脚拉和灌。

712VCC该管脚是操控集成电路的正电源。

814Vref该管脚为参看输出，它经过电阻RT向电容CT供应充电电流。

8电源地该管脚是一个连回至电源的别离电源地回来端（仅14管脚封装如此），用于削减操控电路中开关瞬态噪声的影响。

UC3873 友顺UTC 电子元器件芯片

VOH
VDD=12V,IO= 20mA
tR
CL=1.0nF
tF
CL=1.0nF
0.8
V
8
V
500
ns
160
ns
UNISONIC TECHNOLOGIES CO., LTD
3 of 9
QW-R103-068.J
UC3873
LINEAR INTEGRATED CIRCUIT
ELECTRICAL CHARACTERISTICS (Cont.)
BLOCK DIAGRAM
UNISONIC TECHNOLOGIES CO., LTD
2 of 9
QW-R103-068.J
UC3873
LINEAR INTEGRATED CIRCUIT
ABSOLUTE MAXIMUM RATINGS (TA=25°C, VDD =15V, unless otherwise specified)
I
Current sense input pin. Connected to MOSFET current sensing resistor node.
P
Power supply.
O The totem-pole output driver for driving the power MOSFET.
UNISONIC TECHNOLOGIES CO., LTD
UC3873
LINEAR INTEGRATED CIRCUIT
LOW COST POWER-SAVING MODE PWM CONTROLLER FOR FLYBACK CONVERTERS
DESCRIPTION
The UC3873 is a high performance current mode PWM controller ideally suited for low standby power. Low VDD startup current make the power reliable on startup design and a large value resistor could be used in the startup circuit to minimize the standby power. At no load condition, the IC operates in power-saving mode for lower standby power, decreasing frequency for Higher conversion efficiency at light load condition.

uc3843工作原理

uc3843工作原理UC3843是一款常见的PWM控制器芯片，它常用于开关电源和LED驱动等电子设备中。

UC3843通过控制开关管的开关时间和非开关时间，实现对输出电压的稳定调节。

接下来，我将详细解释UC3843的工作原理。

UC3843的基本工作原理是基于PWM（脉宽调制）技术。

PWM技术是一种通过调整周期内的开关时间和非开关时间的方法，来控制输出电压和电流的技术。

UC3843的工作原理可以分为以下几个部分：1.参考电压生成器：UC3843内部有一个参考电压生成器，它提供一个稳定的参考电压作为比较器的参考。

这个参考电压通常为2.5V。

2.错误放大器：UC3843内部有一个比较器，它将输出电压与参考电压进行比较，并产生一个误差信号。

如果输出电压低于参考电压，那么误差信号就会为高电平，而输出电压高于参考电压时，误差信号为低电平。

3.脉宽调制逻辑：UC3843将误差信号输入给一个脉宽调制逻辑，这个逻辑会根据误差信号的高低来控制开关管的开关时间和非开关时间。

当误差信号为高电平时，开关管会被开启，使得电流能够通过电感进入负载。

当误差信号为低电平时，开关管会被关闭，使得电流无法通过电感进入负载。

4.反馈电路：UC3843通过反馈电路来测量输出电压，并将测量值与参考电压进行比较，从而产生误差信号。

这个反馈电路通常由电阻和电容组成。

通过调整反馈电路中的电阻和电容的数值，可以实现对输出电压的调节。

5.输出滤波：UC3843的输出端通常会连接一个输出滤波电路，它由电感和电容组成。

这个滤波电路可以滤除输出端的高频噪声，保证输出电压的稳定性。

6.保护电路：UC3843还内置有过电流保护和过温保护等保护电路，以保护电路和负载的安全性。

总结起来，UC3843的工作原理是通过控制开关管的开关时间和非开关时间，来实现对输出电压的稳定调节。

它通过参考电压生成器、比较器、脉宽调制逻辑、反馈电路和滤波电路等器件和电路组成，实现了精确可靠的PWM调节功能。

UC3842A UC3843A 中文资料

这些集成电路具有可微调的振荡器、能进行精确的占空比控制、温度补偿的参考、高增益误差放大器。

电流取样比较器和大电流图腾柱式输出，是驱动功率MOSFET的理想器件。

其它的保护特性包括输入和参考欠压锁定，各有滞后、逐周电流限制、可编程输出静区时间和单个脉冲测量锁存。

这些器件可提供8脚双列直插塑料封装和14脚塑料表面贴装封装（SO-14）。

SO-14封装的图腾柱式输出级有单独的电源和接地管脚。

UC3842A 有16V（通）和10 伏（断）低压锁定门限，十分适合于离线变换器。

UC3843A是专为低压应用设计的，低压锁定门限为8.5伏（通）和7.6V（断）。

特点:微调的振荡器放电电流，可精确控制占空比.电流模式工作到500KHZ自动前馈补偿锁存脉宽调制，可逐周限流内部微调的参考电压，带欠压锁定大电流图腾柱输出欠压锁定，带滞后低启动和工作电流直接与安森美半导体的SENSEFET产品接口图1图2 引脚图引脚功能引脚功能说明8管脚14管脚1 1 补偿该管脚为误差放大器输出，并可用于环路补偿。

2 3 电压反馈该管脚是误差放大器的反相输入端，通常通过一个电阻分压器连至开关电源输出。

3 5 电流取样一个正比于电感器电流的电压接至此输入，脉宽调制器使用此信息中止输出开关的导通。

4 7 RT/CT 通过将电阻RT连接至Vref以及电容CT连接至地，使振荡器频率和最大输出占空比可调。

工作频率可达500kHz 。

5 - 地该管脚是控制电路和电源的公共地（仅对8管脚封装如此）6 10 输出该输出直接驱动功率MOSFET的栅极，高达1.OA 的峰值电流经此管脚拉和灌。

7 12 VCC 该管脚是控制集成电路的正电源。

8 14 Vref 该管脚为参考输出，它通过电阻RT向电容CT 提供充电电流。

UC3853A 友顺UTC 电子元器件芯片

UNISONIC TECHNOLOGIES CO., LTDUC3853A Advance LINEAR INTEGRATED CIRCUITCURRENT MODE PWMCONTROLLER FOR FORWARDAND FLYBACK APPLICATIONS⏹DESCRIPTIONThe UTC UC3853A is a high performance current mode PWMcontroller ideally suited for low standby power. Low V DD startupcurrent make the power reliable on startup design and a largevalue resistor could be used to minimize the standby power. At noload condition, the IC operates in power-saving mode for lowerstandby power, decreasing frequency for Higher conversionefficiency at light load condition. It contains protection withautomatic recovery including OLP, OCP, V CC OVP, BNO and OTP.To protect the power MOSFET, Gate-drive output is fixed up to 15Vmax.Excellent EMI performance is achieved with UTC proprietaryfrequency hopping technique (ZL201020615247.1) together withsoft driver control. The controller offers everything needed to buildcost−effective and reliable ac−dc switching supplies dedicated toATX power supplies. Finally a SOP-8 package saves PCB spaceand represents a solution of choice in cost sensitive project.⏹FEATURES*Peak Current Mode Control*Adjustable Switching Frequency*Adjustable Soft−start Timer*Adjustable Internal Ramp Compensation*Jittering Frequency ±6% of the Switching Frequency *Power-saving mode for high standby efficiency*Auto−recovery Primary OCP with 10ms Fixed Delay *Auto−recovery Brown−Out Detection *Delayed Operation Upon Start−up via an Internal Fixed Timer*UC384X−like UVLO Thresholds*V CC from 9V to 28V with Auto−recovery UVLO*Internal 350ns Leading Edge Blanking*Gate output voltage clamped at 15V*UC3853A: Maximum 47% Duty Cycle⏹ORDERING INFORMATION⏹MARKINGL: Lead FreeG: Halogen Free Duty CycleA: 47%⏹PIN CONFIGURATION1 2 3 48 7 6 5FB BO CS RT SS V CC DRV GND⏹PIN DESCRIPTIONBLOCK DIAGRAMGNDCSBORTV CCDrv FB⏹ABSOLUTE MAXIMUM RATINGAbsolute maximum ratings are stress ratings only and functional device operation is not implied.⏹THERMAL DATA⏹ELECTRICAL DATA(V CC=15V, R T=43kΩ, C DRV=1nF. For typical values T J=25°C, for min/max values T J=–25°C~+125°C, unlessELECTRICAL CHARACTERISTICS (Cont.)2.V ramp, R ramp Guaranteed by design.APPLICATION INFORMATIONIntroductionThe UTC UC3853A hosts a high−performance current−mode controller specifically developed to drive power supplies designed for the ATX and the adapter market:Current Mode operationI mplementing peak current−mode control topology, the circuit offers UC384X−like features to build rugged power supplies.Adjustable switching frequencyA resistor to ground precisely sets the switching frequency.Internal frequency jitteringFrequency jittering softens the EMI signature by spreading out peak energy within a band ±6% from the center frequency.Wide V CC excursionThe controller allows operation up to 28V continuously and IC will be shutdown when V CC transient voltage up to 29V.Gate drive clampingThe controller includes a low−loss clamping voltage which prevents the gate from going beyond 15V typical.Low startup−currentThe start−up current is guaranteed to be less than 5μA maximum, helping the designer to reach a low standby power level.Open Loop&Over Load&Short−circuit protectionWhen V CS exceeds 0.96V , the controller detects a fault and starts an internal digital timer. On the condition that the digital timer elapses 20mS, the controller will shutdown. Reset occurs when: a) a BO reset is sensed, b) V CC is cycled down to V CC(min) level.Adjustable soft−startT he soft−start is activated upon a start−up sequence after a minimum internal time delay of 120m (SS delay). But also when the brown−out pin is reset without in that case timer delay. The so ft start pin I grounded until the internal delay is ended.Shutdownif an external transistor brings the BO pin down, the controller is shut down, but all internal biasing circuits are alive. When the pin is released, a new soft−start sequence takes place.Brown−Out protectionWhen BO pin voltage is below the V BO threshold, the circuit stays off and does not switch. When BO pin voltage comes back within safe limits, the pulses are re−started via a start−up sequence including soft−start. The hysteresis I implemented via a current source connected to the BO pin, which sinks a current (I BO) from the pin to the ground. it can easily be used for hysteresis purposes.Internal ramp compensationA resistor connected from the CS pin to the sense resistor allows the designer to inject ramp compensation inside his design.APPLICATION INFORMATION (Cont.)Burst modeIf the output loads disappear, the FB is allowed to decreases down to V FB_IN , zero duty cycle is imposed. This mode helps to ensure no−load outputs conditions as requested by recently updated ATX specifications. Bust mode easily obtains 100mW standby power. The following figure illustrates the different mode of operation versus the FBpin level.V FBOLV FB_outTimeFigure 1. Mode Of Operation Versus The FB Pin LevelV FB_INStartup SequenceThe startup sequence is activated when Vcc pin reaches V CC(on) level ，and the internal delay timer (SS delay ) runs. Only when the internal delay end ，the soft start can be allowed if the BO pin level is above V BO level. The soft start is allowed if the BO pin threshold is reached ，and the voltage on the SS pin is rising from the ground. An external capacitor connected on SS pin is used to defined SS time. The voltage variation of the SS pin divided by 4 gives the peak current variation on the CS pin.The following figures illustrate the different startup cases.VV VV V V Figure 2. Startup Sequence (A) & (B)APPLICATION INFORMATION (Cont.)For the (A), when the V CC pin reaches the V CC(on) level, the internal timer starts. As the BO pin level is above the V BO threshold at the end of the internal delay, a soft start sequence is started. For the (B), at the end of the internal delay, the BO pin level is below the V BO threshold thus the soft start sequence can not start. A new soft start sequence will start only when the BO pin reaches the V BO threshold.When the BO pin is grounded, the controller is shut down and the SS pin is internally grounded. If the BO pin is released, a new soft start sequence happens after its level reaches the V BO level.V CCVVV CC pinV CC(on)BO pinV BOSS pinDRV pin(C)(D)Figure 3. Brown Out ProtectionSoft StartAs illustrated by the following figure, the rising voltage on the SS pin voltage divided by 4 controls the peak current sensed on the CS pin. Thus as soon as the CS pin voltage becomes higher than the SS pin voltage divided by 4 thedriver is off cycle by cycle.Figure 5. Soft StartAPPLICATION INFORMATION (Cont.)The following figure illustrates a soft start sequence.Figure 6. Soft Start ExampleBrown−Out ProtectionThe controller protects converter against low input voltage conditions by monitoring the Voltage on BO pin. When the BO pin voltage falls below the V BO , the controllers stops pulsing until the input level goes back to normal and resumes the operation via a new soft start sequence.The hysteresis is implemented by using the internal current connected between the BO pin and the ground when the BO pin is below the V BO .Figure 7. BO Pin SetupThe following equations show how to calculate the resistors for BO pin. First of all, select the bulk voltage value at which the controller must start switching (V bulkon ) and the bulk voltage for shutdown (V bulkoff ) the controller. Where: V bulkon =370V, V bulkoff =350V, V BO =0.96V, I BO =9.8μA . When BO pin voltage is below V BO , the internal current source (I BO ) is activated. The following equation can be written:ON bulk V =R BO1(BO I +2BO R V BO +BOV(eq. 1)APPLICATION INFORMATION (Cont.)When BO pin voltage is higher than V BO , the internal current source is now disabled. The following equation can be written:BO V =122bulk BO BO BO off R R R V +(eq. 2)From Equation 2 it can be extracted the R BO1:R BO1=(BOBObulkoff V V -V )2BO R (eq. 3)Equation 3 is substituted in Equation 1 and solved for R BO2, yields:R BO2=(BO BOI V 1-V -V V -V BObulkoff BO bulkon ) (eq. 4)R BO1 can be also written independently of R BO2 by substituting Equation 4 into Equation 3 as follow: R BO1=BObulkoffbulkon I V -V (eq. 5)From Equation 4 and Equation 5, the resistor divider value can be calculated: R BO2=(μ8.996.01-96.0-50396.0-703)=5613Ω, R BO1=μ8.9350-703=2.04MΩShort Circuit or Open Loop&Over Load ProtectionA short circuit or an open loop&overload situation is detected when the CS pin voltage reaching 0.96V. If the condition continued for 15ms, the fault is latched and the controller permanently stops the pulses on the driver pin. If the fault is latched the controller can be reset if a BO reset is sensed or if V CC is cycled down to V CC(off).Figure 8. Short Circuit Detection ExampleShut DownThere is one possibility to shut down the controller; this possibility consists at grounding the BO pin as illustrated in Figure 7.APPLICATION INFORMATION (Cont.)Ramp CompensationRamp compensation is a known mean to cure subharmonic oscillations. These oscillations take place at half of the switching frequency and occur only during CCM with a duty−cycle above 50%. To lower the current loop gain, one usually injects between 50 and 100% of the inductor down slope.The ramp compensation applied on CS pin is from the internal oscillator ramp buffered. A switch placed between the buffered internal oscillator ramp and R ramp disconnects the ramp compensation during the off time Ton signal.Figure 9. Ramp Compensation SetupIn the UTC UC3853A , the internal ramp swings with a slope of:int S =SW max ramp F DC V (eq. 6) In a forward application the secondary−side downslope viewed on a primary side requires a projection over the sense resistor R sense . Thus:CS S =out f out L )V V (+CSp s R N N (eq. 7) where:•V out is output voltage level•V f the freewheel diode forward drop•L out , the secondary inductor value•N s /N p the transformer turn ratio•R CS : the sense resistor on the primary side Assuming the selected amount of ramp compensation to be applied is δcomp , then we must calculate the division ratio to scale down S int accordingly:Ratio=intcomp CS S δR (eq. 8) A few line of algebra determined R comp :comp R =Ratio-1Ratio R ramp (eq. 9) The previous ramp compensation calculation does not take into account the natural primary ramp created by the transformer magnetizing inductance. In some case illustrated here after the power supply does not need additional ramp compensation due to the high level of the natural primary ramp.The natural primary ramp is extracted from the following formula:n a t u r a S =CSmag bulk R L V (eq. 10) Then the natural ramp compensation will be:comp _natural δ=CS natural S S (eq. 11)If the natural ramp compensation (δnatural_comp ) is hig her than the ramp compensation needed (δcomp ), the power supply does not need additional ramp compensation. If not, only the difference (δcomp −δnatural_comp ) should be used to calculate the accurate compensation value.Thus the new division ratio is:If comp _natural δ<comp δ⇒Ratio=intcomp _natural comp CS S )δ-δ(S (eq. 12) Then R comp can be calculated with the same equation used when the natural ramp is neglected (Equation 9).APPLICATION INFORMATION (Cont.)Ramp Compensation Design Example2 switch−Forward Power supply specification:•Regulated output: 12V•L out =27μH•V f =0.62V (drop voltage on the regulated output)•Current sense resistor: 0.75Ω•Switching frequency: 100kHz•V bulk =350V, minimum input voltage at which the power supply works.•Duty cycle max: DC max =75%•V ramp =3.5V, Internal ramp level.•R ramp =26.5kΩ, Internal pull−up resistance•Targeted ramp compensation level: 100%•Transformer specification: L mag =13mH, N s /N p =0.085 Internal ramp compensation levelint S =⇒SW max rampF DC V int S =00kHz 1*75.05.3=467mV/μS Secondary−side downslope projected over the sense resistor is:CS S =⇒+CS p s out f out R N N L )V V (CS S =75.0*085.010*27)7.012(6-+=30mV/μS Natural primary ramp:natural S =⇒CS mag bulk R L V natural S =75.0*10133503-•=20.19mV/μS Thus the natural ramp compensation is:comp _natural δ=⇒CS natural S S comp _natural δ=3019.20=67.3%APPLICATION INFORMATION (Cont.)Here the natural ramp compensation is lower than the desired ramp compensation, so an external compensation should be added to prevent sub−harmon ics oscillation. Ratio=int comp _natural comp CS S )δ-δ(S ⇒Ratio=467)673.0-00.1(*30=0.021 We can know calculate external resistor (R comp ) to reach the correct compensation level.comp R =⇒Ratio -1Ratio R ramp comp R =021.0-1021.0*10*5.263=568.4Ω Thus with Rcomp = 570Ω, 100% compensation ramp is applied on the CS pin.The following example illustrates a power supply where the natural ramp offers enough ramp compensation to avoid external ramp compensation.2 switch−Forward Power supply specification:•Regulated output: 12V•L out =27μH•V f =0.7V•Current sense resistor: 0.75Ω•Switching frequency: 100kHz•V bulk =350V, minimum input voltage at which the power supply works.•Duty cycle max: DCmax =75%•V ramp =3.5V, Internal ramp level.•R ramp =26.5kΩ, Internal pull−up resistance•Targeted ramp compensation level: 100%•Transformer specification: L mag =8mH, N s /N p =0.085Secondary−side downslope projected over the sense resistor is:CS S =⇒+CS p s out f out R N N L )V V (CS S =75.0085.01027)7.012(6-×•+=30mV/μS The natural primary ramp is:natural S =⇒CS mag bulk R L V natural S =75.010*83503-=32.8mV/μS And the natural ramp compensation will be:c o m p _n a t u r a l δ=⇒CS natural S S comp _natural δ=308.32≈110% So in that case the natural ramp compensation due to the magnetizing inductance of the transformer will be enough to prevent any sub−harmonics oscillation in case of duty cycle above 50%.TYPICAL APPLICATION CIRCUITVout。

UC3843中文资料

UC3843固定频率电流模式控制器型号：UC3843A封装：DIP8主要应用：开关电源UC3842 、UC3843 是高性能固定频率电流模式控制器专为离线和直流至直流变换器应用而设计，为设计人员提供只需最少外部元件就能获得成本效益高的解决方案。

这些集成电路具有可微调的振荡器、能进行精确的占空比控制、温度补偿的参考、高增益误差放大器。

电流取样比较器和大电流图腾柱式输出，是驱动功率MOSFET的理想器件。

其它的保护特性包括输入和参考欠压锁定，各有滞后、逐周电流限制、可编程输出静区时间和单个脉冲测量锁存。

UC3842A 有16V（通）和10 伏（断）低压锁定门限，十分适合于离线变换器。

UC3843A是专为低压应用设计的，低压锁定门限为8.5伏（通）和7.6V（断）。

特点:微调的振荡器放电电流，可精确控制占空比.电流模式工作到500KHZ自动前馈补偿锁存脉宽调制，可逐周限流内部微调的参考电压，带欠压锁定大电流图腾柱输出欠压锁定，带滞后低启动和工作电流直接与安森美半导体的SENSEFET产品接口引脚图引脚功能引脚功能说明8管脚 14管脚1 1 补偿该管脚为误差放大器输出，并可用于环路补偿。

2 3 电压反馈该管脚是误差放大器的反相输入端，通常通过一个电阻分压器连至开关电源输出。

3 5 电流取样一个正比于电感器电流的电压接至此输入，脉宽调制器使用此信息中止输出开关的导通。

4 7 RT/CT通过将电阻RT 连接至Vref 以及电容CT连接至地，使振荡器频率和最大输出占下图是一个显示器的UC3842应用电路图UC3842好坏的判断鉴别方法在国内电子设备当中，电源PWM控制电路最常用的集成电路型号就是UC3842（或KA3842）。