如何采用固定导通时间控制器进行设计 How to Design with a Fixed On-Time Controller 您优化轻载能效的关键所在 Your Key to Optimizing Light Load Efficiency.

Presentation on theme: "如何采用固定导通时间控制器进行设计 How to Design with a Fixed On-Time Controller 您优化轻载能效的关键所在 Your Key to Optimizing Light Load Efficiency."— Presentation transcript:

1 如何采用固定导通时间控制器进行设计 How to Design with a Fixed On-Time Controller 您优化轻载能效的关键所在 Your Key to Optimizing Light Load Efficiency

2 议程Agenda 当前水准：准谐振和固定频率 State of the art: quasi resonant and fixed frequency 用于反激的固定导通时间(FON)控制介绍 Introduction to the fixed on time control for flybacks 固定频率、准谐振和固定导通时间比较 Fixed frequency, quasi resonant, and fixed on time comparison 设计方法学及示例 Design methodology and example 将您的固定频率适配器更新为固定导通时间模式 Update your fixed frequency adapter to fixed on time 增添额外功能性的技巧与决窍 Tips and tricks to add additional functionality 面向快速简单的固定导通时间设计的资源 Resources for quick and easy fixed on time designs

3 议程Agenda 当前水准：准谐振和固定频率 State of the art: quasi resonant and fixed frequency 用于反激的固定导通时间(FON)控制介绍 Introduction to the fixed on time control for flybacks 固定频率、准谐振和固定导通时间比较 Fixed frequency, quasi resonant, and fixed on time comparison 设计方法学及示例 Design methodology and example 将您的固定频率适配器更新为固定导通时间模式 Update your fixed frequency adapter to fixed on time 增添额外功能性的技巧与决窍 Tips and tricks to add additional functionality 面向快速简单的固定导通时间设计的资源 Resources for quick and easy fixed on time designs

4 准谐振和固定频率 Quasi Resonant and Fixed Frequency
固定开关频率 Fixed Fsw 准谐振 Quasi resonant 频率 Frequency 固定Fixed 可变Variable (开关频率最小时功率最高(max power at min Fsw) 轻载能效 Light Load Efficiencies 正常 Normal (采用跳周期或频率反走with skip mode or freq foldback) 谷底跳适问题(噪声) Valley jumping problem (noise) Max Fsw at min Pout 满载能效 Full Load Efficiencies 正常 Normal 最佳 Best 工作模式 Operating mode 连续导电模式/非连续导电模式CCM/DCM 边界导电模式 BCM (Borderline) 变压器尺寸 Transformer Size 较大 Larger 电磁干扰 EMI 较小 Smaller 必须提升宽输出负载范围下的能效 Must improve the efficiency for a wide output load range 必须改善待机能耗 Must improve the standby

5 议程Agenda 当前水准：准谐振和固定频率 State of the art: quasi resonant and fixed frequency 用于反激的固定导通时间(FON)控制介绍 Introduction to the fixed on time control for flybacks 固定频率、准谐振和固定导通时间比较 Fixed frequency, quasi resonant, and fixed on time comparison 设计方法学及示例 Design methodology and example 将您的固定频率适配器更新为固定导通时间模式 Update your fixed frequency adapter to fixed on time 增添额外功能性的技巧与决窍 Tips and tricks to add additional functionality 面向快速简单的固定导通时间设计的资源 Resources for quick and easy fixed on time designs

6 固定导通时间(FOT)–工作原理 Fixed On Time (FOT) – Principle of Operation
峰值电流保持恒定，可用用户选择 Constant peak current, user selectable Pout1 Pout2 Pout1 > Pout2 峰值电流保持恒定，而开关频率则会变化(改变关闭时间)，以提供必需的输出功率：The peak current is constant, switching frequency changes (Off time gets longer) to deliver the necessary output power: 频率最高时提供的功率最大 Maximum Power is delivered at maximum frequency

7 固定导通时间(FOT)–工作原理 Fixed On Time (FOT) – Principle of Operation
峰值电流通过控制器来保持恒定 the peak current is kept constant by the controller 频率发生变化以满足上述等式 the frequency varies to satisfy the above equations 缺少环路控制(短路，启动)时， Fsw被(Ct针对NCP1351进行)钳位 in lack of loop control (short-circuit, startup), Fsw is clamped (by Ct for the NCP1351) 开关频率由反馈回路进行控制 The FB loop controls the switching frequency

8 固定导通时间(FOT) – 可变开关频率 FOT – Variable Switching Frequency
Load Ct 由回路控制Controlled by the loop (时序电容电压 Timing capacitor voltage) Fsw 钳位clamp 在正常操作模式，回路固定着频率，而非Ct ！In normal operation, the loop fixes the frequency, NOT Ct! 轻载条件下，峰值电流减小，开关频率下降。这就限制了可听噪声问题。In light load conditions, Ipeak reduces and Fsw goes down. This limits audible noise problems. 满载条件下，开关频率增加，直至其碰到Ct钳位：故障 In full load conditions, Fsw increases until it hits the Ct clamp: fault

9 固定导通时间(FOT) – 开关损耗 FOT – Switching Losses
由于频率可变，与开关频率相关的损耗减少：As the frequency is variable, Fsw related losses decrease: Coss和门电荷损耗 Coss and gate charge losses 泄漏感抗损耗 Leakage inductance losses FOT大幅提高轻载能效 FOT dramatically improves light load efficiency

10 议程Agenda 当前水准：准谐振和固定频率 State of the art: quasi resonant and fixed frequency 用于反激的固定导通时间(FON)控制介绍 Introduction to the fixed on time control for flybacks 固定频率、准谐振和固定导通时间比较 Fixed frequency, quasi resonant, and fixed on time comparison 设计方法学及示例 Design methodology and example 将您的固定频率适配器更新为固定导通时间模式 Update your fixed frequency adapter to fixed on time 增添额外功能性的技巧与决窍 Tips and tricks to add additional functionality 面向快速简单的固定导通时间设计的资源 Resources for quick and easy fixed on time designs

11 控制拓扑结构比较 Control Topology Comparison
固定开关频率 Fixed Fsw 准谐振 Quasi resonant 固定导通时间 Fixed on time 频率 Frequency 固定Fixed 可变Variable (开关频率最小时功率最高(max power at min Fsw) 可变Variable (开关频率最小时功率最高max power at max Fsw) 轻载能效 Light Load Efficiencies 正常 Normal (采用跳周期或频率反走with skip mode or freq foldback) 谷底跳适问题(噪声) Valley jumping problem (noise) Max Fsw at min Pout 最佳 Best 满载能效 Full Load Efficiencies 正常 Normal 工作模式 Operating mode 连续导电模式/非连续导电模式CCM/DCM 边界导电模式 BCM (Borderline) 变压器尺寸Transformer Size 较大 Larger 电磁干扰 EMI 较小 Smaller 固定导通时间(FOT)：适合极宽输出功率范围，是您改善待机能耗和优化工作能效的关键！！！FOT : your key to improve standby and optimize efficiency for a wide output power range !!!

12 议程Agenda 当前水准：准谐振和固定频率 State of the art: quasi resonant and fixed frequency 用于反激的固定导通时间(FON)控制介绍 Introduction to the fixed on time control for flybacks 固定频率、准谐振和固定导通时间比较 Fixed frequency, quasi resonant, and fixed on time comparison 设计方法学及示例 Design methodology and example 新的NCP1351固定导通时间控制器 The new NCP1351 FOT controller 设计方法学 Design methodology 设计示例 Design example 将您的固定频率适配器更新为固定导通时间模式 Update your fixed frequency adapter to fixed on time 增添额外功能性的技巧与决窍 Tips and tricks to add additional functionality 面向快速简单的固定导通时间设计的资源 Resources for quick and easy fixed on time designs

13 NCP1351 – 固定导通时间、可变关闭时间控制器 Fixed On Time Variable Off Time Controller
Value Proposition NCP1351是一款瞄准总成本极为重要的低功率离线反激开关电源(SMPS)应用的电流模式控制器 The NCP1351 is a current-mode controller targeting low power off-line flyback Switched Mode Power Supplies (SMPS) where total cost is of utmost importance Unique Features Benefits Application Data 准固定导通时间，可变关闭时间Quasi fixed Ton, variable Toff 带峰值电流压缩的频率反走Frequency foldback with Peak Current Compression 短路保护(闭锁A&C或自动恢复B&D)Short circuit protection 固有的频率反走 Natural frequency foldback 无噪声，轻载能效提高 Noise free & improved efficiency in light load 独立于辅助绕组 Independent of the aux. winding Others Features 适应大输出功率瞬态现象(打印机) Accommodates large output power transients (printers) 初级端或次级端稳压 Primary or secondary side regulation 闩锁输入 Latch input 低启动电流 Low start-up current 固有的频率抖动 Natural frequency jittering 带可编程电流感测电阻的负电流感测功能 Negative current sensing with programmable current sense resistor 扩展的Vcc范围：28 V Extended Vcc range: 28 V 简单而紧凑的设计 Simple and compact design Ordering & Package Information Market & Applications 适配器 Adapters 离线电池充电器 Offline battery chargers 辅助电源 Auxiliary power supplies NCP1351XDR2G: SOIC8 X = A, B, C ,D Pb O, DW

14 NCP1351 – 输入输出功率和功能描述 NCP1351 – Pinout and Function Description
Timer: 设定故障确认前的持续时间 Sets the time duration before fault validation FB: 在此引脚注入电流，降低频率Injecting current in this pin reduces the frequency Latch: 高于5 V的正电压完全闩锁控制器 A positive voltage above 5 V fully latches off the controller Ct: 没有反馈电流时设定最大开关频率 sets the maximum switching frequency at no feedback current Vcc: 为控制器提供高达28伏电压 Supplies the controller up to 28 V CS: 感测初级端电流 Senses the primary current DRV: 驱动脉冲至功率MOSFET Driving pulses to the power MOSFET

15 NCP1351 – 峰值电流压缩 NCP1351 – Peak Current Compression
Ioffset 60 µA 80 µA 270 µA 70 µA 40 µA FAULT (A, B versions) Vds light load 峰值电流从100%降至26% Peak current reduction from 100% to 26% FB current 大负载时峰值电流恒定 Constant peak current at high load 轻载时峰值电流下降 Reduced peak current at light load 没有饱和 No saturation 没有可听噪声 No Audible noise

16 NCP1351 – 负电流感测…… NCP1351 – Negative Current Sensing…
Vsense VCS 不用担心！ Do not be afraid ! ICS x Roffset产生正偏置(如1 V) ICS x Roffset generates a positive offset (e.g. 1 V) 电流流过时， Vsense 为负值 Vsense is negative when current flows 两路信号的和接近零时，MOSFET关闭 When the sum of both signal reaches  0, MOSFET is off

17 NCP1351 – 负电流感测…… NCP1351 – Negative Current Sensing…
洁净的电压图像：没有开启尖峰，更好的噪声免疫性 Clean voltage image: no turn-on spikes, better noise immunity 一种微调最大感测电压的途径 A way to fine tune the maximum sense voltage 如何计算感测电阻和偏置电阻？ How to calculate Rsense and Roffset ? 想要降低感测电阻的功率耗散？Want to reduce Rsense power dissipation? 选择Select Vsense = 0. 5 V Roffset = 0.5 / 270u = 1.8 k

18 NCP1351 – 过载/短路保护 NCP1351 – Overload / Short-Circuit Protection
FB 45k GND Vdd NCP1351 + - 100mV Timer 10µA 5V 保护模式Protection mode (闩锁或自动恢复latched or autorecovery) 过载OVERLOAD  输出电压减小 Vout decreases time V(CTIMER) 5V V OUT Vcc 反馈电流减小Less FB current D2 故障比较器切换 FAULT comparator toggles C TIMER 500mV 过载检测仅依赖于反馈变化Overload detection only dependent of FB variation 2个选项：闩锁或自动恢复 2 options: latched or auto recovery

19 NCP1351 – 过载定时器 Overload Timer
输出仍在稳压 Output still in regulation 故障定时器启动 Fault timer starts 故障定时器启动Fault timer starts Vout Vout 过载Over load 过载Over load 瞬态峰值功率Transient peak power 最大输出功率Max output power 最大直流功率Max DC power 输出负载Output load 最大峰值功率Max peak power 输出负载Output load A&B版本 versions C&D版本 versions 适应大输出功率瞬态现象Accommodates large output power transients 适合于打印机应用Suitable for printers

20 NCP1351 – 设计方法学 Design Methodology
对MOSFET的BVdss降额后定义变比Define turn ratio after derating the BVdss of the MOSFET: kc: 钳位系数clamp coefficient＝Vclamp / Vr Vds,max = 85% BVdss 计算最大占空比 Calculate maximum duty cycle: 在功率最大期间输入电压最低时选择最大开关频率Choose the maximum switching frequency Fsw at Vin,min during power peaks. 然后通过下列公式计算初级端感抗值：Then calculate the primary inductance value by: (仅对非连续导电模式有效 valid for DCM only)

21 NCP1351 – 设计方法学 NCP1351 – Design Methodology
推导初级端最大峰值电流 Deduce the maximum primary peak current: 最后通过下列公式估计时序电容值 Finally estimate the timing capacitor value by: MOSFET、整流器、电感和缓冲器根据平均输出功率(非峰值功率)来计算 (仅对非连续导电模式有效 valid for DCM only) (设计示例中将涉及连续导电模式 design example will cover CCM) 时序电容的正常值为 Normalized values for CT are: - 65 kHz: 270 pF - 100 kHz: 180 pF MOSFET, rectifiers, inductors and snubbers are designed according to the average delivered power (not the peak)

22 NCP1351 – 设计示例 NCP1351 – Design Example
输出电压 Output voltage: 19 V – 57 W 输入电压 Input voltage: 90 – 265 Vrms 待机能耗(空载) Standby power (no-load) < 200 mW 自动恢复过载保护 Auto-recovery overload protection 闩锁过压保护(OVP) Latched over-voltage protection (OVP) 工作频率 Operating frequency: 65 kHz

23 NCP1351 – 设计示例 NCP1351 – Design Example
减小MOSFET最大的BVdss Derate maximum MOSFET BVdss: BVdss Vds,max 15%降额derating 针对最大高电压来选择钳位电压 For a maximum bulk voltage, select the clamping voltage : 钳位电压Vclamp Vbulk,max 选择钳位系数的变比为1.6 Select turn ratio for a kc of 1.6: 计算最大占空比 Calculate maximum duty-cycle: 在输入电压为85 Vac及满载时， Cbulk 选择为100 Vdc的最低等级 Cbulk selected for min level of 100 Vdc at Vin = 85 Vac, full load

24 NCP1351 – 设计示例 NCP1351 – Design Example
对于通用的主设计而言，选择K = 0.8 For a universal mains design, select K = 0.8

25 NCP1351 – 设计示例 NCP1351 – Design Example
用它作为导电损耗 Use it for conduction losses

26 NCP1351 – 设计示例 NCP1351 – Design Example
如果我们想要VCS = 0.5 V而非1 V If we want VCS = 0.5 V instead of 1 V 0.2 x 1.1² = 242 mW 0.5 0.2 Ω 1.8 kΩ 如果你没有0.4欧姆电阻 If you do not have 0.4 Ω resistor: Rsense = 0.5 Ω 使用200 V的二极管 Use a 200 V diode 通过270 pF的Ct 电容来选定65 kHz频率 The 65 kHz selection is made via Ct capacitor of 270 pF

27 NCP1351 – 设计示例 NCP1351 – Design Example

28 NCP1351 – 设计示例 NCP1351 – Design Example
VIN POUT 110 Vac (60 Hz) 230 Vac (50 Hz) 57 W 88.5% 90.7% 30 W 89.4% 90.9% 10 W 89.3% 89% 1 W 70.4% 67.2% 0.5 W 64.7% 62% 尽管负载变化，但效 率仍维持在较高水平 Efficiency is kept good despite load variations. 高于80% Above 80% Above 80 % VIN POUT 110 Vac 230 Vac 0.5 W 817 mW 855 mW = 143 mW, Vin = 230 Vrms = 112 mW, Vin = 100 Vrms

29 NCP1351 – 设计示例 NCP1351 – Design Example
Vds 200 V / div. Vout 1 mV / div. Vds 200 V / div. Vout 1 mV / div. 5 W负载，小输出纹波 5 W load, small output ripple 空载，小输出纹波 No load, small output ripple

30 NCP1351 – 设计示例 NCP1351 – Design Example
Vout 50 mV / div. 瞬态响应，高线，低线 Transient response, high line, low line

31 议程Agenda 当前水准：准谐振和固定频率 State of the art: quasi resonant and fixed frequency 用于反激的固定导通时间(FON)控制介绍 Introduction to the fixed on time control for flybacks 固定频率、准谐振和固定导通时间比较 Fixed frequency, quasi resonant, and fixed on time comparison 设计方法学及示例 Design methodology and example 将您的固定频率适配器更新为固定导通时间模式 Update your fixed frequency adapter to fixed on time 增添额外功能性的技巧与决窍 Tips and tricks to add additional functionality 面向快速简单的固定导通时间设计的资源 Resources for quick and easy fixed on time designs

32 将您的固定频率适配器更新为固定导通时间模式！ Update Your Fixed Frequency Adapter to FOT!
提升轻载条件下的能效，但没有纹波 Improved efficiency in light load conditions without ripple 轻载条件下输出纹波更少 Less output ripple in light load conditions 易于应用过载保护(非耗散型) Ease of OPP implementation (non dissipative) 基于定时器的保护与辅助电压监控对比 Timer-based protection versus auxiliary voltage monitoring

33 将您的固定频率适配器更新为固定导通时间模式！ Update Your Fixed Frequency Adapter to FOT!
采用NCP1200的12 V/24 W适配器原理图 12 V / 24 W adapter schematic with NCP1200 仅用于非连续导电模式 DCM onlyDSS -> 无辅助绕组 DSS -> No auxiliary winding 通用主电源 Universal mains 开关频率为65 kHz Switching frequency: 65 kHz 内部固定短路保护 Internal fixed short circuit protection

34 将您的固定频率适配器更新为固定导通时间模式！ Update Your Fixed Frequency Adapter to FOT!
开关频率65 kHz Switching frequency 65 kHz 选择choose Ct = 270 pF NCP1200的最大电流设定点为1 V Maximum current setpoint of NCP1200 is 1 V 选择choose VCS= 1 V，并计算Roffset : 无须修改感测电阻 No need to modify Rsense 光耦合器配置 Optocoupler configuration 2.4 kΩ NCP1200: 共发射极 common emitter NCP1351: 共集电极 common collector

35 将您的固定频率适配器更新为固定导通时间模式！ Update Your Fixed Frequency Adapter to FOT!
采用NCP1351的12 V/24 W适配器原理图 12 V / 24 W adapter schematic with NCP1351

36 将您的固定频率适配器更新为固定导通时间模式！ Update Your Fixed Frequency Adapter to FOT!
输入电压为230 Vrms时的效率和空载能耗 Efficiency and no-load power consumption at Vin = 230 Vrms NCP1200 NCP1351 24 W 85% 85 % 17 W 84% 10.7 W 83% 1.5 W 66% 75% 0.7 W 57% 70% 0.5 W 52% 65% 空载 No load 234 mW 78 mW 动态自供电功率耗散！DSS power dissipation !

37 将您的固定频率适配器更新为固定导通时间模式！ Update Your Fixed Frequency Adapter to FOT!
输出纹波比较 Output ripple comparison Vout 10 mV / div. Vds 100 V / div. Vout 1 mV / div. Vds 200 V / div. NCP1200, 空载 No load NCP1351, 空载 No load NCP1351的输出纹波要小10倍 The output ripple is 10 times smaller with NCP1351

38 议程Agenda 当前水准：准谐振和固定频率 State of the art: quasi resonant and fixed frequency 用于反激的固定导通时间(FON)控制介绍 Introduction to the fixed on time control for flybacks 固定频率、准谐振和固定导通时间比较 Fixed frequency, quasi resonant, and fixed on time comparison 设计方法学及示例 Design methodology and example 将您的固定频率适配器更新为固定导通时间模式 Update your fixed frequency adapter to fixed on time 增添额外功能性的技巧与决窍 Tips and tricks to add additional functionality 面向快速简单的固定导通时间设计的资源 Resources for quick and easy fixed on time designs

39 启动技巧与决窍 Start-Up Tip & Trick
传统配置 Classical configuration 改善的启动耗散 Improved startup dissipation 启动电阻可被任意连接 The startup resistor can either be connected: 至带启动电阻的大电容 To the bulk capacitor with Rstartup 至半波 – 对于相似的充电电流，选择Rstartup/pi To the half-wave – for a similar charging current, take Rstartup/pi 半波提供最佳的闩锁恢复时间 Half-wave gives the best latch recovering time

40 启动技巧与决窍 Start-Up Tip & Trick
轻载条件下，Vcc崩溃 In light load conditions, Vcc collapses: 增加Vcc电容，减小启动电阻 Increase Vcc capacitor degrades startup 将Vcc分解为两个电容 Split Vcc with two capacitors Cvcc单独正常启动(D1) CVcc starts-up normally alone (D1) Creser在待机时维持Vcc工作状态 Creser keeps Vcc alive in standby 4.7 µF 47 µF

41 启动电压调节 Startup Voltage Adjustment
启动电阻 Start-up resistors 最小启动电压调节Minimum voltage start-up adjustment 极低的启动电流/大启动电阻值 Extremely low start-up current / High start-up resistors values 工作时固定最小高电压 Fix the minimum bulk voltage for operation

42 门驱动技巧与决窍 Gate Drive Tip & Trick
No PNP 200 ns / div 采用小型PNP来提高驱动能力 Improve drive capability with a small PNP 更好的传播延迟 better propagation delay 改进故障电流控制 improves current control in fault with PNP 200 ns / div

43 过载保护 Over Power Protection
在任意电压条件下控制最大输出功率 Control the maximum output power under any voltage condition 非耗散型！ Non dissipative! 二极管避免C3被反激充电 The diode avoids C3 charged by flyback 只需数量很少的外部元件 Requires limited number of external components 兼容于现有辅助绕组 Compatible with existing Aux winding

44 频率抖动技巧与决窍 Frequency Jittering Tip & Trick
注入全波纹波至CS引脚 Inject full wave ripple into CS pin 注入半波纹波至CS引脚 Inject half wave ripple into CS pin 注入一些全波或半波纹波来增加固有频率抖动 Inject some full-wave or half-wave ripple to increase the natural frequency jittering

45 闩锁输入技巧与决窍 Latch Input Tip & Trick
NTC 参考电压 Reference voltage 在FB引脚插入齐纳二极管，造就更便宜的参考 Inserting zener with FB pin, creates cheap reference. 与闩锁引脚一起提供简单的过压保护和过温度保护Combined with the latch pin gives easy OVP and OTP protection.

46 欠压 Brown Out 欠压关闭BO off 欠压导通BO on

47 斜波补偿 Ramp Compensation
斜坡补偿1：正向斜坡补偿至FB引脚，以降低峰值 Ramp compensation 1 : a positive ramp into the FB pin reduces the peak

48 斜波补偿 Ramp Compensation
斜坡补偿2：负电流在导通时间将Ct维持在低位 Ramp compensation 2 : a negative current keeps Ct low during ton 接近Ct引脚 Close to the Ct pin

49 软启动 Soft Start 在电源开启期间通过软启动序列来限制应力
Limit the stress at power-on via a soft-start sequence. VCS t 软启动(如果有必要) Soft Start (if necessary)

50 将NCP1351与其他控制器相连接 Interfacing NCP1351 with Other Controllers
NCP1351怎样能够与其它控制器共享接地信号？(将负电流和正电流感测混合在一起) How NCP1351 can share ground signal with other controller? (mixing negative and positive current sensing) 1 2 3 4 5 8 6 7 Laux D2 D1 Caux 100u Cstbvcc 4.7u Rsense Rcs NCP1351 连接至其它控制器的 VCC引脚 To other controller VCC pin or Lp 连接至其它控制的接地 引脚和大电容 To other controller GND pin and bulk cap 主接地 Main ground NCP1351接地 NCP1351 ground 主接地 Main ground

51 布线建议 Layout Suggestions
22 pF Vcc Roffset Rsense 低阻抗点 Low impedance point 为了改善噪声免疫性，需要将元件布置在临近控制器的位置 To improve the noise immunity, keep components close to the controller

52 改变最大开关频率 Changing the Maximum Switching Frequency
开始START 计算新的峰值电流Ipeak Calculate new Ipeak 计算 Calculate Ct 保持Lp值不变 Keep Lp value 保持Rsense值不变 Keep Rsense (仅适用于非连续导电模式DCM only) 否no 减小开关频率FSW? FSW decreases ? 结束 END 是yes 保持变压器参数 Keep transformer 修改偏置电阻值Roffse以设定新的峰值电流Ipeak Modify Roffset value to set new peak current 否no 计算磁芯磁通量 Calculate core flux B > Bsat ? 是yes 修改变压器参数 Modify transformer

53 改变最大输出功率 Changing the Maximum Output Power
改变最大开关频率 Change the maximum switching frequency: 最大输出功率Pout,max增加=> 最大开关频率Fsw,max增加 Pout,max increases => Fsw,max increases 最大输出功率Pout,max减小=> 最大开关频率Fsw,max减小Pout,max decreases => Fsw,max decreases 开始START 计算提供Pout2所需的开关频率Fsw Calculate needed Fsw to deliver Pout2 计算Calculate Ct 保持变压器参数(Lp, Bsat)不变 Keep transformer (Lp, Bsat) 保持Rsense、Roffset不变Keep Rsense, Roffset (适适用于非连续导电模式DCM only) 检查回路响应 VCheck loop response 查看反馈噪声 Look out for FB noise 使用平均模型来稳定电源 Use the averaged model to stabilize the power supply 否no 是否稳定Stable ? 是yes 结束END

54 议程Agenda 当前水准：准谐振和固定频率 State of the art: quasi resonant and fixed frequency 用于反激的固定导通时间(FON)控制介绍 Introduction to the fixed on time control for flybacks 固定频率、准谐振和固定导通时间比较 Fixed frequency, quasi resonant, and fixed on time comparison 设计方法学及示例 Design methodology and example 将您的固定频率适配器更新为固定导通时间模式 Update your fixed frequency adapter to fixed on time 增添额外功能性的技巧与决窍 Tips and tricks to add additional functionality 面向快速简单的固定导通时间设计的资源 Resources for quick and easy fixed on time designs

55 NCP1351 – 设计资源 Collaterals 应用笔记 Application notes:
40 W打印机电源设计AND8278 Design of a 40 W Printer PSU AND8278 50 W适配器电源设计AND8263 Design of a 57 W Adapter PSU AND8263 12 W适配器电源设计AND8288 Design of a 12 W Adapter PSU AND8288 使用脉宽调制(PWM)开关技术建模：AND8280 Modeling Using the PWM Switch Technique: AND8280 评估板 Evaluation board: 40 W额定/80瓦峰值功率打印机板 40 W nominal/ 80 W peak printer board 57 W适配器板 57 W adapter board 参考设计 Reference design: 40 W打印机电源：TND320/D 40 W Printer Power Supply: TND320/D 设计与开发 Design & Development: NCP1351电感计算数据表 NCP1351 inductor calculation Spreadsheet 仿真工具：Simulations tools: Spice模型(PSPICE和ISPICE) Spice model (PSPICE and ISPICE)

56 谢谢！如有问题，敬请提出！ Thank You! Any Questions?