www. onsemi. com. cn 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
www. onsemi. com. cn 议程Agenda 1. 当前水准：准谐振和固定频率 State of the art: quasi resonant and fixed frequency 2. 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 3. 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 4. 设计方法学及示例 Design methodology and example 5. 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 6. 增添额外功能性的技巧与决窍 Tips and tricks to additional functionality 7. 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 2
www. onsemi. com. cn 议程Agenda 1. 2. 用于反激的固定导通时间(FON)控制介绍 3. 固定频率、准谐振和固定导通时间比较 4. 设计方法学及示例 5. 将您的固定频率适配器更新为固定导通时间模式 6. 增添额外功能性的技巧与决窍 7. 3 当前水准：准谐振和固定频率 面向快速简单的固定导通时间设计的资源 State of the art: quasi resonant and fixed frequency Introduction to the fixed on time control for flybacks Fixed frequency, quasi resonant, and fixed on time comparison Design methodology and example Update your fixed frequency adapter to fixed on time Tips and tricks to additional functionality Resources for quick and easy fixed on time designs
www. onsemi. com. cn 准谐振和固定频率 Quasi Resonant and Fixed Frequency 固定开关频率 resonant 固定Fixed 频率 准谐振 Fixed Fsw 可变Variable (开关频率 最小时功率最高(max Frequency 轻载能效 Light Load Efficiencies power at min Fsw) 正常 Normal (采用跳 周期或频率反走with skip mode or freq foldback) 满载能效 Quasi Full 正常 Normal 谷底跳适问题(噪声) Valley jumping problem (noise) Max Fsw at min Pout 最佳 Best Load Efficiencies 作模式 Operating mode 变压器尺寸 连续导电模式/非连续 边界导电模式CCM/DCM BCM (Borderline) 正常 Normal 较大 Larger Transformer Size 电磁干扰 EMI 正常 Normal 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 4
www. onsemi. com. cn 议程Agenda 1. 2. 用于反激的固定导通时间(FON)控制介绍 3. 固定频率、准谐振和固定导通时间比较 4. 设计方法学及示例 5. 将您的固定频率适配器更新为固定导通时间模式 6. 增添额外功能性的技巧与决窍 7. 5 当前水准：准谐振和固定频率 面向快速简单的固定导通时间设计的资源 State of the art: quasi resonant and fixed frequency Introduction to the fixed on time control for flybacks Fixed frequency, quasi resonant, and fixed on time comparison Design methodology and example Update your fixed frequency adapter to fixed on time Tips and tricks to additional functionality Resources for quick and easy fixed on time designs
www. onsemi. com. cn 固定导通时间(FOT)– 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 Fsw 1 @ Pout 1 Fsw 2 @ Pout 2 Pout 1 > Pout 2 • 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 6
www. onsemi. com. cn 固定导通时间(FOT)– 作原理 Fixed On Time (FOT) – Principle of Operation q 峰值电流通过控制器来保持恒定 the peak current is kept constant by the controller q 频率发生变化以满足上述等式 the frequency varies to satisfy the above equations q 缺少环路控制(短路，启动)时， Fsw被(Ct针对NCP 1351进行)钳位 in lack of loop control (short-circuit, startup), Fsw is clamped (by Ct for the NCP 1351) 开关频率由反馈回路进行控制 The FB loop controls the switching frequency 7
www. onsemi. com. cn 固定导通时间(FOT) – 可变开关频率 Load Ct FOT – Variable Switching Frequency (时序电容电压 Timing capacitor voltage) 由回路控制 Controlled by the loop Fsw 钳位clamp q 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! q 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. q 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 8
www. onsemi. com. cn 固定导通时间(FOT) – 开关损耗 FOT – Switching Losses q 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: Ø Coss和门电荷损耗 Coss and gate charge losses Ø 泄漏感抗损耗 Leakage inductance losses q FOT大幅提高轻载能效 FOT dramatically improves light load efficiency 9
www. onsemi. com. cn 议程Agenda 1. 2. 用于反激的固定导通时间(FON)控制介绍 3. 固定频率、准谐振和固定导通时间比较 4. 设计方法学及示例 5. 将您的固定频率适配器更新为固定导通时间模式 6. 增添额外功能性的技巧与决窍 7. 10 当前水准：准谐振和固定频率 面向快速简单的固定导通时间设计的资源 State of the art: quasi resonant and fixed frequency Introduction to the fixed on time control for flybacks Fixed frequency, quasi resonant, and fixed on time comparison Design methodology and example Update your fixed frequency adapter to fixed on time Tips and tricks to additional functionality Resources for quick and easy fixed on time designs
www. onsemi. com. cn 控制拓扑结构比较 Control Topology Comparison 固定开关频率 固定导通时间 Quasi resonant Fixed on time 固定Fixed 频率 准谐振 Fixed Fsw 可变Variable (开关频 率最小时功率最高max 率最小时功率最高 Frequency (max power at min Fsw) power at max Fsw) 轻载能效 Light Load Efficiencies 正常 Normal (采用跳 谷底跳适问题(噪声) 最佳 Best 周期或频率反走with Valley jumping problem skip mode or freq foldback) 正常 Normal 最佳 Best 正常 Normal 连续导电模式/非连 续导电模式 CCM/DCM 正常 Normal 边界导电模式 BCM (Borderline) 连续导电模式/非连续 导电模式CCM/DCM 较大 Larger 正常 Normal 满载能效 (noise) Max Fsw at min Pout 较小 Smaller 正常 Normal Full Load Efficiencies 作模式 Operating mode 变压器尺寸 Transformer Size 电磁干扰 EMI 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 作能效的关键！！！FOT : your key to improve standby and optimize efficiency for a wide output power range !!! 11
www. onsemi. com. cn 议程Agenda 1. 当前水准：准谐振和固定频率 2. 用于反激的固定导通时间(FON)控制介绍 3. 固定频率、准谐振和固定导通时间比较 4. 设计方法学及示例 Design methodology and example 新的NCP 1351固定导通时间控制器 The new NCP 1351 FOT controller 设计方法学 Design methodology 设计示例 Design example 5. 将您的固定频率适配器更新为固定导通时间模式 6. 增添额外功能性的技巧与决窍 7. 面向快速简单的固定导通时间设计的资源 12 State of the art: quasi resonant and fixed frequency to the fixed on time control for flybacks Fixed frequency, quasi resonant, and fixed on time comparison Update your fixed frequency adapter to fixed on time Tips and tricks to additional functionality Resources for quick and easy fixed on time designs Introduction
NCP 1351 – 固定导通时间、可变关闭时间控制器 Fixed On Time Variable Off Time Controller Value Proposition NCP 1351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 NCP 1351 is a currentmode 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 § 固有的频率反走 Natural frequency foldback 时间Quasi fixed Ton, variable Toff § 带峰值电流压缩的频率反走 § 无噪声，轻载能效提高 Frequency foldback with Peak Current Compression § 短路保护(闭锁A&C或自动 恢复B&D)Short circuit protection 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 Market & Applications § 适配器 Adapters § 离线电池充电器 Offline battery chargers § 辅助电源 Auxiliary power supplies 13 简单而紧凑的设计 Simple and compact design Ordering & Package Information § NCP 1351 XDR 2 G: SOIC 8 § X = A, B, C , D Pb O, DW
www. onsemi. com. cn NCP 1351 – 输入输出功率和功能描述 NCP 1351 – Pinout and Function Description FB: 在此引脚注入电流，降 低频率Injecting current in this pin reduces the frequency Ct: 没有反馈电流时设 定最大开关频率 sets the Timer: 设定故障确认前的持续 时间 Sets the time duration before fault validation Latch: 高于5 V的 正电压完全闩锁控 制器 A positive voltage maximum switching frequency at no feedback above 5 V fully latches off the controller current Vcc: 为控制器提供 高达 28伏电压 Supplies CS: 感测初级端电流 Senses the primary current the controller up to 28 V DRV: 驱动 脉冲至功率 MOSFET Driving pulses to the power MOSFET 14
www. onsemi. com. cn NCP 1351 – 峰值电流压缩 Ioffset NCP 1351 – Peak Current Compression Vds µA 270 light load 峰值电流从100%降至 26% Peak current reduction from 100% to 26% FAULT (A, B versions) 70 µA 40 µA 60 µA 80 µA FB current 大负载时峰值电流恒定 没有饱和 Constant peak current at high load No saturation 轻载时峰值电流下降 Reduced peak current at light load 15 没有可听噪声 No Audible noise
www. onsemi. com. cn NCP 1351 – 负电流感测…… NCP 1351 – Negative Current Sensing… VCS 0 V 不用担心！ Do not be afraid ! 0 V Vsense • 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 16
www. onsemi. com. cn NCP 1351 – 负电流感测…… NCP 1351 – 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 Ø 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 / 270 u = 1. 8 k 17
www. onsemi. com. cn NCP 1351 – 过载/短路保护 NCP 1351 – Overload / Short-Circuit Protection 过载OVERLOAD 输出电压减小 Vout + 保护模式Protection mode (闩锁或自动恢复latched or autorecovery ) decreases VOUT 5 V Vdd Vcc 5 V time 反馈电 流减小 Less FB current V(CTIMER) - 10µA D 2 Timer + FB 45 k CTIMER 100 m. V 500 m. V 故障比较器切换 GND FAULT comparator toggles. NCP 1351 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 18 2 options: latched or auto recovery
www. onsemi. com. cn NCP 1351 – 过载定时器 Overload Timer Vout 故障定时器启动 Vout Fault timer starts 过载 Over load 最大输出 功率Max A&B版本 output power versions Fault timer starts 瞬态峰值 功率 Transient peak power 输出负载 Output load 适应大输出功率瞬态现象 Accommodates large output power transients 19 输出仍在稳压 故障定时器启动 Output still in regulation 最大直流功率 Max DC power 过载 Over load 最大峰值 功率Max peak power 输出负载 Output load C&D版本 versions 适合于打印机应用 Suitable for printers
www. onsemi. com. cn NCP 1351 – 设计方法学 Design Methodology q 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 q 计算最大占空比 Calculate maximum duty cycle: q 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. q 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) 20
www. onsemi. com. cn NCP 1351 – 设计方法学 NCP 1351 – Design Methodology q 推导初级端最大峰值电流 Deduce the maximum primary peak current: (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) q 最后通过下列公式估计时序电容值 Finally estimate the timing capacitor value by: Ø时序电容的正常值为 Normalized values for CT are: - 65 k. Hz: 270 p. F - 100 k. Hz: 180 p. F q 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 MOSFET, rectifiers, inductors and snubbers are designed according to the average delivered power (not the peak) 21
www. onsemi. com. cn NCP 1351 – 设计示例 NCP 1351 – Design Example q 输出电压 Output voltage: 19 V – 57 W q 输入电压 Input voltage: 90 – 265 Vrms q 待机能耗(空载) Standby power (no-load) < 200 m. W q 自动恢复过载保护 Auto-recovery overload protection q 闩锁过压保护(OVP) Latched over-voltage protection (OVP) q 作频率 Operating frequency: 65 k. Hz 22
www. onsemi. com. cn NCP 1351 – 设计示例 NCP 1351 – Design Example BVdss q 减小MOSFET最大的BVdss Derate maximum MOSFET BVdss: Vds, max q 针对最大高电压来选择钳位电压 For a maximum bulk voltage, select the clamping voltage : 15%降额derating 钳位电压 Vclamp Vbulk, max q 选择钳位系数的变比为 1. 6 Select turn ratio for a kc of 1. 6: q 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 23
www. onsemi. com. cn NCP 1351 – 设计示例 NCP 1351 – 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 24
www. onsemi. com. cn NCP 1351 – 设计示例 NCP 1351 – Design Example 用它作为导电损耗 Use it for conduction losses 25
www. onsemi. com. cn NCP 1351 – 设计示例 NCP 1351 – Design Example q 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. 5 1. 8 kΩ 0. 5 0. 2 Ω 如果你没有0. 4欧姆电阻 you do not have 0. 4 Ω resistor: 0. 2 x 1. 1² = 242 m. W 使用 200 V的二极管 Use a 200 V diode 通过270 p. F的Ct 电容来选定 65 k. Hz频率 The 65 k. Hz selection is made via Ct capacitor of 270 p. F 26 Rsense = 0. 5 Ω If
www. onsemi. com. cn NCP 1351 – 设计示例 NCP 1351 – Design Example 27
www. onsemi. com. cn NCP 1351 – 设计示例 NCP 1351 – Design Example VIN POUT Above 80% 230 Vac (50 Hz) 57 W 高于80% 110 Vac (60 Hz) 88. 5% 90. 7% 30 W 89. 4% 90. 9% 10 W 89. 3% 89% 70. 4% 67. 2% 64. 7% 62% 110 Vac 230 Vac 817 m. W 855 m. W 1 W 0. 5 W VIN POUT 0. 5 W Above 80 % 尽管负载变化，但 效 率仍维持在较 高水平 Efficiency is kept good despite load variations. Pin @空载no-load = 143 m. W, Vin = 230 Vrms Pin @空载no-load = 112 m. W, Vin = 100 Vrms 28
www. onsemi. com. cn NCP 1351 – 设计示例 NCP 1351 – Design Example Vds Vout 200 V / div. 1 m. V / div. Vout 1 m. V / div. 5 W负载，小输出纹波 5 W load, small output ripple 29 Vds 200 V / div. 空载，小输出纹波 No load, small output ripple
www. onsemi. com. cn NCP 1351 – 设计示例 NCP 1351 – Design Example Vout 50 m. V / div. 瞬态响应，高线，低线 Transient response, high line, low line 30
www. onsemi. com. cn 议程Agenda 1. 2. 用于反激的固定导通时间(FON)控制介绍 3. 固定频率、准谐振和固定导通时间比较 4. 设计方法学及示例 5. 将您的固定频率适配器更新为固定导通时间模式 6. 增添额外功能性的技巧与决窍 7. 31 当前水准：准谐振和固定频率 面向快速简单的固定导通时间设计的资源 State of the art: quasi resonant and fixed frequency Introduction to the fixed on time control for flybacks Fixed frequency, quasi resonant, and fixed on time comparison Design methodology and example Update your fixed frequency adapter to fixed on time Tips and tricks to additional functionality Resources for quick and easy fixed on time designs
www. onsemi. com. cn 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! q 提升轻载条件下的能效，但没有纹波 Improved efficiency in light load conditions without ripple q 轻载条件下输出纹波更少 Less output ripple in light load conditions q 易于应用过载保护(非耗散型) Ease of OPP implementation (non dissipative) q 基于定时器的保护与辅助电压监控对比 Timer-based protection versus auxiliary voltage monitoring 32
www. onsemi. com. cn 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! q 采用NCP 1200的12 V/24 W适配器原理图 12 V / 24 W adapter schematic with NCP 1200 • • 33 仅用于非连续导电模式 DCM 通用主电源 Universal mains only. DSS -> 无辅助绕组 DSS -> No auxiliary winding • • 开关频率为 65 k. Hz Switching frequency: 65 k. Hz 内部固定短路保护 Internal fixed short circuit protection
www. onsemi. com. cn 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! q 开关频率65 k. Hz Switching frequency 65 k. Hz Ø 选择choose Ct = 270 p. F q NCP 1200的最大电流设定点为 1 V Maximum current setpoint of NCP 1200 is 1 V Ø 选择choose VCS= 1 V，并计算Roffset : Ø 无须修改感测电阻 No need to modify Rsense q 光耦合器配置 Optocoupler configuration 2. 4 kΩ Ø NCP 1200: 共发射极 common emitter 34 Ø NCP 1351: 共集电极 collector common
www. onsemi. com. cn 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! q 采用NCP 1351的12 V/24 W适配器原理图 35 12 V / 24 W adapter schematic with NCP 1351
www. onsemi. com. cn 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! q 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 24 W 17 W 10. 7 W 1. 5 W 0. 7 W 0. 5 W NCP 1200 85% 84% 83% 66% 57% 52% NCP 1351 85 % 85% 84% 75% 70% 65% 空载 No load 234 m. W 78 m. W 动态自供电功率耗散！ DSS power dissipation ! 36
www. onsemi. com. cn 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! q 输出纹波比较 Output ripple comparison Vout 10 m. V / div. Vds 200 V / div. Vout 1 m. V / div. Vds 100 V / div. Ø NCP 1200, 空载 No load Ø NCP 1351, 空载 No load NCP 1351的输出纹波要小 10倍 output ripple is 10 times smaller with NCP 1351 37 The
www. onsemi. com. cn 议程Agenda 1. 当前水准：准谐振和固定频率 2. 用于反激的固定导通时间(FON)控制介绍 State of the art: quasi resonant and fixed frequency Introduction to the fixed on time control for flybacks 1. 固定频率、准谐振和固定导通时间比较 2. 设计方法学及示例 3. 将您的固定频率适配器更新为固定导通时间模式 4. 增添额外功能性的技巧与决窍 5. 面向快速简单的固定导通时间设计的资源 38 Fixed frequency, quasi resonant, and fixed on time comparison Design methodology and example Update your fixed frequency adapter to fixed on time Tips and tricks to additional functionality Resources for quick and easy fixed on time designs
www. onsemi. com. cn 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 ü半波提供最佳的闩锁恢复时间 Half-wave gives the best latch recovering time 39
www. onsemi. com. cn 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 ü将Vcc分解为两个电容 Split Vcc with two capacitors • Cvcc单独正常启动(D 1) CVcc starts-up normally alone (D 1) • Creser在待机时维持Vcc 作状态 Creser keeps Vcc alive in standby 4. 7 µF 40 47 µF
www. onsemi. com. cn 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 作时固定最小高电压 Fix the minimum bulk voltage for operation 41
www. onsemi. com. cn 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 42
www. onsemi. com. cn 过载保护 Over Power Protection q 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C 3被反激充电 The diode avoids C 3 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 43
www. onsemi. com. cn 频率抖动技巧与决窍 Frequency Jittering Tip & Trick 注入全波纹波至CS引脚 注入半波纹波至CS引脚 Inject full wave ripple into CS pin 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 44
www. onsemi. com. cn 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. 45
www. onsemi. com. cn 欠压 Brown Out 欠压导通 BO on 46 欠压关闭 BO off
www. onsemi. com. cn 斜波补偿 Ramp Compensation q 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 47
www. onsemi. com. cn 斜波补偿 Ramp Compensation q 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 48
www. onsemi. com. cn 软启动 Soft Start q 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) 49
www. onsemi. com. cn 将NCP 1351与其他控制器相连接 Interfacing NCP 1351 with Other Controllers q NCP 1351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 NCP 1351 can share ground signal with other controller? (mixing negative and positive current sensing) 连接至其它控制器的 VCC引脚 To other or D 1 controller VCC pin Caux 100 u Laux D 2 1 8 2 7 3 6 4 5 Rcs NCP 1351 连接至其它控制的接地 引脚和大电容 To other controller GND pin and bulk cap Cstbvcc 4. 7 u Rsense 主接地 Main ground 50 主接地 Main ground NCP 1351接地 NCP 1351 ground Lp
www. onsemi. com. cn 布线建议 Layout Suggestions 22 p. F Vcc Roffset 低阻抗点 Low impedance point Rsense 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 51
www. onsemi. com. cn 改变最大开关频率 Changing the Maximum Switching Frequency 开始START • 保持Lp值不变 Keep 计算新的峰值电流Ipeak 计算 Calculate Ct Calculate new Ipeak 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 结束 END 修改偏置电阻值Roffse以设定 新的峰值电流Ipeak 2 FSW decreases ? 保持变压器参数 是yes Keep transformer 否no Modify Roffset value to set new peak current 计算磁芯磁通量 Calculate core flux B > Bsat ? 是yes 修改变压器参数 Modify transformer 52 减小开关频率FSW?
www. onsemi. com. cn 改变最大输出功率 Changing the Maximum Output Power q改变最大开关频率 Change the maximum switching frequency: Ø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 Ø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 保持变压器参数(Lp, Bsat)不变 Keep transformer (Lp, Bsat) 保持Rsense、Roffset不变 Keep Rsense, Roffset 计算提供Pout 2所需的开关 频率Fsw Calculate needed 计算Calculate Ct Fsw to deliver Pout 2 (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 53
www. onsemi. com. cn 议程Agenda 1. 当前水准：准谐振和固定频率 2. 用于反激的固定导通时间(FON)控制介绍 State of the art: quasi resonant and fixed frequency Introduction to the fixed on time control for flybacks 1. 固定频率、准谐振和固定导通时间比较 2. 设计方法学及示例 3. 将您的固定频率适配器更新为固定导通时间模式 4. 增添额外功能性的技巧与决窍 5. 面向快速简单的固定导通时间设计的资源 54 Fixed frequency, quasi resonant, and fixed on time comparison Design methodology and example Update your fixed frequency adapter to fixed on time Tips and tricks to additional functionality Resources for quick and easy fixed on time designs
www. onsemi. com. cn NCP 1351 – 设计资源 Collaterals q 应用笔记 Application notes: – – 40 W打印机电源设计AND 8278 Design of a 40 W Printer PSU AND 8278 50 W适配器电源设计AND 8263 Design of a 57 W Adapter PSU AND 8263 12 W适配器电源设计AND 8288 Design of a 12 W Adapter PSU AND 8288 使用脉宽调制(PWM)开关技术建模：AND 8280 Modeling Using the PWM Switch Technique: AND 8280 q 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 q 参考设计 Reference design: – 40 W打印机电源：TND 320/D 40 W Printer Power Supply: TND 320/D q 设计与开发 Design & Development: – NCP 1351电感计算数据表 NCP 1351 inductor calculation Spreadsheet q 仿真 具：Simulations tools: – Spice模型(PSPICE和ISPICE) Spice model (PSPICE and ISPICE) 55
www. onsemi. com. cn 谢谢！如有问题，敬请提出！ Thank You! Any Questions?
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