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Presentation on theme: "Agenda 功率转换 LDO,开关电源 锂电充电管理 音频功放."— Presentation transcript:

1 Agenda 功率转换 LDO,开关电源 锂电充电管理 音频功放

2 功率转换概述 线性稳压器、开关稳压器和电荷泵 Good morning (afternoon)
Thank you for taking the time to learn about ON Semiconductor. 线性稳压器、开关稳压器和电荷泵

3  功率转换 –基础知识 Pout=Vo×Io =Pout/Pin 称为效率 Pin=Vin×Iin
这里越来越热了! 输出电压:2.85V,2.8V,2.5V1.8V,1.5V 并有继续下降的趋势 输入电压Vin对手持设备来说就是电池供电电压 锂电:3~4.2V Pin=Vin×Iin Pout=Vo×Io 转换过程产生热量Ploss=Pin-Po, 这部分损耗对系统的正常工作没有任何贡献,唯一的作用就是缩短待机时间 A converter is a device that delivers power to a given load from a known source. You usually need a converter when the load must operate at a different voltage from that of the input source or filtering is required. Unfortunately, the work associated with the conversion process cannot be perfect and a loss is generated in the form of heat. =Pout/Pin 称为效率

4 功 率 器 件 预 备 知 识 Ⅱ Ⅲ MOSFET三个工作区 截止工作区Ι
栅源电压Vgs低于开通阈值时MOSFET处于截止状态,电流为零,不产生功耗 线性工作区 Ⅱ Vgs高于开启电压时,随着Vgs电压升高,导通电阻也在减小。导通电阻受栅源电压控制,因此漏源电压Vds=Id*Rdson也受栅源电压控制 饱和工作区 Ⅲ Vgs增大到某个值以上,导通电阻达到最小值,再增加Vgs, 导通电阻不会发生变化 导通电阻Rdson与栅源电压Vgs关系

5 功率转换存在两种选择 线性方式: 效率低 噪声小 小或低电流时可以接受 只能降压 功率器件工作在线性工作区 开关方式: 效率高
电压和电流同时具有较大值,功耗较大 调整速度快,可以获得极快的动态响应时间 开关方式: 效率高 要求一个储能元件–电感或电容 存在噪声和EMI问题 输入输出压差大时是理想的选择 可对输入电平 升压/降压/反向 功率器件工作在开关状态 截止时电流为零,没有损耗,导通时由于导通电阻很小,因此电压几乎为零,也不会产生损耗 线性降压 LDO 开关降压Buck Vout Cout Cfly Vbat CONTROL 电荷泵Charge Pump Among the available methods, the linear option is the more costly in term of loss, especially when the input voltage is high compared to the output one. The switching approach requires some charge storage element such as and inductor or capacitor

6 线性稳压器 线性稳压器的作用相当于一个可控制的可变电阻,通过改变与负载之间的电阻比例来调整输出电压,使输出电压保持稳定
R1相当于MOSFET的导通电阻Rdson,可以由栅源驱动电压来控制,对三极管来说是控制基极电流 输入和输出电容用于改善稳定性和瞬态响应性能

7 反馈电路控制功率元件中的偏置电压或偏置电流来控制调整管两端的电压来保证输出电压恒定
线性稳压器特性 功率元件工作在线性区: 1。功率器件两端电压和流过的电流同时存在,功耗较大 2。动态响应速度快 输出电压调整元件相当于可变电阻 可以为三极管或MOSFET Iin=Io Vout 100 mA 1.8V 100mA 3.6V By inserting a resistor (called a pass-element or a ballast) whose value is permanently adjusted by a feedback loop, you obtain a mean to regulate the power delivered to a load. Unfortunately, the insertion losses (or the dropout) generate a lot of wasted power.... 反馈电路控制功率元件中的偏置电压或偏置电流来控制调整管两端的电压来保证输出电压恒定

8 } } 线性稳压器分类 一般的线性稳压器 低压差线性稳压
Min (V - V ) 2V IN O V V IN OUT 主要区别是最小压差,为了保持输出电压稳定输入和输出电压之间必须有一定的压差来保证调整器件正常的工作 低压差稳压器的最小压差较小,一般小于0.5V,用于手持设备的典型值为150mV REF GAIN 低压差线性稳压 } Min (V - V ) 0.5V IN O V V IN OUT I B REF GAIN

9 开 关 稳 压(电感型) 降 压 升 压 In the switching approach, dedicated logic manages the time the switch stays ON and OFF. Because the voltage drop of the switch is ideally zero during the ON and OFF times (Pon = Amps . 0 or Poff = Volts . 0), the component does not dissipate heat: Pswitch = 0! 采用的元件类似,放置方法不同

10 基本降压转换器 BUCK 输出总是小于或等于输入 输入电流不连续(斩波) 输出电流平滑 Basic operation:
Switch turns on to apply input voltage to inductor. Current in the inductor ramps up at a rate of V/L. Current will step up if in continuous mode of operation. Switch turns off . Inductor voltage reverses. Conduction continues through diode. Inductor current ramps down at a rate of V/L. 输出总是小于或等于输入 输入电流不连续(斩波) 输出电流平滑

11 控制功率流 脉冲宽度调制 PWM 占空比 Vin Vo
The duty-cycle (D) is defined by the ratio of the time the switch stays ON over the switching period: D = ton/Tsw. By adjusting the duty-cycle, you can control the amount of power delivered to the load. This technique is called: Pulse Width Modulation. The vast majority of SMPS which work according to this principle, need a Pulse Width Modulator to manage the output power demands. A 10% duty-cycle with a 100kHz switching frequency means an « ON time » of 1µs. 占空比

12 对脉冲串进行滤波 对输入脉冲电压进行平均滤波 电感是平均元件 电容提供附加滤波和瞬态响应
For high efficiency we need lossless components. These are: Inductors Capacitors Switches (Controlled or not) If the input voltage is switched “on & off” we generate a pulse train, of which we can control the duty cycle but not the peak. With an averaging filter, we can adjust the duty cycle to maintain a constant average signal regardless of the input voltage. Average voltage across inductor must be zero. Can not have a DC voltage across it. Therefore the output voltage is the average of the input voltage.

13 PWM 脉冲的产生 锯齿波 FRamp V2(t) 误差比较器输出 开关控制信号

14 线性输出的误差信号» K1 * (Vref- K2* Vout)
“典型的”开关模式架构 电压模式 PWM 反馈电压Vfb从 Vout 分压器引出 线性误差放大器输出与(Vref – Vfb)成正比 固定频率锯齿波与误差信号比较 比较器输出是固定频率、可变脉冲宽度信号,用于驱动功率开关 线性输出的误差信号» K1 * (Vref- K2* Vout) V out 可变占空比,固定频率 Illustration of how the Pulse width modulator works, as you can see some of the elements are similar to the LDO where there is a voltage reference, a resistive divider sensing element and an error amplifier to control how the PWM modulation signal is generated V fb (又叫 “PWM”) 开关驱动信号 V ramp V ref T T

15 实际MOSFET 开关 CGS: Gate to Source Capacitance
CGD: Gate to Drain, or “Miller” capacitance CDS: Drain to Source, or “Coss” capacitance RGi: Internal Series Gate Resistance VT: Gate Threshold Voltage LS: Source Inductance LD: Drain inductance RDS(on): Drain to Source Resistance

16 Turn-On Characteristics: Step 1
Charge CGS to the threshold level.

17 Turn-On Characteristics: Step 2
OUCH! Step 2. Charge CGS from VTH to VGS,MIN required to carry ID. (linear region) Note: The Switch voltage cannot change until the output diode is turned off

18 Turn-On Characteristics: Step 3
OUCH AGAIN! Step 3. Discharge CGD and CDS as VDS falls close to GND.

19 Turn-On Characteristics: Step 4
Apply overdrive by charging CISS to the final gate voltage. 功耗由导通电阻决定Ploss=Id**2*Rdson

20 导通损耗,与MOSFET导通电阻和负载电流有关,负载已知时为固定值
损耗由4部分组成: 开关损耗,与开关频率成正比 导通损耗,与MOSFET导通电阻和负载电流有关,负载已知时为固定值 重载时,导通损耗所占比重较大,效率主要由导通损耗决定 轻载时,导通损耗很小,开关损耗所占比重较大,效率主要由开关损耗决定 ,因为手机大部分时间都处在待机状态负载较轻,因此轻载时的转换效率对系统待机时间影响很大。 如何提高轻载时的转换效率是电源管理非常重要的内容

21 各种脉冲控制方法 在PWM (脉冲宽度调制)中 ,开关频率恒定。占空比取决于脉冲宽度(ton)。NCP1508/09/10/11/20,NCP1402 在PFM (脉冲频率调制)中,脉冲宽度(ton) 恒定。 toff 随着负载和输入电压变化而改变。所以,开关周期不恒定。它是ton 和 toff的和。轻载时可以降低开关频率,提高转换效率NCP1403/NCP1406/NCP5006/NCP5007 脉冲方式Pulse ,PFM模式结合突波模式。即在轻负载下,一些开关周期被忽略,来进一步减小开关次数。NCP1508/09/10/11/20 Switch 开关 Vripple 纹波 Pulse skipping and Pulse Frequency modulation are techniques to address operation under light loads and improve overall system efficiency PFM 模式

22 电压控制 PWM Fixed & Well Known Ripple Frequency Noise Easy to control
Verror FRamp V2(t) V2 Verror Fixed & Well Known Ripple Frequency Noise Easy to control High Quiescent Current (oscillator)

23 电流控制 PWM Fixed & Well Known Ripple Frequency Noise Easy to control
V2 Verror ISense V2(t) FPulse Fixed & Well Known Ripple Frequency Noise Easy to control High Quiescent Current (oscillator) Bit Easier To Stabilize

24 PFM模式 开通时间固定,关断时间由误差比较器决定,如NCP1410,NCP1421或 关断时间固定,开通时间由比较器决定
开或关定时 开通时间固定,关断时间由误差比较器决定,如NCP1410,NCP1421或 关断时间固定,开通时间由比较器决定 如NCP5006,NCP5007

25 Pulse模式

26 频率敏感系统,如电信/无线–开关频率固定。不会干扰系统信号。 PWM信号也可以和主系统时钟同步 PFM,Pulse
一般应用– 占空比范围大 频率敏感系统,如电信/无线–开关频率固定。不会干扰系统信号。 PWM信号也可以和主系统时钟同步 PFM,Pulse 便携式设备–在低占空比/低频时可以降低静态电流和开关损耗。 Summary – PWM is commonly used in cellphone applications because switching frequency range and spectrum is very predicatable – also the PWM clock can be generated from the main system clock

27 不同控制方法效率对比 PULSE模式是转换效率最高的控制方式,轻载时比LDO效率还要高 输出电压纹波也响应的会增大

28 BUCK 降压 Vo = D×VIN ΔIL = ΔIC = D VIN-Vo FL ΔVOUT = D(VIN – VOUT) 8F2LC
VL - V1 Is + Io + + Ton Toff + Vout < VIn F VIn V1 IS Id Ic - - - ID Vo = D×VIN ΔIL = ΔIC = D VIN-Vo FL ΔVOUT = D(VIN – VOUT) 8F2LC + RC DVIN IL ΔIL IL MOY = IO IC 功率器件工作在开关状态,器件两端的电压和其中的电流不会同时存在,器件功耗小,因此效率高 ΔIC Vout ΔVout

29 与降压类似,但是电感、开关和二极管重新安排。 输出总是大于或等于输入 (忽略二极管的正向压降)。 输入电流平滑。 输出电流不连续(斩波)。
升压 负载 把输入升压到一个更高的电压。 与降压类似,但是电感、开关和二极管重新安排。 输出总是大于或等于输入 (忽略二极管的正向压降)。 输入电流平滑。 输出电流不连续(斩波)。 The boost converter topology is quite different than the Buck, as you can see in this drawing there is a direct path between the output and the input. As can be seen here the switch is located between the inductor and ground

30 同步整流 二极管可以由开关替代,以控制电流和提高效率 NCP1410 250mA Boost 升压转换器 NCP15XX 控制逻辑
Also referred to as “Synch-Rec” – the diode used has a loss element associated – Forward voltage can range from V depending on the diode - by replacing this with a power mosfet, this loss can be reduced

31 True Cutoff 关断时电流通路

32 Effect of Ring Killer Circuit
NCP mA, Sync-Rect, PFM, Step-Up DC-DC Converter with Low-Battery Detector and Ring Killer Ring Killer Improves EMI in Discontinuous Conduction Mode Normal DC-DC NCP1411 Effect of Ring Killer Circuit The MAX1676 has a similar function but requires: an additional external resistor a larger 10-pin package

33 基于电荷泵的功率转换 电容可以用来存储能量! 基于电感的升压转换器 基于开关电容的升压转换器
Vbat Vout Vbat Cout Cfly Vout CONTROL 控制 The other mechanism to store charge is a capacitor and with a set of switches and a controller they can be configured to, boost, buck, or invert a voltage source. Also called a switched capacitor converter CONTROL控制 Cout Vbat 基于电感的升压转换器 基于开关电容的升压转换器

34 基本倍压器 Vout = Vbat + Vcfly
S2 Vout S1 Cout Cfly Vout = Vbat + Vcfly S3 S4 U1 CLOCK时钟 Example of a using 4 switches, 2 capacitors, and a clock oscillator to double a voltage

35 第1阶段 – 把电荷传输到加速电容 Vbat S2 Vout S1 Load 负载 Cout Cfly S3 S4 Vcfly = Vbat U1 CLOCK时钟 In the first phase the flying capacitor is charged

36 第2阶段 – 将Vbat加到Cfly上 + - + -
Vout Vbat S2 S1 Cout 负载 Cfly Vcout = Vbat + Cfly S3 S4 U1 CLOCK时钟 Once the flying capacitor has received charge, it is disconnected from the source and connected to the output

37 倍压器 – 非稳压 Cout = 陶瓷 ESR = 0.050 ohm ESR = 0.050  无负载
This is a simulation to show how the output is charged up over a number of switching cycles 时间

38 倍压器(稳压) – Vout上的波纹 Cout = 陶瓷 ESR = 0.050 ohm ESR = 0.050  负载 = 50 
500mVpp Cout = 陶瓷 ESR = ohm ESR =  负载 = 50  This illustrates the real world case of the output being loaded so you can see the Cout charge and discharge cycles which results in ripple 时间

39 需要的电容大小是开关速度和输出负载要求的函数。 总的PCB面积通常小于中等负载的开关稳压器。 可以不稳压或由外加的控制电路稳压
电荷泵小结 在开关周期中,电荷存储在电容中 与电感方法比较,开关元件的数量增加 需要的电容大小是开关速度和输出负载要求的函数。 总的PCB面积通常小于中等负载的开关稳压器。 可以不稳压或由外加的控制电路稳压 也可以用于使电压反相 效率比电感方式低 Charge pumps can be used in a wide variety of applications and when the load is light and the input source is somewhat regulated, the output voltage is relatively stable. The main advantages of charge pumps is the small size of the external components versus and inductive solution, the drawback is a more complicated IC

40 电荷泵作为电压反相器 电容 输出电压 This is an example of an ON Semiconductor device the NCP1729 which is a simple charge pump inverter, the graphs illustrate the Vout as a function of load current 输出电流

41 DC/DC Vs LDO Low Dropout Linear Regulator – LDO/Charge Pump
PWM Buck Regulator PFM/Pulse Simple design Minimum external components Low cost No Switching noise/EMI Simple layout Complex design External Inductor and capacitors required Switching noise&EMI Noise over wide frequency spectrum Output voltage tolerance Low efficiency High power dissipation Thermal/heat issues High efficiency at medium and high loads Predictable switching noise High efficiency at light loads

42 小结 这是对低压、低功率应用中最常用的电路拓扑结构的综述 还有各种其它的拓扑结构,但是大多数是这里的变形或组合
每种拓扑结构包含一组独特的设计折衷: 系统效率的影响 噪声产生和控制 器件的数量和大小

43 锂离子电池充电管理

44 Li-ion电池充电要求 需要4个阶段 预充电(pre-charge) 恒流充电(full-charge) 恒压充电(final-charge) 涓流充电(trickle-charge)

45 Li-ion电池充电要求

46 预充电 (pre-charge) 条件判断-如果电池电压<0.9V,将判断为电池已经损坏,不会再对电池进行充电,因为对已经损坏的电池进行充电可能会造成安全问题(爆炸或燃烧)。 电池电压低于放电终了电压(3V)并且大于0.9V时,以恒流充电电流的1/10的电流进行小电流充电,时间较短,一般为几分钟 如果用大电流对完全放电的电池进行充电,会对电池造成损害。

47 恒流充电 (full charge) 电池电压大于一定阈值后,将进入恒流充电 特点 恒流 电池的大部分能量(80%)在这一阶段储存 时间较长 充电电流一般在0.5C,过大影响充电效率,充满后的容量会减少。

48 恒压充电 (final charge) 电池电压达到充电的终了电压时进入恒压充电 特点 电池电压保持恒定。 充电电流逐渐较小。 充电电流小于1/10恒流充电电流时,可以认为充电结束。 电池容量将完全得到补充

49 涓流充电 (trickle-charge)
充电电流小于1/10恒流充电值时,为涓流充电 特点 电池电压恒定 充电电流逐渐接近0 目的是补充电池的自放电 锂电的自放电速率一般在5%-10%每月

50 功率器件的设计 Ploss=(Vin-Vbat)*Icharg NTHD4P02 NTHD3101
功率器件持续流过充电电流,会产生热量,温度会有上升。 功率器件上的功耗为 Ploss=(Vin-Vbat)*Icharg Vin-充电器输出电压 Vbat-电池电压 Icharg-充电电流 降低温度的方法 降低充电器输出电压 减小充电电流 改善散热条件 NTHD4P02 NTHD3101

51 音 频 功 放

52 根据功率器件工作状态的不同,类似线性电源和开关电源
音频功放分类 根据功率器件工作状态的不同,类似线性电源和开关电源 D类 Vce A类 Ic AB类 B类

53 音频功放分类 A类 B类 D类 AB类

54 GSM手持设备开关噪声实例 Without Supply Rejection!
电话在接通时, GSM射频功放从电源端间断性的拉电流 脉冲宽度为0.577mS,周期为4.6mS,峰值电流可达2。5A. 由于电池有内阻存在,在功放的供电电压Vp端上会造成较大的电压纹波 Vp端的电压纹波频率贷款为 [217 Hz, 1,5 kHz] ,在音频范围内。 为了获得好的声音效果,音频功放必须对这一噪声具有抑制能力,经分析PSRR值最小要大于60dB才能 C0 = 38 mV C1 = 74 mV C2 = 68 mV C3 = 59 mV Without Supply Rejection! C4 = 48 mV C5 = 35 mV C6 = 22 mV

55 电池内阻的影响 内阻在器件断续的从电源拉电流时会造成输出电压的波动 例: 手机在 射频功放工作和空闲时的电压变化
例: 手机在 射频功放工作和空闲时的电压变化 Volts 4.2 Standby Recharge 3.9 电池内阻R = DV/DI随着通话时间而变化 As the load current is switching, noise is created by the IR drop of the internal resistance – with GSM is quite significant since peak currents can be 1.5A. 负载电流切换时,电池内阻压降将会产生噪声,GSM 系统尤其严重,因为其峰值电流可能达到1.5A。 Operation 3.7 1 2 3 4 5 6 Hours

56 音频功放的关键参数-PSRR Amplifier PSRR-电源注入抑制比(power supply rejection ratio)
Power supply PEAK to PEAK RIPPLE OUTPUT PEAK to PEAK PSRR (DB) = 20 Log OUTPUT PEAK to PEAK RIPPLE INPUT PEAK to PEAK RIPPLE

57 输出功率和谐波畸变 桥接负载输出 输出波形的失真(即谐波畸变)将影响音质,谐波畸变与输出功率有关,输出功率越大,畸变越大
输出最大值没有超过供电电压,畸变较小,输出功率较小 The Bridge Tied Load connects two complementary outputs across the speaker to get around the

58 输出功率和谐波畸变 桥接负载输出 输出波形的失真(即谐波畸变)将影响音质,谐波畸变与输出功率有关,输出功率越大,畸变越大
输出最大值超过供电电压,失真较大,最大输出功率较大 The Bridge Tied Load connects two complementary outputs across the speaker to get around the


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