功率转换器概述

Buck Regulator
i1 v1 Vin = 15 V i2
i3 Vout = 5 V Load (R) 负载
v1 0
电感 开关
Buck Operation – Switch Off 降压工作– 开关断开
-
Vout
I V = out t L
+ +
•Current decreases in inductor 电感中的电流减少 •Diode is conducting 二极管导通
I inductor I diode
电感 二极管
Input 输入 Output 输出
Voltage 电压
Voltage 电压
Basic Buck Converter 基本降压转换器
Input 输入 Control Circuit 控制电路
Output 输出
Output is always less than or equal to the input 输出总是小于或等于输入 Input current is discontinuous (chopped) 输入电流不连续（斩波） Output current is smooth 输出电流平滑
Q1 Cin 1 uF
Enable
启用
+ Vref
Cout 1 uF
Addition of Switching Element 增加开关元件 I feel much cooler
now... 现在温度低得多了
Vout (avg)
100mA 3.6V 1.8V
Vin
Vout
0
Vout
Controlling the Power Flow
Where to use PWM, PFM? Why? PWM, PFM用在哪里?为什么?
PWM General application – duty ratio range is large 一般应用– 占空比范围大 Frequency sensitive system such as telecom/ radio – switching frequency is fixed. No interface is made to system signals 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 signal can also be synchronized to a master system clock PWM信号也可以和主系统时钟同步 PFM Portable Devices – quiescent current is saved at low duty-ratio/ low frequency 便携式设备–在低占空比/低频时可以降低静态电流。
Power Conversion Overview 功率转换概述
Linear Regulators, Switching Regulators and Charge Pumps 线性稳压器、开关稳压器和电荷泵
Power Conversion – Basics 功率转换 –基础知识
It ’s getting hot in here! 这里越来越热了！
Two Options Exist for Power Conversion 功率转换存在两种选择
The linear approach: R 线性方式： 线性 •efficiency is poor 效率低 0到∞ •good noise performance 噪声小 •acceptable when (Vin-Vout) is small or low current (Vin-Vout) 小或低电流时可以接受 •can only decrease the input level 只能降低输入电平 The switching approach: 开关方式： 开关 ON or OFF •efficiency is high 接通或关断 效率高 •Requires a storage element – inductor or capacitor 要求一个储能元件–电感或电容 •noise performance is poor 噪声大 •Ideal with large (Vin-Vout) (Vin-Vout)大时是理想的 •increase/decrease/invert the input level 可对输入电平 升压/降压/反向
Pin
/
Pout
The conversion mechanism generates heat... 转换过程产生热量... η=Pout/Pin is called the efficiency η=Pout/Pin 称为效率
Ploss = Pin − Pout = Pout
η
1 − Pout = Pout ⋅ η − 1
Output voltage controlled by the error amplifier 输出电压由误差放大器控制 Input and output capacitors for stability and transient response performance 输入和输出电容用于改善稳定性 和瞬态响应性能 Can be optimized for low quiescent current or transient behavior 可以针对静态电流或瞬态响应进 行优化 FET (Q1) size is based on output current and the desired dropout performance FET (Q1)容量根据输出电流和要 求的电压降性能决定
Switch 开关 Vripple 纹波
In PFM (Pulse Frequency Modulation), the pulse width (ton) is constant. The toff will change with load and input voltage changes. Therefore, the switching period is NOT constant. It is the sum of ton and toff. 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。
Vfb Vref Vramp T
Various Pulse Control Methods 各种脉冲控制方法
In PWM (Pulse Width Modulation), the switching frequency is constant. Duty ratio depends on pulse width (ton). 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)。 One variation on PWM is “Pulse Skipping” where under light loads some switching cycles are completely ignored to lower duty cycle. PWM的一种变形是“跳周期”，即在轻负载下，一些开关周期被忽略，来减小导致占空比。
What Happens if Vin Amplitude Varies? 如果Vin的幅度改变，会发生什么?
t on high Vpk High Line 高电平 Vpk Low Line 低电平 Average 平均 t on low T
Βιβλιοθήκη Baidu
¾ Feedback Circuit Controls the Pulse Width 反馈电路控制脉冲宽度
Vout Linear output: Error Signal ≈ K1 * (Vref- K2* Vout) 线性输出的误差信号≈ K1 * (Vref- K2* Vout) Variable Duty Cycle, Fixed Frequency 可变占空比，固定频率 (a.k.a. “PWM”) Switch Drive Signal (又叫 “PWM”) 开关驱动信号 T
Pulse Width Modulation 控制功率流 脉冲宽度调制
1 Voutavg = ⋅ Ts
Ts
∫
0
Vout (t ) ⋅ dt =
ton ⋅Vin = D ⋅Vin Ts
TON
TOFF TS
Duty Cycle = Duty Ratio = D =
TON TON = TOFF TOFF TS
Basic Linear Regulator 基本线性稳压器
线性传输元件
Power is Dissipated In the pass element 功率在传输元件中损耗
Vout
100mA
100 mA
3.6V
1.8V
η=50%
Low Dropout Regulator 低压降稳压器
Vin Vout
Buck Operation – Switch On 降压工作 – 开关接通
Vin
+
Vout
+ +
•Current increases in inductor 电感中的电流上升 •Diode is not conducting 二极管不导通
I V V = in out t L
I inductor I switch
(Continuous Conduction)
降压稳压器 （连续导通）
Inductor current is continuous 电感电流连续 – Vout is the average of the voltage at its input (V1). Vout是电感输入电压(V1)的平均值。 – Output voltage is the input voltage times the duty ratio (D) of the switch. 输出电压是输入电压乘以占空比(D)。 – When switch in on, inductor current flows from the battery. 开关接通时，电感电流从电池流入。 – When switch is off, it flows through the diode. 开关断开时，电感电流流过二极管。 – Neglecting losses in the switches and inductor, D is independent of load current. 忽略开关和电感中的损耗， D与负载 电流无关。
“Classical” Switch-mode Architecture Voltage Mode PWM “典型的”开关模式架构 电压模式 PWM
Feedback voltage Vfb is derived from Vout divider 反馈电压Vfb从 Vout 分压器引出 Linear error amplifier output is proportional to (Vref – Vfb) 线性误差放大器输出与(Vref – Vfb)成正比 Fixed-frequency triangular ramp compared to error signal 固定频率锯齿波与误差信号比较 Comparator output is fixed-frequency, variable pulse width signal used to drive the power switch 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
=
TON TS
占空比
D' = 1 - D = TOFF TON
TOFF
Filtering the Pulse Train 对脉冲串进行滤波
•Averaging filter with pulsed voltage input 对输入脉冲电压进行平均滤波 •Inductor is averaging element 电感是平均元件 •Capacitor provides added filtering, and transient response 电容提供附加滤波和瞬态响应