Popular Inductor for Buck Converter_101124_EMC
DC_DCconverter tutorial
DC-DC Converter TutorialSwitching regulators offer higher efficiency than linear regulators. In addition,they can step-up, step-down and invert the input voltage. This article outlines the different types of switching regulators used in DC-DC conversion. It also reviews and compares the various control techniquesfor these converters.What Is a Switching Regulator?A switching regulator is a circuit that uses an inductor, a transformer, or a capacitor as an energy-storage element to transfer energy from input to output in discrete packets. Feedback circuitry regulates the energy transfer to maintain a constant voltage within the load limits of the circuit. The basic circuit can be configured to step up (boost), step down (buck), or invert output voltage with respect to input voltage.Why Use a Switching Regulator?For battery management, the only other choice is a linear regulator. Linear regulators only step down, and efficiency is equivalent to the output voltage divided by the input voltage.On the other hand, switching regulators operate by passing energy in discrete packets over a low-resistance switch, so they can step up, step down, and invert. In addition, they offer higher efficiency than linearregulators. Using a transformer as the energy-storage element also allows the output voltage to be electrically isolated from the input v oltage. The one disadvantage of the switching regulator is noise.Any time you move charge in discrete packets, you create noise or ripple. But the noise can often be minimized using specific control techniques and through careful component selection.Charge PhaseA basic boost configuration is depicted in Figure 1. Assuming that the switch has been open for a long time, the voltage across the capacitor is equal to the input voltage. During the charge phase, when the switch closes the input voltage is impressed across the inductor and the diode prevents the capacitor from discharging to ground. Because the input voltage is DC, current through the inductor rises linearly with time at a rate that is proportional to the input voltage divided by the inductance. The energy stored in the inductor for the duration shown is equal to one-half the inductance times the square of the peak current.Figure 1. Charge phase: When the switch closes, current ramps up through the inductor.Discharge PhaseFigure 2 shows the discharge phase. When the switch opens again, the voltage across the inductor changes instantaneously to whatever is required to maintain current flow, because the inductor current can't change instantly. In order for current to continue flowing, the inductor voltage must change enough to forward-bias the diode. The voltage on top of the switch (at the diode anode) is equal to a diode forward voltage (VD) above the voltage on the capacitor, and the voltage across the inductor actually switches polarity relative to the charge phase. In this initial cycle, V-switch is equal to VIN plus VD. If we assume that the capacitor is relatively large such that the dV/dt for the resulting inductor peak current is negligibly small, then VOUT remains relatively constant during the second half of the cycle. As V-switch remains at a diode drop above VOUT, the voltage across the inductor also remains relatively constant. This results in a linear di/dt opposite in polarity from the charge phase and proportional to the inductor voltage divided by the inductance, -VD over L in this initial cycle.Figure 2. Discharge phase: When the switch opens, current flows to the load.If we continue this process over and over, the voltage across the capacitor (VOUT) will rise with every cycle. If we then employ some feedback and control (see Figure 7), the output voltage can be regulated at any value within the breakdown tolerance of the selected components. If we take the same basic elements and rearrange their positions, we can create the other configurations such as the buck converter topology (see Figure 3). Here, when the switch closes, the voltage across the inductor is equal to VIN minus VOUT. Initially this is VIN, because VOUT is zero at startup. Current will ramp up linearly, as in the boost case (Figure 4), and flow into the output capacitor. When the switch opens, the voltage across it will change instantaneously to allow current to flow through the diode and the inductor, and into the output capacitor. Because energy is gated to the output capacitor in each half of the cycle,the buck topology typical ly offers the greatest efficiency.Figure 3. Buck converter topologyFigure 4. Simple boost converterKeeping the switch in the same place and swapping the inductor and diodepositions in the circuit yields the inverting topology (Figure 5). When the switch closes, VIN is impressed across the inductor and the current ramps up as before. When the switch opens again, the current wants to continue toflow in the same direction. Thus, it flows through the diode and charges the output capacitor in the reverse direction, creating an output voltage with the opposite polarity to the input voltage.Figure 5. Inverting topologyUsing a transformer, you can realize boost, buck, or inverting topologies and isolate the output voltage fromthe input voltage. The circuit shown in Figure 6 is a boost transformer flyback topology.Figure 6. Transformer flyback topologyControl TechniquesPopular control techniques include pulse-frequency modulation, where the switch is cycled at a 50% duty cycle until the output voltage comes into regulation; current-limited pulse-frequency modulation, where the charge cycle terminates when a predetermined peak inductor current is reached; and pulse-width modulation, where the switch frequency is constant and the duty cycle varieswith the load. Each of these control techniques has advantages and disadvantages.Clocked pulse-frequency modulation, or PFM, is the simplest control technique. With this method, when the output voltage is below the regulation point the control circuit gates a free-running oscillator to the switch. The inductive charge pumping action boosts the output voltage back up to the regul ation point. However, the inductor selection is complicated, the peak-to-peak voltage ripple can be quite high, and the noise/ripple spectrum will vary greatly with the load.Current-limited pulse-frequency modulation is similar to standard PFM; but instead of using a 50% duty cycle oscillator, this control scheme employs a peak inductor current limit and a one shot. As soon as the output voltage goes outof regulation, the switch turns on until the inductor current reaches the programmed current limit, usually set with a current sense resistor in the inductor-current path. Once the inductor current reaches the programmed limit, the switch turns off for a time constant set by an internal one shot, generally on the order of a microsecond. At the end of the one-shot time constant, the feedback circuit compares VOUT to the regulation voltage and either turns the switch on again if VOUT remains out of regulation or holds the switch off until VOUT falls out of regulation.Because the inductor peak current is fixed , this control scheme makes inductor selection easier; you only need to size the inductor core to meet the fixed limit. Also, because the peak current is fixed, the peak-to-peak ripple is reduced over the standard PFM, although the noise spectrum still varies with the load.Figure 7. Adding feedback and controlThe pulse-width modulation, or PWM, control technique maintains a constant switching frequency and varies the ratio of charge cycle to discharge cycle as the load varies.This technique affords high efficiency over a wide load range. In addition, because the switching frequency is fixed, the noise spectrum is relatively narrow, allowing simple low-pass filter techniques to greatly reduce the peak-to-peak voltage ripple. For this same reason, PWM is popular with telecom applications where noise interference is of concern. Figure 8 shows an example of the clocked PFM control scheme. VOUT is fed back through a voltage dividerto one input of a comparator whose other input is connected to a reference voltage. When the divided-down VOUT falls below VREF, the comparator gates the square-wave oscillator to the switch. This causes it to rapidly open and close, storing energy in the inductor and transferring it to the output capacitor in each cycle.Figure 8. Clocked pulse-frequen cy modulationThe current-limited minimum-off-time PFM scheme, depicted in Figure 9, is a bit more complicated. As with the clocked PFM, VOUT is fed back through a voltage divider to one input of a comparator whose other input is connected to a reference. The output of this comparator controls the trigger of a one-shot multivibrator. Another comparator looks at the peak inductor current as a voltage across a current sense resistor in the source of the N-channel MOSFET switch. When the output is out of regulation, the SR flip-flop turns the NMOS switch on until the voltage across the current sense resistor is equal to the reference voltage. The flip-flop resets,turning off the NMOS switch, the one-shot timer is triggered, and the switch remains off for the duration ofthe one shot, usually 1 microsecond. If the output voltage limiting comparator is still indicating an out-of-regulation condition, the flip-flop sets again and the cycle repeats itself.Figure 9. Current-limited minimum-off-time pulse-frequency modulationPulse-width modulation comes in a couple of different flavors. In voltage-mode PWM, shown in Figure 10, the divided-down output voltage is fedto an amplifier whose output is the difference between a voltage reference and the divided-down output voltage. This "error voltage" sets the threshold of a comparator whose other input is connected to a ramp generator. The output of the comparator drives the main switch. On a cycle-by-cycle basis, the greater the error voltage, the higher the comparator threshold on the comparator, and the longer the switch is held on.As the switch is held on longer, the peak current in the inductor is allowed toclimb higher, storing more energy to serve the load and maintain regulation.Figure 10. Voltage-mode pulse-width modulationCurrent-mode pulse-width modulation (Figure 11) works in a similar fashion but with a key difference. As with the voltage-mode PWM, the divided-down VOUT is fed to a different amplifier whose output is the difference between the fed-back VOUT and a voltage reference. However, instead of setting the threshold on a ramp generator, this scheme employs a current sense resistor to sense theinductor current and flip-flop to control the switch. With each cycle, the switch is turned on by a pulse oscillator and the current in the inductor ramps up to the threshold set by the error voltage. This control scheme tends to be a bit easier to stabilize than the voltage-mode PWM.Figure 11. Current-mode pulse-width modulationIn striving for maximum efficiency, one of the largest power-loss factors to consider is that through the diode. The power dissipated is simply the forward voltage drop multiplied by the current going through it. This power dissipation (loss) reduces overall efficiency.To minimize this loss, most DC-DC switching regulator circuits use Schottky-type diodes whose relatively low forward voltage drop and high speed minimize losses. However, for maximum efficiency, you can use a switch in place of the diode.This is known as "synchronous rectification" (see Figures 12 and 13). The synchronous rectifier switch is open when the main switch is closed, and thesame is true conversely. To prevent "crowbar" current that would flow if both switches were closed at the same time, the switching scheme must be break-before-make. Because of this, the diode is still required to conduct the first bit of current during the interval between the opening of the main switch andthe closing of the synchronous rectifier switch.Figure 12. Synchronous rectificationFigure 13. Example: Synchronous rectified buck regulatorAnother variant of PWM is the Idle-Mode PWM scheme (Figure 14). This technique combines the best of PFM's efficiency at light loads and PWM's efficiency and low-noise characteristics at higher loads. Thus, at light loads it acts similar to a PFM, skipping pulses as necessary, and at higher loads it acts as a PWM, affording the maximum efficiency over the widest possible load range.Figure 14. Idle Mode PWMIn Figure 15, we see that the efficiency with Idle-Mode PWM is greater than 90% with V+ = 6V from 20mA or to just over 5A!Figure 15. Efficiency with Idle Mode。
Buck转换器的电流纹波系数
王信雄AN009 – Jul 20141. 介绍 (2)2. 纹波系数 (3)3. 电感的面积积 (4)4. 一个设计示例 (6)5. 总结 (7)Buck 转换器的电流纹波系数L in o V (t)V V =- ; on 0 t T ≤≤ (Q 1 “ON”)(1)电感电流将从 i L (0) 开始线性增加：in oL L V V i (t)i (0)t L-=+⋅ (2)当功率开关截至 (OFF) 时，加在电感上的电压与输出电压相同，但极性相反：L o V (t)V =- ; on s T t T ≤≤(Q 1 “OFF”) (3)Buck 转换器的电流纹波系数在此期间，电感电流将以斜率 从 i L (T on ) 开始线性减少：oL on L on on V i (t T )i (T )(t T )L-=-⋅- (4)根据电感伏秒平衡的特性，很容易从式 (1) 和 (3) 得到电压传输比：o on sV TD (duty cycle)Vin T =≡(5)L L on)L i i (T i (0)∆=-(6)很明显，负载电流可表达为L on)L o i (T i (0)I 2+=(7)Buck 转换器的电流纹波系数纹波系数可被定义为L oi γI ∆≡(8)当纹波系数小于2时，转换器工作在连续导通模式 (Continous Conduction Mode, CCM)，否则就是非连续导通模式 (Discontinuous Conduction Mode, DCM)。
由于连续导通模式下功率元件所受电流应力较低，工作在满载状态下的 Buck 转换器一般都被设计成工作在这种模式下。
因此，本文也只对连续导通模式进行讨论。
等式(8)可以被表现为电压相关的形式：in os in s os L o o o oV V D T V (1D)D T V (1D)T Δi L γ or I I L I L I -⋅⋅⋅-⋅⋅⋅-⋅===⋅⋅ (9)对于一个固定的电感量而言，输入电压越高，纹波系数就越高。
Multisim10元器件大全
Multisim8.0中的元件库和元器件2009-03-23 15:54 电子仿真软件“Mumsim8.3.30特殊版”的元件库中把元件分门别类地分成13个类别，每个类别中又有许多种具体的元器件，为便于读者在创建仿真电路时寻找元器件，现将电子仿真软件“Mumsim8.3.30特殊版”元件库和元器件的中文译意整理如下，供读者参考。
电子仿真软件Mumsim8.3.30特殊版的元件工具条如图1所示。
图11.点击“放置信号源”按钮，弹出对话框中的“系列”栏如图2所示。
图2(1). 选中“电源(POWER_SOURCES)”，其“元件”栏下内容如图3所示：图3(2). 选中“信号电压源(SIGNAL_VOLTAGE_SOURCES)”，其“元件”栏下内容如图4所示：图4(3). 选中“信号电流源(SIGNAL_CURRENT_SOURCES)”，其“元件”栏下内容如图5所示：图5(4). 选中“控制函数块(CONTROL_FUNCTION_BLOCKS)”，其“元件”栏下内容如图6所示：图6(5). 选中“电压控源(CONTROLLED_VOLTAGE_SOURCES)”，其“元件”栏下内容如图7所示：图7(6). 选中“电流控源(CONTROLLED_CURRENT_SOURCES)”，其“元件”栏下内容如图8所示：图82. 点击“放置模拟元件”按钮，弹出对话框中“系列”栏如图9 所示。
图9(1). 选中“模拟虚拟元件(ANALOG_VIRTUAL)”，其“元件”栏中仅有虚拟比较器、三端虚拟运放和五端虚拟运放3个品种可供调用。
(2). 选中“运算放大器(OPAMP)”。
其“元件”栏中包括了国外许多公司提供的多达4243种各种规格运放可供调用。
(3). 选中“诺顿运算放大器(OPAMP_NORTON)”，其“元件”栏中有16种规格诺顿运放可供调用。
(4). 选中“比较器(COMPARATOR)”，其“元件”栏中有341种规格比较器可供调用。
buck converter
Introduction
The step-down and step-up voltage converters are the two basic converter topologies . these are referred as the buck and boost converters respectively . it must , however , be kept in mind that a tep-down voltage converter is also a step-up current converter and vice versa because the input must equal the output power . the buck-boost converter does both stepping up and down tion . the cuk converter is a dual of the buck-boost converter . all these converters have single , o and four quadrant variations in topologies.
Fig.1
Buck converter
Buck converter
a prominent application of the buck con-verter is a dc regulated power supply in which the output voltage is regulated against the variations in the load resistance and the input voltages . There are three modes of buck converter ： continuous conduction mode （ CCM ） , boundary conduction mode （ BCM ) ， discontinuous conduction mode （DCM ) .
DC-DC电路中电感的意义及选择
ILP ILT
VD VOUT t OFF
L
(5)
Current flow in the coil L is almost the same as the output current; consequently,
ILP ILT 2 IOUT
From equations (3) and (6), ILP during Q1 ON-state is
(6)
ILP IOUT
VIN VSW
VOUT t ON 2L
(7)
Using equations (5) and (6), ILP can be calculated during the period when the switching element is OFF:
VIN fSW r IOUT
(17)
Then, solve (17) for L to calculate the inductance value:
VL( OFF ) VD VOUT
VD: VOUT: Forward Voltage Drop across D1 (V) Output Voltage (V)
(4)
Using equations (2) and (4), the current flowing through coil L when Q1 is OFF is as follows:
● Inductor Current Waveform Fig. 3 shows the inductor’s current waveform. IOUT is the average inductor current value. When switching element Q1 is ON, current flow is shown during ON period tON of Q1, and voltage VL(ON) of coil L can be calculated by the following equation:
共正极buck电路
共正极buck电路英文回答：Buck converters are a type of DC-DC converter that step down the input voltage to a lower output voltage. They are widely used in various applications, such as power supplies, battery chargers, and LED drivers. In a buck converter, the input voltage is applied to the switch, which is typicallya MOSFET. When the switch is closed, current flows through the inductor and stores energy. When the switch is open,the energy stored in the inductor is transferred to the output capacitor and load.One advantage of a buck converter is its high efficiency. Since the switch operates in a switching mode,it dissipates less power compared to linear regulators.This results in less heat generation and higher overall efficiency. Another advantage is its ability to step down the input voltage. This is particularly useful when theinput voltage is higher than the required output voltage.By adjusting the duty cycle of the switch, the output voltage can be regulated within a desired range.Let me give you an example to illustrate how a buck converter works. Suppose you have a 12V battery and you want to power a 5V device. Using a buck converter, you can step down the 12V input voltage to 5V. By adjusting the duty cycle of the switch, you can regulate the output voltage to exactly 5V. This allows you to efficiently power your device without wasting excess power.中文回答：共正极降压电路是一种将输入电压降低到更低输出电压的直流-直流转换器。
RC Snubber Design for Buck Converter(Reduce spike)
How to Reduce the Spike Voltage forSynchronous Rectifier Buck ConverterBY James Yeh and Hunter HoAbstractSynchronous rectifier buck operation in high switch frequency will generate the spike voltage and ringing due to the stray inductance and capacitance exist in practical PCB. In this paper will discuss the source of the spike voltage in detail and how to select and design suitable snubber circuit to decrease it. Theoretical analysis, simulation and experimental result could provide some information, for related engineer.1.I ntroductionSynchronous rectifier buck is widely used in the power supply of many electronic equipment, due to it has fast response, simple topology, higher efficiency for a low voltage and high current need. But it still has a serious problem “EMI”. While the switch turn on and turn off in a high frequency, the stray inductance and capacitance exist in practical PCB, it will generate high frequency ringing and spike voltage. The high frequency ringing and spike voltage will interference the equipment or damage the switch. In order to solve this problem, there are some methods such as “soft switching”, “snubber circuit”, and ”add EMI filter”. In this paper, we will discuss what cause spike and ringing in detail, and how to place a simple passive component (snubber circuit) to solve this drawback.2.Sourse analysis of spike voltage and how to suppressFigure 1 shows a typical synchronous rectifier Buck converter, where Ls1 and Ls2 are the stray inductance due to the finite size of the circuit layout. In practical circuits operation, while the Vg2 signal has been low and Vg1 has not reach high yet, it is called the dead time. The load current flows through the body diode D2 and stray inductance Ls2. During the dead time, item the Vg1 has been already high, then the M1 has been turned on and D2 start to add reverse voltage. But the body diode with reverse voltage exist a reverse recovery current (I rr), it practical turn off has to across a reverse recovery time (t rr) and has the snap-off current during the extremely short time t s. The snap-off body diode current as show in Figure 2 can produce the transient high peak voltage, and ringing. It may be generate EMI to inference the controller or others equipment and the high peak voltage may be to damage the MOSFET (M2). For different position of stray inductance, a high frequency capacitor (Cd) and RC Snubber circuit must be placed across the drain of M1 to ground and lower switch (M2) of the synchronous rectifier buck converter, respectively, to reduce the peak voltage and to damp the ringing. The circuit as shows in Figure 3. Although the spike and the ringing are due to snap-off current of body diode (D2), accordingto the different position of stray inductance, we can provide the different solution. Find a proper capacitance (Cd) is enough to decrease the spike and ringing, if there is only L s1 in circuit. But if the L s2 is existence simultaneously, the snubber circuit (Rs-Cs) must be placed across the low-side MOSFET (M2) to protect the Mosfet and damp the ringing. It will be discussed in the different situation and solved as below:VdD1RLFigure 1. Typical Synchronous Rectifier Buck converteri D2tFigure 2. Body diode currentVdD1RLFigure 3. Synchronous Rectifier Buck converter with high frequencyinput capacitor and R-C snubber circuitCase 1:First, assume the stray inductance 02»s L , at the instant of body diode reverse-recovery current snap off, the equivalent circuit as shows in Figure 4, Cp is the stray capacitance includes the junction capacitance of the switch and stray capacitance due to circuit layout and mounting. For analyzing this equivalent circuit the instant of diode snap-off is treated as t=0. The initial inductor current is Irr as showed in Figuere2 and initial capacitor voltage iszero. While the body diode snap-off the d ss phase V t IrrL V +=1, it is a large value of spike voltage at the instant, and the Ls1 and Cp will generate high frequency ringing. Theoscillated frequency is p s o C L 11=w , it is damped by only equivalent- series -resister (ESR). In this case, we could place the high frequency capacitor (Cd), and enough to decrease the spike and ringing. Figure 5 shows the equivalent circuit of converter with the high frequency input capacitance, and the initial capacitance voltage of Cd is Vd, so Cdmust has capability to provide Qrr. The 2rr rr rr tI Q =, andd rr V QCd 10>: (1)Ls1Cp-Figure 4. Body diode snap-off equivalent circuitLs1Cp-Figure 5. Body diode snap-off equivalent circuit with high frequency input capacitor.In the component selection of Cd, at least one low ESR capacitor should be used to provide good performance. Here, to adopt either the ceramic or the tantalum type is suitable, and it should be as close to M1 (up-side Mosfet) as possible when layout.Example 1. Consider Figure 3.circuit, assume Io=10A, Ls1=1nH, Ls2=0, Vd=12V, Vo=5V,L1=10m H, Cin=C L =1000m F, f s =100kHz , body diode trr=19nS, Irr=78A Figure 6 shows the wave of Vphase that is simulated by Pspice. While thebody diode reverse recovery, the Vphase has a 30 V spike voltage.TimeV(R2:2)(IS(M3)+IB(M3))-100A0A100ASEL>>IrrFigure 6.The wave of Vphase that is simulated by Pspice. While the body diode snap-offIn order to reduce spike, we add a capacitor Cd. According equation (1), Cd=0.1m F. The simulated result is shown in Figure 7. Figure 8 shows the simulated result which theCd=1m F, According to simulated result, we can see a greater value of Cd with a better capability to reduce spike voltage. Here, the Cd is also an EMI filter.Time8.01992ms8.01996ms8.02000ms8.02004ms 8.02008ms8.02012ms8.02016msV(R2:2)0V10V20V30VVphase(IS(M3)+IB(M3))-100A0A100ASEL>>IrrFigure 7. The simulated result which Cd=0.1m ..Time8.01992ms8.01996ms 8.02000ms 8.02004ms 8.02008ms 8.02012ms 8.02016msV(R2:2)10V20V30V-2VSEL>>Vphase(IS(M3)+IB(M3))-100A0A100AIrrFigure 8. The simulated result which the Cd=1mCase 2:Assume 01»s L , the equivalent circuit is the same as Figure 4. But in this case should be added a snubber circuit to decrease the spike voltage across M2, the equivalent circuit is shown in Figure 6.RsCsFigure 9. Body diode snap-off equivalent circuit with R-C snubberIn this two-order transient circuit, the initial inductor current is Irr and the initial capacitor voltage is zero, at t=0. The differential equation of the body diode voltage and the boundary condition are as showed below:d df df ss df ss V t V dtt dV C R dtt V d C L -=++)()()(22 (2)s rr df R I V -=+)0( (3)222)0(s s rr s d s s rr df L R I L V R C I dtdV ---=+ (4)The solution of equation (2) is)cos()cos()(2g f w j a ----=-t e I C L V t V a t rrs s d df (5)where2021w a w -=a , 02w a s R = , )2/("tan 21rr s a s rr d I L R I V w f -=-, and )(tan 1a w g a -= (6)In equation (5), the maximum voltage across body diode can be found by setting the derivative 0/)(=dt t dV df , and we can get m t which is the maximum voltage time.02³-+=am t w p g j (7)To substitute t=t m into equation (4) and define 22)/(d rr s base V I L C =, rr d base I V R /= we can get the maximum reverse voltage which across the low side Mosfets M2 as shown in equation (8).tm bases base s s base d e R RR R C C V V a --+++=])(75.01[13max (8)From equation (8), we can detect the oscillations are damped out by R s and the maximumvoltage is depended on the values of Rs and Cs.The energy loss in the resistor is2222121d s rr s R V C I L W += (9)The energy stored in Cs is equal to221d s C V C W = (10)The total energy dissipation is22221d s rr s Cs R tot V C I L W W W +=+= (11)The above design equation is too complex. In most cases a simple design technique is need to determine suitable values for the snubber components (Rs and Cs). Here, we introduce a simple method. First select a snubber capacitor with a value that is 4-10 times larger than the estimated capacitance of the synchronous switch (M2) and which mountingcapacitance. Rs is selected so that od I VRs =. This means that the initial voltage step due tothe current flowing in Rs is no greater than the clamped input voltage. The dissipated power in Rs can be estimated from peak energy stored in Cs:s d s diss f V C P 2» (12)wherefs is the switch frequency.Example 2. To consider the same conditions of example 1, the difference is Ls1=0 andLs2=0.5nH. Figure 10 shows the body diode reverse recovery current and voltage across the synchronous switch (M2), it exist a 35 V spike voltage.Time8.0699800ms8.0700000ms8.0700200ms8.0700400ms8.0700600ms8.0700800ms8.0699694ms V(L2:1)102030(IS(M3)+IB(M3))-50A0A50A-94ASEL>>Figure 10.The body diode reverse recovery current and voltage across thesynchronous switch (M2), in Ls2=0.5nHIn order to decrease this spike voltage, we can add the Rs=1 Ω, and Cs=0.1m F .The result of simulation is shown in Figure 11.The spike voltage has been suppressed to 23V,and the ringing has been reduced, too. AS the amount of Cs increase , the spike voltage will reducefurther. However, the total energy dissipation increases linearly with Cs.Time 8.0599800ms8.0600000m s 8.0600200ms 8.0600400ms8.0600600ms 8.0600800ms 8.0601000ms 8.0601200ms8.0599616ms V (L2:2)10V20V30V-2VSEL>>Vph ase(IS(M3)+I B(M3))-100A0A100AIrrFigure 11. The result of simulation which is added thesnubber circuit (Rs=1 Ω, and Cs=0.1m F ).Case 3:Assume Ls1 and Ls2 are exist simultaneously, as shows in Figure3. Adding Cd to decrease the ringing and noise of V phase and filter high frequency noise , moreover adding the snubber circuit (Rs-Cs) will suppress the spike voltage across the synchronous switch (M2).Sometimes we need to sense the Vphase signal, then the serious ringing and spike voltage will influence normal operation of the control IC. Adding a high frequency capacitor Cd, will not able to reduce the ringing that is due to stray inductance Ls2. In this case, adding a suitable snubber circuit can get a better performance.3.Experimental ResultsThe following a practical design example is for further understand the snubber.The experimental circuit is shown in Figure3.The parameters are Vd=5V, Vo=2.5V, Io=5A, L1=7.8m H, Cin= 3000m F, C L =1680m F, M1and M2 are Philips ’s 66NQ03LT, and control IC is RT9202 which is made by RichTek. We are measured the stray inductances L s1= 0.1nH, L s2=0.2nH. For how to measure the stray inductance, we provide a simple method. At first, measure the drain to source voltage ringing cycle (T1) of the synchronous switch (M2), then to add a known capacitor C test in parallel with the switch and finally re-measuring the period (T2). The L s1+L s2 can be get from:)41)((212221tests s st C T T L L L p -=+= (13)Usually C test is approximately equal to twice the switch capacitance. Next, adding a large Cd to decouple the influence of L s1, and follow the above method to measure again to get the L s2, then L s1=L st -L s2.Figure 12 shows a practical measured wave of the V phase and the voltage across thesynchronous rectifier switch (M2) without any snubber circuit. According to Figure 12 we can tell the ringing is very serious, and the efficiency of converter is 89%. Figure 13 shows the wave which only adding Cd=3m F, the ringing will not improve further due to the Ls2 existence. For reduce the ringing in Vphase, consider adding snubber circuit (Rs=1Ω,Cs=0.01m F). Figure 14 shows the wave which circuit have been added the snubber without adding Cd. Then observation, the ringing and spike voltage have been reduced, and in this condition the efficiency of converter is also 88%. Figure 15 shows the same wave which Cd=3m F, and the snubber circuit (Rs=1Ω, Cs=0.01m F), its efficiency is 88%. We find the ringing and spike voltage have been reduced. Figure16, 17,18 and 19 shows the same wave, the difference is load current Io=20A.V phaseV DS2I DS2Figure 12 The wave of Vphase and the voltage across the synchronousrectifier switch (M2) without snubber.(CH1:2A/div, Ch2: 10V/div, Ch3:1V/div,t:40ns/div)V PHASEV DS2I DS2Figure 13. The wave of Vphase and the voltage across the synchronousrectifier switch (M2) which is added .Cd=3m F(CH1:2A/div, Ch2: 10V/div, Ch3:1V/div,t:40ns/div)V PHA SEV DS2I DS2Figure 14. The wave of Vphase and the voltage across the synchronous rectifier switch (M2) which is added snubber circuit(Rs=1Ω, Cs=0.01m F)(CH1:2A/div, Ch2: 10V/div, Ch3:1V/div,t:40ns/div)V p h a s eV D S2I D S2Figure 15.The wave of Vphase and the voltage across the synchronous rectifier switch (M2) which is added snubber circuit(Rs=1Ω, Cs=0.01m F) and Cd=3m F(CH1:2A/div, Ch2: 10V/div, Ch3:1V/div,t:40ns/div)VphaseVDS2IDS2Figure.16 The wave of Vphase and the voltage across the synchronous rectifier switch (M2) without snubber. When Io=20A(CH1:2A/div, Ch2: 2V/div, Ch3:1V/div,t:80ns/div)VphaseVDS2IDS2F17 The wave of Vphase and the voltage across the synchronous rectifier switch (M2) which is added .Cd=3m F When Io=20A (CH1:2A/div, Ch2: 2V/div, Ch3:1V/div,t:80ns/div)VphaseVDS2IDS2F18 The wave of Vphase and the voltage across the synchronous rectifier switch (M2) which is added snubber circuit(Rs=1Ω, Cs=0.01m F) When Io=20A(CH1:2A/div, Ch2: 2V/div, Ch3:1V/div,t:80ns/div)VphaseVDS2IDS2F19 The wave of Vphase and the voltage across the synchronous rectifier switch (M2) which is added snubber circuit(Rs=1Ω, Cs=0.01m F) and Cd=3m F When Io=20A(CH1:2A/div, Ch2: 2V/div, Ch3:1V/div,t:80ns/div)For efficiency consideration, adding snubber circuit cannot improve the total energy loss of converter further. Because the energy loss due to the reverse recovery current of body diode has been transmit to snubber resistance (Rs). But it is really effective to restrict the voltage spike. In this way, we can reduce power device rating, and improve the EMI, output noise.4.ConclusionOne of the primary reasons for using snubbers is the presence of the stray inductance in the circuit that generate voltage spikes and ringing when excited by the switching action and diode turn off. Larger stray inductance means larger snubber components and more dissipation. As power levels rise, this becomes progressively more important because of the increasing di/dt. So before actually designing the snubber, it is important to minimize the circuit stray inductance and take good care of circuit layout.Reference[1] William McMurray, “ Optimum Snubbers for Power Semiconductors”, IEEE IASTransactions, Vol. IA-8, No,5, Sep/Oct 1972,pp. 593-600.[2] Jim Hagerman and Hagerman Technology, “Calculating Optimum Snubbers”.[3] Rudy Severns ”Design of Snubbers for Power Circuit”.[4] Mohan, Undeland, and Robbins, “ Power electronics Converters, Applications, andDesign”.。
大电流buck降压电路
大电流buck降压电路英文回答：Buck converters are widely used in power electronics to step down voltage levels efficiently. The goal of a buck converter is to convert a high input voltage to a lower output voltage, while maintaining a high current capability. This is achieved by using a power semiconductor switch (usually a MOSFET) and an inductor.The basic operation of a buck converter involves two main stages: the on-state and the off-state. During the on-state, the switch is closed and current flows through the inductor, storing energy in its magnetic field. This causes the output voltage to rise. In the off-state, the switch is opened and the energy stored in the inductor is released, transferring it to the output capacitor and load. This causes the output voltage to decrease.One important aspect of a high current buck converteris the choice of components. The inductor and the output capacitor should be selected to handle the desired output current without excessive heating or voltage drop. Additionally, the MOSFET switch should have a low on-resistance to minimize power losses.Another consideration is the control strategy used in the buck converter. There are various control techniques, such as voltage mode control and current mode control. Voltage mode control adjusts the duty cycle of the switch to regulate the output voltage, while current mode control adjusts the duty cycle based on the inductor current. The choice of control strategy depends on the specific requirements of the application.In my experience, I have used a high current buck converter in a project where I needed to power a high power LED. The LED required a specific voltage level, and the buck converter allowed me to efficiently step down the voltage from a higher source. I selected a suitable inductor and capacitor to handle the high current and ensured that the MOSFET switch had a low on-resistance. Iused voltage mode control to regulate the output voltage, and the buck converter performed well in providing a stable power supply to the LED.中文回答：大电流降压电路（buck converter）在电力电子学中被广泛应用，可以高效地将电压降低。
BUCK电路环路补偿 Compensator Design Procedure for Buck Converter with Voltage-Mode Error-Amplifier
Compensator Design Procedure for Buck Converter with Voltage-Mode Error-Amplifier
By: Amir M. Rahimi, Parviz Parto, and Peyman Asadi
Table of Contents
Page 1. Introduction to Synchronous Buck Converter ...................................2 2. Loop Gain of the System..................................................................5 3. Step by Step Compensator Design Procedure.................................6 4. Type II Compensator Design............................................................7 4.1 Design Example of Type II Compensator.......................................11 5. Type III Compensator.......................................................................13 5.1 Type III- A Compensator ................................................................14 5.2 Design Example of Type III-A Compensator ..................................16 5.3 Type III- B Compensator ................................................................19 5.4 Design Example of Type III-B Compensator ..................................20 6. Conclusion .......................................................................................23 Appendices: Designing the Power Stage of the Synchronous Buck Converter ........24 Some Special Cases of Compensator Design .....................................28 Loop Response Measurement .............................................................33
一种新型软开关 BUCK变换器
一种新型软开关 BUCK变换器刘吉星;沈锦飞【摘要】磁耦合谐振式无线电能传输采用直流斩波调压控制传输功率，传统的直流斩波电路开关损耗大，因此提出了一种新型的软开关BUCK变换器的改进电路，在电路中添加耦合电感、辅助电感和二极管，可以实现零电流开通和零电压关断。
变换器结构简单，便于控制。
介绍了电路工作原理和过程，设计了电路参数，进行了仿真和实验研究，最后给出了仿真和实验波形。
%The magnetically coupled resonant wireless power transmission adopts DC chopper control over transmission power,while traditional DC chopper circuit switching has a high loss.This paper presents an improved circuit for a novel soft-switching BUCK DC-DC converter,where a coupled inductor,auxiliary inductor and diode are added to realize zero current switching-on and zero voltage switching-off.The converter has a simple structure and is easy tocontrol.Furthermore,the paper describes the working principle and process of the circuit,designs circuit parameters,completes simulation and experimental research,and finally gives simulation and test waveforms.【期刊名称】《电气自动化》【年(卷),期】2014(000)006【总页数】3页(P14-15,32)【关键词】BUCK变换器;软开关;耦合电感;零电流开通;无线电能传输【作者】刘吉星;沈锦飞【作者单位】江南大学物联网学院电气自动化研究所，江苏无锡 214122;江南大学物联网学院电气自动化研究所，江苏无锡 214122【正文语种】中文【中图分类】TN624磁耦合谐振式无线电能传输技术是一种新型的电能传输技术，比传统的直接接触式电能传输更加灵活、安全、可靠。