高速 MOS 驱动电路设计和应用指南
- 格式:pdf
- 大小:1.20 MB
- 文档页数:67
大功率mos管驱动电路大功率MOS管驱动电路是一种常见的电路设计,它能够有效地驱动高功率的MOS管,以实现电路的高效工作。
本文将从电路原理、设计要点和常见问题等方面进行介绍。
一、电路原理大功率MOS管驱动电路主要由信号发生器、驱动电路和MOS管组成。
信号发生器产生所需的驱动信号,驱动电路将信号进行放大和整形,然后通过电流放大器将信号输出给MOS管。
MOS管根据驱动信号的变化,控制其通断状态,从而实现对电路的控制。
二、设计要点1.选择合适的MOS管:在大功率应用中,选择合适的MOS管至关重要。
一方面,要考虑其额定电流和功率,确保能够承受所需的负载;另一方面,还要考虑其开关特性和导通电阻等参数,以提高电路的效率和稳定性。
2.驱动电路的设计:驱动电路应能够提供足够的电流和电压来驱动MOS管。
一般采用放大器和电流放大器的组合来实现。
放大器负责放大信号的幅度,而电流放大器则负责提供足够的电流给MOS管。
同时,还要考虑到驱动电路的响应速度和抗干扰能力。
3.防止过热和电磁干扰:由于大功率MOS管在工作过程中会产生较大的功耗和电磁干扰,因此需要采取相应的措施来防止过热和干扰。
例如,可以在电路中加入散热器和滤波电路,以提高电路的稳定性和抗干扰能力。
4.保护电路的设计:在大功率应用中,由于电流和电压较大,一旦发生故障可能会对电路和设备造成严重损坏。
因此,需要在电路中加入过流、过压和过温等保护电路,以保证电路和设备的安全运行。
三、常见问题1.如何选择合适的MOS管?选择MOS管时,需要考虑所需的电流和功率,以及其开关特性和导通电阻等参数。
同时,还需要考虑其封装形式和散热性能等因素。
2.如何设计驱动电路?驱动电路应能够提供足够的电流和电压来驱动MOS管。
一般采用放大器和电流放大器的组合来实现。
同时,还要考虑到驱动电路的响应速度和抗干扰能力。
3.如何防止过热和电磁干扰?可以在电路中加入散热器和滤波电路,以提高电路的稳定性和抗干扰能力。
MOS管及MOS管的驱动电路设计免费版MOS管是一种主要用于开关和放大电路的半导体器件。
其驱动电路设计是为了能够提供足够的电流和电压来控制MOS管的导通和截止状态。
MOS管的驱动电路通常由两个主要部分组成:输入驱动和输出驱动。
输入驱动部分负责接收控制信号,将其转换为所需的电压和电流来驱动MOS管。
输出驱动部分负责将转换后的信号传递给MOS管的栅极或基极。
在MOS管的驱动电路设计中,有几个关键的因素需要考虑。
首先是输入电压和电流的要求。
输入信号的电压和电流应根据MOS管的规格来选择,以确保能够有效地控制MOS管的导通和截止状态。
其次是电源电压和电流的要求。
电源电压和电流应能够提供足够的能量来驱动MOS管。
此外,还需要考虑到输入输出电阻、功率损耗以及噪声抑制等因素。
为了设计一个高效且稳定的MOS管驱动电路,以下是一些建议和步骤:1.了解MOS管的规格和特性。
在设计中需要了解MOS管的最大电压、电流和功率等规格,以便确定输入输出电压和电流的要求。
2.选择适当的电源。
根据MOS管的规格,选择合适的电源电压和电流。
同时考虑到稳定性和功率损耗等因素。
3.确定输入信号电压和电流。
根据MOS管的输入电阻和输入电流的规格,确定输入信号的电压和电流。
4.设计输入驱动电路。
输入驱动电路通常由电流源和电压源组成。
电流源用于提供足够的电流来驱动MOS管的栅极或基极,而电压源用于提供所需的电压。
5.设计输出驱动电路。
输出驱动电路通常由放大器和电压跟随器组成。
放大器用于放大输入信号,而电压跟随器用于提供足够的电流和电压来控制MOS管。
6.进行仿真和调试。
使用电子设计自动化工具进行电路仿真,以确保电路的性能和稳定性。
如果发现问题,需要对电路进行调试和优化。
7.考虑过热和噪声抑制。
在设计中需要考虑电路的散热和噪声抑制问题,以确保电路的可靠性和稳定性。
总之,MOS管的驱动电路设计需要综合考虑MOS管的规格,输入输出信号的要求,电源电压和电流,以及电路的稳定性和可靠性。
mos管高边驱动芯片MOS管高边驱动芯片是一种常见的电子元件,广泛应用于各种电路和系统中。
本文将介绍MOS管高边驱动芯片的原理、特点以及应用领域。
一、原理MOS管高边驱动芯片是一种用于驱动高边MOS管的集成电路。
它通过控制输入信号,实现对高边MOS管的开关控制。
其工作原理主要包括两个方面:电平转换和电流放大。
在电平转换方面,MOS管高边驱动芯片能够将低电平的输入信号转换为高电平,以满足高边MOS管的驱动需求。
通过内部的电平转换电路,它能够将输入信号的电平提升到高于高边MOS管的阈值电平,从而实现对其的控制。
在电流放大方面,MOS管高边驱动芯片能够将输入信号的电流放大,以提供足够的电流驱动能力给高边MOS管。
通过内部的电流放大电路,它能够将输入信号的电流放大到足够大的程度,以确保高边MOS管能够正常工作。
二、特点MOS管高边驱动芯片具有以下几个特点:1. 高可靠性:MOS管高边驱动芯片采用了先进的工艺和设计技术,具有较高的可靠性和稳定性。
它能够在各种环境条件下正常工作,并具有较长的使用寿命。
2. 低功耗:MOS管高边驱动芯片采用了低功耗设计,能够在工作时尽量减少能量的消耗,从而提高系统的能效。
3. 快速响应:MOS管高边驱动芯片具有快速的响应速度,能够在短时间内完成对高边MOS管的开关控制,提高系统的响应速度。
4. 多种保护功能:MOS管高边驱动芯片内部集成了多种保护功能,如过压保护、过流保护和过温保护等,能够有效保护高边MOS管和芯片本身的安全。
三、应用领域MOS管高边驱动芯片广泛应用于各种电路和系统中,特别是需要对高边MOS管进行驱动控制的场合。
以下是一些常见的应用领域:1. 电源管理系统:MOS管高边驱动芯片可以用于电源管理系统中的开关电源控制、电池管理和充放电控制等方面,提高系统的稳定性和效率。
2. 电机驱动系统:MOS管高边驱动芯片可以用于电机驱动系统中的电机控制、速度调节和位置控制等方面,实现对电机的精确控制。
高速MOSFET门极驱动电路的设计应用指南author Laszlo Baloghtranslator Justin Hu摘要本文主要演示了一种系统化的方法来设计高速开关装置的高性能门极驱动电路。
文章收集了大量one-stop-shopping 主题的信息来解决最普通的设计挑战。
因此它应当对各种水平的电力电子工程师都适用。
最常用的电路方案和它们的性能都经过了分析,包括寄生参数、瞬时和极端运行条件的影响。
文章首先回顾了MOSFET技术和开关运行模式,然后由简入繁地讨论问题。
详细的描述了参考地和高端门极驱动电路的设计程序、交流耦合和变压器隔离方案。
专门的一章用来介绍同步整流装置中MOSFET的门极驱动要求。
文章另举出了几个设计的实例,一步一步进行了说明。
Ⅰ.引言MOSTET是金属氧化物半导体场效应晶体管(Metal Oxide Semiconductor Field Effect Transistor)的缩写,是电子工业中高频、高效率开关装置的关键器件。
令人惊叹的是,场效应晶体管技术发明于1930年,比双极性晶体管早了大约20年。
第一个信号级别的场效应晶体管20世纪50年代末期被制造出来,功率级别的MOSFET在20世纪70年代中期出现。
而今天无数的MOSFET被集成到现代电子器件中,无论是微处理器还是分立的功率晶体管。
本文所关注的是功率MOSFET在各种各样的开关模式功率变换器装置中门极驱动的要求。
Ⅱ.MOSFET技术双极型和MOSFET晶体管都使用了同样的工作原理。
从根本上讲,这两种晶体管都是电荷控制的器件,这就意味着它们的输出电流和控制电极在半导体中建立的电荷成比例。
当这些器件用作开关时,它们都必须被一个低阻抗的电源驱动,电源要能提供足够的充放电电流来使它们快速建立或释放控制电荷。
从这一点来看,MOSFET在开关过程中必须和双极性晶体管一样通过“硬”驱动才能获得类似的开关速度。
理论上,双极型和MOSFET器件的开关速度几乎一样,由载流子运动经过半导体区域所需要的时间决定。
一、引言随着电子技术的飞速发展,大功率MOS管在工业、军事、民用等领域得到了广泛应用。
然而,由于MOS管的特性,使用不当很容易导致其损坏,甚至危及设备和人员安全。
因此,设计一种可靠的保护电路,对于确保MOS管的正常工作和延长其寿命具有重要意义。
本文将介绍一种基于大功率MOS管的驱动保护电路,主要包括电流保护、过压保护、过温保护和ESD保护四个方面。
二、电流保护电流保护是防止MOS管过电流损坏的主要手段。
一般来说,电流过大会导致MOS管发热严重,从而对其内部结构产生不可逆的损伤。
因此,需要通过设置合理的电流限制值和保护电路来保护MOS 管。
具体实现方式如下:1.1 电流检测在MOS管的源极和负载之间增加一个小电阻,通过检测该电阻两端的电压来实现对MOS管的电流监测。
为了减小误差,可以采用差分放大器、精密电阻等器件进行检测。
1.2 电流限制当检测到MOS管电流超过设定值时,可以通过控制信号,直接将MOS管的驱动电压降低或关闭MOS管,以保护其不受过电流损伤。
三、过压保护过压保护是保护MOS管免受过高电压损害的重要手段。
在实际应用中,由于干扰、电源波动等因素,系统中可能会出现过压情况,如果MOS管无法承受这样的压力,就会导致其损坏。
具体实现方式如下:2.1 过压检测通过设置一个合适的过压检测电路,来监测系统中的电压变化情况。
一旦检测到过压情况,则需要立即采取相应的保护措施。
2.2 过压保护当检测到过压情况时,可以通过控制信号,直接将MOS管的驱动电压降低或关闭MOS管,以避免其受到过高的电压影响。
四、过温保护过温保护是保护MOS管免受高温损害的重要手段。
由于工作环境的限制,MOS管在高温环境下长时间工作会导致其内部结构损坏或退化,影响其寿命和性能。
具体实现方式如下:3.1 温度检测通过设置一个合适的温度检测电路,来监测MOS管周围的温度变化情况。
可以采用热敏电阻、热敏电偶等器件进行检测,并将其转换为电信号。
nmos 管高边驱动电路
摘要:
1.引言
2.nmos 管高边驱动电路的定义和作用
3.nmos 管高边驱动电路的工作原理
4.nmos 管高边驱动电路的分类
5.nmos 管高边驱动电路的应用领域
6.nmos 管高边驱动电路的发展趋势和展望
正文:
mos 管高边驱动电路是一种将nmos 管的栅极电压提高到足够高的程度,以使其导通的电路。
它的主要作用是在nmos 管的控制端施加一个适当的电压,使得nmos 管能够正常工作。
mos 管高边驱动电路的工作原理是,当电路的控制端输入电压达到一定值时,驱动电路会将这个电压放大并施加到nmos 管的栅极,使得nmos 管导通。
这样,就可以通过控制输入电压的大小来控制nmos 管的导通程度。
mos 管高边驱动电路可以分为两类:一类是采用晶体管作为驱动器的电路,另一类是采用专用驱动芯片的电路。
这两类电路各有优缺点,具体选择哪种类型的电路,需要根据实际应用需求来决定。
mos 管高边驱动电路广泛应用于各种电子设备中,如电源、放大器、控制器等。
在这些设备中,nmos 管高边驱动电路起到了关键的作用,它能够有效地控制nmos 管的工作状态,从而保证设备的正常运行。
随着科技的不断发展,nmos 管高边驱动电路也在不断进步。
未来的发展趋势是,驱动电路将更加集成化、智能化,能够更好地满足各种应用场景的需求。
总的来说,nmos 管高边驱动电路是一种非常重要的电路,它在电子设备中的应用非常广泛。
nmos 管高边驱动电路(原创实用版)目录1.NMOS 管概述2.高边驱动电路的概念3.NMOS 管在高边驱动电路中的应用4.高边驱动电路的优点5.高边驱动电路的设计要点正文【1.NMOS 管概述】MOS 管,全称为 N 沟道金属氧化物半导体场效应晶体管,是一种常见的场效应晶体管。
其结构主要由 n 型半导体、金属栅极和 p 型半导体基底构成,具有高输入阻抗、低噪声和低功耗等特点,在数字电路和模拟电路中都有广泛应用。
【2.高边驱动电路的概念】高边驱动电路,是一种驱动能力强、输出电压高的电路,主要用于驱动电容性负载,例如 LED 显示屏、液晶显示屏等。
它可以提供较大的驱动电流,使得负载能够正常工作,同时具有较低的输出阻抗,能够减小信号在传输过程中的衰减。
【3.NMOS 管在高边驱动电路中的应用】在高边驱动电路中,NMOS 管可以作为开关元件使用。
由于其高输入阻抗的特点,可以大大减少输入信号的衰减,提高电路的驱动能力。
同时,NMOS 管具有较低的导通电阻,可以提供较大的驱动电流,使得负载能够正常工作。
【4.高边驱动电路的优点】高边驱动电路具有以下优点:(1)驱动能力强:高边驱动电路可以提供较大的驱动电流,使得负载能够正常工作。
(2)输出电压高:高边驱动电路具有较低的输出阻抗,能够减小信号在传输过程中的衰减,提高输出电压。
(3)稳定性好:高边驱动电路采用 NMOS 管作为开关元件,具有较高的工作稳定性。
【5.高边驱动电路的设计要点】在设计高边驱动电路时,需要注意以下几点:(1)选择合适的 NMOS 管:需要根据负载的驱动电流和输出电压选择合适的 NMOS 管,以保证电路的正常工作。
(2)设计合理的电路结构:需要设计合理的电路结构,以提高电路的驱动能力和稳定性。
pwm驱动mos管电路设计
PWM驱动MOS管电路是一种常用的电源控制电路,它可以通过改变脉冲宽度来控制MOS管的导通时间,从而达到控制输出电压和电流的目的。
相比于传统的线性调节电路,PWM驱动电路具有更优异的能量转换效率和更高的控制精度,特别适用于高功率电源和LED驱动等领域。
在PWM驱动MOS管电路设计中,需要考虑多个因素,包括输入电压范围、输出电压和电流、负载类型、开关频率等。
一般来说,通用的PWM驱动电路由三部分组成:输入电阻分压、比较器和MOS管驱动芯片。
其中,输入电阻分压用于将输入电压分压到比较器工作范围内,比较器用于比较输入电压和一个内部参考电压,从而产生PWM信号,MOS管驱动芯片则负责将PWM信号转化为驱动MOS管的高低电平信号。
在实际电路设计中,需要根据具体需求选择合适的元器件和参数,例如比较器的阈值电压、MOS管的额定电压和电流、驱动芯片的最大输出电流等。
此外,还需要合理设计电路板布局和散热系统,以确保电路的可靠性和稳定性。
总之,PWM驱动MOS管电路是一种高效能的电源控制电路,可以广泛应用于各种电源和驱动控制场合。
在电路设计中,需要综合考虑多个因素,采用合适的元器件和参数,保证电路的稳定性和可靠性。
- 1 -。
简介通常来说,高速电路是指电路处理的信号频率足够高使得传输线对该频率表现的阻抗足以对信号产生影响,工作在这种频率上的电路。
《高速电路设计指南》以ADI官方网站的技术文章和模拟对话为基础资料来源整理成册。
从设计实践角度出发,介绍在高速电路设计中需要掌握的各项技术及技能。
ADI智库是ADI公司面向中国工程师打造的一站式资源分享平台,除了汇聚ADI官网的海量技术资料、视频外,还有大量首发的、免费的培训课程、视频直播等。
九大领域、十项技术,加入ADI智库,您可以尽情的浏览收藏、下载相关资源。
此外,您还可一键报名线上线下会议活动,更有参会提醒等贴心服务。
目录终结高速转换器带宽术语 (3)高速转换器:内涵、原因和原理概述 (8)高速差分ADC驱动器设计指南 (16)高速放大器测试需要足够多的数学知识以使巴伦运转! (44)高速DAC宽带输出网络知识与设计 (52)高速ADC的电源设计 (57)低频和高频电路接地 (66)了解JESD204B规范的各层——从高速ADC的角度出发 (74)高速模数转换器精度透视 (83)第一部分 (83)第二部分 (89)高速ADC PCB布局布线规则 (103)第一部分 (103)第二部分 (103)第三部分 (104)第四部分 (105)高速ADC PCB布局布线技巧 (106)终结高速转换器带宽术语有很多令人困惑的规格都与转换器带宽有关。
为了在新的设计中选用适当的转换器,我应当使用什么带宽术语呢?开始一个新设计时,需要决定的首要参数就是带宽。
带宽为设计指明方向,引导设计人员开辟通往成功之路。
本质上有三类前端可供选择:基带型、带通或超奈奎斯特型(有时也称为窄带或子采样型——基本上不会用到第1奈奎斯特区)以及宽带型,如图1所示。
前端的选用取决于具体应用。
图1. 基带、带通与宽带,F SAMPLE =200MSPS。
基带设计要求的带宽是从直流(或低kHz/MHz区)到转换器的奈奎斯特频率。
高速MOSFEMOSFET T栅极驱动电路的设计与应用指南摘要本文将展示一个用来设计高速开关应用所需的高性能栅极驱动电路的系统性方案。
它综合了各方面的信息,可一次性解决一些最常见的设计问题。
因此,各个层面的电力电子工程师都值得一读。
文中分析了一些最流行的电路方案及其性能,包括寄生元件、瞬间和极端工作条件的影响。
首先,文章对MOSFET技术和开关操作进行了大致讨论,从简单问题逐渐转向复杂问题,并详细讲述了低端和高端栅极驱动电路以及交流耦合和变压器隔离式方案的设计程序。
另外,文章还专门用一个章节的内容来讨论同步整流器应用中MOSFET的栅极驱动要求。
最后,本文还提供了多个分步骤的设计案例。
简介MOSFET,全称为金属氧化物半导体场效应晶体管,是电子产品领域各种高频高效开关应用的关键元器件。
FET技术发明于1930年,比双极晶体管还要早大约20年,这一点令人感到意外。
最早的信号级FET晶体管出现在20世纪50年代末,而功率MOSFET则是在70年代中期问世的。
如今,数百万的MOSFET 晶体管被集成到了各种电子元器件中,从微控制器到“离散式”功率晶体管。
本话题的重点在于各种开关模式电源转换应用中功率MOSFET的栅极驱动要求。
Design And Application GuideFor High Speed MOSFET Gate Drive CircuitsBy Laszlo BaloghABSTRACTThe main purpose of this paper is to demonstrate a systematic approach to design high performance gate drive circuits for high speed switching applications. It is an informative collection of topics offering a “one-stop-shopping” to solve the most common design challenges. Thus it should be of interest to power electronics engineers at all levels of experience.The most popular circuit solutions and their performance are analyzed, including the effect of parasitic components, transient and extreme operating conditions. The discussion builds from simple to more complex problems starting with an overview of MOSFET technology and switching operation. Design procedure for ground referenced and high side gate drive circuits, AC coupled and transformer isolated solutions are described in great details. A special chapter deals with the gate drive requirements of the MOSFETs in synchronous rectifier applications.Several, step-by-step numerical design examples complement the paper.INTRODUCTIONMOSFET – is an acronym for Metal Oxide Semiconductor Field Effect Transistor and it is the key component in high frequency, high efficiency switching applications across the electronics industry. It might be surprising, but FET technology was invented in 1930, some 20 years before the bipolar transistor. The first signal level FET transistors were built in the late 1950’s while power MOSFETs have been available from the mid 70’s. Today, millions of MOSFET transistors are integrated in modern electronic components, from microprocessors, through “discrete” power transistors.The focus of this topic is the gate drive requirements of the power MOSFET in various switch mode power conversion applications. MOSFET TECHNOLOGYThe bipolar and the MOSFET transistors exploit the same operating principle. Fundamentally, both type of transistors are charge controlled devices which means that their output current is proportional to the charge established in the semiconductor by the control electrode. When these devices are used as switches, both must be driven from a low impedance source capable of sourcing and sinking sufficient current to provide for fast insertion and extraction of the controlling charge. From this point of view, the MOSFETs have to be driven just as “hard” during turn-on and turn-off as a bipolar transistor to achieve comparable switching speeds. Theoretically, the switching speeds of the bipolar and MOSFET devices are close to identical, determined by the time required for the charge carriers to travel across the semiconductor region. Typical values in power devices are approximately 20 to 200 picoseconds depending on the size of the device. The popularity and proliferation of MOSFET technology for digital and power applications is driven by two of their major advantages over the bipolar junction transistors. One of these benefits is the ease of use of the MOSFET devices in high frequency switching applications. The MOSFET transistors are simpler to drive because their control electrode is isolated from the current conducting silicon, therefore a continuous ON current is not required. Once the MOSFET transistors are turned-on, their drive current is practically zero. Also, the controlling charge and accordingly the storage time in the MOSFET transistors is greatly reduced. This basically1eliminates the design trade-off between on state voltage drop – which is inversely proportional to excess control charge – and turn-off time. As a result, MOSFET technology promises to use much simpler and more efficient drive circuits with significant economic benefits compared to bipolar devices.Furthermore, it is important to highlight especially for power applications, that MOSFETs have a resistive nature. The voltage drop across the drain source terminals of a MOSFET is a linear function of the current flowing in the semiconductor. This linear relationship is characterized by the R DS(on) of the MOSFET and known as the on-resistance. On-resistance is constant for a given gate-to-source voltage and temperature of the device. As opposed to the -2.2mV/°C temperature coefficient of a p-n junction, the MOSFETs exhibit a positive temperature coefficient of approximately 0.7%/°C to 1%/°C. This positive temperature coefficient of the MOSFET makes it an ideal candidate for parallel operation in higher power applications where using a single device would not be practical or possible. Due to the positive TC of the channel resistance, parallel connected MOSFETs tend to share the current evenly among themselves. This current sharing works automatically in MOSFETs since the positive TC acts as a slow negative feedback system. The device carrying a higher current will heat up more – don’t forget that the drain to source voltages are equal – and the higher temperature will increase its R DS(on) value. The increasing resistance will cause the current to decrease, therefore the temperature to drop. Eventually, an equilibrium is reached where the parallel connected devices carry similar current levels. Initial tolerance in R DS(on) values and different junction to ambient thermal resistances can cause significant – up to 30% – error in current distribution.Device typesAlmost all manufacturers have got their unique twist on how to manufacture the best power MOSFETs, but all of these devices on the market can be categorized into three basic device types. These are illustrated in Figure 1.Figure 1. Power MOSFET device types Double-diffused MOS transistors were introduced in the 1970’s for power applications and evolved continuously during the years. Using polycrystalline silicon gate structures and self-aligning processes, higher density integration and rapid reduction in capacitances became possible. The next significant advancement was offered by the V-groove or trench technology to further increase cell density in power MOSFET devices. The better performance and denser integration don’t come free however, as trench MOS devices are more difficult to manufacture.The third device type to be mentioned here is the lateral power MOSFETs. This device type is constrained in voltage and current rating due to its inefficient utilization of the chip geometry. Nevertheless, they can provide significant benefits in low voltage applications, like in microprocessor power supplies or as synchronous rectifiers in isolated converters.2The lateral power MOSFETs have significantly lower capacitances, therefore they can switch much faster and they require much less gate drive power.MOSFET ModelsThere are numerous models available to illustrate how the MOSFET works, nevertheless finding the right representation might be difficult. Mostof the MOSFET manufacturers provide Spice and/or Saber models for their devices, but these models say very little about the application traps designers have to face in practice. They provide even fewer clues how to solve the most common design challenges.A really useful MOSFET model which would describe all important properties of the device from an application point of view would be very complicated. On the other hand, very simple and meaningful models can be derived of the MOSFET transistor if we limit the applicabilityof the model to certain problem areas.The first model in Figure 2 is based on the actual structure of the MOSFET device and can be used mainly for DC analysis. The MOSFET symbol in Figure 2a represents the channel resistance and the JFET corresponds to the resistance of the epitaxial layer. The length, thus the resistance of the epi layer is a function of the voltage rating of the device as high voltage MOSFETs require thicker epitaxial layer.Figure 2b can be used very effectively to model the dv/dt induced breakdown characteristic of a MOSFET. It shows both main breakdown mechanisms, namely the dv/dt induced turn-on of the parasitic bipolar transistor - present in all power MOSFETs - and the dv/dt induced turn-onof the channel as a function of the gate terminating impedance. Modern power MOSFETs are practically immune to dv/dt triggering of the parasitic npn transistor due to manufacturing improvements to reduce the resistance between the base and emitter regions.It must be mentioned also that the parasitic bipolar transistor plays another important role. Its base – collector junction is the famous body diode of the MOSFET.Figure 2. Power MOSFET models34Figure 2c is the switching model of the MOSFET. The most important parasitic components influencing switching performance are shown in this model. Their respective roles will be discussed in the next chapter which is dedicated to the switching procedure of the device.MOSFET Critical ParametersWhen switch mode operation of the MOSFET is considered, the goal is to switch between the lowest and highest resistance states of the device in the shortest possible time. Since the practical switching times of the MOSFETs (~10ns to 60ns) is at least two to three orders of magnitude longer than the theoretical switching time (~50ps to 200ps), it seems important to understand the discrepancy. Referring back to the MOSFET models in Figure 2, note that all models include three capacitors connected between the three terminals of the device. Ultimately, the switching performance of the MOSFET transistor is determined by how quickly the voltages can be changed across these capacitors.Therefore, in high speed switching applications, the most important parameters are the parasitic capacitances of the device. Two of these capacitors, the C GS and C GD capacitors correspond to the actual geometry of the device while the C DS capacitor is the capacitance of the base collector diode of the parasitic bipolar transistor (body diode).The C GS capacitor is formed by the overlap of the source and channel region by the gate electrode. Its value is defined by the actual geometry of the regions and stays constant (linear) under different operating conditions.The C GD capacitor is the result of two effects. Part of it is the overlap of the JFET region and the gate electrode in addition to the capacitance of the depletion region which is non-linear. The equivalent C GD capacitance is a function of the drain source voltage of the device approximated by the following formula:DS1GD,0GD V K 1C C ⋅+≈The C DS capacitor is also non-linear since it is the junction capacitance of the body diode. Its voltage dependence can be described as:DS 2DS,0DS V K C C ⋅≈Unfortunately, non of the above mentioned capacitance values are defined directly in the transistor data sheets. Their values are given indirectly by the C ISS , C RSS , and C OSS capacitor values and must be calculated as: RSSOSS DS RSS ISS GS RSSGD C C C C C C C C −=−== Further complication is caused by the C GD capacitor in switching applications because it is placed in the feedback path between the input and output of the device. Accordingly, its effective value in switching applications can be much larger depending on the drain source voltage of the MOSFET. This phenomenon is called the “Miller” effect and it can be expressed as:()GD L fs eqv GD,C R g 1C ⋅⋅+=Since the C GD and C DS capacitors are voltage dependent, the data sheet numbers are valid only at the test conditions listed. The relevant average capacitances for a certain application have to be calculated based on the required charge to establish the actual voltage change across the capacitors. For most power MOSFETs the following approximations can be useful: offDS,spec DS,spec OSS,ave OSS,off DS,spec DS,spec RSS,ave GD,V V C 2C V V C 2C ⋅⋅=⋅⋅=The next important parameter to mention is the gate mesh resistance, R G,I . This parasitic resistance describes the resistance associated by the gate signal distribution within the device. Its importance is very significant in high speed switching applications because it is in between the driver and the input capacitor of the device, directly impeding the switching times and the5dv/dt immunity of the MOSFET. This effect is recognized in the industry, where real high speed devices like RF MOSFET transistors use metal gate electrodes instead of the higher resistance polysilicon gate mesh for gate signal distribution. The R G,I resistance is not specified in the data sheets, but in certain applications it can be a very important characteristic of the device. In the back of this paper, Appendix A4 shows a typical measurement setup to determine the internal gate resistor value with an impedance bridge.Obviously, the gate threshold voltage is also a critical characteristic. It is important to note that the data sheet V TH value is defined at 25°C and at a very low current, typically at 250μA. Therefore, it is not equal to the Miller plateau region of the commonly known gate switching waveform. Another rarely mentioned fact about V TH is its approximately –7mV/°C temperature coefficient. It has particular significance in gate drive circuits designed for logic level MOSFET where V TH is already low under the usual test conditions. Since MOSFETs usually operate at elevated temperatures, proper gate drive design must account for the lower V TH when turn-off time, and dv/dt immunity is calculated as shown in Appendix A and F.The transconductance of the MOSFET is its small signal gain in the linear region of its operation. It is important to point out that every time the MOSFET is turned-on or turned-off, it must go through its linear operating mode where the current is determined by the gate-to-source voltage. The transconductance, g fs , is the small signal relationship between drain current and gate-to-source voltage:GSD fs dV dI g =Accordingly, the maximum current of the MOSFET in the linear region is given by: ()fs th GS D g V V I ⋅−=Rearranging this equation for V GS yields the approximate value of the Miller plateau as a function of the drain current.fs D th Miller GS,g IV V +=Other important parameters like the source inductance (L S ) and drain inductance (L D ) exhibit significant restrictions in switching performance. Typical L S and L D values are listed in the data sheets, and they are mainly dependant on the package type of the transistor. Their effects can be investigated together with the external parasitic components usually associated with layout and with accompanying external circuit elements like leakage inductance, a current sense resistor, etc.For completeness, the external series gate resistor and the MOSFET driver’s output impedance must be mentioned as determining factors in high performance gate drive designs as they have a profound effect on switching speeds and consequently on switching losses.SWITCHING APPLICATIONSNow, that all the players are identified, let’s investigate the actual switching behavior of the MOSFET transistors. To gain a better understanding of the fundamental procedure, the parasitic inductances of the circuit will be neglected. Later their respective effects on the basic operation will be analyzed individually. Furthermore, the following descriptions relate to clamped inductive switching because most MOSFET transistors and high speed gate drive circuits used in switch mode power supplies work in that operating mode.Figure 3. Simplified clamped inductive switchingmodelThe simplest model of clamped inductive switching is shown in Figure 3, where the DC current source represents the inductor. Its current can be considered constant during the short switching interval. The diode provides a path for the current during the off time of the MOSFET and clamps the drain terminal of the device to the output voltage symbolized by the battery.Turn-On procedureThe turn-on event of the MOSFET transistor can be divided into four intervals as depicted in Figure 4.Figure 4. MOSFET turn-on time intervalsIn the first step the input capacitance of the device is charged from 0V to V TH. During this interval most of the gate current is charging the C GS capacitor. A small current is flowing through the C GD capacitor too. As the voltage increases at the gate terminal and the C GD capacitor’s voltage has to be slightly reduced. This period is called the turn-on delay, because both the drain current and the drain voltage of the device remain unchanged.Once the gate is charged to the threshold level, the MOSFET is ready to carry current. In the second interval the gate is rising from V TH to the Miller plateau level, V GS,Miller. This is the linear operation of the device when current is proportional to the gate voltage. On the gate side, current is flowing into the C GS and C GD capacitors just like in the first time interval and the V GS voltage is increasing. On the output side of the device, the drain current is increasing, while the drain-to-source voltage stays at the previous level (V DS,OFF). This can be understood looking at the schematic in Figure 3. Until all the current is transferred into the MOSFET and the diode is turned-off completely to be able to block reverse voltage across its pn junction, the drain voltage must stay at the output voltage level. Entering into the third period of the turn-on procedure the gate is already charged to the sufficient voltage (V GS,Miller) to carry the entire load current and the rectifier diode is turned off. That now allows the drain voltage to fall. While the drain voltage falls across the device, the gate-to-source voltage stays steady. This is the Miller plateau region in the gate voltage waveform. All the gate current available from the driver is diverted to discharge the C GD capacitor to facilitate the rapid voltage change across the drain-to-source terminals. The drain current of the device stays constant since it is now limited by the external circuitry, i.e. the DC current source.The last step of the turn-on is to fully enhance the conducting channel of the MOSFET by applying a higher gate drive voltage. The final amplitude of V GS determines the ultimate on-resistance of the device during its on-time. Therefore, in this fourth interval, V GS is increased from V GS,Miller to its final value, V DRV. This is accomplished by charging the C GS and C GD capacitors, thus gate current is now split between the two components. While these capacitors are being charged, the drain current is still constant, and the drain-to-source voltage is slightly decreasing as the on-resistance of the device is being reduced.6Turn-Off procedureThe description of the turn-off procedure for the MOSFET transistor is basically back tracking the turn-on steps from the previous section. Start with V GS being equal to V DRV and the current in the device is the full load current represented by I DC in Figure 3. The drain-to-source voltage is being defined by I DC and the R DS(on) of the MOSFET. The four turn-off steps are shown in Figure 5. for completeness.Figure 5. MOSFET turn-off time intervals The first time interval is the turn-off delay which is required to discharge the C ISS capacitance from its initial value to the Miller plateau level. During this time the gate current is supplied by the C ISS capacitor itself and it is flowing through the C GS and C GD capacitors of the MOSFET. The drain voltage of the device is slightly increasing as the overdrive voltage is diminishing. The current in the drain is unchanged.In the second period, the drain-to-source voltage of the MOSFET rises from I D⋅R DS(on) to the final V DS(off) level, where it is clamped to the output voltage by the rectifier diode according to the simplified schematic of Figure 3. During this time period – which corresponds to the Miller plateau in the gate voltage waveform - the gate current is strictly the charging current of the C GDcapacitor because the gate-to-source voltage is constant. This current is provided by the bypass capacitor of the power stage and it is subtracted from the drain current. The total drain current still equals the load current, i.e. the inductor current represented by the DC current source in Figure 3.The beginning of the third time interval is signified by the turn-on of the diode, thus providing an alternative route to the load current.The gate voltage resumes falling from V GS,Miller to V TH. The majority of the gate current is coming out of the C GS capacitor, because the C GDcapacitor is virtually fully charged from the previous time interval. The MOSFET is in linear operation and the declining gate-to-source voltage causes the drain current to decrease and reach near zero by the end of this interval.Meanwhile the drain voltage is steady at V DS(off)due to the forward biased rectifier diode.The last step of the turn-off procedure is to fully discharge the input capacitors of the device. V GSis further reduced until it reaches 0V. The bigger portion of the gate current, similarly to the third turn-off time interval, supplied by the C GScapacitor. The drain current and the drain voltage in the device are unchanged.Summarizing the results, it can be concluded that the MOSFET transistor can be switched between its highest and lowest impedance states (either turn-on or turn-off) in four time intervals. The lengths of all four time intervals are a function of the parasitic capacitance values, the required voltage change across them and the available gate drive current. This emphasizes the importance of the proper component selection and optimum gate drive design for high speed, high frequency switching applications.7Characteristic numbers for turn-on, turn-off delays, rise and fall times of the MOSFET switching waveforms are listed in the transistor data sheets. Unfortunately, these numbers correspond to the specific test conditions and to resistive load, making the comparison of different manufacturers’ products difficult. Also, switching performance in practical applications with clamped inductive load is significantly different from the numbers given in the data sheets.Power lossesThe switching action in the MOSFET transistorin power applications will result in some unavoidable losses, which can be divided into two categories.The simpler of the two loss mechanisms is the gate drive loss of the device. As described before, turning-on or off the MOSFET involves chargingor discharging the C ISS capacitor. When the voltage across a capacitor is changing, a certain amount of charge has to be transferred. The amount of charge required to change the gate voltage between 0V and the actual gate drive voltage V DRV, is characterized by the typical gate charge vs. gate-to-source voltage curve in the MOSFET datasheet. An example is shown in Figure 6.Figure 6. Typical gate charge vs. gate-to-sourcevoltage This graph gives a relatively accurate worst case estimate of the gate charge as a function of the gate drive voltage. The parameter used to generate the individual curves is the drain-to-source off state voltage of the device. V DS(off) influences the Miller charge – the area below the flat portion of the curves – thus also, the total gate charge required in a switching cycle. Once the total gate charge is obtained from Figure 6, the gate charge losses can be calculated as:DRVGDRVGATEfQVP⋅⋅=where V DRV is the amplitude of the gate drive waveform and f DRV is the gate drive frequency – which is in most cases equal to the switching frequency. It is interesting to notice that the Q G⋅f DRV term in the previous equation gives the average bias current required to drive the gate. The power lost to drive the gate of the MOSFET transistor is dissipated in the gate drive circuitry. Referring back to Figures 4 and 5, the dissipating components can be identified as the combination of the series ohmic impedances in the gate drive path. In every switching cycle the required gate charge has to pass through the driver output impedances, the external gate resistor, and the internal gate mesh resistance. As it turns out, the power dissipation is independent of how quickly the charge is delivered through the resistors. Using the resistor designators from Figures 4 and 5, the driver power dissipation can be expressed as:OFFDRV,ONDRV,DRVIG,GATELODRVGDRVLOOFFDRV,IG,GATEHIDRVGDRVHIONDRV,PPPRRRfQVR21PRRRfQVR21P+=++⋅⋅⋅⋅=++⋅⋅⋅⋅=In the above equations, the gate drive circuit is represented by a resistive output impedance and this assumption is valid for MOS based gate drivers. When bipolar transistors are utilized in the gate drive circuit, the output impedance becomes non-linear and the equations do not yield the correct answers. It is safe to assume that with low value gate resistors (<5Ω) most gate drive losses are dissipated in the driver. If R GATE is sufficiently large to limit I G below the output89current capability of the bipolar driver, the majority of the gate drive power loss is then dissipated in R GATE .In addition to the gate drive power loss, the transistors accrue switching losses in the traditional sense due to high current and high voltage being present in the device simultaneously for a short period. In order to ensure the least amount of switching losses, the duration of this time interval must be minimized. Looking at the turn-on and turn-off procedures of the MOSFET, this condition is limited to intervals 2 and 3 of the switching transitions in both turn-on and turn-off operation. These time intervals correspond to the linear operation of the device when the gate voltage is between V TH and V GS,Miller , causing changes in the current of the device and to the Miller plateau region when the drain voltage goes through its switching transition.This is a very important realization to properly design high speed gate drive circuits. It highlights the fact that the most important characteristic of the gate driver is its source-sink current capability around the Miller plateau voltage level. Peak current capability, which is measured at full V DRV across the driver’s output impedance, has very little relevance to the actual switching performance of the MOSFET. What really determines the switching times of the device is the gate drive current capability when the gate-to-source voltage, i.e. the output of the driver is at ~5V (~2.5V for logic level MOSFETs).A crude estimate of the MOSFET switching losses can be calculated using simplified linear approximations of the gate drive current, drain current and drain voltage waveforms during periods 2 and 3 of the switching transitions. First the gate drive currents must be determined for the second and third time intervals respectively:()G.I GATE HI MillerGS,DRV G3G.IGATE HI TH Miller GS,DRVG2R R R V V I R R R V V 0.5V I ++−=+++⋅−=Assuming that I G2 charges the input capacitor of the device from V TH to V GS,Miller and I G3 is the discharge current of the C RSS capacitor while the drain voltage changes from V DS(off) to 0V, the approximate switching times are given as:G3offDS,RSS G2THMillerGS,ISS I V C t3I V V C t2⋅=−⋅=During t2 the drain voltage is V DS(off) and the current is ramping from 0A to the load current, I L while in t3 time interval the drain voltage is falling from V DS(off) to near 0V. Again, using linear approximations of the waveforms, the power loss components for the respective time intervals can be estimated:Loff DS,Loff DS,I 2V T t3P32I V T t2P2⋅⋅=⋅⋅=where T is the switching period. The total switching loss is the sum of the two loss components, which yields the following simplifed expression:Even though the switching transitions are well understood, calculating the exact switching losses is almost impossible. The reason is the effect of the parasitic inductive components which will significantly alter the current and voltage waveforms, as well as the switching times during the switching procedures. Taking into account the effect of the different source and drain inductances of a real circuit would result in second order differential equations to describe the actual waveforms of the circuit. Since the variables, including gate threshold voltage, MOSFET capacitor values, driver output impedances, etc. have a very wide tolerance, the above described linear approximation seems to be a reasonable enough compromise to estimate switching losses in the MOSFET.Effects of parasitic componentsThe most profound effect on switching performance is exhibited by the source inductance. There are two sources for parasitic source inductance in a typical circuit, the sourceTt3t22I V P L DS(off)SW +⋅⋅=。
高速MOSFET门极驱动电路的设计应用指南一、背景介绍二、设计步骤及要点1.确定MOSFET型号和工作条件:根据实际应用需求,选择合适的MOSFET型号,并确定其工作电压和电流。
这些参数将直接影响到驱动电路的设计。
2.确定驱动电源电压和电流:根据MOSFET的特性参数,选择合适的驱动电源电压和电流。
一般来说,高速应用中通常需要较高的电源电压和电流,以确保MOSFET能够迅速开关。
3.选择驱动芯片或设计驱动电路:根据以上参数,选择合适的驱动芯片或自行设计驱动电路。
常用的驱动芯片有IR2110、TC4420等,可以根据实际应用需求选择合适的芯片。
4.进行驱动电路的布局和连接:根据驱动芯片或电路设计,进行布局和连接。
注意保持短而稳定的门极连接线路,尽量减小电流环路和电磁干扰。
5.添加保护电路:考虑MOSFET的过电流、过压等保护问题,设计相应的保护电路,以确保MOSFET的安全工作。
6.进行仿真和测试:通过仿真软件进行仿真分析,验证电路设计是否满足要求。
同时,进行实际测试,检查电路的性能和稳定性。
三、高速MOSFET门极驱动电路的典型设计示例下图为一种常用的高速MOSFET门极驱动电路设计示例,以IR2110为例:[电路图]该驱动电路可实现高速的MOSFET开关控制,具有较高的转换效率和可靠性。
其中VCC为驱动电源电压,VDD为MOSFET的工作电源电压,VIN为控制信号输入端,VD为MOSFET的漏极电压,R1和R2为限流电阻,D1为反向恢复二极管。
四、设计注意事项1.选择合适的驱动芯片或自行设计驱动电路时,要充分考虑芯片的最大驱动电流和工作频率等参数,以确保其满足实际应用需求。
2.在设计驱动电路时,要注意尽量减小电流回路和电磁干扰,保持稳定的门极连接线路。
3.添加合适的保护电路,以保护MOSFET免受过电流、过压等故障的影响。
4.在设计完成后,进行仿真分析和实际测试,检查电路的性能和稳定性,并及时进行调整和改进。
超高速mos导致驱动不工作的原因-概述说明以及解释1.引言概述部分的内容应该对超高速MOS导致驱动不工作的问题进行一个简要的介绍,并提出本文主要讨论的内容。
可以参考以下示例:1.1 概述超高速MOS(Metal-Oxide-Semiconductor)是一种先进的半导体器件,具有较高的速度和性能优势。
然而,在实际应用中,我们有时会遇到驱动不工作的问题,这给电子设备的正常运行带来了一定的挑战。
在本文中,我们将深入探讨超高速MOS导致驱动不工作的原因。
首先,我们将介绍超高速MOS的定义与特点,以便读者能够更好地理解后续内容。
然后,我们将列举一些常见的导致驱动不工作的原因,涵盖了硬件和软件两个方面。
通过深入研究这些原因,我们可以更好地理解超高速MOS的特性和限制,并为解决这些问题提供有益的参考和建议。
本文的目的是帮助读者更好地理解超高速MOS导致驱动不工作的原因,并在实际应用中遇到类似问题时,能够通过合理的方法进行排查和解决。
通过对这一问题的深入探讨,我们也可以为超高速MOS的进一步发展提供一定的参考和展望。
在接下来的章节中,我们将详细介绍超高速MOS的定义与特点,并分析导致驱动不工作的常见原因。
最后,我们将对全文进行总结,并展望超高速MOS驱动不工作的原因在未来的解决方向。
让我们一起深入探讨这一有趣且具有挑战性的话题。
1.2文章结构文章结构:本文将从以下几个方面来探讨超高速MOS导致驱动不工作的原因。
首先,我们将介绍超高速MOS的定义和其特点,以便读者能够更加全面地了解与理解这项技术。
接着,我们将详细讨论导致驱动不工作的常见原因,包括电压波动、温度过高、信号干扰等等。
此外,我们还将分析这些原因对驱动造成的影响,并尝试提供一些解决方案和建议。
最后,我们将综合总结文章的内容,并对超高速MOS导致驱动不工作的原因进行展望,探讨未来可能的解决方案和发展方向。
总之,通过本文的阐述,希望能够为读者提供更多关于超高速MOS 导致驱动不工作的原因的了解,并为相关领域的工程师和研究人员提供一些有益的参考和启发。
高速MOS驱动电路设计和应用指南摘要本篇论文的主要目的是来论证一种为高速开关应用而设计高性能栅极驱动电路的系统研究方法。
它是对“一站买齐”主题信息的收集,用来解决设计中最常见的挑战。
因此,各级的电力电子工程师对它都应该感兴趣。
对最流行电路解决方案和他们的性能进行了分析,这包括寄生部分的影响、瞬态的和极限的工作情况。
整篇文章开始于对MOSFET技术和开关工作的概述,随后进行简单的讨论然后再到复杂问题的分析。
仔细描述了设计过程中关于接地和高边栅极驱动电路、AC耦合和变压器隔离的解决方案。
其中一个章节专门来解决同步整流器应用中栅极驱动对MOSFET的要求。
另外,文章中还有一些一步一步的参数分析设计实例。
简介MOSFET是Metal Oxide Semiconductor Field Effect Transistor的首字母缩写,它在电子工业高频、高效率开关应用中是一种重要的元件。
或许人们会感到不可思议,但是FET是在1930年,大约比双极晶体管早20年被发明出来。
第一个信号电平FET晶体管制成于二十世纪60年代末期,而功率MOSFET是在二十世纪80年代开始被运用的。
如今,成千上万的MOSFET晶体管集成在现代电子元件,从微型的到“离散”功率晶体管。
本课题的研究重点是在各种开关模型功率转换应用中栅极驱动对功率MOSFET 的要求。
场效应晶体管技术双极晶体管和场效应晶体管有着相同的工作原理。
从根本上说,,两种类型晶体管均是电荷控制元件,即它们的输出电流和控制极半导体内的电荷量成比例。
当这些器件被用作开关时,两者必须和低阻抗源极的拉电流和灌电流分开,用以为控制极电荷提供快速的注入和释放。
从这点看,MOS-FET在不断的开关,当速度可以和双极晶体管相比拟时,它被驱动的将十分的‘激烈’。
理论上讲,双极晶体管和MOSFET的开关速度是基本相同的,这取决与载流子穿过半导体所需的时间。
在功率器件的典型值为20 ~ 200皮秒,但这个时间和器件的尺寸大小有关。
mos管控制电机驱动电路设计MOS管控制电机驱动电路设计MOS管控制电机驱动电路设计是工业电气领域的一个重要环节。
其主要目的是通过设计合理的电路,实现对电机的驱动控制,从而使得机器能够正常运转,能够适应不同的工作条件,提高其运行的效率和稳定性。
下文将依次介绍该过程的具体步骤。
第一步:明确工作要求在进行MOS管控制电机驱动电路设计之前,需要明确电机的种类和具体的工作要求。
比如,需要确定电机的额定电压和额定功率,需要了解其负载类型和工作环境等情况,以此为基础,才能进行后续的电路设计。
同时,还需要确定驱动电路的控制要求,比如需要实现速度控制、反向控制等功能。
第二步:选取MOS管驱动电路MOS管驱动电路分为多种类型,常用的有单路和双路驱动,需要根据实际情况选取适合的驱动电路。
一般情况下,如果电机功率较小,可以采用单路驱动电路,而大功率电机则需要使用双路驱动电路。
同时,需要考虑驱动电路的可靠性和稳定性等因素。
第三步:设计电路图设计电路图是MOS管控制电机驱动电路设计的核心环节。
在这一步中,需要将选取的MOS管驱动电路与电机连接起来,实现电机的驱动控制。
电路图需要精确明确,符合实际工作要求,在避免冗余的同时,也需要保证电路的可靠性和稳定性。
第四步:制作电路板电路图设计完成之后,需要进行电路板的制作。
制作电路板时需要注意,要保证电路板上的元器件位置准确无误,且对于大功率电机,需要选择耐高温、高电压的元器件。
第五步:电路测试电路制作完成后,需要进行电路测试。
测试时,需要仔细检查各个元器件的连接是否正确,以及是否存在接触不良等因素。
同时,还需要使用相应的工具进行电路的测量,查看电路是否能达到预期的控制效果。
综上所述,MOS管控制电机驱动电路设计需要进行多个步骤的精心设计和实现。
在实际操作中,需要对每个步骤都进行仔细的分析和考虑,避免出现影响驱动效果的问题。
只有经过严谨、逐步的实验和测试,才能完成一个性能稳定、可靠性好的驱动电路的设计与制造。
高速MOS驱动电路设计和应用指南摘要本篇论文的主要目的是来论证一种为高速开关应用而设计高性能栅极驱动电路的系统研究方法。
它是对“一站买齐”主题信息的收集,用来解决设计中最常见的挑战。
因此,各级的电力电子工程师对它都应该感兴趣。
对最流行电路解决方案和他们的性能进行了分析,这包括寄生部分的影响、瞬态的和极限的工作情况。
整篇文章开始于对MOSFET技术和开关工作的概述,随后进行简单的讨论然后再到复杂问题的分析。
仔细描述了设计过程中关于接地和高边栅极驱动电路、AC耦合和变压器隔离的解决方案。
其中一个章节专门来解决同步整流器应用中栅极驱动对MOSFET的要求。
另外,文章中还有一些一步一步的参数分析设计实例。
简介MOSFET是Metal Oxide Semiconductor Field Effect Transistor的首字母缩写,它在电子工业高频、高效率开关应用中是一种重要的元件。
或许人们会感到不可思议,但是FET是在1930年,大约比双极晶体管早20年被发明出来。
第一个信号电平FET晶体管制成于二十世纪60年代末期,而功率MOSFET是在二十世纪80年代开始被运用的。
如今,成千上万的MOSFET晶体管集成在现代电子元件,从微型的到“离散”功率晶体管。
本课题的研究重点是在各种开关模型功率转换应用中栅极驱动对功率MOSFET 的要求。
场效应晶体管技术双极晶体管和场效应晶体管有着相同的工作原理。
从根本上说,,两种类型晶体管均是电荷控制元件,即它们的输出电流和控制极半导体内的电荷量成比例。
当这些器件被用作开关时,两者必须和低阻抗源极的拉电流和灌电流分开,用以为控制极电荷提供快速的注入和释放。
从这点看,MOS-FET在不断的开关,当速度可以和双极晶体管相比拟时,它被驱动的将十分的‘激烈’。
理论上讲,双极晶体管和MOSFET的开关速度是基本相同的,这取决与载流子穿过半导体所需的时间。
在功率器件的典型值为20 ~ 200皮秒,但这个时间和器件的尺寸大小有关。
与双极结型晶体管相比,MOSFET在数字技术应用和功率应用上的普及和发展得益于它的两个优点。
优点之一就是在高频率开关应用中MOSFET使用比较方便。
MOSFET更加容易被驱动,这是因为它的控制极和电流传导区是隔离开的,因此不需要一个持续的电流来控制。
一旦MOSFET导通后,它的驱动电流几乎为0。
另外,在MOSFET中,控制电荷的积累和存留时间也大大的减小了。
这基本解决了设计中导通电压降(和多余的控制电荷成反比)和关断时间之间的矛盾。
因此,MOSFET技术以其更加简单的、高效的驱动电路使它比晶体管设备具有更大的经济效益。
此外,有必要突出强调下,尤其是在电源应用上,MOSFET本身具有阻抗特性。
MOSFET漏源端的电压降和流经半导体的电流成线性关系。
这种线性关系,以MOSFET的R DS(on)表现出来,即导通阻抗。
对于一个给定的栅源电压和温度的器件,其导通阻抗是恒定的。
和p-n结-2.2mV/℃的温度系数相反,MOSFET 有一个正的温度系数,约为0.7% /℃到1%/℃。
MOSFET的这一正温度系数使得它成为在大功率电源应用的并联工作(由于使用一个器件是不实际或不可能的)上的理想选择。
由于MOSFET较好的温度系数,并联的管子通常是均分电流。
电流的均分是自动实现的,这是因为它的温度系数作为一个缓慢的负反馈系统。
当电流较大时设备温度将会升高,但是不要忘记源漏极间的电压是不变的,温度升高将会使源漏极间电阻变大,增大的电阻又会使电流减小,因此管子的温度又会下降。
最后,会达到一个动态平衡,并联的管子都通过相同的电流。
在电流分配中,源漏极导通电阻的初始值和有不同温度特性的结电阻在均分电流时将会引起较大的误差,最高可达30%。
器件类型几乎所有的MOSFET制造厂商都有制造最佳管子的独特制造技术,但所有这些在市场上的管子都可分为基本的三类,如图1所示。
1970年开始应用于电源方面并在以后的时间里不断的发展。
使用多晶硅闸门结构和自动调整过程,使高密度的集成和电容迅速的减小成为可能。
下一个重大的进步是在功率MOSFET器件上V沟槽技术或者称为沟渠技术,使集成度进一步的提高。
更好的性能和更高的集成度并不是由你随便就能得来的,这是因为这将导致MOS器件沟渠更难制造。
在这里第三个器件类型是横向功率MOSFET。
该器件的电压、电流是受限制的,这是由于其对芯片形状的低效利用。
然而,他们能在低电压应用上提供很大的效益, 如在微型电源或在隔离转换同步整流器中。
由于横向功率MOSFET有着相当小的电容,因此他们的开关速度可以很快而且栅极驱动损耗也比较小。
场效应晶体管模型有很多的模型来说明MOSFET如何工作,然而找到正确的适合的模型是比较困难的。
大多数MOSFET制造商为他们的器件提供普通或者军用(Spice and/or Saber)模型,但是这些模型很少告诉使用者在实际使用中的陷阱。
他们甚至很少提供在使用中最常见的最普通问题的解决方案。
一个真正有用的MOSFET模型会从应用的角度描述器件所有重要的性质,这使得其模型可能会相当复杂。
另一方面,如果我们把模型限制在某一问题领域,那么我们可以得到十分简单并有意义的MOSFET模型。
在图2中第一个模型是基于MOSFET器件的实际结构, 它主要用于直流的分析。
它表示出了沟道阻抗和JFET(相当于外延层的阻抗)。
外延层的厚度(决定外延层的阻抗)是器件额定电压的函数,而高电压的MOSFET需要一个厚的外延层。
图2b可以非常好的展示MOSFET的dv/dt引发的击穿特性。
它主要展现了两种击穿机制,即诱发寄生晶体管(所有的管子均有)的导通和dv/dt根据栅极阻抗诱发沟道导通。
现代的功率MOSFET由于生产工艺的提高减小了基极和发射极的电阻,因此,实际上对dv/dt诱发寄生npn晶体管导通是有免疫的。
必须指出的是,寄生性双极晶体管还扮演着另一个重要的角色。
它的基集结就是有名的MOSFET的体二极管。
图2c是场效应晶体管的开关模型。
影响开关性能的最重要的寄生部分都展现在这个模型中。
它们对器件的开关过程的影响将在下一章中讨论。
MOSFET的重要参数当MOSFET工作在开关状态下,目标是在可能的最短时间内实现器件在最低阻抗和最高阻抗之间的切换。
由于MOSFET实际的开关时间(10ns—60ns)至少比理论开关时间(50ps—200ps)大2~3个数量级,因此有必要了解其差异。
参考图2中MOSFET的模型,可以发现所有的模型在器件的三端之间都连有一个等效电容。
毫无疑问,开关速度和性能决定于这三个电容上电压变化的快慢。
因此,在高速开关应用中,器件的寄生电容是一个重要的参数。
电容C GS 和电容C GD与器件的实际几何尺寸有关,而电容C DS是寄生在双集晶体管的基集二极管间的电容。
电容C GS是由于源极和栅极形成的沟道区域的重叠形成的。
它的值由器件实际的区域几何尺寸决定而且在不同的工作条件下保持不变。
电容C GD由两个因素决定。
一是耗尽层(是非线性的)的电容;二是JFET区域和栅极的重叠。
等效电容C GD是器件漏源极电压的函数,大致可用下面公式计算得到:电容C DS也是非线性的,这是由于它是体二极管的结电容。
它和电压间关系为:不幸的是,上述的所有电容在器件的资料表中均未涉及和说明。
它们的值由Ciss (栅短路共源输入电容)、Crss(栅短路共源反向传输电容)、Coss(栅短路共源输出电容)间接给出,而且必须用下列公式计算:在开关应用中,电容C GD会引起其他复杂问题,这是由于它处于器件输入与输出间的反馈回路中。
因此,它在开关应用中有效值可能会很大,它的值取决于MOSFET的漏源极电压。
这种现象被称为“Miller”效应,而且可以用下式表示:由于电容C GD和C GS是和电压有关的,因此只有把测试条件列出来时,那些资料中的数据才是有效的。
对于一个确定的应用,有关的平均电容值必须由计算得来,而计算是基于建立于实际电压所需要的电荷。
对于大多数的功率MOSFET 来说,下面公式将会十分有用:下一个将要谈及的重要的参数是栅极网格阻抗,Rg,I。
这个寄生阻抗描述了器件内部栅极信号分配与阻抗之间的联系。
在高速开关应用中它的重要性尤为突出,因为它介于驱动和器件输入电容之间,直接影响MOSFET的开关时间和dv/dt 能力。
在工业生产中已经意识到这个问题,实际中的高速MOSFET器件如RF MOSFET在栅极信号分配中使用金属栅极用来代替高阻抗的硅栅极。
在资料表中阻抗Rg,I并没有指明,但在实际的应用中它可能是器件一个十分重要的特性。
在这篇文章的后面,附录A4展示了通过使用阻抗电桥采用一种典型的测量装置来确定栅极内部阻抗值。
很明显,栅极阈值电压也是一个临界特性。
有必要注意一下,在器件资料表中V TH(开启电压)的值是指在25℃,而且在漏极电流很小的情况下,电流典型值是250uA。
因此,它并不等同于被大家公认的栅极开关波形的Miller平坦区。
关于开启电压V TH的另一个很少提到的是约为-7mV/℃的温度系数,在MOSFET 逻辑电平栅极电路驱动中它有着尤为重要的意义,它的开启电压V TH比在正常的测试条件下已经变低了。
由于MOS FET工作在较高的温度,栅极驱动设计必须中适当的考虑到在截止时较低的开启电压,dv/dt 免疫能力的计算见附录A和F。
场效应晶体管的跨导是线性工作区中小信号的增益。
有必要指出在管子每次导通或截止时,都要必须经过线性工作区,此时的电流取决于栅源电压。
正向跨导g fs,反映了漏极电流和栅源电压之间的小信号关系,具体关系如下:因此,MOSFET在线性区的最大电流公式为:变换V GS,Miller平坦区电压可近似写成漏极电流的函数:其他重要的参数如L D---漏极电感和Ls---源极电感在开关性能中也有显著的限制。
典型的L D和Ls值会在器件资料单中列出,而且他们的值主要和器件的封装类型有关。
它们的影响通常可以和外部寄生元件(通常和布局和外电路因素如漏电感、检测电阻等等)一同分析。
完整的,外部系列栅极电阻和MOSFET的输出阻抗在高速栅极驱动设计中是决定性的因素,因为它们在开关速度和最终开关损耗上有着深远的意义。
开关应用现在,所有的角色都讨论完了,让我们来研究下MOSFET的真实开关行为。
为了更好的理解其基本过程,电路中的寄生电感将会被忽略掉。
随后,它们在基本工作中各自的影响将会单独的分析。
此外,下面的说明和钳位感应开关有关,这因为大多数被用于电源模式的MOSFET晶体管和高速门驱动电路工作于那个模式。
一个最简单的钳位感应开关模型如图三(Figure)所示,直流电流源代表感应器。
在开关间隔比较小的情况下,它的电流可看作是连续的。