开关电源和LDO的区别室外一体化电源机柜,高频开关电源，-48V开关电源

介绍了TOP250Y在大功率开关电源中的应用，论述了TOP250Y 开关电源的基本工作原理，重点分析了关键电路参数的设计方法，并给出了设计实例和试验结果。  

        关键词： TOPSwitch；大功率；开关电源  

引 言  

        TOPSwitch电源技术是近年来迅速发展的一种开关电源技术，因其在体积、效率和可靠性等方面的优势，目前在通信、计算机和家用电器等众多领域中得到了非常广泛的应用。但由于前几代TOPSwitch遍存在输出功率受限的不足之处，使其在要求有较大输出功率的电源应用中受到很大的限制。针对这种情况， Power Integrations公司推出了TOPSwitch的第四代单芯片高压IC系列： TOPSwitch-GX系列。  

        TOPSwitch-GX单芯片高压IC 系列将高压功率MOSFET、PWM控制、故障保护和其他控制电路等高性价比地集成在单片CMOS芯片上。其内建特性包括用于在启动时消除过冲和降低元件应力的软启动、减小EMI 的频率抖动、欠压保护和过压保护、可编程限流等优异特性。  

        与TOPSwitch-GX系列其它产品一样，因为其采用了单芯片控制的设计理念，而且TOP250Y只有很少的三四个外围元器件，这就使得相同设计的电源尺寸更小、待机效率更高、系统成本更低，并保持了用途广泛和设计简单的特色，使电源设计能为290W以下的应用创造出高性价比的方案。  

        本文具体分析了TOP250Y开关电源的工作原理，并详细介绍了TOP250Y型芯片在大功率开关电源应用中关键电路参数的设计方法，并给出了设计实例。该实例中电源最大输出功率达到了288 W，对单芯片TOPSwitch在大功率开关电源领域内的应用研究具有指导意义。  

TOP250Y开关电源的基本原理  

TOP250Y型芯片有六个管脚：D、S、C、F、X、L，简单的TO220-7C 封装外形简图如图1所示。  

        图1 TOP250Y封装外形图 

图1各管脚功能如下：  

        漏极管脚(D)：高压功率MOSFET漏极输出。控制管脚(C)：用于调节占空比的误差放大器与电流输入脚。  

        源极管脚(S)：将其连接至输出MOSFET源极时可得到高压功率回馈。  

        电压检测管脚(L)：具有欠压保护、过压保护、减少Dmax的线性前馈及远程开关等功能。外部限流管脚(X)：用于外部电流限制值设置的输入脚。  

        频率管脚(F)：用于选择开关频率的输入脚。由TOP250Y构成288W(24V/12A)大功率高效开关电源的电路如图2所示。  

        图2 由TOP250Y构成的开关电源电路 

其交流输入电压范围是交流176～264V ，满载时电源效率可达86%。交流电压UI 依次经过电磁干扰(EMI) 滤波器(C1，L1)、输入整流滤波器(V1，C2) 获得直流高压。直流高压经过R1 后接N1 的L端，为TOP250Y提供电压前馈信号，实现过压保护、欠压保护以及使电源随输入电压改变Dmax功能。这里将N1的X 脚接地，使TOP250Y 工作在最大占空比，因此，即使在宽范围输入时，电源也能达到最大连续输出功率PoM=290W。将N1的F脚接地，使TOP250Y工作在较高的132kHz频率上，采用这种设计方法允许高频变压器选用尺寸较小的磁芯，并防止出现磁饱和现象。  

        次级电压经过V5，C8～C11，L2和C12整流滤波后，获得+ 24V/12A的稳压输出。C8～C11滤除纹波电压，L2和C12则用来消除开关噪声。该电源采用一个简单的串联稳压管方式的光耦反馈电路。E1为4N25型线性光耦合器。V7和V8分别采用1N963 和1N962 型稳压管。其稳压原理如下：当由于某种原因致使输出电压Uo↑，所产生的误差电压使E1中LED的IF↑，光耦接收管的IE↑，使得N1 控制端电流Ic↑，而占空比D ↓，导致Uo↓，从而实现了稳压目的。反之， Uo↓→I F↓→I E↓→Ic↓→D↑→Uo↑，同样起到稳压作用。  

        当开关电源空载时，TOP250Y能采用跳过周期的方式极大地降低最大输出占空比，使得Dmax<2%。因此，在输出端无须接假负载，这样还可降低空载或待机状态下的功耗。  

        V6和C14为次级提供软启动，C14为软启动电容，能消除刚接通电源时产生的电压过冲现象，使反馈绕组提供给N1的C脚电压先于输出电压，这样就保证了即使在低输入电压和满载情况下，也能使输出电压在启动时正常调整。电阻R5和电容C13构成控制环路补偿电路。  

        反馈绕组电压经过V4和C5整流滤波后，产生12 V的反馈电压，经过E1 给TOP250Y 的控制端提供偏压。C4 是旁路电容，它还与R3 和C3 构成控制环路的补偿电路。  

        齐纳箝位管V2、超快速二极管V3、电阻R2和电容C6组成尖峰吸收电路。用于吸收在TOP250Y关断时由高频变压器漏感产生的尖峰电压， 对TOP250Y中MOSFET管的漏极起到保护作用。  

        由于V2上并联R2和C6，在正常工作时，R2几乎承担了所有的泄放能量，而在启动或超载的情况下，V2又限制了尖峰电压不超过N1中MOSFET管的安全电压(700V)。  

关键电路设计与实例 

        举例电路参数： 交流UI=176～264V， f=132kHz， D =0.5， Uo=24V， Io=12A， Po=288W，纹波≤1%。  

输入滤波电容的设计  

        考虑市电掉一个脉冲的时间是10 ms ，取电源输出的保持时间td=10ms ，电容C2 上的直流电压从250V(176V×1.414)下降到220 V后，输出才开始下降。故  

        取标准值C2 = 470μF  

变压器磁芯的选择 

        实际功率容量乘积计算：  

PQ3535的功率容量乘积为1.72 ，为0.66的3倍，如果按50%的余量计算，在132kHz开关频率工作时，PQ3535的输出功率可达375W ，因此设计值为288W是充分留有余量的。  

变压器的各电参数设计 

        a.计算初级绕组的电感量  

        b.计算变压器初级绕组匝数  

开关电源和LDO的区别

线性稳压电源(LDO)是通过改变晶体管的导通程度来改变和控制其输出的电压和电流，在线性稳压电源(LDO)中晶体管相当于一个可变电阻，串接在供电回路中。由于可变电阻与负载流过相同的电流，因此要消耗掉大量的能量并导致升温，电压转换效率低。线性稳压电源(LDO)有一个共同的特点就是它的功率器件调整管工作在线性区，靠调整管极间的电压降来稳定输出。由于调整管静态损耗大，需要安装一个很大的散热器给它散热。由于线性电源的变压器工作在工频 (50Hz)上，所以质量较大。

         线性稳压电源(LDO)常用于低压场合，像LDO需要满足一定的电压差。输出电压调整率和纹波比较好，效率比较低，需要的外围元器件比较少，成本低。电路比较简单。

  　线性稳压电源(LDO)优点是稳定性高，纹波小，可靠性高，易做成多路输出连续可调的电源。缺点是体积大、较笨重、效率相对较低。这类稳压电源又有很多种，从输出性质可分为稳压电源、稳流电源和集稳压、稳流于一身的稳压稳流(双稳)电源。从输出值来看可分固定输出电源、波段开关调整式和电位器连续可调式几种。从输出指示上可分指针指示型和数字显示式型等。

      开关电源适用于全电压范围，不需要压差，可以采用不同的电路拓扑实现不同的输出要求。调整率和输出纹波不如线性电源，效率高。需要外围元件多，成本高。电路相对复杂。开关型直流稳压电源它的电路型式主要有单端反激式、单端正激式、半桥式、推挽式和全桥式。它和线性稳压电源(LDO)的根本区别在于电路中的变压器不工作在工频而是工作在几十千赫兹到几兆赫兹。功率管不是工作在线性区，而是饱和及截止区，即工作在开关状态；开关型直流稳压电源也因此而得名。    

       线性稳压电源(LDO)和开关电源最大的区别是线性稳压电源(LDO)中管子(无论是双极型还是MOSFET)工作于线性状态，而开关电源中管子工作于开关状态。线性稳压电源(LDO)和开关电源也因此而得名。

本人，擅长MATLAB/SIMULINK软件，有十多年的经验，做过大量的项目以及课题；涵盖控制辨识，金融，机电液，图像处理识别，数据处理可视化，数字信号处理等领域。我的博客也包含大量的硬件设计方面的积累

The application of TOP250Y in high power switching power supply is introduced, the basic working principle of TOP250Y switching power supply is discussed, the design method of key circuit parameters is emphatically analyzed, and the design example and test result are given.

Key words: TOPSwitch; high power; switching power supply

Introduction

TOPSwitch power technology is a kind of switching power technology which has developed rapidly in recent years. Because of its advantages in volume, efficiency and reliability, it has been widely used in many fields, such as communication, computer and household appliances. However, due to the shortage of output power in previous generations, TOPSwitch has been limited in applications requiring large output power. In view of this situation, Power Integrations has introduced TOPSwitch's fourth generation single chip high voltage IC series: TOPSwitch-GX series.

The TOPSwitch-GX single chip high voltage IC series integrates high voltage power MOSFET, PWM control, fault protection and other control circuits on a monolithic CMOS chip. Its built-in characteristics include excellent characteristics such as eliminating overshoot at startup and reducing the soft start of component stress, reducing the frequency jitter of EMI, undervoltage protection and overvoltage protection, programmable current limiting and so on.

As with other TOPSwitch-GX products, because it uses a single chip control design concept, and TOP250Y has only a few three or four peripheral components, this makes the same design smaller, more efficient, lower system cost, and maintains a wide range and simple design features to make the power supply. The design can create a cost-effective scheme for applications below 290W.

In this paper, the working principle of TOP250Y switching power supply is analyzed, and the design method of key circuit parameters in the application of TOP250Y type chip in the application of high power switching power supply is introduced in detail, and the design example is given. The maximum output power of the example is up to 288 W, which is instructive to the application of single chip TOPSwitch in the field of high-power switching power supply.

The basic principle of TOP250Y switching power supply

The TOP250Y chip has six pins: D, S, C, F, X and L. A simple TO220-7C package outline is shown in Figure 1.

Figure 1 TOP250Y package figure

Figure 1 the functions of each foot are as follows:

Drain pin (D): high voltage power MOSFET drain output. Control pin (C): error amplifier and current input pin used to adjust duty cycle.

Source pin (S): high voltage power feedback is achieved when it is connected to the output MOSFET source.

Voltage detection pin (L): it has the functions of under voltage protection, over voltage protection, Dmax reduction, linear feedforward and remote switch. External current limiting pins (X): input pins for external current limiting settings.

Frequency pin (F): input pin used to select switching frequency. The circuit of 288W (24V/12A) high power and high efficiency switching power supply constituted by TOP250Y is shown in Figure 2.

Figure 2 switch power circuit made up of TOP250Y

The AC input voltage range is 176 to 264V AC, and the power efficiency can reach 86% when full load. AC voltage UI successively obtains DC high voltage through EMI (C1) filter (C1) and input rectifier filter (V1, C2). The DC high voltage is connected to the L end of N1 after R1, and the voltage feedforward signal is provided for the TOP250Y to realize overvoltage protection, undervoltage protection and the power supply to change the Dmax function with the input voltage. Here, the X foot of N1 is grounded to enable TOP250Y to work in the maximum duty cycle, so the power can reach the maximum continuous output power of PoM=290W even in a wide range of input. The F foot of N1 is grounded to make TOP250Y work at a higher 132kHz frequency. This method is used to allow high frequency transformers to choose smaller size cores and to prevent magnetic saturation.

After the secondary voltage is filtered by V5, C8 to C11, L2 and C12, the output voltage of + 24V/12A is obtained. C8 to C11 filter ripple voltage, L2 and C12 are used to eliminate switching noise. The power supply adopts a simple optocoupler feedback circuit with series voltage stabilizer. E1 is a 4N25 linear optical coupler. V7 and V8 are 1N963 and 1N962 regulator respectively. The principle of the voltage stabilizing is as follows: when the output voltage is Uo for some reason, the error voltage produces the IF of the LED in the E1 and the IE of the optocoupler receiver, which makes the N1 control end current Ic, and the duty ratio D. On the other hand, Uo, I, F, I, E, Ic, D, Uo Uo also play a role in stabilizing pressure.

When the switching power supply is empty, TOP250Y can greatly reduce the maximum duty cycle of the Dmax<2% by skipping cycle. Therefore, no load is required at the output side, which can also reduce the power consumption under no load or standby mode.

V6 and C14 provide the secondary soft start. C14 is a soft start capacitor. It can eliminate the overshoot of the voltage when the power is connected to the power supply. The feedback winding provides the C foot voltage of the N1 before the output voltage. This ensures that the output voltage can be adjusted normally even at the low input voltage and full load condition. The resistor R5 and capacitor C13 constitute the control loop compensation circuit.

The feedback winding voltage is generated by V4 and C5 rectification, and generates a feedback voltage of 12 V, which provides bias voltage to the control end of TOP250Y through E1. C4 is a bypass capacitor, and it also forms a compensation circuit of the control loop with R3 and C3.

Zener clamp tube V2, ultra fast diode V3, resistor R2 and capacitance C6 constitute a spike absorption circuit. Used to absorb spikes generated by leakage of high-frequency transformers when TOP250Y is turned off.

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