1、 附录A PWM技术介绍随着电子技术的发展，出现了多种PWM技术，其中包括：相电压控制PWM、脉PWM法、随机PWM、SPWM法、线电压控制PWM等，而在镍氢电池智能充电器中采用的脉宽PWM法，它是把每一脉冲宽度均相等的脉冲列作为PWM波形，通过改变脉冲列的周期可以调频，改变脉冲的宽度或占空比可以调压，采用适当控制方法即可使电压与频率协调变化。可以通过调整PWM的周期、PWM的占空比而达到控制充电电流的目的。模拟信号的值可以连续变化，其时间和幅度的分辨率都没有限制。9V电池就是一种模拟器件，因为它的输出电压并不精确地等于9V，而是随时间发生变化，并可取任何实数值。与此类似，从电池吸收的电流也不
2、限定在一组可能的取值范围之内。模拟信号与数字信号的区别在于后者的取值通常只能属于预先确定的可能取值集合之内，例如在0V,5V这一集合中取值。模拟电压和电流可直接用来进行控制，如对汽车收音机的音量进行控制。在简单的模拟收音机中，音量旋钮被连接到一个可变电阻。拧动旋钮时，电阻值变大或变小；流经这个电阻的电流也随之增加或减少，从而改变了驱动扬声器的电流值，使音量相应变大或变小。与收音机一样，模拟电路的输出与输入成线性比例。尽管模拟控制看起来可能直观而简单，但它并不总是非常经济或可行的。其中一点就是，模拟电路容易随时间漂移，因而难以调节。能够解决这个问题的精密模拟电路可能非常庞大、笨重(如老式的家庭立
3、体声设备)和昂贵。模拟电路还有可能严重发热，其功耗相对于工作元件两端电压与电流的乘积成正比。模拟电路还可能对噪声很敏感，任何扰动或噪声都肯定会改变电流值的大小。通过以数字方式控制模拟电路，可以大幅度降低系统的成本和功耗。此外，许多微控制器和DSP已经在芯片上包含了PWM控制器，这使数字控制的实现变得更加容易了。附录PWM Technology IntroductionWith the development of electronic technology, a variety of PWM technology, including: phase voltage control PWM, P
4、WM pulseMethod, random PWM, SPWM method, line voltage control PWM, etc., and a nickel-hydrogen battery smart charger using pulse width PWM method, it is the pulse train each pulse width of the PWM waveform are equal, by changing the pulse train The cycle can be FM, changing the pulse width or duty c
5、ycle may regulator, the use of appropriate control methods can vary the voltage and frequency coordination. You can adjust the PWM period, PWM duty cycle to achieve the purpose of controlling the charging current.Value of the analog signal can be continuously changed, the time and amplitude resoluti
6、on are not restricted. 9V battery is a kind of analog devices, because its output voltage is not precisely 9V, but change over time, and can take any real value. Similarly, the current drawn from the battery is not limited to a finite set of possible values range. The difference between analog and d
7、igital signals is that the latter usually only values are within a pre-determined set of possible values, such as the value of the 0V, 5V this collection.Analog voltage and current can be directly used for control, such as the volume of the car radio control. In a simple analog radio, a knob is conn
8、ected to a variable resistor. As you turn the knob, the resistance value becomes larger or smaller; the current flowing through the resistor also will increase or decrease, thus changing the current driving the speakers, so that the volume correspondingly larger or smaller. And radio, the output and
9、 input is linearly proportional to the analog circuit.Although analog control may seem intuitive and simple, but it is not always economical or feasible. For one thing, analog circuits tend to drift over time, making it difficult to adjust. Can solve this problem precision analog circuits can be ver
10、y large, heavy (like older home stereo equipment), and expensive. Analog circuits can also get very hot, the power consumption is proportional to the product of a working element with respect to the voltage across the current. Analog circuitry can also be very sensitive to noise, any disturbance or
11、noise will certainly change the size of the current value.By digitally controlled analog circuits, it can greatly reduce system cost and power consumption. In addition, many microcontrollers and DSP have included PWM controller on the chip, which enables digital control of implementation has become much easier.3
