光探测器文献翻译原文及译文本科毕业论文.doc

黄河科技学院毕业设计（文献翻译） 第12页

光探测器
1 引言
在发光二极管系列的最后一部分，我们展示了如何把光电二极管运用为精确的光敏元件，通过生成与光强相对应的光电流，光电二极管产生一个被测光源对等的电学特性，光强变化60%或70%仍能保持线性。
此外,通过光电二极管基本功能与外加电路结合。半导体厂商已经生产出各种感光元件，它能直接输出电压生成可直接输出电压，或者，例如光频率转换器，一个方波信号的频率随检测到的光强变化而变化。
然而，在许多光传感应用中，往往需要检测的是光的变化，而不是光强度的线性响应。典型的例子是数字闹钟，它是当环境光水平相对较低时使用光传感器微弱的7段发光显示的产品，或汽车的光传感器，天黑了时提醒司机打开大灯。本项目使用的也是作为一个简单的光传感器产生一个电压随光照强度的变化。由电压具有可变参考电压比较，该光检测器提供数字输出信号改变状态时，监测的光穿过一个预设的阈值。
该探测器还通过照明传感器也当光超过预定水平提供视觉指示。这样，这也提供了一个双重功能，作为两者的传感器和指示器。一个可选的，光隔离输出也可。
2 长期的生活中的应用
当监控光超过预设的阈值，该电路锁存到其“绊倒”状态，并保持这样，即使光枪度下降，下降到低于阈值电平。在静态的“解锁”状态，该电路只需要很小的电源电流，允许它运行几个月，甚至几年，从一个单一的PP3 9V电池。
探测器应该找到在气象和环境实验中的应用，那里是一个需要监测的环境光条件下记录的时刻，光超过一个特定的水平。该电路也可以用来提供一个危险的警告。例如，当位于在一个黑暗的库，它可以被用来作为一个基本的火灾探测器，可以感测所产生的火焰光产生报警信号。探测器也非常适合应用在安全，监控光可以用来表示一个入侵者的存在，或警告的未经授权的使用的一个房间或对象。例如，通过定位探测器接近一个房间的天花板或墙壁灯，它可用于信号，入侵者进入房间，打开灯。
另外，通过定位单元内的橱柜或抽屉，它将被触发时，环境光落在它，探测器可以提供视觉的或电子的迹象表明有人获得了未经授权的访问到橱柜的内容。事实上，该探测器保持在锁定状态，事件，即使橱柜或抽屉关闭再次记录。
3 微功耗比较器和参考
比较器的部分功能，就像一个正常的电压比较器，但随着可编程迟滞的加入。根据HYST端子之间的电压差（引脚5）和参考端，比较器的输入端之间出现滞后可以从零至约100mV。然而，我们很快就会看到，光检测器的锁存比较器的磁滞行为意味着不是必需的，从而简化了电路HYST引脚直接连接到REF引脚，在零滞后。
磁滞和微功率比较器的更多信息可以在施密特触发器中发现。
4 电池供电
当操作从一个单一的供应，max931具有2.5V至11V的电源电压范围内，和在室温下的最大只有3.2毫安电源电流。较宽的电源电压范围，连同小功率的要求，使装置的电池理想。
1、供电应用
max931可以从两个串联的碱性电池标称电源电压的3V左右，光检测器利用一个9V的电源。这不仅提供“驱动”照亮LED和功率可选的光隔离器大量（IC2），它还允许电路工作在其静止状态数月或数年无需更换电池。此外，所需的PP3电池连接器相对简单。
2、光电压
光伏，VF，由LED产生的光落在D1输入到比较器的非反相输入+（引脚3）通过一个单一的极低通滤波器包括R2和C1。电压是一个可变参考电压，虚拟现实相比，在比较器的反相输入端，9（引脚4）。可变参考电压（由电阻R4和C2过滤）是由预设VR1在IC1引脚6连接到1~182v参考电压输出调节。
在低光照条件下，当电压VF小于VR，比较器输出电压，VOUT端子，低（大约在0V）和二极管D2反向偏置，没有电流流过R3。然而，当光照强度下降D1增加到VF刚刚超过虚拟现实点，比较器输出变高，从而正向偏置D2，允许正向电流流入D1通过限流电阻R3。
D1功能的变化从光探测器的光发射器，和也说明表明监测光穿过由VR1阈值。
3、锁存
该电路是现在在锁定状态，和电压，VF，出现在D1不再是由光的能量产生的光电压，但仅仅是因为一个LED的正向电压约为1~6V以上的正向偏置的LED的正向电压VF，现在明显大于VR（其中可不大于1~182v），所以电路锁存到其“绊倒”状态。
从本质上讲，组件R3和D2提供积极的反馈路径的比较器的输出非反相输入（通过R2），从而确保电路进行快速清洁过渡到锁定状态。
二极管D2中起着重要的作用。没有它，“弱”的光所产生的D1将看到一个非常低阻抗路径通过R3和比较器的输出。这将沼泽地的电压，并将它降低到其正常的“卸载”价值的一小部分。
D2中，存在然而，确保在D1的静载荷是R1并联比较器的同相输入阻抗非常高的结合（以这样的小电流，它可以假设可以忽略不计）。因此，考虑到R1的价值很高，D1可以考虑卸载时的电路在解锁状态。
当电路跳闸，可重置（解锁）关闭S1，一瞬间的动作，常开按钮。这短裤比较器的非反相输入为0V，使得它的输出变低，从而剥夺D1正向电流。现在电路恢复到其静止，解锁状态在VOUT = 0V，D2反向偏置，和VF是落在D1光产生的光电压。当然，如果VF大于VR，电路就立刻锁了。
5 过滤器
两个低通滤波器的C1 / R2和C2 / R4形成明显减轻任何电气噪声比较器的输入端出现。这可以在检测器中使用的电“噪音”的环境是重要的，例如当监测光荧光灯管，或如果位于靠近一个电动马达的电刷装置。
然而，C1 / R2过滤器提供了一个额外的功能。如果探测器是用来监测由交流电压供电的光源，如白炽灯的电源供电，由D1光电压VF将包括一个直流电压加上一个较小的交流分量。提供D1已正确连接到检测器电路，电气噪声将只提供这种交流分量的一小部分。相反，另一种机制是负责大部分变频交流部。
大多数电源电压供应与50Hz或60Hz频率大致正弦波形，根据国家。在英国，例如，国内电网频率是50Hz的名义上的，而在北美国主要是60Hz。这意味着通过一个交流电源驱动灯丝电流在一个正弦的方式不同，增加和减少，达到一个正峰和负峰，50或60倍的每一秒。
6 发热物体
现在，白炽灯本质上是一种热光源，在灯所发出的光是由灯丝的闪闪发光的白色热加热引起的。由于灯有一个比较大的热时间常数，它不能对每一个峰和电源波形正弦槽。换句话说，由于灯丝加热或冷却缓慢，不闪烁和关闭，而产生一种“平均”的辉光，是根比例均方根（RMS）的电源电压值。
请注意，每个跟踪了相同的电压，即，两个示波器通道连接到相同的也不过，顶部的痕迹显示在灵敏度与通道直流耦合500mV的每分光，而底部的跟踪灵敏度与海峡交流耦合的每分左右。
顶部的迹线表示平均，或直流，的光伏组件，在这种情况下，大约是1~5V，和调制可以被视为“对直流电平波动”。追根寻底，另一方面，描述了调制，或交流，光伏组件的，大约18MV振幅，振荡不在50Hz，但在100Hz。的交流分量的振荡频率在两倍电源由于电源正弦波形达到峰值（一个正，负）每周期的两倍，每个峰的原因在灯的光强度略有增加。回到图，我们看到，C1/R2滤波器的时间常数：100nF：兆瓦= 100ms，比100Hz调制周期的大十倍。因此，过滤器显然对VF的交流分量，使得在比较器的出现的交流波形非反相输入是小到可以忽略不计。
在这种方式中，C1/R2过滤器确保光检测器只响应的监测光的平均值，而不是由任何电源问题产生的调制。
设计的RC（电阻电容）过滤器，大的电阻值应谨慎使用，因为它们可以产生较大的直流电压的变化，可以引入不可接受的误差。例如，一个直流1mA的只是流经1MW滤波电阻器的电流会使电阻两端的电位差为1V。这是足够大的严重的一个数字系统的噪声免疫力和导致错误触发的一个逻辑门。
在一个模拟系统，为1V电压可能大于被测信号，从而产生巨大的错误！因此，大的电阻值应只用于在输入设备，它具有很高的阻抗，需要非常低的偏置电流。对max931 compara - Tor的输入有一个最大漏电流只是±5nA。因此，电压降临了R2上或R4的输入漏电流不大于±5mV，这是足够小的，可以忽略不计的光检测器电路。
在4部分的led系列（上个月），一个LED的使用作为一个光检测器被讨论的一些细节。通过这部分的阅读，你会看到，并不是所有的led都能做出好的光探测器：有些是非常有效的，其他的都是没用的。因此，你可能需要不同类型的实验，以获得最佳的性能。
来源于《应用电子学》
附：英文原文
Light Detector
1 Introduction
IN the final part of the Light Emitting Diodes series, we showed how the photodiode can be used as a precision light sensor. By generating a photocurrent proportional to light intensity, the photodiode produces an electrical analogue of the measured light source that remains linear over some six or seven decades of light intensity.
Furthermore, by combining the basic photodiode function with additional circuitry, semiconductor manufacturers have produced a variety of light-sensitive devices that generate either a direct voltage output or, for example, in the case of light-to-frequency converters, a square signal whose frequency varies according to the strength of the detected light source.
However, in many light sensing applications, there is often a need to detect simply a change in light level, rather than a linear response to light intensity. Typical examples are products like digital alarm clocks that use a light sensor to dim the 7-segment led. display when the ambient light level is relatively low, or automobile light sensors which prompt the driver to switch on the headlamps when it is getting dark. This project makes use of an led. as a simple light sensor that generates a photovoltaic that varies with light intensity. By comparing the photovoltaic with a variable reference voltage, this Light Detector provides a digital output signal that changes state when the monitored light level crosses a preset threshold.
The detector also provides visual indication by illuminating the sensor led. when the light exceeds the preset level. In this way, the led. provides a dual function, acting as both the sensor and the indicator. An optional, optically-isolated output is also available.

2 Long Life Applications
When the monitored light exceeds the preset threshold, the circuit latches into its“tripped” state, and remains that way even if the light intensity decreases and falls to a level below the threshold. In its quiescent“unlatched” state, the circuit requires very little supply current, allowing it to operate for many months, or possibly several years, from a single PP3 9V battery.
The detector should find applications in meteorological or environmental experiments, where there is a need to monitor ambient light conditions and to record the precise moment at which the light exceeds a particular level. The circuit could also be used to provide a warning of a dangerous situation. For example, when located in a darkened storeroom, it could be used as a rudimentary fire detector that could generate an alarm signal on sensing the light produced by the flames. The detector is also ideally suited to security applications, where a monitored light level can be used to indicate the presence of a trespasser, or to warn of the unauthorized use of a room or object. For example, by locating the detector close to a room's ceiling or wall lights, it can be used to signal that an intruder has entered the room and turned on the lighting.
Alternatively, by positioning the unit inside a cupboard or drawer such that it will be triggered when ambient light falls on it, the detector can provide visual or electronic indication that someone has gained unauthorized access to the cupboard's contents. The fact that the detector remains in its latched state means that the event is recorded even if the cupboard or drawer is closed again.
3 Micropower Comparator and Reference
The comparator section functions just like a normal voltage comparator, but with the addition of programmable hysteresis. Depending on the voltage difference between the HYST terminal (pin 5) and the REF terminal, the hysteresis appearing between the comparator's input terminals can be varied from zero to around 100mV. However, as we shall see shortly, the light detector's latching behavior means that comparator hysteresis is not required, and so to simplify the circuit the HYST pin is connected directly to the REF pin, resulting in zero hysteresis.
More information on hysteresis and micropower comparators can be found in The Schmitt Trigger, Part 7, May 2001.
4 Battery Powered
When operating from a single supply, the MAX931 has a supply voltage range of 2.5V to 11V, and a maximum supply current of just 3.2mA at room temperature. The relatively wide supply voltage range, together with the minuscule power requirements, make the device ideal for battery-
1、powered applications.
Although the MAX931 could operate from just two series-connected alkaline cells with a nominal supply voltage of around 3·0V, the light detector makes use of a 9V supply. Not only does this provide plenty of “drive” to illuminate the led. and to power the optional optoisolator (IC2), it also allows the circuit to operate in its quiescent state for months or years without needing to replace the battery. Furthermore, the requisite PP3 battery connector is relatively simple and inexpensive – an additional bonus.
2、Photovoltaic
The photovoltaic, VF, generated by light falling on led. D1 is fed to the comparator's non-inverting input IN+ (pin 3) via a single-pole low pass filter comprising R2 and C1. The photovoltaic is compared with a variable reference voltage, VR, at the comparator's inverting input, IN9 (pin 4). The variable reference voltage (filtered by R4 and C2) is adjusted by preset VR1 connected to the 1·182V reference voltage output at IC1 pin 6.
In low light conditions, when photovoltaic VF is less than VR, the comparator output voltage, VOUT, is low (roughly at 0V) and diode D2 is reverse biased such that no current flows through R3.However, when the light intensity falling on D1 increases to the point where VF just exceeds VR, the comparator output goes high, thus forward biasing D2, allowing forward current to flow into D1 via current limiting resistor R3.
The function of D1 now changes from light detector to light emitter, and the led. illuminates to indicate that the monitored light has crossed the threshold set by VR1.
3、Latched
The circuit is now in its latched state, and the voltage, VF, appearing across D1 is no longer a photovoltaic generated by light energy, but is now simply the forward voltage of the forward biased led. Since the forward voltage of an led. is around 1·6V or more, VF is now significantly larger than VR (which can be no greater than 1·182V), and so the circuit latches into its “tripped” state.
Essentially, components R3 and D2 provide a positive feedback path from the comparator's output to its non-inverting input (via R2), thereby ensuring that the circuit makes a swift and clean transition into its latched state.
Diode D2 plays an important part. Without it, the “weak” photovoltaic generated by D1 would see a very low impedance path through R3 and into the comparator's output. This would swamp the photovoltaic, and would pull it down to a fraction of its normal “unloaded” value.
The presence of D2, however, ensures that the quiescent load on D1 is simply the combination of R1 shunted by the very high impedance of the comparators noninverting input (which takes such little current that it can be assumed negligible). Therefore, given that the value of R1 is very high, D1 can be considered unloaded when the circuit is in its unlatched state.
When the circuit has tripped, it can be reset (unlatched) by closing S1, a momentary action, normally-open pushbutton. This shorts the comparator’s non-inverting input to 0V, such that its output goes low, thereby depriving D1 of forward current. The circuit now reverts to its quiescent, unlatched state, where VOUT = 0V, D2 is reverse biased, and VF is the photovoltaic generated by light falling on D1. Of course, if VF is greater than VR, the circuit will immediately latch again.
5 Filters
The two low pass filters formed by C1/R2 and C2/R4 significantly attenuate any electrical noise appearing at the comparator’s input terminals. This can be important if the detector is used in an electrically “noisy” environment, for example when monitoring the light from fluorescent tubes, or if located close to the brush gear of an electric motor.
However, the C1/R2 filter provides an additional function. If the detector is used to monitor a light source powered from an a.c. voltage, such as a mains-powered incandescent filament lamp, the photo voltage VF generated by D1 will consist of a d.c. voltage plus a smaller a.c. component. Provided D1 is properly connected to the detector circuit, electrical noise will contribute only a relatively small part of this a.c. component. Instead, another mechanism is responsible for most of the alternating portion of VF.
Most mains voltage supplies have a roughly sinusoidal waveshape with a frequency of 50Hz or 60Hz, depending on the country. In the UK, for example, the domestic mains frequency is nominally 50Hz, whereas in North America it is predominantly 60Hz. This means that the current flowing through a mains-powered filament lamp will vary in a sinusoidal manner, increasing and decreasing, and reaching a positive and negative peak, 50 or 60 times every second.
6 Hot Stuff
Now, an incandescent lamp is essentially a thermal light source, in that the light emitted by the lamp is caused by heating of the filament which glows white hot. Since the lamp has a relatively large thermal time constant, it cannot respond to each peak and trough of the mains sinusoidal waveform. In other words, because the filament heats up and cools down relatively slowly, it does not flicker on and off, but instead produces an “average” glow which is proportional to the root mean square (r.m.s.) value of the mains voltage.
Note that each trace depicts the same photovoltaic, that is, the two oscilloscope channels are connected to the same led. However, the top trace shows the photovoltaic at a sensitivity of 500mV per division with the channel d.c. coupled, whereas the bottom trace has a sensitivity of 20mV per division with the channel a.c. coupled.
The top trace represents the average, or d.c., component of the photovoltaic, which in this case is around 1·5V, and the modulation can just be seen as “ripple” on the d.c. level. The bottom trace, on the other hand, depicts the modulated, or a.c., component of the photovoltaic, approximately 18mV in amplitude, which oscillates not at 50Hz, but at 100Hz. The a.c. component oscillates at twice the mains frequency because the mains sinusoidal waveform reaches a peak (one positive, one negative) twice every cycle, and each peak causes a slight increase in the lamp's light intensity.Returning to Fig.1, we see that the C1/R2 filter has a time constant of: 100nF:1MW = 100ms, some ten times greater than the period of the 100Hz modulation. Therefore, the filter significantly attenuates the a.c. component of VF, such that the a.c. waveform appearing at the comparator's non-inverting input is small enough to be negligible.
In this way, the C1/R2 filter ensures that the light detector responds only to the average value of the monitored light, and is not troubled by any mains-generated modulation.
When designing RC (resistor-capacitor) filters, large resistance values should be used with caution as they can produce relatively large d.c. voltage shifts that can introduce unacceptable errors. For example, a d.c. current of just 1mA flowing through a 1MW filter resistor will produce a pot