Photodiode From Wikipedia, the free encyclopedia Photodetector from a CD-ROM Drive. 3 photodiodes are visible. Symbol for photodiode. A photodiode is a type of photodetector capable of converting light into either current orvoltage , depending upon the mode of operation. [1] The common, traditional solar cell used to generate electric solar power is a large area photodiode. Photodiodes are similar to regular semiconductor diodes except that they may be either exposed (to detect vacuum UV or X-rays ) or packaged with a window or optical fiber connection to allow light to reach the sensitive part of the device. Many diodes designed for use specifically as a photodiode will also use a PIN junction rather than the typicalPN junction . Contents [hide ] 1 Principle of operation o 1.1 Photovoltaic mode o 1.2 Photoconductiv
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PhotodiodeFrom Wikipedia, the free encyclopedia
Photodetector from a CD-ROM Drive. 3 photodiodes are visible.
Symbol for photodiode.
A photodiode is a type of photodetector capable of converting light into either current orvoltage, depending
upon the mode of operation.[1] The common, traditional solar cellused to generate electric solar power is a large
area photodiode.
Photodiodes are similar to regular semiconductor diodes except that they may be either exposed (to
detect vacuum UV or X-rays) or packaged with a window or optical fiberconnection to allow light to reach the
sensitive part of the device. Many diodes designed for use specifically as a photodiode will also use a PIN
photodetector, . The NEP is roughly the minimum detectable input power of a
photodiode.
When a photodiode is used in an optical communication system, these parameters contribute
to the sensitivity of the optical receiver, which is the minimum input power required for the
receiver to achieve a specified bit error ratio.
[edit]Applications
P-N photodiodes are used in similar applications to other photodetectors, such
as photoconductors, charge-coupled devices, andphotomultiplier tubes.
Photodiodes are used in consumer electronics devices such as compact disc players, smoke
detectors, and the receivers for remote controls in VCRs and televisions.
In other consumer items such as camera light meters, clock radios (the ones that dim the
display when it's dark) and street lights,photoconductors are often used rather than
photodiodes, although in principle either could be used.
Photodiodes are often used for accurate measurement of light intensity in science and
industry. They generally have a better, more linear response than photoconductors.
They are also widely used in various medical applications, such as detectors for computed
tomography (coupled with scintillators) or instruments to analyze samples (immunoassay).
They are also used in pulse oximeters.
PIN diodes are much faster and more sensitive than ordinary p-n junction diodes, and hence
are often used for optical communications and in lighting regulation.
P-N photodiodes are not used to measure extremely low light intensities. Instead, if high
sensitivity is needed, avalanche photodiodes,intensified charge-coupled
devices or photomultiplier tubes are used for applications such
as astronomy, spectroscopy, night vision equipment and laser rangefinding.
[edit]Comparison with photomultipliersThis section does not cite any references or sources.Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged andremoved. (January 2011)
Advantages compared to photomultipliers:
1. Excellent linearity of output current as a function of incident light
2. Spectral response from 190 nm to 1100 nm (silicon), longer wavelengths with
For example, for the common PT100 sensor, α = 0.00385 or 0.385 %/°C.
This αT coefficient should not be confused with the α parameter below
Thermistors' Fundamentals and Applications
Introduction
Thermistors are a generic name given to thermally sensitive resistors. The word comes from a combination of "thermal resistor". NTC(negative temperature coefficient) type has characteristics in that as its temperature goes up, its resistance comes down. PTC(positve temperature coefficient) type has characteristics in that as its temperature goes up, its resistance goes up too.
It is a semiconducting ceramic resistor produced by sintering the materials at high temperature and uses metal oxide as its main component. The most commonly used oxides are those of manganese, nickel, cobalt, iron, copper and titanium.
Resistance-Temperature Curves
The thermistor resistance values are normally classified at a standard temperature of 25 °Celcius. B constant is the value calculated from the resistance values at 25 °Celcius and 85 °Celcius.
Most NTC type manufacturers provide tables of either resistance or resistance-ratio versus temperature for each of the material systems that they offer in their respective product lines. Often the manufacturer will also provide the coefficients for the various parts equations in order to assist the designer or user to interpolate the R-T data.
The resistance of a temperature is a function of its absolute temperature. As electrical power being dissipated within a temperature may heat up above its ambient temperature, thus reducing its resistance, it is necessary to test for resistance with temperature. The resistance measured in this way is called RT, which means the resistance is at zero power.
B is the constant which depends on the material used
A typical RT characteristics for different B values are as shown below.
DEFINITION
Temperature coefficient The temperature coefficient of a thermistor(%/°C) = [-B/(T*T)]*100
Dissipation factor Dissipation factor is the power in mW required to raise itstemperature by 1° Celcius.
Dissipation factor(mW/°C) = P/dT where
P is Power
dT is raised temperature
Current-time characteristicThe current-time characteristic is the relationship at a specified ambient temperature between the current through it and time,upon application or interruption of voltage to it.
Maximum operating temperatureThe maximum operating temperature is the maximum body temperature atwhich the thermistor will operate for an extended period of time with acceptable stability of its characteristics. This temperature is the result of internal or external heating, or both, and should not exceed the maximum value specified.
Maximum power ratingThe maximum power rating is the maximum power whicha thermistor will dissipate for an extended period of time with acceptable stability of its characteristics.
Thermal time constantThermal time constant is the time required by the thermistor to change 63% of the difference between its initial and finaltemperature. The figure below illustrates this.
Applications
There are various applications of thermistors. Some of them are listed as below:
Industrial process controls Hot glue dispensing equipment
Thermistor temperature sensors are constructed from sintered metal oxide in a ceramic matrix that changes electrical resistance with temperature. They are sensitive but highly non-linear. Their sensitivity, reliability, ruggedness and ease of use, has made them popular in research application, but they are less commonly applied to industrial applications, probably due to a lack on interchangeability between manufactures.Thermistors are available in large range of sizes and base resistance values (resistance at 25°C). Interchangeability is possible to ±0.05°C although ±1°C is more common.
Thermistor constructionThe most common form of the thermistor is a bead with two wires attached. The bead diameter can range from about 0.5mm (0.02") to 5mm (0.2'').
Three YSI Inc Thermistors
Mechanically the thermistor is simple and strong, providing the basis for a high reliability sensor. The most likely failure mode is for the lead to separate from the body of the thermistor - an unlikely event if the sensor is mounted securely and with regard to likely vibration. The sintered metal oxide material is prone to damage by moisture, so are passivated by glass or epoxy encapsulation. If the encapsulation is compromised and moisture penetrates, silver migration under the dc bias can eventually cause shorting between the electrodes.Like other temperature sensors, thermistors are often mounted in stainless steel tubes, to protect them from the environment in which they are to operate. Grease is typically used to improve the thermal contact between the sensor and the tube.
Thermistor characteristicsThe following are typical characteristic for the popular 44004 thermistor from YSI:
Parameter Specification
Resistance at 25°C 2252 ohms (100 to 1M available)
Measurement range -80 to +120°C typical (250°C max.)
Interchangeability (tolerance) ±0.1 or ±0.2°C
Stability over 12 months < 0.02°C at 25°C, < 0.25°C at 100°C
Time constant < 1.0 seconds in oil, < 60 seconds in still air
self-heating 0.13 °C/mW in oil, 1.0 °C/mW in air
Coefficients a = 1.4733 x 10-3, b = 2.372 x 10-3, c = 1.074 x 10-7
To ensure the interchangeability specification, thermistors are laser trimmed in the manufacturing process.
LinearizationThe thermistor's resistance to temperature relationship to temperature is given by the Steinhart & Hart equation:
T = 1 / ( a + b.ln(R) + c.ln(R)3 )
where a, b and c are constants, ln() the natural logarithm, R is the thermistors resistance in ohms and T is the absolute temperature in Kelvins. While the Steinhart & Hart equation is a close fit to practical devices, it does not always provide the precision required over the full temperature range. This can be corrected by fitting the Steinhart & Hart equation over a series of narrow temperature ranges and then 'splicing' these fits together to cover the required range.Manufacturers will normally supply the constants as part of the specification for each part type, or alternatively will provide the resistance versus temperature tables. For precision measurement, tight tolerance parts are available, but at a premium price.It is possible to determine the three constants by calibrating at three different temperatures and solving three simultaneous equations (based on the Steinhart & Hart equation above). This is a tedious calculation, so use the multifunctional Thermistor Calculator provided.
Hardware 'linearization'A problem with the thermistor is the varying measured temperature resolution that is achieved over the temperature range. Usually the resolution is good at lower temperatures, but poor at higher temperatures. If the measuring device has a single scale, this can be an irritating characteristic. One way to simply fix this problem is to connect a resistor in parallel with the thermistor. The resistors value should equal the thermistor's resistance at the mid-range temperature. The result is a significant reduction in non-linearity, as the following diagram illustrates:
The plot in the above diagram shows the impact of a 2200 ohm resistor in parallel with a 2252 ohm (at 25°C) thermistor. Note the 5x scale factor difference for the 'linearized curve'. This technique is recommended whenever thermistors are used with simple measuring devices that have low ADC resolution (i.e. <12 bit).
Thermistor ManufacturersManufacturers of the thermistor element include: Alpha Thermistors Inc, BetaTHERM Corp, Cornerstone Sensors Inc,Murata Manufacturing Co Ltd, Pyromation Inc, Quality Thermistor Inc, Therm-O-Disc Inc, Thermometrics Inc, U.S. Sensor Corp, Victory Engineering Corp, and YSI Temperature Inc.
Related DevicesOne form of the NTC thermistor is used in power circuits for in-rush current protection. At low temperatures they exhibit
high resistance, but as current flows and self-heating warms the device, its resistance drops to allow the flow of operating current.Related to the thermistor temperature sensor is the "Posistor" or positive temperature coefficient thermistor (PTC). These devices are useful in limiting current to safe levels. In normal operation their resistance is low, causing minimum impedance to current flow. Should the current exceed a certain level, self-heating will begin to warm the device causing higher impedance and hence more self-heating. This enters a 'thermal run away' state, with the device heating to such temperature that the current is limited to a safe level. The higher the fault current the faster the PTC thermistor will switch off.
UM66
UM66.pdf UM66T is a melody integrated circuit. It is designed for use in bells, telephones, toys etc. It has an inbuilt tone and a beat generator. The tone generator is a programmed divider which produces certain frequencies. These frequencies are a factor of the oscillator frequency. The beat generator is also a programmed divider which contains 15 available beats. Four beats of these can be selected. There is an inbuilt oscillator circuit that serves as a time base for beat and tone generator. It has a 62 notes ROM to play music. A set of 4 bits controls the scale code while 2 bits control the rhythm code. When power is turned on, the melody generator is reset and melody begins from the first note. The speaker can be driven by an external npn transistor connected to the output of UM66. Many versions of UM66T are available which generate tone of different songs. For example, UM66T01 generates tone for songs ‘Jingle bells’, ‘Santa Claus is coming to town’ and ‘We wish you a merry X’mas’. Pin Diagram:
Here is the simplest melody generator circuit you can make using an IC.The UM66 series are CMOS IC’s designed for using in calling bell, phone and toys. It has a built in ROM programmed for playing music. The device has very low power consumption.Thanks for the CMOS technology.The melody will be available at pin3 of UM66 and here it is amplified by using Q1 to drive the speaker.Resistor R1 limits the base current of Q1 within the safe values.Capacitor C1 is meant for noise suppression.
Read more: http://www.circuitstoday.com/melody-generator-using-ic-um66#ixzz2jMsMWyhN Under Creative Commons License: Attribution
Notes
Power supply must be between 1.5V & 4.5V .Do not exceed 4.5 V. Speaker can be driven with external NPN transistor.
Melody begins from the first note if power is reseted.
Assemble the circuit on a good quality common board.
If transistor HE8050S is not available use any NPN transistor like BC548 or 2N2222.