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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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Page 1: Photodiode THERMISTOR UM66

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

junction rather than the typicalPN junction.

Contents

 [hide]

1   Principle of operation

o 1.1   Photovoltaic mode

o 1.2   Photoconductive mode

o 1.3   Other modes of

operation

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2   Materials

o 2.1   Unwanted photodiodes

3   Features

4   Applications

o 4.1   Comparison with

photomultipliers

5   Photodiode array

6   See also

7   References

8   External links

[edit]Principle of operation

A photodiode is a PN junction or PIN structure. When a photon of sufficient energy strikes the diode, it excites

an electron, thereby creating a free electron and a (positively charged electron hole). If the absorption occurs in

the junction's depletion region, or one diffusion lengthaway from it, these carriers are swept from the junction by

the built-in field of the depletion region. Thus holes move toward the anode, and electrons toward the cathode,

and a photocurrent is produced.

[edit]Photovoltaic mode

When used in zero bias or photovoltaic mode, the flow of photocurrent out of the device is restricted and a

voltage builds up. This mode exploits the photovoltaic effect, which is the basis for solar cells – in fact, a

traditional solar cell is just a large area photodiode.

[edit]Photoconductive mode

In this mode the diode is often reverse biased, dramatically reducing the response time at the expense of

increased noise. This increases the width of the depletion layer, which decreases the

junction's capacitance resulting in faster response times. The reverse bias induces only a small amount of

current (known as saturation or back current) along its direction while the photocurrent remains virtually the

same. For a given spectral distribution, the photocurrent is linearly proportional to the illuminance (and to

the irradiance).[2]

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Although this mode is faster, the photoconductive mode tends to exhibit more electronic noise. [citation needed] The

leakage current of a good PIN diode is so low (< 1nA) that the Johnson–Nyquist noise of the load resistance in

a typical circuit often dominates.

[edit]Other modes of operation

Avalanche photodiodes have a similar structure to regular photodiodes, but they are operated with much

higher reverse bias. This allows each photo-generated carrier to be multiplied by avalanche breakdown,

resulting in internal gain within the photodiode, which increases the effective responsivity of the device.

Phototransistors also consist of a photodiode with internal gain. A phototransistor is in essence nothing more

than a bipolar transistor that is encased in a transparent case so that light can reach the base-

collector junction. The electrons that are generated by photons in the base-collector junction are injected into

the base, and this photodiode current is amplified by the transistor's current gain β (or h fe). Note that while

phototransistors have a higher responsivity for light they are not able to detect low levels of light any better than

photodiodes.[citation needed] Phototransistors also have significantly longer response times.

[edit]Materials

The material used to make a photodiode is critical to defining its properties, because only photons with

sufficient energy to excite electronsacross the material's bandgap will produce significant photocurrents.

Materials commonly used to produce photodiodes include[3]:

Material Electromagnetic spectrumwavelength range (nm)

Silicon 190 – 1100

Germanium 400 – 1700

Indium gallium arsenide 800 – 2600

Lead(II) sulfide <1000 – 3500

Because of their greater bandgap, silicon-based photodiodes generate less noise than germanium-based

photodiodes, but germanium photodiodes must be used for wavelengths longer than approximately 1 µm.

[edit]Unwanted photodiodes

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Since transistors and ICs are made of semiconductors, and contain P-N junctions, almost every active

component is potentially a photodiode. Many components, especially those sensitive to small currents, will not

work correctly if illuminated, due to the induced photocurrents. In most components this is not desired, so they

are placed in an opaque housing. Since housings are not completely opaque to X-rays or other high energy

radiation, these can still cause many ICs to malfunction due to induced photo-currents.

[edit]Features

Response of a silicon photo diode vs wavelength of the incident light

Critical performance parameters of a photodiode include:

Responsivity

The ratio of generated photocurrent to incident light power, typically expressed in A/Wwhen used in

photoconductive mode. The responsivity may also be expressed as aQuantum efficiency, or the ratio

of the number of photogenerated carriers to incident photons and thus a unitless quantity.

Dark current

The current through the photodiode in the absence of light, when it is operated in photoconductive

mode. The dark current includes photocurrent generated by background radiation and the saturation

current of the semiconductor junction. Dark current must be accounted for by calibration if a

photodiode is used to make an accurate optical power measurement, and it is also a source

of noise when a photodiode is used in an optical communication system.

Noise-equivalent power

(NEP) The minimum input optical power to generate photocurrent, equal to the rms noise current in a

1 hertz bandwidth. The related characteristic detectivity (D) is the inverse of NEP, 1/NEP; and

the specific detectivity ( ) is the detectivity normalized to the area (A) of the

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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

other semiconductor materials

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3. Low noise

4. Ruggedized to mechanical stress

5. Low cost

6. Compact and light weight

7. Long lifetime

8. High quantum efficiency, typically 80%

9. No high voltage required

Disadvantages compared to photomultipliers:

1. Small area

2. No internal gain (except avalanche photodiodes, but their gain is typically 102–

103 compared to up to 108 for the photomultiplier)

3. Much lower overall sensitivity

4. Photon counting only possible with specially designed, usually cooled photodiodes,

with special electronic circuits

5. Response time for many designs is slower

[edit]Photodiode array

A one-dimensional array of hundreds or thousands of photodiodes can be used as a position

sensor, for example as part of an angle sensor.[4] One advantage of photodiode arrays (PDAs)

is that they allow for high speed parallel read out since the driving electronics may not be built

in like a traditional CMOS or CCD sensor.

thermistor

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A thermistor is a type of resistor whose resistance varies significantly with temperature, more so than in

standard resistors. The word is a portmanteau of thermal and resistor. Thermistors are widely used as

inrush current limiters, temperature sensors, self-resetting overcurrent protectors, and self-

regulating heating elements.

Thermistors differ from resistance temperature detectors (RTD) in that the material used in a thermistor is

generally a ceramic or polymer, while RTDs use pure metals. The temperature response is also different;

RTDs are useful over larger temperature ranges, while thermistors typically achieve a higher precision

within a limited temperature range [usually −90 °C to 130 °C].

Thermistor symbol

Assuming, as a first-order approximation, that the relationship between resistance and temperature

is linear, then:

where

ΔR = change in resistance

ΔT = change in temperature

k = first-order temperature coefficient of resistance

Thermistors can be classified into two types, depending on the sign of k.

If k is positive, the resistance increases with increasing temperature, and the device

is called a positive temperature coefficient (PTC) thermistor, or posistor. If k is

negative, the resistance decreases with increasing temperature, and the device is

called a negative temperature coefficient (NTC) thermistor. Resistors that are not

thermistors are designed to have a k as close to zero as possible(smallest possible

k), so that their resistance remains nearly constant over a wide temperature range.

Instead of the temperature coefficient k, sometimes the temperature coefficient of

resistance α (alpha) or αT is used. It is defined as[1]

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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.

The mathematical expression of it is as below:

Ra=Rbexp[B(1/T1-1/T2)]

of which

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Ra is the resistance at absolute temperature T1

Rb is the resistance at absolute temperature T2

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.

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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

Fire protection and safety equipment

Auto & truck tire curing

Engine temperatures

Temperature controlled Soldering irons

Meteorology

Burglar alarm detectors

Oven temperature   control

Refrigeration and air conditioning

Fire detection

Medical Applications Food Handling Application

Introduction to Thermistors

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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

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(see Linearization below)

Dimensions ellipsoid bead 2.5mm x 4mm

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

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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: 

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Pin Description: Pin No Function Name

1 Melody output Output2 Supply voltage (1.5V - 4.5V) Vcc3 Ground (0V) Ground

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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.

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Read more: http://www.circuitstoday.com/melody-generator-using-ic-um66#ixzz2jMrxpzn7 Under Creative Commons License: Attribution