documentation 2

IR Music Transmitter & Receiver

1. INTRODUCTION

Using this circuit of IR music transmitter and receiver, audio musical notes can be generated and can be heard up to a distance of 10 meters. The receiver can be placed at a maximum distance of 1 meter from the transmitter without any considerable noise interference. However the communication distance can be improved by using Far IR LEDs. The range of communication can be increased to about 250 meters by using Far IR LEDs.

The circuit of the transmitter and receiver are quite simple and can be placed and carried any where easily. The small apparatus provided with the infrared communication function is in many cases operated by a battery incorporated inside so that it is convenient when a user carries it during movement. We do not make use of any modulation technique when working with IR rays and hence there is obviously no necessity of carrier wave generation. This makes the transmitter and receiver designs much simpler

This project emphasizes the way by which music is generated and driven by IR rays and gives an explanation to one of the methods of receiving IR rays without considerable noise interference.

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2. CIRCUIT DIAGRAM

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IR AUDIO RECEIVER CIRCUIT

IR AUDIO TRANSMITTER


3. BASIC PRINCIPLE OF OPERATION

The entire circuit can be divided into two parts: IR music transmitter and receiver.

The IR music transmitter circuit includes a melody generator IC UM66 that can continuously generate musical tones when it receives supply. The output of this IC is fed to the IR driver stage which includes two IR LEDs which transmit infrared rays corresponding to the musical tones generated.

The IR music receiver circuit uses a photo transistor L14F1 that receives the infrared rays transmitted by the IR LED’s in the transmitter. The output of this photo transistor is fed to inverting input terminal of IC µA741. Its gain can be varied using pot meter. The output of op-amp is fed to a low voltage audio power amplifier IC LM386. The melody produced is heard through the receiver’s loud speaker.

For maximum sound transmission the IR LEDs in the transmitter should be oriented towards the IR photo transistor in the receiver.

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4. TRANSMITTER SECTION

The transmitter section further comprises of two parts: melody generator and IR driver section. Melody generator section is build around the IC UM66 which is a music generator and IR driver section is built across the transistors BC547 (T1) and SK100 (T2) and includes two IR LEDs.

The IR music transmitter works off a 9V battery. The figure shows the circuit of the IR music transmitter. A Zener diode with breakdown voltage 3.3V is used at the input of the transmitter section. It is operated in reverse breakdown voltage to provide constant voltage to the transmitter. The transmitter section uses popular melody generator IC UM66 (IC1) that can continuously generate musical tones. The output of IC1 is fed to the IR driver stage to get the maximum range. Here the orange LED (LED1) flickers according to the musical tones generated by UM66 IC, indicating modulation. Infrared LEDs (LED2 and LED3) are infrared transmitting LEDs. They transmit IR rays corresponding to the music generated.

4.1. MELODY GENERATOR IC UM66 [6]:

4.1.1. Introduction:

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.

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¡¯.

4.1.2. Pin Diagram:

Fig 4.1: Pin diagram of IC UM66

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4.1.3. Pin Description:

Pin No Function Name

1. Output (Melody output).

2. +Vcc (Supply voltage (1.5V - 4.5V)).

3. -Vss (Ground (0V)).

4.1.4. Features:

1. 62-Note ROM memory.2. 1.5V ~ 4.5V power supply and low power consumption.3. Dynamic speaker can be driven with external NPN transistor.4. OSC resistor hold mode.5. Power on reset: melody begins from the first note.6. Built in level hold mode.

4.2. LIGHT EMITTING DIODE (LED) [1]:

Light Emitting Diode is an optical diode, which emits light when forward biased. When a p-n junction is forward biased, the electrons cross the junction and recombine with holes by falling from conduction band to valence band. Thus the energy level associated with it changes from higher value to lower value. The energy corresponding to the difference between higher level and lower level is released by an electron while travelling from the conduction band to the valence band. In normal diodes, this energy is released in the form of heat. But LEDs are made up of some special materials which release this energy in the form of photons which emit the light energy. Hence such diodes are called light emitting diodes. This process is called Electroluminescence.

The LEDs use the materials like gallium arsenide (GaAs), gallium arsenide phosphide (GaAsP) or gallium phosphide (GaP). The colour of emitted light depends on the composition of the semiconductor material used and can be infrared, ultraviolet or visible.

LEDs are widely used as indicator lights on electronic devices and increasingly in higher power applications such as flashlights and area lighting. An LED is usually a small area (less than 1 mm2) light source, often with optics added directly on top of the chip to shape its radiation pattern and assist in reflection.

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4.2.1. IR Light Emitting Diode:

An infrared emitter is an LED made from gallium arsenide, which emits light radiations which are infrared and hence invisible.

There are a couple key differences in the electrical characteristics of infrared LEDs versus visible light LEDs. Infrared LEDs have a lower forward voltage, and a higher rated current compared to visible LEDs. This is due to differences in the material properties of the junction. A typical drive current for an infrared LED can be as high as 50 milliamps

4.3. ZENER DIODE [1]:

Zener diode is heavily doped PN junction diode, which is generally operated in its reverse breakdown region. The Zener diodes are fabricated with precise breakdown voltages, by controlling the doping level during manufacturing. They have breakdown voltages that range from 3V to 200V.

The Zener diode is designed to be operated in the reverse biased condition. In reverse biased condition, the diode carries reverse saturation current till the reverse voltage applied is less than the reverse breakdown voltage. When the reverse voltage exceeds reverse breakdown voltage, the current through it changes drastically but the voltage across it remains almost constant. Thus, the voltage across the Zener diode serves as a reference voltage. Hence, the Zener can be used as a voltage regulator to provide

4.4. INFRARED RADIATION [5]:


Infrared (IR) radiation is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.7 micrometers, and extending conventionally to 300 micrometers. These wavelengths correspond to a frequency range of approximately 430 to 1 THz, and include most of the thermal radiation emitted by objects near room temperature. Microscopically, IR light is typically emitted or absorbed by molecules when they change their rotational-vibrational movements.

Infrared radiation is popularly known as "heat" or sometimes known as "heat radiation", since many people attribute all radiant heating to infrared light and/or all infrared radiation to heating. This is a widespread misconception, since light and electromagnetic waves of any frequency will heat surfaces that absorb them.

4.4.2. Applications of IR:

1. Night vision.

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2. Thermography.

3. IR Tracking.

4. Heating.

5. Communications.

6. Spectroscopy.

7. Meteorology.

8. Climatology.

9. Astronomy.

10. Photobiomodulation

4.5. DRIVER STAGE [3]:

It includes a CE-CE transistor pair, of which one is npn and the other is pnp. The npn transistor namely BC547 is operated in common emitter configuration. An orange LED is connected at its collector which flickers according to musical tones generated by the melody generator. To the same collector node, the base of pnp transistor SK100 is connected. Hence the music generator output signal, which is amplified by the CE amplifier, is applied to the base of pnp transistor SK100. To the collector of pnp transistor, an IR LED is connected which transmits infrared radiations according to the generated musical tones.

4.6. BIPOLAR JUNCTION TRANSISTOR [1]:


A BJT is a three terminal semiconductor device in which the operation depends on the interaction of both majority and minority carriers and hence the name Bipolar. It is used in amplifier and oscillator circuits, and as a switch in digital circuits. It has wide applications in computers, satellites and other modern communication system.

The BJT consists of a silicon crystal in which a thin layer of N-type Silicon is sandwiched between two layers of P-type silicon. This transistor is referred to as PNP. Alternatively, in a NPN transistor, a layer of P-type material is sandwiched between two layers of N-type material. The three portions of the transistor are Emitter, Base, and Collector. Emitter is heavily doped so that it can inject a large number of charge carriers into the base. Base is lightly doped and very thin. It passes most of the injected charge carriers from the emitter into the collector. Collector is moderately doped.

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4.6.2. Operation:

The forward bias applied to the emitter base junction of an NPN transistor causes a lot of electrons from the emitter region to crossover to the base region. As the base is lightly doped with P-type impurity, the number of holed in the base region is very small and hence the number of electrons that combine with holes in the P-type base region is also very small. Hence a few electrons combine with holes to constitute a base current Ib. The remaining electrons crossover into the collector region to constitute a collector current Ic. Thus the base and collector current summed up gives the emitter current, i.e. Ie = -( Ic + Ib).

4.7. RESISTOR:

When a current flows in a material, the free electrons move through the material and collide with other atoms. These collisions cause the electrons to lose some of their energy. This loss of energy per unit charge is the drop in potential across the material. The amount of energy lost by the electrons is related to the physical property of the material. These collisions restrict the movement of electrons. The property of a material to restrict the flow of electrons is called resistance, denoted by R.

The unit of resistance is ohm. Ohm is defined as the resistance offered by the material when a current of one ampere flows between two terminals with one volt applied across it. According to Ohm’s law, the current is directly proportional to the voltage and inversely proportional to the total resistance of the circuit,i.e.

I = V / R

4.8. CAPACITOR:

Any two conducting surfaces separated by an insulating medium exhibit the property of a capacitor. The conducting surfaces are called electrodes, and the insulating medium is called dielectric. A capacitor stores energy in the form of an electric field that is established by the opposite charges on the two electrodes. The electric field is represented by lines of force between the positive and negative charges, and is concentrated within the dielectric. The amount of charge per unit voltage that a capacitor can store is its capacitance, denoted by C.

The unit of capacitance is Farad denoted by F. By definition, one farad is the amount of capacitance when one coulomb of charge is stored with one volt across the plates. A capacitor is said to have greater capacitance it can store more charge per unit voltage and the capacitance is given by,

C = Q / V

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5. RECEIVER SECTION

The IR music receiver section works off regulated 9V to 12V. The IR music receiver uses popular op-amp IC µA741 and audio-frequency amplifier IC LM386 along with phototransistor L14F1 and some discrete components.

The melody generated by IC UM66 in the transmitter section is transmitted through IR LEDs, received by phototransistor T3 and fed to the inverting input terminal of op-amp IC µA741 (IC2). Here the op-amp acts as a difference amplifier. The resistors R8 and R13 act as potential dividers and provide half-supply voltage of 4.5 volts to its non-inverting input terminal. The resistor R6 and phototransistor L14F1 provide variable input voltage to the inverting input terminal of op-amp whose gain can be varied using pot meter VR1. The output of IC µA741 is fed to IC LM386 (IC3), an audio amplifier, via capacitor C5 and pot meter VR2. The melody produced is heard through the receiver’s loudspeaker. Pot meter VR2 is used to control the volume of loudspeaker LS1 (8-ohm, 1W).

5.1. PHOTO TRANSISTOR [1]:

Fig 5.1: Photo transistor (both the circuits are equivalent)

5.1.1. Structure:

Although ordinary transistors exhibit the photosensitive effects if they are exposed to light, the structure of the phototransistor is specifically optimized for photo applications. The photo transistor has much larger base and collector areas than would be used for a normal transistor. These devices were generally made using diffusion or ion implantation.

Early photo transistors used germanium or silicon throughout the device giving a homo-junction structure. The more modern phototransistors use type III-V materials such as gallium arsenide and the like

Photo transistors that use different materials on either side of the p-n junction are also popular because they provide high conversion efficiency. These are generally fabricated using

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epitaxial growth of materials that have matching lattice structures and are called hetero-junction structures

5.1.2. Operation:

Photo Transistor is a light sensitive semiconductor photo device. It combines a photo diode and a transistor amplifier. The most common form of it is an NPN bipolar transistor with an exposed base region. Here, light striking the base replaces the voltage applied to the base. So, a phototransistor amplifies variations in the light striking it.

Photo transistors are usually connected in a CE configuration with the base open. A lens focuses the light on the base-collector junction. Although the photo transistor like any other transistor has three sections, only two leads, the emitter and collector leads, are generally used. In this device, base current is supplied by the current created by the light falling on the base-collector photo diode junction. The light enters the base region of the phototransistor where it causes hole-electron pairs to be generated. This mainly occurs in the reverse biased base-collector junction. The hole-electron pairs move under the influence of the electric field and provide the base current, causing electrons to be injected into the emitter.

When there is no radiant excitation, the minority carriers are generated thermally, and the electrons crossing from the base to the collector and the holes crossing from the collector to the base constitute the reverse saturation collector current.

Current in a photo transistor is dependent mainly on the intensity of light entering the lens and is less affected by the voltage applied to the external circuit.

5.1.3. Characteristics:

1. Photo transistors have a high level of gain. For homo-structures, this may be of the order of about 50 up to a few hundred. However, for the hetero-structure devices, the levels of gain may rise to ten thousand.

2. Very low noise.3. Poor high frequency response due to the large capacitance associated with base-

collector junction.4. For homo-structure devices, the bandwidth may be limited to about 250 kHz. Hetero-

junction devices have a much higher limit and can be operated at frequencies as high as 1 GHz.

5.1.4. Applications:1. High speed reading of computer punched cards and tapes.2. Light detection system.3. Light operated switches.

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4. Reading of film sound track.5. Production line counting of objects which interrupt a light beam.

5.2. OPERATIONAL AMPLIFIER (IC 741) [2]:

An operational amplifier ("op-amp") is a DC coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. An op-amp produces an output voltage that is typically hundreds of thousands times larger than the voltage difference between its input terminals.

5.2.1 Pin Diagram:

Fig 5.2: Pin Diagram of IC 741

5.2.2. Circuit notation:

Fig 5.3: Circuit schematic of an Op-amp

The circuit schematic of an Op-amp is shown in the fig , where

1. V+ : non-inverting input.

2. V- : inverting input.

3. Vout: output.

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4. Vs+: positive power supply.

5. Vs-: negative power supply.

5.2.3. Operation:

The amplifier's differential inputs consist of a V+ input and a V-input, and ideally the op-amp amplifies only the difference in voltage between the two, which is called the differential input voltage. The output voltage of the op-amp is given by the equation,

Where, V+ is the voltage at the non-inverting terminal, V- is the voltage at the inverting terminal and AOL is open loop gain of the amplifier (the term "open-loop" refers to the absence of a feedback loop from the output to the input).

The magnitude of AOL is typically very large, 10,000 or more for integrated circuit op-amp, and therefore even a quite small difference between v+ and v- drives the amplifier output nearly to the supply voltage. This is called saturation of the amplifier.

Fig 5.4: An Op-amp without feedback

Without feedback, an op-amp acts as a comparator. If the inverting input is held at ground (0 V) directly or by a resistor, and the input voltage VIN applied to the non-inverting input is positive, the output will be maximum positive; if VIN is negative, the output will be maximum negative. Since there is no feedback from the output to either input, this is an open loop circuit acting as a comparator.

Negative feedback is obtained by applying a portion of the output voltage to the inverting inputas shown in fig: 5.5. The closed loop feedback greatly reduces the gain of the amplifier. If negative feedback is used, the circuit's overall gain and other parameters become determined more by the feedback network than by the op-amp itself.

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http://en.wikipedia.org/wiki/Negative_feedback_amplifier

http://en.wikipedia.org/wiki/Comparator

http://en.wikipedia.org/wiki/Electronic_feedback_loops

http://en.wikipedia.org/wiki/Electronic_feedback_loops

http://en.wikipedia.org/wiki/Comparator


Fig 5.5: An Op-amp with negative feedback.

5.2.4. Applications:

1. Applications without using feedback:

Voltage level detector. Zero voltage level detector.

2. Applications using negative feedback:

Non Inverting Amplifier:

In a non-inverting amplifier, the output voltage changes in the same direction as the input voltage.

Fig 5.6: An op-amp connected in non-inverting amplifier configuration.

The gain equation for the op-amp is:

However, in this circuit V– is a function of Vout because of the negative feedback through the R1R2 network. R1 and R2 form a voltage divider, and as V– is a high-impedance input, it does not load it appreciably.

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http://en.wikipedia.org/wiki/Voltage_divider


Where,

Inverting Amplifier:

In an inverting amplifier, the output voltage changes in an opposite direction to the input voltage.

The gain equation of the op-amp:

Fig 5.7: An op-amp connected in inverting amplifier configuration.

This time, V– is a function of both Vout and VIN due to the voltage divider formed by Rf and Rin.

.

3. Negative feedback applications:

Schmitt trigger.

4. Other applications:

Audio- and video-frequency pre-amplifiers and buffers.

Differential amplifiers.

Differentiators and integrators.

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Filters.

Precision rectifiers.

Precision peak detectors.

Voltage and current regulators.

Analog calculators.

Analog-to-digital converters.

Digital-to-analog converters.

Voltage clamps.

Oscillators and waveform generators.

5.3. LOW VOLTAGE AUDIO POWER AMPLIFIER LM386 [6]:

The LM386 is a power amplifier designed for use in low voltage consumer applications. The gain is internally set to 20 to keep external part count low, but the addition of an external resistor and capacitor between pins 1 and 8 will increase the gain to any value from 20 to 200. The inputs are ground referenced while the output automatically biases to one-half the supply voltage. The quiescent power drain is only 24 milliwatts when operating from a 6 volt supply, making the LM386 ideal for battery operation.

5.3.1. Pin Diagram:

Fig 5.8: Pin diagram of LM386

5.3.2. Features:

1. Battery operation.

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http://en.wikipedia.org/wiki/Waveform_generator


2. Minimum external parts.3. Wide supply voltage range: 4V–12V or 5V–18V.4. Low quiescent current drain: 4mA.5. Voltage gains from 20 to 200.6. Ground referenced input.7. Self-centering output quiescent voltage.8. Low distortion: 0.2% (AV = 20, VS = 6V, RL = 8W, PO =125mW, f = 1 kHz).9. Available in 8 pin MSOP package.

5.3.3. Applications:1. AM-FM radio amplifiers.2. Portable tape player amplifiers.3. TV sound systems.4. Line drivers.5. Ultrasonic drivers.6. Power converters.

5.4. LOUD SPEAKER [6]:

A loudspeaker (or "speaker") is an electro acoustic transducer that produces sound in response to an electrical audio signal input.

Fig 5.9: Loud Speaker

The loudspeakers are almost always the limiting element on the fidelity of a reproduced sound in either home or theater. The other stages in sound reproduction are mostly electronic, and the electronic components are highly developed. The loudspeaker involves electromechanical processes where the amplified audio signal must move a cone or other mechanical device to produce sound like the original sound wave. This process involves many difficulties, and usually is the most imperfect of the steps in sound reproduction.

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The term "loudspeaker" may refer to individual transducers (known as "drivers") or to complete speaker systems consisting of an enclosure including one or more drivers. The most common type of driver uses a lightweight diaphragm, or cone, connected to a rigid basket, or frame, via a flexible suspension that constrains a coil of fine wire to move axially through a cylindrical magnetic gap. When an electrical signal is applied to the voice coil, a magnetic field is created by the electric current in the voice coil, making it a variable electromagnet. The coil and the driver's magnetic system interact, generating a mechanical force that causes the coil (and thus, the attached cone) to move back and forth, thereby reproducing sound under the control of the applied electrical signal coming from the amplifier.

To make sound, a loudspeaker is driven by modulated electrical current (produced by an amplifier) that pass through a "speaker coil" (a coil of copper wire), which then (through resistance and other forces) magnetizes the coil, creating a magnetic field. The electrical current variations that pass through the speaker are thus converted to varying magnetic forces, which move the speaker diaphragm, which thus forces the driver to produce air motion that is similar to the original signal from the amplifier.

5.5. RHEOSTAT [5]:

The most common way to vary the resistance in a circuit is to use a variable resistor or a rheostat. A rheostat is a two-terminal variable resistor. Often these are designed to handle much higher voltage and current. Typically these are constructed as a resistive wire wrapped to form a toroid coil with the wiper moving over the upper surface of the toroid, sliding from one turn of the wire to the next. Sometimes a rheostat is made from resistance wire wound on a heat-resisting cylinder with the slider made from a number of metal fingers that grip lightly onto a small portion of the turns of resistance wire.

The 'fingers' can be moved along the coil of resistance wire by a sliding knob thus changing the 'tapping' point. They are usually used as variable resistors rather than variable potential dividers. Any three-terminal potentiometer can be used as a two-terminal variable resistor, by not connecting to the third terminal. It is common practice to connect the wiper terminal to the unused end of the resistance track to reduce the amount of resistance variation caused by dirt on the track.

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6. ADVANTAGES

1. Highly sensitive.

2. Very low noise.

3. Low cost and reliable circuit.

4. Capable of transmitting up to 10 meters.

5. Two stage gain control.

6. Low power consumption.

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7. APPLICATIONS

Today everyone is looking for portability of electronic gadgets. The IR rays communication can play a crucial role in developing such wireless gadgets. Here are a few gadgets that can be built using IR transmission and reception system.

1. Wireless music system:

The speaker that we use today in our desktop computers can be made wireless by using infrared transmission

2. Mobile gadgets:

The principle of IR audio transmission can be used in cordless earphones which can be very useful especially when you are driving.

3. CC Cameras:

IR ray transmission can be employed in microphones that can be used in CC Cameras. This reduces the complexity to a great extent. The audio systems that are employed today for security purpose in cc cameras can be replaced with IR transmission systems which are quite simple and easy to handle.

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8. CONCLUSION AND FUTURE SCOPE

IR ray communication is very easy to understand and simple to implement. Using this project, audio musical notes can be generated and can be heard up to a distance of 10 meters. It finds various applications in short distance field of communications. The range of communication can be increased by using far IR LEDs.

In future there is scope of building virtual environment using the principles of IR ray transmission and reception. It is one of the best ways of building wireless gadgets. Virtual gaming which also employs IR reception techniques is still in research process which is soon going to rule the world of gaming.

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9. BIBLIOGRAPHY

1. Electronic Devices and Circuits by Jacob Millmann, Christos C Halkias and Satyabrata jit.

2. Linear Integrated Circuits by D. Roy Choudhury and Shail B. jain.

3. Electronic Circuit Analysis by K.S. Srinivasan

4. www.efymag.com.

5. www.wikipedia.org.

6. www.google.com.

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10. APPENDIX

10.1. BC547:

NPN Epitaxial Silicon Transistor

Absolute Maximum Ratings :Ta:=250C unless otherwise noted

Electrical Characteristics: Ta:=250C unless otherwise noted

hFE Characteristics:

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Typical Characteristics:

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10.2. LM386 LOW VOLTAGE AUDIO POWER AMPLIFIER:

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10.3. IC 741 OPERATIONAL AMPLIFIER:

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10.4. IN4148:

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Typical Characteristics:

Fig: Typical forward current vs forward voltage

Fig: Typical reverse current vs reverse voltage

NOTE:

All temperatures shown on graphs are junction temperatures.

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documentation 2

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