Automatic cooler fan for amplifiers

Automatic cooler fan for amplifiers

Description.
The schematic of an automatic cooler fan for audio amplifiers is given here. The circuit automatically switch ON the cooler fan whenever the temperature of the heat sink exceeds a preset level. This circuit will save a lot of energy because the cooler fan will be OFF when the amplifier is running on low volume. At low volume less heat will be dissipated and it will not trigger the cooler fan ON.

The temperature is sensed using an NTC (negative temperature coefficient) thermistor R2. Junction of thermistor r2 and resistor R1 is connected to the inverting input (pin3) of IC1 which is wired as a comparator. The non-inverting input (pin2) is given with a reference voltage using the preset R3. As temperature increases the resistance of NTC thermistor will drop and so do the voltage across it. When the voltage at the inverting input becomes less than that of the reference voltage (set for a particular threshold temperature) the output of the comparator goes high and switches the transistor Q1 ON. This will activate the relay and the cooler fan will be switched ON. When the temperature decreases the reverse happens. LED D2 will glow when the fan is ON. Diode D1 is a freewheeling diode.

Notes.
The circuit can be assembled on a Vero board.
Use 12V DC for powering the circuit.
The circuit can be calibrated by adjusting the preset R3.
K1 can be a 12V, 200 ohm, SPST relay.
LM311 must be mounted on a holder.

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Cell inspired electronics

Cell  inspired electronics

A single cell in the human body is approximately 10 000 times more energy-efficient than any nanoscale digital transistor, the fundamental building block of electronic chips. In one second, a cell performs about 10 million energy-consuming chemical reactions, which altogether require about one picowatt (one millionth millionth of a watt) of power.
Rahul Sarpeshkar of the Massachusetts Institute of Technology (MIT) is now applying architectural principles from these ultra-energy-efficient cells to the design of low-power, highly parallel, hybrid analogue-digital electronic circuits. Such circuits could one day be used to create ultra-fast supercomputers that predict complex cell responses to drugs. They may also help researchers to design synthetic genetic circuits in cells.

In his new book, Ultra Low Power Bioelectronics (Cambridge University Press, 2010), Sarpeshkar outlines the deep underlying similarities between chemical reactions that occur in a cell and the flow of current through an analogue electronic circuit. He discusses how biological cells perform reliable computation with unreliable components and noise (which refers to random variations in signals — whether electronic or genetic). Circuits built with similar design principles in the future can be made robust to electronic noise and unreliable electronic components while remaining highly energy efficient. Promising applications include image processors in cellphones or brain implants for the blind.

"Circuits are a language for representing and trying to understand almost anything, whether it be networks in biology or cars," says Sarpeshkar, an associate professor of electrical engineering and computer science. "There's a unified way of looking at the biological world through circuits that is very powerful."

Circuit designers already know hundreds of strategies to run analogue circuits at low power, amplify signals, and reduce noise, which have helped them design low-power electronics such as mobile phones, MP3 players and laptop computers.

"Here's a field that has devoted 50 years to studying the design of complex systems," says Sarpeshkar, referring to electrical engineering. "We can now start to think of biology in the same way." He hopes that physicists, engineers, biologists and biological engineers will work together to pioneer this new field, which he has dubbed "cytomorphic" (cell-inspired or cell-transforming) electronics.

To read more, go to
http://web.mit.edu/newsoffice/2010/cytomorphic-0225.html
 

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STK4132II - Schematic audio amplifier - power amplifier 2x20w

STK4132II - Schematic audio amplifier - power amplifier 2x20w

STK4132II  - Schematic audio amplifier.STK4132II  power audio amplifier schematic

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stk392 datasheet - schematic circuit diagram -

                                                                                              internal equlvalant ciruit

The STK392-020 is a hybrid IC for video projector
convergence correction. Since this IC integrates three
output amplifier circuits in a single package, the six
convergence correction output circuits, i.e., the vertical
and horizontal directions for each CRT of the RGB can be
formed from only two ICs.

Applications
Video projectors (both standard and high definition)                                            test circuit

                                                                                             
Features
•Three output amplifier circuits integrated in a single
22-pin package
•High absolute maximum supply voltage
(VCC max = ±44 V)
•Low thermal resistance (θj-c = 2.1 °C/W)
•High thermal stability (TC max = 125°C)
•Isolated early stage and output stage power supplies
•Output stage power supply switching supports high
efficiency designs.

•The input system, power supply system and output
system pins are isolated in the pin arrangement, thus
reducing the influence of the pattern layout on the
characteristics and easing design.
•Since constant current circuits are used in the pre-driver
stage, operation is stable with respect to the power
supply switching.
•The Sanyo convergence correction circuit product
lineup (the STK392-000 series) handles a wide range of
end-product classes. Therefore, the same PCB can be
used for end products from popularly-priced units to
top-of-the-line models.
Package Dimensions

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Low voltage DC motor speed control circuit using TDA7274

 Low voltage DC motor speed control circuit using TDA7274

Description.
Here is the circuit diagram of a low voltage /low power DC motor speed controller based on the IC TDA 7274 from ST Microelectronics. The IC TDA 7274 is a monolithic integrated DC motor speed controller intended for low voltage/ low power applications. Built in internal voltage reference voltage, wide input voltage range (1.8 t0 6V), high linearity, 700mA output current, excellent temperature stability etc make this IC well suitable for almost all low power DC motor speed control applications.
The motor to be controlled is connected between pin3 (Vs) and pin4 (output) of the IC. Resistor network comprising of R1, R2, and R3 is the section that deals with the speed control. Control pin (pin8) of the IC is connected to the junction of R2 and R3 and the speed of the motor varies linearly according to the position of POT R3. Capacitor C1 rectifies the fluctuations in motor speed and capacitor C2 cancels the motor spikes.

Notes.
The circuit can be assembled on a Perf board.
Power supply Vs can be anything between 1.8V to 6V and it must be selected according to the rating s of the motor.
Maximum output current capacity of this circuit is 700mA.
TDA7274 must be mounted on a holder.
POT R3 can be used to vary the motor speed

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Audio line driver

Audio line driver

Description.

This is the circuit diagram of a two channel audio line driver using the high performance dual opamp IC TSH22 from ST Microelectronics. The 25 MHz bandwidth, low distortion and high output current of the IC makes it possible to drive medium impedance loads at a high level of modulation.

Here both of the opamps inside the IC are wired as non inverting amplifiers with 3X gain, one for each channel. Input line 1 is connected to the non inverting input of IC1a and input line 2 is connected to the non inverting input of IC1b. The non inverting inputs of the opamps IC1a and IC1b are pulled to a slight positive voltage using the R1 and R9 respectively. The resistance R4 and R2 are used to make a phantom ground at half the supply voltage.


Notes.
Assemble the circuit on a good quality PCB.
The circuit can be powered from 12V DC.
At 12V supply, a 600 ohm impedance line can be driven at +10dBm with a distortion less than 0.05% at 1kHz.
Gain of line 1 can be set using the equation, Gain1 = (R5+R6)/R6.
Gain of line 2 can be set using the equation, Gain2 = (R7+R8)/R8.
The load at the output must be at least 100 ohms in order to avoid stability issues.

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