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Temperature Controller Circuit

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This is the design circuit for control the temperature that is will temperature-control an oven at 75 degrees Celcius. This is the figure of the circuit.


This is ideal for most types of quartz crystals. 5V single supply operation allows the circuit to be powered directly from TTL-type rails. A1, operating at a gain of 100, determines the voltage difference between the temperature set point and the LM335 temperature sensor, which is located inside the oven. The temperature set point is established by the LM103-3.9 reference and the 1k-6.8k divider. A1's output biases C1, which functions as a pulse width modulator and biases Q1 to deliver switched mode power to the heater. When power is applied, A1's output goes high, causing C1's output to saturate low. Q1 comes on and delivers DC to the heater. When the oven warms to the set point, A1's output falls and C1 begins to pulse width modulate the heater in servo control fashion. In practice the LM335 should be in good thermal contact with the heater to prevent servo oscillation. [Schematic’s source: National Semiconductor Notes]

Servo Amplifier Using LM12

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When making servo systems with a power op amp, there is a temptation to use it for frequency shaping to stabilize the servo loop. This is a circuit for implementation the servo amplifier. This is the figure of the circuit.


This motor/tachometer servo gives an output speed proportional to input voltage. A low-level op amp is used for frequency shaping while the power op amp provides current drive to the motor. Current drive eliminates loop phase shift due to motor inductance and makes high-performance servos easier to stabilize. [Circuit’s source: National Semiconductor Notes].

Sample Hold Circuit Using Op Amp

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This is an implementation for sample hold circuit function that using op amp LM324. This is the figure of the circuit.


In this circuit, the input-to-output wiring has similar to standard configuration, but its operating principle is different. Key advantages include simplicity, no hold step, essentially zero gain error and operation from a single 5V supply. The sample-hold command pulse is applied to Q3, which turns on, causing current source transistor Q4's collector to go to ground potential. Amplifier A1 follows Q4's collector voltage and provides the circuit's output. When the sample-hold command pulse falls, Q4's collector drives a constant current into the 0.01 mF capacitor.

When the capacitor ramp voltage equals the circuit's input voltage, comparator C1 switches, causing Q2 to turn off the current source. At this point the collector voltage of Q4 sits at the circuit's input voltage. Q1 insures that the comparator will not self trigger if the input voltage increases during a ``hold'' interval. When a DC biased sine wave is applied to the circuit the sampled output is available at the circuit's output. The ramping action of the Q4 current source during the ``sample'' states is just visible in the output. [Schematic circuit source: National Semiconductor Notes].

Linear Platinum RTD Thermometer Circuit

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This is the design for a thermometer. This circuit is work with based on LM392. The IC is used to provide gain and linearization for a platinum RTD in a single supply thermometer circuit which measures from 0 degrees C to 500 degrees C with g 1 degrees C accuracy. This is the figure of the circuit.


Q1 functions as a current source which is slaved to the LM103-3.9 reference. The constant current driven platinum sensor yields a voltage drop which is proportionate to temperature. A1 amplifies this signal and provides the circuit output. Normally the slight nonlinear response of the RTD would limit accuracy to about g3 degrees. C1 compensates for this error by generating a breakpoint change in A1's gain for sensor outputs above 250 degrees C. When the sensor's output indicates 250§C, C1's ``a'' input exceeds the potential at the ``b'' input and C1's output goes high. [Circuit’s source: National Semiconductor Notes].

Fed Forward Low Pass Filter Circuit

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This is a circuit that useful for common filtering problems. This single supply circuit allows a signal to be rapidly acquired to final value but provides a long filtering constant. This characteristic is useful in multiplexed data acquisition systems and has been employed in electronic infant scales where fast, stable readings of infant weight are desired despite motion on the scale platform. This is the figure of the circuit.


How is the circuit work? When an input step is applied, C1's negative input will immediately rise to a voltage determined by the 1k pot-10 kX divider. C1's ``a'' input is biased through the 100 kX-0.01 mF time constant and phase lags the input. Under these conditions C1's output will go low, turning on Q1. This causes the capacitor to charge rapidly towards the input value. When the voltage across the capacitor equals the voltage at C1's positive input, C1's output will go high, turning off Q1. Now, the capacitor can only charge through the 100k value and the time constant will be long. Waveform B clearly shows this. The point at which the filter switches from short to long time constant is adjustable with the 1 kX potentiometer. Normally, this is adjusted so that switching occurs at 90%±98% of final value, but the photo was taken at a 70% trip point so circuit operation is easily discernible. A1 provides a buffered output. When the input returns to zero the 1N933 diode, a low forward drop type, provides rapid discharge for the capacitor. [Circuit’s source: National Semiconductor Notes].

Exponential Voltage - Frequency Converter for Electronic Music

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In an electronic music synthesizers require voltage controlled frequency generators whose output frequencies are exponentially related to the input voltages. This is one solution for the problem. This is a circuit for convert voltage to frequency. This is the figure of the circuit.


This circuit has performs this function with 0.25% exponential conformity over a range from 20 Hz to 15 kHz using a single LM392 and an LM3045 transistor array. The exponential function is generated by Q1, whose collector current will vary exponentially with its base-emitter voltage in accordance with the well known relationship between BE voltage and collector current in bipolar transistors. Normally, this transistor's operating point will vary wildly with temperature and elaborate and expensive compensation is required. In this circuit, Q1 is part of an LM3045 transistor array. Q2 and Q3, located in the array, serve as a heater sensor pair for A1, which servo controls the temperature of Q2. This causes the entire LM3045 array to be at constant temperature, eliminating thermal drift problems in Q1's operation. Q4 acts as a clamp, preventing servo lock-up during circuit start-up.

Adjustable Ratio Digital Divider Circuit

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This circuit is allows a digital pulse input to be divided by any number from 1 to 100 with control provided by a single knob. The function of this circuit is ideal for bench type work where the rapid set-up and flexibility of the division ratio is highly desirable. When the circuit input is low, Q1 and Q3 are off and Q2 is on. This is the figure of the circuit.


When the input goes high Q2 goes off and Q1 turns on Q3. This causes Q3 to displace the 100 pF capacitor's charge into A1's summing junction. A1's output responds by jumping to the required value to maintain the summing junction at 0V. This sequence is repeated for every input pulse. During this time A1's output will form the staircase shape. When A1's output is great enough to just bias C1's ``a'' input below ground, C1's output goes low and resets A1 to 0V. [Circuit’s source: National Semiconductor Notes].

The Basic of Op Amp

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The op-amp is basically a differential amplifier having a large voltage gain, very high input impedance and low output impedance. The op-amp has a "inverting" or (-) input and "non-inverting" or (+) input and a single output. This is a form of op amp.


The inverting op-amp is connected using two resistors RA and RB such that the input signal is applied in series with RA and the output is connected back to the inverting input through RB. The non-inverting input is connected to the ground reference or the center tap of the dual polarity power supply. In operation, as the input signal moves positive, the output will move negative and visa versa. The amount of voltage change at the output relative to the input depends on the ratio of the two resistors RA and RB. As the input moves in one direction, the output will move in the opposite direction, so that the voltage at the inverting input remains constant or zero volts in this case.

The non-inverting amplifier is connected so that the input signal goes directly to the non-inverting input (+) and the input resistor RA is grounded. In this configuration, the input impedance as seen by the signal is much greater since the input will be following the applied signal and not held constant by the feedback current. As the signal moves in either direction, the output will follow in phase to maintain the inverting input at the same voltage as the input (+). The voltage gain is always more than 1 and can be worked out from Vgain = (1+ RB/RA).

Simple Inverter Circuit for Florescent Lamps

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This circuit is very easy to construct, reliable, and even powerful enough to light up a 15W florescent tube. This circuit is constructs from transistor NPN and some components. This is the figure of the circuit.


This is a single transistor oscillator circuit. Current passed through primary winding inducts a magnetic field to the core and the core gives the energy back to the feedback winding with a delay determined by the core material and windings. System then oscillates continuously on a frequency depending on this timing. You cannot use 2SD882 with voltages over 4.5 volts. It is only needed if you are going to feed the circuit with only 4.5 volts.

Simple 1,3 Volt Power Supply Circuit

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This is the design for a replacement power source for 1.3V mercury cells or other small batteries. This circuit is useful for computer to power a front panel multi adapter which has a digital thermometer. This circuit is a simplest form of the schematic. This is the figure of the circuit.


This circuit takes it power from a PC. The power connectors have color coded wirings, red and black are a 12V supply, black and yellow are a 5V supply. These are extremely high current so absolute care must be taken to avoid short circuits and an inline fuse of 100mA is recommended. The 1.3V is derived from a Red LED. When on and forward biased the LED's voltage drop between anode and cathode is about 1.9V, this is too high for mercury cell powered equipment, but fed in series with a 1N4148 signal diode drops around 0.6V, the supply is then ideal to drive battery powered peripherals. This is not suitable for clocks, because when the computer is turned off the 5V supply is also switched off. It is however ideal for the independent temperature displays often included with PC peripherals such as case mounted usb connectors.

Notch Filter Circuit

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This is a design for a filter. This circuit is called as variable notch filter with both high and low pass filters. This is the figure of the circuit.


This circuit is based on LF351 for sensing the filter processing. At first glance this circuit looks fairly complex, but when broken down, it can be divided into high pass and low pass filter sections followed by a summing amplifier with a gain of around 20 times. Supply rail voltage is +/- 9V DC. The controls may also be adjusted for use as a band stop (notch) filter or band pass filter.

High Voltage Regulator Power Supply

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This is a design circuit for a power supply. This circuit is basic for high power supply that is based on LM317 for the regulator IC. This is the figure of the circuit.


How is the circuit work? Zener diode D1 ensures that the LM317H sees only a 5V input-output differential over the entire range of output voltage from 1.2V to 160V. Since high-voltage transistors by necessity have a low β, a Darlington is used to stand off the high voltage. The zener impedance is low enough that no bypass capacitor is required directly at the LM317 input. (In fact, no capacitor should be used here if the circuit is to survive an output short!) R3 limits short circuit current to 50 mA. The RC network on the output improves transient response as does by passing the ADJUST pin, while R4 and D2 protect the ADJUST pin during shorts. [Circuit schematic source: National Semiconductor Notes].

50V 3A Stabilized Power Supply

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This is a design for power supply. This is a complete circuit for the stabilized power supply. This is the figure of the circuit.


This circuit can give in his exit + 40V until + 60V 3A, with simultaneous stabilization. The materials that use is very simple and will not exist difficulties in the manufacture, is enough you are careful certain points. For output voltages smaller of + 50V until + 40V, the Q1 is hot enough, so that it needs one big heat sink. This circuit is work using transistor 2N3055.

Broadband Random Noise Generator Circuit

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This circuit is often needed in testing any type of electronic systems such as filter, audio, or RF communication. The circuit presented here generates an RMS amplitude regulated noise source with selectable bandwidth. This circuit is work based on op amp. This is the figure of the circuit.


With 1 KHz to 5 MHz decade ranges selectable bandwidth and 300mV RMS output, this noise generator is suitable for wide range of application. Noise is generated by D1 that is AC coupled to A2, an amplifier with broadband gain 100. The output of A2 is fed to a simple selectable low-pass filter. The filter’s output is applied to LT1228 operational trans-conductance amplifier A3. A3’s output feeds current feedback amplifier LT1228 A4. A4’s output, which is also the circuit’s output, is sampled by the A5-based gain control configuration. This closes a gain control loop to A3. A3’s ISET current controls gain, allowing overall output level control.

Audio Mixer Using FET

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This is a simple project circuit for mixes two or more channels into one channel (eg. stereo into mono). The circuit can mix as many or as few channels as you like and consume very little power. This is the figure of the circuit.


This circuit is based on or built by FET 2N3819. The circuit can be powered by a single 9 volt battery. As many or as few channels as are required can be added to the mixer. A shielded case is probably needed to reduce hum and help stop oscillations.

Part:
R1, R3 10K Pot
R2, R4 100K 1/4 W Resistor
R5 6.8K 1/4 W Resistor
C1, C2, C3 0.1uF Capacitor
Q1 2N3819 Junction FET
MISC Wire, Shielded (Metal) Case, Phone or Other Plug For Output

Open Loop Fast Peak Detector Circuit Using Op Amp

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This is a design for peak detector. This circuit is a fast peak detector similar but faster than previous peak detector, can be implemented using open loop configuration. This circuit is based on op amp LT1190. This is the figure of the circuit.


In this design, D1 is the detector diode and D2 is a level shifting or compensating diode. A load resistor RL is connected to – 5V and an identical bias resistor, RB, is used to bias the compensating diode. This equal value resistor is RL and RB makes sure that the diode drops are equal. Low values of RB and RL (1k to 10k) yield in fast response, at the expense of poor low frequency accuracy. High values of RB and RL provide good low frequency accuracy but cause the amplifier to slew rate limit, resulting in poor high frequency accuracy. A solution can be made by adding a feedback capacitor CFB, which improve the negative slew rate on the (–) input. We can expect under 15% amplitude error for 2Vpp-6Vpp input at 20MHz, much faster than closed loop design. [Circuit source: Linear Technologies, Inc].

Stepper Motor Controller Circuit

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This is a circuit for motor stepper controller. A stepper motor controller is needed to run a stepper motor, since a stepper motor cannot work by just connecting it to a power supply. To program a stepper motor to make a complex movement, we usually need a micro controller. This is the figure of the circuit.


This stepper motor controller circuit is still need an external input. If we look at the table, the input pattern is similar to a 2 bits binary counter. If you have an up-down binary counter, then you get a forward-reverse control for your stepper motor. This circuit is very simple design.

Phase Control

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This is a phase control circuit that can be used to control the power delivered to an AC load. The phase control circuit is to control the AC waveform, cutting the cycle to give full cycle, half cycle, zero cycle, or somewhere in between. This circuit is similar to a dimmer circuit, but the switching is synchronized with the zero crossing of the waveform. This is the figure of the circuit.


The benefit of switching the power in zero crossing condition is that the triacs doesn’t suffer power dissipation, thus increasing the overall efficiency. This phase control circuit is suitable for brushed AC motor, heater filament, or incandescent lamps. The integrated circuit, U208B, is designed as a phase control circuit in bipolar technology with internal supply-voltage monitoring. As the voltage is built up, uncontrolled output pulses are avoided by internal monitoring. Furthermore, it has internal-current and voltage synchronization. It is recommended as a low cost open-loop control.

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