Variable Voltage Regulator Circuit

This is a design for voltage regulator that can adjust from 1.25 to 37 volts. This circuit is a simple design. The voltage regulator is control by op amp LM317. The device also has built in current limiting and thermal shutdown which makes it essentially blow-out proof. This is the figure of the circuit.


Output voltage is set by two resistors R1 and R2 connected as shown below. The voltage across R1 is a constant 1.25 volts and the adjustment terminal current is less than 100uA. The output voltage can be closely approximated from Vout=1.25 * (1+(R2/R1)) which ignores the adjustment terminal current ``but will be close if the current through R1 and R2 is many times greater. A minimum load of about 10mA is required, so the value for R1 can be selected to drop 1.25 volts at 10mA or 120 ohms. Something less than 120 ohms can be used to insure the minimum current is greater than 10mA. The example below shows a LM317 used as 13.6 volt regulator. The 988 ohm resistor for R2 can be obtained with a standard 910 and 75 ohm in series. When power is shut off to the regulator the output voltage should fall faster than the input.

Trans-impedance Amplifier Equivalent Circuit

This is an equivalent circuit of a trans-impedance amplifier and a high-impedance source. This is very simple design. This design step sets the DC gain and bias point to ensure proper operation. It also addresses DC offsets. This is the figure of the circuit.


At low frequencies, the op amp’s inverting input is forced to be at ground potential and IS must flow through RF. This combination of effects creates an output voltage of ISRF. At higher frequencies, the capacitors will affect the circuit response. The output capacitance of a current sensor has a strong effect on the stability of the op amp feedback loop. Bode plots are aids in both analyzing this effect and in properly compensating the trans-impedance amplifier using the capacitor (CF). The capacitors also limit the bandwidth of the trans-impedance amplifier.

Simple High Input Impedance DC Summing Amplifier Using CMOS

This is a design circuit for DC summing amplifier that has high input impedance of 10 MOhm. This circuit is built by CMOS op amps. This is the figure of the circuit.


10 MOhmis used as basic summing amplifier input resistor. The input leakage current of the op amps therefore limits the input voltage resolution and the minimum discernable voltage signals. The CMOS op amps that used is very low input leakage current specifications guaranteed would be required for the application. This circuit is simplest form of the circuit. The recommended CMOS op amps that can be used is ALD1701, ALD1702 and ALD1704. [Circuit source: Advanced Linear Technology, Inc].

Positive Feedback Circuit Using LM111

This is the circuit that is due to the high gain and wide bandwidth of comparators. This circuit is built by op amps LM111. This is the figure of the circuit.


The trim pins (pins 5 and 6) act as unwanted auxiliary inputs. If these pins are not connected to a trim-pot, they should be shorted together. If they are connected to a trim-pot, a 0.01 mF capacitor C1 between pins 5 and 6 will minimize the susceptibility to AC coupling. A smaller capacitor is used if pin 5 is used for positive feedback. When the signal source is applied through a resistive network, RS, it is usually advantageous to choose an RSÊ of substantially the same value, both for DC and for dynamic (AC) considerations. Carbon, tin-oxide, and metal-film resistors have all been used successfully in comparator input circuitry. Inductive wire wound resistors are not suitable. [Circuit source: National Semiconductor, Inc]

Non Interacting Adjustments for Expanded Scale Meter

This is one application for function of LM3814. This circuit is called expanded scale meter. This is the figure of the circuit.


This arrangement allows independent adjustment of LED brightness regardless of meter span and zero adjustments. First, V1 is adjusted to 5V, using R2. Then the span (voltage across R4) can be adjusted to exactly 0.5V using R6 without affecting the previous adjustment. R9 programs LED currents within a range of 2.2mA to 20mA after the above settings are made. [Schematic diagram source: National Semiconductor, Inc]

There are many ways to construct Low pass filter. In this schematic, we shall consider some of circuits when we using to current. This is the simplest of Low Pass Filter. This circuit can called Multiple Feedback circuit. Why? Because of the two of feedback paths through C1 and R2, and because of this op amp is serving as an infinite gain device rather than a finite gain device.


Because of its relative simplicity, the MFB filter is one of the more popular inverting gain types. Is also has the advantages of good stability characteristics and low output impedance. Thus it can be readily cascaded with other sections to form a higher order filter. A disadvantages of the circuit is that it cannot attain a high pole pair quality factor without large spreads of element values and high sensitivities to changes in the element values

Low Pass Filter Circuit for Subwoofer

This is a design schematic for filter the subwoofer that is purpose for distinguishes these frequencies, in order to him we lead to the corresponding amplifier. The acoustic filters are met in various points in the sound systems. In the circuit is built by op amps. This is the figure of the circuit.


The acoustic spectrum is extended by very low frequencies 20Iz and reaches as the 20000Iz in high frequencies. In the low frequencies is degraded the sense of direction. This reason is leads to the utilization speaker for the attribution of very low frequencies. The application is a simple filter of region that limits the acoustic region (20-20000Hz) in the region 20-100Hz. This circuit is constitutes mixed, amplifier with variable aid and a variable filter.

Parts:

R1 = 39 Kohm R2 = 39 Kohm
R3 = 47 Kohm R4 = 10 Ohm
R5 = 22 Kohm R6 = 4,7 Kohm
R7 = 22 Kohm R8 = 4,7 Kohm
R9 = 10 Ohm R10 = 220 Ohm
C1 = 39 pF C2 = 0.1 uF
C3 = 0.1 uF C4 = 0.2 uF
C5 = 0.4 uF C6 = 0.1 uF
C7 = 0.1 uF IC1 = TL064

Low Impedance Loads Using LT1210 IC

This is a circuit for impedance load of voltage. This circuit is work using transformer coupling that is frequently used to step up transmission line signals. This circuit is based on LT1210 IC. This IC is fast and capable of delivering high levels of current. They can be readily compensated for reactive loads and are fully protected against thermal and short-circuit faults. This circuit is simple design. This is the figure of the circuit.


The operation of this circuit is begun from a transformer-coupled application for ADSL in which an LT1210 drives a 100W twisted pair. The 1:3 transformer turns ratio allows just over 1W to reach the load at full output. Resistor RT acts as a primary side back termination and also prevents large DC currents from flowing in the coil. The overall frequency response is flat to within 1dB from 500Hz to 2MHz. Distortion products at 1MHz are below – 70dBc at a total output power of 0.56W (load plus termination), rising to –56dBc at 2.25W. If RT is removed, the amplifier will see a load of about 11W and the maximum output power will increase to 5W. A DC blocking capacitor should be used in this case. [Schematic source: Linear Technology Corporation, Inc].

Infra Red Link Circuit

This is a battery powered IR Link which may be used in more than one room. This circuit is built by CMOS IC and transistor. This is the figure of the circuit.


This circuit is not powered directly from the battery. When a remote control signal is received, the energy stored in C2 drives the emitter diode. At the same time, Q1 switches on briefly to allow the battery to recharge C2. The green LED shows that the circuit is transmitting; and the yellow LED confirms that C2 has been topped-up. There is unwanted IR radiation in both daylight and tungsten lighting. To minimize its effect use an opaque housing and do not make the opening too large. The depth of shading required will depend on the lighting conditions. When the source of the unwanted radiation is removed the unit may be reset by interrupting the power supply for a few seconds or by pushing the (optional) reset button. If you do neither then it will reset itself after about an hour when C2 has recharged through R7.

A Frequency Doubler Effect for Electric Guitar

This circuit is a octave shifting that is used for electric guitar is done by rectifying the original signal, just like AC to DC conversion inside your AC-DC power supply adapter. This circuit is use single supply instead of symmetric power supply. This is the figure of the circuit.


The rectifying is done by four 1N4148 silicon diodes, configured as full-wave rectifier bridges. Because the bridge is inserted inside the negative feedback of the operational amplifier (op-amp) U1B, the nonlinear characteristic of the diodes around the turn-on point (the forward bias voltage) is compensated by the op-amp’s feedback mechanism. As the result, the output of the rectifier looks like coming from ideal diode with no bias voltage needed. The pre-amp gain can be adjusting by R3 potentiometer between clean and slightly overdriven, hear the effect, and set as you want. The R4 pot is provided to adjust the processed signal so the output level after the frequency doubling is equal to the level before entering this analog effect processor. Make R7, R8, and C3 layout as close as possible to the pin 10 of the LM324 IC (U1C) with shortest possible wiring to minimize capturing any noise. This voltage (at pin 10 U1) is the reference for internal “virtual ground” coming out from U1C output (pin 8). Make sure that the PCB tracks for this “virtual ground” (pin 8 U1) are wider than other signal tracks to give consistent reference for all op-amps. Make sure C4 and C5 have the shortest possible connection to the power pins (pin 4, pin 11) and the “virtual ground” line (pin 8).

20 Segment Meter Circuit with Mode Switch

This is a schematic circuit for ones application for segment meter circuit using mode switch. This circuit is based on LM3914 that is a monolithic integrated circuit that senses analog voltage levels and drives 10 LEDs, providing a linear analog display. This is the figure of the circuit.


The most difficult problem occurs when large LED currents are being drawn, especially in bar graph mode. These currents flowing out of the ground pin caused voltage drops in external wiring, and thus errors and oscillations. Bringing the return wires from signal sources, reference ground and bottom of the resistor string (as illustrated) to a single point very near pin 2 is the best solution. In cases where proper wiring and bypassing fail to stop oscillations, V+ voltage at pin 3 is usually below suggested limits. Expanded scale meter applications may have one or both ends of the internal voltage divider terminated at relatively high value resistors. These high-impedance ends should be bypassed to pin 2 with at least a 0.001μF capacitors, or up to 0.1μF in noisy environments. Power dissipation, especially in bar mode should be given consideration.[Schematic source: Linear Technology Corporation].

Wien Bridge Oscillator Using CA3140

This is a bridge oscillator circuit. This circuit is excellent use of its high input impedance, high slew rate, and high voltage qualities and it is called the Wien Bridge sine wave oscillator. This is the figure of the circuit.


Oscillator stabilization takes on many forms. It must be precisely set, otherwise the amplitude will either diminish or reach some form of limiting with high levels of distortion. The element, RS, is commonly replaced with some variable resistance element. Thus, through some control means, the value of RS is adjusted to maintain constant oscillator output. A FET channel resistance, a thermistor, a lamp bulb, or other device whose resistance increases as the output amplitude is increased are a few of the elements often utilized. As the output signal amplitude increases, the zener diode impedance decreases resulting in more feedback with consequent reduction in gain; thus stabilizing the amplitude of the output signal. [Project Schematic source: Intersil Corporation].

Tone Control Circuits Using CA3140

This is a circuit for tone control in the amplifier. High slew rate, wide bandwidth, high output voltage capability and high input impedance are all characteristics required of tone control amplifiers. This circuit is built by CA3140 IC. Ca3140 is a op amp for audio signal. This is the figure of the circuit.


The Baxandall tone control circuit which is provides unity gain at mid band and uses standard linear potentiometers. The high input impedance of the CA3140 makes possible the use of low cost, low-value, small size capacitors, as well as reduced load of the driving stage. Bass treble boost and cut are 15 dB at 100 Hz and 10 KHz, respectively. Full peak-to-peak output is available up to at least 20 KHz due to the high slew rate of the CA3140. The amplifier gain is 3dB down from its “flat” position at 70 KHz.

[Project Schematic source: Intersil Corporation]

Symmetric Power Supply without CT Transformer

This is a kind design of power supply. It is like a center tapped transformer with a bridge diode is common solution to provide symmetric supply, but we can actually do it with simple solution, using a voltage double - rectifier diodes. This is the figure of the circuit.


The capacitor need to be large because the rectifying is half wave, so you can avoid power line hum. With the component values shown, the power supply is capable supplying 10mA at ripple voltage about 0.2V (peak to peak). The voltage ripple can be approximated by Vripple = (20 x I)/C, where I is the current drawn by the load in mA, and C is the capacitance in uF (micro farad).

Slave Flash Light Control Circuit

This is a design circuit that is used to give auto trigger for your secondary flash light. This secondary flash will be automati8cally triggered when it receive the light signal from the primary flash. This is the figure of the circuit.


How the circuits work? Look in this explain. The inductor 68mH is connected in parallel with the solar cell to prevent the false trigger by slowly changing environment light. Bright daylight won’t trigger your slave flash lamp because the output will be shorted by the inductor. Only fast luminance change caused by your primary flash lighting will trigger your secondary flash light. The solar cell should be 100mm2 at minimum (about 1cm2), and you can easily find on many electronics part store, and sure you can use a larger one for better sensitivity. For the inductor, because it is relatively huge, you can use a radio frequency choke (RFC) that usually used in AM radio transmitter circuit, but any inductor with low enough resistance could be used.

Octaver Fuzz Guitar Effect Circuit

This is a design for guitar effect. This circuit is used for produces fuzz sound, so it is called fuzz effect. This circuit is built by low noise dual op amp IC and transistor. This is the figure of the circuit.


The GEU is good sounding octave fuzz, with an optional mode of just fuzz. The fuzz is a fully rectified signal and is quite chewy. For some the Fuzz alone might not be loud enough, this can be fixed by raising the value of the 820 ohm resistor and lowering the 39k one. Or one could just replace both with a normal volume pot for a more standard approach. The "struzz" is the fuzz with an octave higher signal mixed in. Good for signal notes and leads.

Ibanez Fat Cat Distortion Guitar Effect

This is a circuit for guitar effect that is good for blues, rock, pop, alternative, but not for metal. You can hear the fat tone even at maximum overdrive. Checkout’s the figure of the circuit.


How this circuit is work? The first transistor 2SC1815/BC546 is configured as voltage follower, giving high impedance for the input. The op-amp (5534 IC) serve an adjustable gain amplifier, to boost the signal until it reach the forward bias voltage (about 0.6 volt) of two 1N4148 diodes, where the signal is clipped. The tone controller is very simple, just adding a high frequency attenuation when the resistance is set to higher value. Finally, 2SK188/BF245 field effect transistor (FET) is used to buffer the tone control circuit to give low impedance output.

Controllable Tremolo Circuit

This is a design circuit for guitar effect. This circuit is a simple design and it is built by FET. This is the figure of the circuit.


This tremolo circuit is not a "plug and play" ready guitar effect, however it could be converted to one switching. with the relative ease. It just needs some buffering on the input and output and perhaps some bypass. This circuit is powered using 18 V DC.

Wien Bridge Oscillator Circuit

This is a circuit that is known as wien bridge oscillator circuit. The circuit has positive and negative feedback loop. This circuit is work with control by op amp. This is the figure of the circuit.


The circuit oscillates at a frequency determined by the RC time constant at frequency and produces a sinusoidal waveform at the output voltage Vout. In many cases this circuit is used as sine wave generator which is using rail to rail op amp. [Schematic’s diagram source: Advanced Linear Devices, Inc]

Volume and Balance Controls Circuit Using Op Amp

The designed by Peter Baxandall of feedback tone control fame, amongst many other designs, there is also an active version of the 'Volume and Balance Control', which uses an op amp and a pot in the feedback loop. The log law is almost identical to that for the passive design above, but it can provide gain as well as attenuation. This circuit is using TL072 as op amp the signal input and output of the circuit. This is the figure of the circuit.


The input buffer enables the inverting stage (needed so the circuit can work) to have a very high input impedance. This would otherwise not be possible without the use of extremely high value resistors, which would increase the noise level considerably. The maximum gain as shown is 10 (20dB) and minimum gain is 0 (maximum attenuation). The input impedance is variable, and is dependent on the pot setting. At minimum gain, input impedance is the full 50k of the pot, falling to about 27k at 50% travel, and around 4k at maximum gain. These impedance figures are very similar to the simple passive version (if a 100k pot is used), and again, a low impedance drive is required or the logarithmic law will not apply properly. The actual value for VR1 does not matter, and anything from 10k to 100k will work just as well, although it will influence the input impedance. The error at 50% of pot travel is less than 5% with values from 10k to 100k.

Tuned Sine Wave Oscillator Circuit With Op Amp

This is a design circuit for sine wave oscillators that will provide both a sine and square wave output for frequencies from below 20 Hz to above 20 KHz. The frequency of oscillation is easily tuned by varying a single resistor. This circuit is controlled by two op amp, LM111 and LM101A. This is the figure of the circuit.


In this circuit, an operational amplifier has function as a tuned circuit, driven by square wave from a voltage comparator. The frequency is controlled by R1, R2, C1, C2, and R3, with R3 used for tuning. Tuning the filter does not affect its gain or bandwidth so the output amplitude does not change with frequency. A comparator is fed with the sine wave output to obtain a square wave. The square wave is then fed back to the input of the tuned circuit to cause oscillation. Zener diode, D1, stabilizes the amplitude of the square wave fed back to the filter input. Starting is insured by R6 and C5 which provide dc negative feedback around the comparator. This keeps the comparator in the active region. [Schematic diagram source: National Semiconductor. Inc]

Relay Toggle Circuit

The circuit in below is a design circuit for toggles a relay when a button is pressed. So, it is called as relay toggle circuit. This circuit is built and control by 555 timers IC. This is the figure of the circuit.


Advantages of this circuit are the large hystersis range at the input which avoids false triggering, and only a few parts are needed for construction. One disadvantage is the relay may be engaged when power is first applied. To solve this problem, you could tie the reset line (pin 4) to another resistor/capacitor combination with the capacitor at ground and the resistor at the +V point. This will cause pin 4 to be held near ground for a short period which will reset the output when power is applied.
[Circuit source: Bill Bawden]

Phase Shift Oscillator Circuit

This is a design circuit of a simple inexpensive amplitude stabilized phase shift sine wave oscillator which requires one IC package, three transistors and runs off a single supply. This circuit is combination with the RC network comprises a phase shift configuration and oscillates at about 12 kHz. The remaining circuitry provides amplitude stability. Here’s the schematic figure of the circuit.


The high impedance output at Q2's collector is fed to the input of the LM386 via the 10 μF-1M series network. This circuit is using op amp LM386 causes it has fixed gain of 20. The 1M resistor in combination with the internal 50 kΩ unit in the LM386 divides Q2's output by 20. The positive peaks at the amplifier output are rectified and stored in the 5 μF capacitor. This potential is fed to the base of Q3. Q3's collector current will vary with the difference between its base and emitter voltages. Since the emitter voltage is fixed by the LM313 1.2V reference, Q3 performs a comparison function and its collector current modulates Q1's base voltage. Q1, an emitter follower, provides servo controlled drive to the Q2 oscillator.a

Low Distortion Sine Wave Oscillator

One approach to generating sine waves is to filter a square wave. This leaves only the sine wave fundamental as the output. Since a square wave is easily amplitude stabilized by clipping, the sine wave output is also amplitude stabilized. For the solution of the problem, you can look at the figure below.


A lower distortion oscillator is needed. It can be used. Instead of driving the tuned circuit with a square wave, a symmetrically clipped sine wave is used. The clipped sine wave, of course, has less distortion than a square wave and yields a low distortion output when filtered. This circuit is not as tolerant of component values as tune sine wave oscillator. To insure oscillation, it is necessary that sufficient signal is applied to the zener for clipping to occur.

Clipping about 20% of the sine wave is usually a good value. The level of clipping must be high enough to insure oscillation over the entire tuning range. If the clipping is too small, it is possible for the circuit to cease oscillation due to tuning, component aging, or temperature changes. Higher clipping levels increase distortion. [Schematic’s diagram source: National Semiconductor. Inc]

Low Current Amplifier Using CA3140

This is a design for amplifier, but in this circuit, it is a low current. The circuit is built by CA3140 as op amp the signal. The low input terminal current needed to drive the CA3140 makes it ideal for use in current amplifier applications like the figure in below.


In this circuit, low current is supplied at the input potential as the power supply to load resistor RL. This load current is increased by the multiplication factor R2/R1, when the load current is monitored by the power supply meter M. Thus, if the load current is 100nA, with values shown, the load current presented to the supply will be 100μA; a much easier current to measure in many systems. [Project circuit source: Intersil Corporation].

Lead Acid Battery Charger Circuit Using MAXIM Chip

This is battery charger circuit that is use a fly back converter topology, and implements a current-limited power supply to charge lead-acid batteries. This circuit is control by MAX471 and MAX733 IC. This is the figure of the circuit.


The flyback transformer provide isolation and voltage input range flexibility, event at supply voltage lower that the battery voltage. Monitoring the charging current is done by sensing the output using MAX471 IC current sense amplifier. The result of the output current monitoring is then used to give a feedback to a threshold detector, to detect if the value falls below the predetermined threshold. This detection is used to switch the charger into trickle mode, when a lower voltage is applied for lower charging current. [Schematic source: Maxim Integrated Products Application Notes]

High Current Toggle Switch Circuit

This is a circuit design for high current toggle switch. This circuit was adapted from the "Toggle Switch Debounced Pushbutton" by John Lundgren. The toggle switch for the circuit is by MOSFET as sensor. It is useful where the load needs to be switched on from one location and switched off from another. Any number of momentary (N/O) switches or push buttons can be connected in parallel. This circuit is work with based on transistor as controller the circuit. This is the figure of the circuit.


The combination (10K, 10uF and diode) on the left side of the schematic insures the circuit powers up with the load turned off and the NPN transistor conducting. These components can be omitted if the initial power-on condition is not an issue. When a switch is closed, the 1uF cap voltage is connected to the junction of the 220 ohm and 33K resistors causing the circuit to change state. When the switch is opened, the cap charges or discharge to the new level through the 1M resistor, and the circuit is ready to toggle again in about 1 second. It takes a little time for the cap to move to the new level, either +V or ground. The (0.1uF) capacitor at the transistor base was added to press noise that might cause false triggering if the switches are located far away from the circuit. The circuit was tested using a 12 volt, 25 watt automotive lamp, and IRFZ44. Other MOSFETs can probably be used. [Circuit project source: Bill Bawden]

Bistable Flip Flop Circuit

This is circuit for two samples for the same circuit. It is two examples of bi stable flip flops which can be toggled between states with a single push button. This is the figure of the circuit.


When the button is pressed, the capacitor connected to the base of the conducting transistor will charge to a slightly higher voltage. When the button is released, the same capacitor will discharge back to the previous voltage causing the transistor to turn off. The rising voltage at the collector of the transistor that is turning off causes the opposite transistor to turn on and the circuit remains in a stable state until the next time the button is pressed and released. Note that in the LED circuit, the base current from the conducting transistor flows through the LED that should be off, causing it to illuminate dimly. The base current is around 1 mA and adding a 1K resistor in parallel with the LED will reduce the voltage to about 1 volt which should be low enough to ensure the LED turns completely off.

Auto Ranging Circuit Using LTCxxxx IC

This is a circuit that is the name called auto ranging circuit. This circuit is useful to extend the measurement range of an available ADC (analog-to-digital converter). The circuit will best implemented for multiplexed input. LTC1257 is appropriate for system auto ranging, adjusting an ADC’s full-scale range. This is the picture of the schematic.


This circuit is use IC with LTC type. During the conversion process, U2 and U3 receive the full and zero scale codes, respectively, that correspond to a selected multiplexer channel. For example, let channel 2’s span begin at 2V and end at 4.5V. When a host processor wants a conversion of channel 2’s input signal, it first sends code that sets the output of U2 to 2V and U3 to 4.5V, fixing the span to 2.5V. The processor then sends data to the LTC1296 selecting channel 2. The processor next clocks the LTC1296 and reads the data generated during the conversion of the 3.5VP-P signal applied to channel 2. As other multiplexer channels are selected the DAC outputs are changed to match their spans.

Wailing Alarm Siren Circuit Using 555

This is a one kind of alarm that is produces warbling sound. The circuit use two 555 IC oscillator. In this alarm siren circuit, the first oscillator is employed to produce audio frequency. The second oscillator is employed to produce a modulating signal. This modulating signal make this alarm siren generates warbling sound. This is the figure of the circuit.


If you want try to change the capacitor C1, it will to change the warbling frequency. Using the component shown in the schematic diagram, this alarm siren gives 6 seconds warbling period. You can lower the C1 capacitor value to get higher warbling frequency, for example, you can try some values between 10 uF to 47 uF to get the suitable effect. This alarm siren circuit works with 5-15V power supply, but note that the 555 IC would suffer a significant self-heating when you use 12 volts or higher, and this may cause a shorter lifetime for the 555 IC chip.

Universal High Quality Preamp

This is a circuit for universal pre-amplifier. This circuit has high quality for amplifying a signal. This circuit should be simple to use it as a low impedance mic amp or as a high input impedance preamp for mic or, with a suitable RIAA equalization, for phone pickup or similar. It can even be used as a balanced input mic preamp. This is the figure of the circuit.


R1 will define the impedance if the high impedance input - say 100K. R4 charges the output capacitor only. R3 defines the operating current in Tr4, say 1K for 500µA or so. The feedback paths have been separated: DC feed back is via the two the 100K resistors, which are decoupled so they don't affect the AC feed back. The AC feed back if via the network Zf, which can be RIAA for phone or whatever as required.

Low Noise Audio Line Driver Circuit

This is a design for audio line driver. This circuit is based on 2 IC as controller the operation. The LT1206 has been naturally selected as the components for video application since it has suitable bandwidth and output derive capability. This high performance features is not only suitable for video application, but also make it definitely suitable for audio application. This is the figure of the circuit.


The schematic diagram shows the LT1206 combined with the LT1115 low distortion, very low noise audio buffer with a gain of 10. With a 5VRMS and 32 Ohm load (780mW), the THD + noise for the circuit is only 0.0009% at 1 KHz, rising to 0.004% at 20 KHz. The frequency response is flat to 0.1dB from DC to 600 KHz, with a – 3dB bandwidth of 4MHz. The circuit is stable with capacitive loads of 250pF or less.
[Schematic diagram source: Linear Technology Application Notes]

Laser Diode Driver Circuit

This is a design circuit for laser diode driver circuit that can be implemented using voltage-controlled current source. This is a simple circuit that is linear laser diode driver gives cleaner drive current than a switched (PWM) drivers. This is the figure of the circuit.


A Howland current pump with a current booster is used as the basic of this laser diode driver. Q1 is used as the current booster on the output of a R-R CMOS OPA350 op amp (U2). Voltage drop across a shunt resistor (RSHUNT) in series with the laser diode is measured differentially to sense the current. An analog voltage from a potentiometer of from a microprocessor controlled DAC can be fed to VIN to control the laser diode current.

Fahrenheit Thermometer Circuit Using LM35

This is a design for thermometer. This is a ones simple circuit. If you have a digital voltmeter, or any voltmeter with milli volt resolution and high input impedance, then you can use this temperature-to-voltage adapter circuit to measure room temperature. This circuit is based on LM35 as temperature sensor. This is the figure of the circuit.


Note that the voltage output of this circuit is floating, not referenced to ground. You have to use separate supply if your voltmeter has single ended (referenced to ground) input. You can set your voltmeter to 200 mV range to give temperature reading directly in Fahrenheit degree. [Schematic source: National Semiconductor Application Notes]

Dynamic Compressor

This is dynamic compressor circuit that will give about 20dB compression, at very wide input signal range 100 mV to 10 V. A part of the signal is rectified by D1 and D2 and is used to charge C1 and C2 Capacitors. This is current control the attenuator diodes D3 and D4, together with R3, R5, and R6. The attenuator diodes work at the nonlinear region of the forward current curve. At low level, the input signal is not attenuated since the rectified voltage is under voltage bias of D3 and D4, since that D3 and D4 become non-conductive. If the level of input signal is increase, at some point, the D3 and D4 begin to conduct and attenuate the signal. This is the figure of the circuit.


The attack time of this compressor circuit is fixed and is determined by time constant of C1, C2, R2, and the output impedance of the input source that feed this compressor input. The decay time can be slightly adjusted by R7 variable resistor. You can see that the signal path of this compressor circuit use a 470k resistor as the attenuators, means that you should only connect the output of this circuit to a high impedance stage.

Simple Audio Level Meter Using LM3915

This is a simple design of audio level meter. This circuit uses just one IC and a very few number of external components. This circuit is based on LM3915 as controller in the operation of the audio level meter circuit. It displays the audio level in terms of 10 LEDs. The input voltage can vary from 12V to 20V, but suggested voltage is 12V. This is the figure of the circuit.


The LM3915 is a monolithic integrated circuit that senses analog voltage levels and drives ten LEDs providing a logarithmic 3 dB/step analog display. LED current drive is regulated and programmable, eliminating the need for current limiting resistors. The IC contains an adjustable voltage reference and an accurate ten-step voltage divider. The high-impedance input buffer accepts signals down to ground and up to within 1.5V of the positive supply. Further, it needs no protection against inputs of 35V. The input buffer drives 10 individual comparators referenced to the precision divider. Accuracy is typically better than 1 dB.

Accelerometer Amplifier Circuit

This is a circuit for accelerometer amplifier. This is a simple circuit. Precision accelerometer needs inverting mode amplifier since they are usually charge-output devices. This amplifier is convert charges into voltage output. The circuit below is an example of accelerometer with DC servo. This circuit built by IC LT1113.


The charge from the transducer is converted to a voltage by C1, which should equal the transducer capacitance plus the input capacitance of the op amp. The low frequency bandwidth of the amplifier will depend on the value of R1 • C1 (or R1 (1 + R2/R3) for a Tee network). [Schematic source: Linear Technology Application Notes]

Video Line Driver Circuit

This is a design schematic for video line driver. This circuit is based on IC LT1206 is suitable for driving multiple video cables since it has 60MHz bandwidth, 250mA output current capability, and low output impedance. Please keep in mind about un-terminated line effect when driving multiple cables. A reflected wave would propagate back to the driver cause a crosstalk to other lines since the driver output is non-zero impedance. This is the figure of the circuit.


The schematic diagram shows the LT1206 connected as a distribution amplifier. To minimize the effect of reflection, each line is separately terminated. Differential gain and phase performance are also important and have been considered in the internal design of the device, especially useful if the signal is video composite. Note that at 5MHz the output impedance of LT1206 is only 0.6W, much smaller than the terminating resistor separators. [Schematic diagram source: Linear Technology Application Notes]

Basic Symmetric Power Supply Circuit

The circuit below is the basic design schematic for standard symmetrical power supply. If your circuit need high current then this circuit is suitable. This circuit is consist of some part component that can buy in all every electro store. The component that is used only transformer and diode. This is the figure of the circuit.


You need a center-tapped transformer to build this symmetric power supply. This power supply circuit is widely used in op-amp application, as well as in high-rated power amplifier. The operation of the circuit is control by diode or bridge diode.

Touch Switch Circuit Using Logic Gate

This is a touch circuit that is used as a latching circuit to switch a LED ON and OFF by physically touching the ON metal plate or OFF metal plate. This circuit is based on logic gate for control the operation. This is the figure of the circuit.


It is important to ensure that 9V battery is used as its DC source. If one uses the mains supply to step down the voltage using a transformer for rectification and filtering to get the 9V DC supply, ensure that the transformer is designed in such a way that it follows the safety standard requirement of UL. This is important to ensure the safety of the user that is using the metal contacts to ON/OFF the LED.[Schematic diagram source: Electronics Project Design].

The Video Limiter Circuit

This circuit is use to avoid exceeding luminance reference level standard or to avoid exceeding the input range of digitizer (ADC), video signal is often needed to be limited. The simple way to do this is by hard limiting the signal in the positive direction (white peak clipping), but this method completely destroy all information contained in the clipped region. This circuit is based on LT1228 IC’s. This circuit is called as video limiter. This is the figure of the circuit.


The better way to limit the signal is while preserving all information contained in the signal is by soft limiting the signal, where the signal will be compressed at the above threshold region. The LT1228 is used here in a slightly unusual, closed-loop configuration. The gain of the closed-loop is set by the feedback and gain resistors (RF and RG) and the open-loop gain by the trans-conductance of the first stage times the gain of the CFA. The level at which the limiting action begins is adjusted by varying the set -current into pin 5 of the trans-conductance amplifier.
[Schematic diagram source: Linear Technology Application Notes]

Simple 10 Watt Audio Power Amplifier Based On Transistors

This is a simple design circuit for audio power amplifier. In this design circuit is use discrete component available on many electronic part stores. This circuit is based on transistor for operation the circuit. This is the figure of the circuit.


The transistor that is using in the circuit is 2N3055 and MJE2055. The MJE2055 is an NPN transistor, but the configuration with TIP42A make the whole combination of TIP42A and MJE2055 are seen as PNP transistor. This audio amplifier circuit is suitable for moderate power application in home sound system.

Open Loop Fast Peak Detector Circuit

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


In this circuit, operation is begun from 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 is under 15% amplitude error for 2Vpp-6Vpp input at 20MHz, much faster than closed loop design. [Schematic diagram source: Linear Technology Application Notes].

Half Wave Precision Rectifiers Circuit

There are several different types of precision rectifier, but it is necessary to explain what a precision rectifier actually is. In it is a simple form of circuit, a half wave precision rectifier is implemented using an op amp, and includes the diode in the feedback loop. This is the figure of the circuit.


For a low frequency positive input signal, 100% negative feedback is applied when the diode conducts. The forward voltage is effectively removed by the feedback, and the inverting input follows the positive half of the input signal almost perfectly. When the input signal becomes negative, the op amp has no feedback at all, so the output pin of the op amp swings negative as far as it can. Assuming 15V supplies, that means perhaps -14V on the op amp output.

Fast Pulse Detector Circuit

This circuit is a schematic diagram for a fast pulse detector. At 100 ns or wider pulse width, the detection should be error free. At 60 ns pulse width, the detection error should be under 10%. This circuit is a simple design. This is the figure of the circuit.


This circuit should be used to detect at least 100 ns wide pulse to ensure an error free performance. This circuit is based on LT1190 for the operation.[Schematic diagram source: Linear Technology Application Notes]

Current Loop Transmitter for Temperature Sensor

This is a design for current loop transmitter circuit. Current loop interface has been widely used in industrial environment because it is robustness. Noise resistance and fail detection capability made it suitable for long distant transmission in harsh environment. This circuit provide current loop transmitter for temperature sensor. This is the schematic figure.


In the temperature measurement is done by LM35 temperature sensor chip. You can use general silicone diode such as 1N4001. The current controller function is done by LM317 current/voltage regulator. This circuit will draw a consistent current proportional to the temperature being measured, regardless the supply voltage variation caused by noise or long wire’s temperature-dependent resistance variation.

Colpitts Crystal Oscillator Circuit

This is a design schematic of a Crystal Colpitts oscillator can be implemented using a transistor and a parallel mode crystal. This is the figure of the circuit.


In this circuit, the crystal is use as an inductance. A large value capacitive divider is used between gate, source, and ground, and a small series capacitor is placed in the crystal circuit. You should choose the components values so that C2+C3 to C1 ratio has the highest possible value. The ratio of 5 to 10 to 1 is usually used. The schematic shows the typical values. This circuit introduce is a little loading on the crystal. The relatively high value is of C2 and C3 “swamp out” variations and drift caused by variations in device characteristics. Frequency can be fine tuned with C1. A clean enough sine wave appears at the emitter of the transistor.

The Butterworth Second Order High Pass Filter Circuit

This is a circuit for high pass filter. This circuit is similar to low-pass filter circuit, but the position for resistors and capacitor are interchanged. This circuit is based on op-amp for the operation. LM833 IC is the op-amp that is used in the circuit. This is the figure of the circuit.


Similar with low pass design guide, the resistor and capacitor should be chosen according to the formula, and the resistor value should be:
· Much higher than equivalent leakage resistance of the capacitor.
· Much higher than the operational-amplifier’s (op-amp’s) input impedance.
· Doesn’t draw excessive current-violating the maximum allowed op-amp’s output current.

In general, for higher capacitor value, it is leakage current would be higher and you must use lower resistors to compensate the capacitor’s current leakage. [Schematic source: National Semiconductor's LM833 Application Notes]

A Phase Control Circuit

This is a phase control circuit that can be used to control the power delivered to an AC load. The phase control circuit can control the AC waveform, cutting the cycle to give full cycle, half cycle, zero cycle, or somewhere in between. You can say this circuit is similar to a dimmer circuit, but the switching is synchronized with the zero crossing of the waveform. This circuit is works using based on IC U208B. 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 IC 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.
[Circuit's schematic diagram source: TEMIC TELEFUNKEN Microelectronic Application Notes]

500 mW Audio Amplifier Using 3 Transistors

This is a design schematic for audio amplifier. This circuit is a small 3 transistors amplifier circuit will be suitable for small battery powered devices, and the circuit is really simple. This tiny power amplifier use same typology as the more complicated version of discrete amplifier in our previous circuit, but with here is in the simplest form. This is the figure of the circuit.


This circuit is a very good start as a DIY amplifier because its simplicity. Since this audio amplifier process only audio signal (not a dc amplifier), both the input and the output are dc-blocked using capacitors. You can see 3.3 ohm resistors connected to the emitter of PNP-NPN transistor couple, and the purpose of this resistor is to stabilize the transistor gain, so the temperature change won’t affect the performance much. Any PNP-NPN transistor couple with identical performance that capable of handling 100mA collector current should be suitable to replace the final transistors. The voltage swing of the output will be 2 Volt at maximum (at 9V DC supply), so the current at 8 ohm speaker will be 0.25A, and the maximum power would be the 2V*0.25A=0.5Watts. [Source: Bill Bowden's Circuits Collection]