The 8 fundamental IC 741 based op amp circuits presented here are not only interesting but also very amusing to build. The included circuit ideas like inverting and non-inverting amplifiers, tone control and regulated power supply will surely intrigue you. Circuit diagrams are also attached with the article.
We all are probably aware regarding the high versatility of the IC 741. Amazingly an infinite number of 741 opamp circuit design ideas can be wired by adding just a few passive components to it. We investigate a few of these projects here.
IC 741 is one of the most versatile and multipurpose op-amp and can be wired up in numerous different ways. Let’s study some of the important 741 opamp applications circuits, as explained below:
1) Inverting DC Amplifier:
Sometimes it becomes important for amplifying DC voltages, the diagram above shows how the IC can be wired up into an inverting DC amplifier circuit. As the name informs a DC input to the IC will be amplified at its output but will be just the opposite with polarity. VR1 may be used for adjusting the gain of the amplifier.
2) Non-inverting DC Amplifier:
This configuration is similar to the above circuit, the only difference being the output response, which is always equal to the polarity of the fed input voltage.
3) Inverting AC Amplifier:
The figure shows how the basic inverting DC mode of the IC can be simply modified into an inverting AC amplifier design. This circuit is intended to be used with AC or oscillating input signals, primarily for amplifying minute frequencies. C1 and C2 form the input and the output coupling capacitors. Again here the gain may be varied using the pot VR1.
4) Non-Inverting AC Amplifier:
The 741 op amp circuit is similar to the above explained design; the only difference being the output of the circuit provides oscillations in phase with the input whereas the previous design produces oscillations with opposite phase to that of the input.
5) Active Tone Control:
The opamp IC741 can be very effectively used for processing audio frequencies and customizing them as per one’s own choice.
Folks who prefer more bass in music may achieve it by just adjusting the bass control shaft whereas those who appreciate extra treble with music may do the same through another similar control reserved for the purpose.
The circuit diagram shows how by adding just a few passive components with the IC 741 a neat little active tone control circuit can be built.
For the given values, the circuit provides a bass boost of 12.5 dB and a cut of 10.5 dB at around 100 Hz.
The treble chill is of 8.8 dB with a cut of 9.8 dB at around 10 kHz, with respect to the set gain of the device at 1 kHz. The circuit also features high input impedance and low output impedance.
6) Stabilized Power Supply Circuit Using opamp IC 741
The final diagram of this article shows a classic stabilized voltage DC power supply using 741 opamp circuit design.
A cheap zener / resistor voltage reference is used to provide a reasonably stable reference to the non-inverting input of the IC.
The pot VR 1 is used to set the output voltage right from zero to a maximum of 15 volts continuously. A Darlington pair transistor is used at the output to enhance high current delivering capacity.
However another transistor T3 has also been incorporated to check the above current if it tends to drift beyond limit.
The control limit may be set by varying the value of the resistor R6.
7) Power Amplifier Circuit using IC 741
Though the maximum power of this amplifier is not more than 4 watts, the amplifier provides relatively good response with the applied frequency. The distortion of less than 0.5% and has a bandwidth of over 20kHz. The amplifier requires a minimum input of around 150 mV.
8) IC 741 Darkness Controller Relay
The darkness activated relay can be used to automatically switch on a doorstep or veranda light, automatically switch on a night lamp inside a kid's bedroom, the application can be countless. What goes on, basically, is that as soon as night fall strikes the LDR, the relay is activated. If you would like the relay to run a low voltage gadget, go with a relay having low voltage contacts.
If you would like it to use anything more substantial, select a relay having contacts that can handle the voltage (and current) equivalent to the load wattage. It's exactly that easy. Just be sure the relay coil is rated not less than 150 ohms. With standard brightness, the R6 LDR's resistance will be low. The input potential at pin 3 of IC U1 will be high, which will cause a high at the output at pin 6.
Since the transistor Q1 is a PNP transistor, and the collector current will be reduced as long as the pin6 of the IC 741 holds it base positive. As soon as light source to the LDR becomes low or when darkness sets in, the R6 LDR resistance increases.
In this situation Pin 3 of the IC 741 turns in a negative course, causing the output of IC 741 at pin 6 to become low or around zero voltage. This situation resources the required negative base current to Q1 base via the 4k7 resistor, R4. Collector current of the transistor now increases, and the relay gets instantly activated. When the relay gets activated, the connected lamp or any load turns ON.
9) 741 Touch Switch Circuit
This IC 741 touch switch circuit a sensitive touch-operated switch, which could also be applied (if you like) like a rain detector. AS shown in the figure Pin 3 of the IC 741 is fixed by resistors R1 and R2. Inverting input (pin 2) is taken to the slider arm of the preset R3, that enables you to set the activation limit. As soon as you put your finger on the touch plate, it bridges the odd and even copper stripes of the touch plate, which causes pin 2 to turn negative, which amplifies the effect, causing pin 6 of the IC 741 to become positive.
In the normal situation the SCR remains in the switched OFF condition, keeping the lamp shut off. When pin6 turns positive due to touching of the touch plate, causes the SCR gate go positive, and the SCR fires and conducts and gets latched, switching ON the lamp, which is kept switched ON until the power supply to the circuit is turned OFF by S1.
Proximity Sensors using IC 741
The proximity sensor displayed below exploits the noise generated by the 50 or 60 Hz AC junk that surrounds us. The main operational element in this circuit is a 741 op-amp IC.
Through a couple of 4M7 feedback resistors hooked up between the negative input at pin 2 and the amp's output at pin 6, the amplifier's gain is adjusted to almost maximum. The metallic pick-up sensor is wired to the input at pin 2 and should be placed extremely near to the IC circuitry.
The output of the amp is sent into a detector/rectifier circuit, which delivers a positive driving voltage to the base of the BC547 NPN transistor. When an item is sensed, the transistor turns on the LED. This sort of noise pick-up circuit requires a sensor no bigger than a half-dollar coin.
Ambient noise might create false triggering if somehow the sensor plate is too big. Simply touch your finger on or near the detector plate to activate it. However, if you try to use this circuit in a location where there is no mains AC power around, it would probably stop working properly.
Proximity Sensor that does not Depend on Mains 50 Hz Hum
The identical 741 op-amp can also be used in a circuit which does not depend on an external signal source (AC mains hum). The 741 op-amp is used in a high-frequency oscillator circuit that operates around its peak frequency in this very unique proximity sensor device described below.
The internal feedback capacitor of the 741 op-amp restricts its peak frequency. As the frequency increases, the gain of the op-amp lowers until it is just little larger than one. When we increase the frequency to that level, the feedback channel turns extremely load sensitive, which is exactly what is required in any load-type proximity sensor circuit. The frequency-determining elements of the oscillator are C1, C3, R6, and R7.
The gain is determined by the feedback resistors R5 and R9. With R2 and R3, the bias of the op-amp is tuned to create a DC output on pin 6 at one-half the supply voltage, which has the benefit of being independent of any specific supply voltage.
We may leverage the greatest allowable output-voltage swing by operating the output at one-half supply. Voltages ranging from 9 to 16 volts will suffice.
The output of the oscillator at pin 6 feeds the rectifier circuit, which is composed of D1, D2, C4, and C6. The positive output of the rectifier activates Q1 and illuminates the LED. R9 should be set to the position where the LED just starts to illuminate for optimal sensitivity.
At a range of two to three inches, a 4- by 6-inch metal sensor sheet, shielded from surrounding objects, can readily detect your hand proximity.
Larger plates can sense larger items from further away. The greatest surface area that permits circuit oscillation depends on the size of the sensor plate.
Too big or too close to a ground mass might prevent the circuit from oscillating. The negative supply of the sensor must be wired to ground or a big metal item that can create capacitance with the ground.
Dual Power Supply
A technique of getting dual balanced supplies can be to employ a supply splitter which provides a low impedance center tap with a single supply, instead of creating a couple of identical supplies and hooking them up in series.
A supply splitter like the one demonstrated in the circuit diagram is designed to be used and powered with an existing bench power supply.
This specific circuit works effectively with supply voltages between 15V and 30V, with each of the output supply lines having a voltage corresponding to one half the input voltage (therefore, for instance 30V will be necessary at the input to provide +/-15V outputs).
The device can conveniently deal with currents of up to 100mA, and it may not be important to mount Tr3 and Tr4 transistors on heatsinks.
The dual power supply circuit is actually simply an unity gain amplifier consisting of a high input impedance and a low output impedance class B output stage.
A class B output stage is applied because it allows the circuit to have a low quiescent current usage (no more than 2mA). Tr1 and Tr3 are common emitter amplifiers, however since there exists 100% negative feedback through Tr3's collector to Tr1's emitter, they provide not more than a unit gain. Tr2 and Tr4 are configured like a complementary output pair with Tr1 and Tr3.