Harmonic Generator With Single Opamp

Quartz crystals have the
property that their amplitude/phase characteristic repeats itself at
frequencies that are an uneven multiple of the fundamental frequency.
There are so-called overtone crystals that are cut in such a manner that
they possess this property to a greater extent. However, in principle,
any crystal may be used on one or more of its harmonic frequencies.
Harmonic generators based on transistors may operate satisfactorily on
the 3rd harmonic, but if the 5th or 7th harmonic are wanted, the circuit
红包扫雷苹果下载地址 becomes less reliable and requires frequent adjustment.

This circuit is based on a single, fast opamp and oscillates readily
at the 3rd, 5th or 7th harmonic. The opamp is set up as a non-inverting
amplifier with the quartz crystal connected between its output and the
non-inverting input. The circuit amplification, which in principle must
be unity to ensure oscillation, is determined by the network formed by
R4, R5 and trimmer capacitor C3. This network is frequency-dependent
such that the amplification increases as the frequency rises. The
红包扫雷苹果下载地址 network gain is adjustable with C3.

The setting of the capacitor must be such that the gain is too small
for oscillation at the fundamental frequency, but sufficient for, say,
the 5th or 7th harmonic. The author uses a standard computer crystal of
10 MHz. Depending on the setting of C3, the circuit provides a stable
output at frequencies between 50 and 70 MHz. It should be noted that
these frequencies are multiples of the series fundamental frequency of
the crystal. Tuning is carried out simply with a frequency counter

Harmonic Generator Circuit With Single Opamp

Harmonic Generator Circuit Diagram With Single Opamp

The output frequency is varied with C3. When the capacitor is
roughly at the correct setting, the frequency ‘locks’ as it were at the
harmonic. The area where locking occurs is not well-defined, however, so
that the setting of C3 is not critical. When tuning is completed, the
output frequency is crystal-stable. In principle, the circuit may be
used for frequencies of up to 100 MHz, when the values of R4 and R5 may
need to be reduced.

When a crystal with a higher fundamental frequency, say, 15 MHz, is
used, the circuit may be tuned to the 3rd harmonic, that is, 45 MHz. The
circuit should be tested with a supply voltage of 5–9 V (the maximum
supply voltage for the IC is 12 V). The peak to peak output voltage has a
value of about that of the supply voltage less a few volts. The output
can provide a current sufficient to drive relatively low-impedance

author: gert baars – copyright: elektor electronics

an Op Amp with Discrete Components

You can use three
discrete transistors to build an operational amplifier with an open-loop
gain greater than 1 million (Figure 1). You bias the output at
approximately one-half the supply voltage using the combined voltage
drops across zener diode D1, the emitter-base voltage of input
红包扫雷苹果下载地址 transistor Q1, and the 1V drop across 1-MΩ feedback resistor R2.

Build an op amp with three discrete transistors figure 1Resistor R3
and capacitor C1 form a compensation network that prevents the circuit
from oscillating. The values in the figure still provide a good
square-wave response. The ratio of R2 to R1 determines the inverting
gain, which is −10 in this example.You can configure this op amp as an
红包扫雷苹果下载地址 active filter or as an oscillator.

It drives a load of 1 kΩ. The square-wave response is good at 10
kHz, and the output reduces by 3 dB at 50 kHz. Set the 50-Hz
low-frequency response with the values of the input and the output
capacitors. You can raise the high-frequency response by using faster
transistors and doing careful layout.

Subwoofer Lowpass Filter using uA741 Single Op-Amp Ic

This is the simplest Sub
woofer Low Pass filter Circuit using uA741 single op amp ic. The
circuit is very low cost with respect to their work. The cut off
frequency of this circuit is 25Hz to 80Hz maximum. Using this circuit ,
you can easily design a 2.1 Sub-woofer Speaker System at your own Home.
The circuit contains very few components.In Pakistan, the cost of this
circuit with PCB红包扫雷苹果下载地址 is Rs:45 The same circuit is working in my own hand made sub-woofer system. So Try this Link:


Circuit diagram

Parts List:

R1,R3,R4 = 10K 1/4W
R2=100K 1/4W
CY1,CY2 = 0.22uF Polyester
C1,C2 = 10uF/25V Electrolytic
IC1 = uA741A Single Op-Amp Ic + 8 Pin Ic Socket
3 Pin Male & Female Connector x 2
2 Pin Male & Female Connector x 1
PCB红包扫雷苹果下载地址 as in required size 4.5 cm x 3.4 cm

Zero Gain Mod For Non-Inverting Opamp

Electronics textbooks
will tell you that a non-inverting opamp normally cannot be regulated
down to 0 dB gain. If zero output is needed then it is usual to employ
an inverting amplifier and a buffer amp in front of it, the buffer
acting as an impedance step-up device. The circuit shown here is a trick
to make a non-inverting amplifier go down all the way to zero output.
The secret is a linear-law stereo potentiometer connected such that when
the spindle is turned clockwise the resistance in P1a increases (gain
goes up), while the wiper of P1b moves towards the opamp output (more
signal). When the wiper is turned anti-clockwise, the resistance of P1a
drops, lowering the gain, while P1b also supplies a smaller signal to
红包扫雷苹果下载地址 the load. In this way, the output signal can be made to go down to zero.

Circuit diagram:

Zero Gain Mod Circuit For Non Inverting Opamp

Zero Gain Mod Circuit Diagram For Non-Inverting Opamp

Opamp With Hysteresis

At first glance, the
circuit in the diagram does not look out of the ordinary, and yet, it
is. This is because it combines two characteristics that are usually
assumed to be incompatible: hysteresis and a high input impedance. In a
standard op amp circuit, this is, indeed, true, because the creation of
hysteresis is normally achieved by positive feedback to the +ve input of
the op amp. Unfortunately, the requisite resistance network causes a
drastic deterioration of the original high input impedance of the op
amp. So, when a high input impedance and hysteresis are wanted, the
solution is to obtain the needed positive feedback by coupling the
红包扫雷苹果下载地址 resistor network not to the +ve input but to the offset correction pin.

Circuit diagram:

Operational amplifier With Hysteresis Circuit

Operational amplifier With Hysteresis Circuit Diagram

When this done, the hysteresis so obtained is calculated from Uh =
1.2/R4Uo, where Uh is the hysteresis voltage and Uo is the output
voltage of the op amp, both in volts The value of R4 must be in kΩ. The
level of Uo depends, of course, on the load.

Low Cost Bass-Treble Controller Using Op-Amp 741

This is simple but
powerful bass, treble, volume control is made by General Op-Amp IC
LM741. The input voltage is 12V, but it will also work with 9V and 6V.
This has inbuilt pre-amplifier also. Left channel is shown. Right
channel is same.

Parts List:

IC LM741 ×1
T/C 10k,22k,100k All x1
Triansistor BC148/548 = 1
220uF/25V = 2
4.7uF/25V = 2
2.2uF/10V = 1
10uF/25V = 1
Small resistors x12p
红包扫雷苹果下载地址 Small PF x5p

Dual Opamp Buffered Power Supply

There will be instances where the currents
from each supply will be unequal. Where this is the case, the resistor
divider is not sufficient, and the +ve and -ve voltages will be unequal.
By using a cheap opamp (such as a uA741), a DC imbalance between
supplies of up to about 15mA will not cause a problem. However, we can
do better with a dual opamp (which will cost the same or less anyway),
and increase the capability for up to about 30mA of difference between
红包扫雷苹果下载地址 the two supplies.


Regulator power supply with op-amp

Power supply circuit has a first amplifier using op-amp is IC uA741. Op amp circuit that is used only one, but it also features an adjustable voltage, which is steered by a trimpot resistors. Rtrim will set the input to the IC input on pin 2, so that if the detainee on Rtrim which will be channeled into ic enlarges the output voltage will be small, and otherwise. After the voltage is boosted and filtered and then the voltage will be regulated and boosted again by a NPN transistor.
Op amp use to regulator voltage
Output voltage 0.5V – 35V

Part List :
R2____1K trim

红包扫雷苹果下载地址 C1____10000uF 80V


LED1_Red Led

U1____uA741 (op-amp ic)

What is the difference between op amps and comparators?

红包扫雷苹果下载地址while both operational amplifiers and voltage comparators have been with us since before 1970, the similarities and differences tend to be vague. this discussion will help in understanding this important issue.

i well remember the first time that i saw an operational amplifier; it was 1965 at cambridge electron accelerator –it was a mysterious box containing numerous transistors that could be connected in various ways for various functions. both analog and digital integrated circuits (rtl –resistor transistor logic) would soon be introduced, but i never could have guessed what the future would hold. now some 50years later having used both op amps and comparators, i have good understanding of these devices and wish to pass some practical information along.

Popular devices

红包扫雷苹果下载地址perhaps the most popular operational amplifiers are the venerable lm741 and the more recent lm324. the most popular comparators include the lm311 and the lm339. these were developed by national semiconductor, soon became industry standards and subsequently licensed and enhanced by numerous manufacturers including ti, motorola etc.


Guts of the LM339 & LM324

a cursory glance may suggest that the two schematics are very similar with both having identical differential inputs, but observe the differences in the output structure. the lm324 has a complementary output while the lm339 is open collector. in the complementary output, current can flow in either direction as required (either source or sink) while the open collector output can only sink current. this basic difference is typical of all op amps and comparators (although a few comparators have complementary outputs).

红包扫雷苹果下载地址another more subtle difference is the presence of a compensation capacitor in the op amp –this is typical of perhaps 99% of all op amps. an operational amplifier is slowed down by the compensation capacitor in order to make it stable (prevent oscillation), while a comparator is intended to be as fast as possible in order to minimize propagation delay and to provide fast transition time at the output. however, both op amps and comparators often share this common problem: unwanted oscillation.

Application issues

红包扫雷苹果下载地址the operational amplifier is intended for linear operation where the output may be at any voltage within the limits of the power supply rails. the voltage comparator is simply a 1bit analog to digital converter where the output is always in positive or negative saturation.

Power supplies (or rails)

the ground rail is generally logic common. in a single supply comparator, it is also generally the negative rail or the most negative voltage in the circuit. some comparators like the lm311 cannot compare voltages at ground potential due to limitations in the common mode input voltage range so they require a negative rail to power the analog section. these devices offer a separate logic ground pin that is tied to logic common. so in the lm311 class of comparators there are (3) rails: common, analog positive and analog negative. a possible 4th rail would be the logic positive rail that is equal or lower in voltage than the analog positive power supply rail –this is what powers the output pull-up resistor. the analog positive and negative rails are often ±12v, but can actually be whatever is desired or required such as ±5v –also, they need not be equal in voltage.

note that some comparators (perhaps 10%) have a complementary rather than open collector output –with such, the analog positive rail must be equal in voltage to the logic positive rail.

Open collector output

the open collector output is the usual means of interfacing the comparator output to the logic input. such requires an external pull-up resistor. it allows the logic positive rail to be lower in voltage than the analog positive rail. open collector outputs also provide the means of a “wired or” connection where multiple open collector outputs are tied together –all open collector outputs must be high (off) in order for the output to go high.

ORing the Outputs

Op amps as comparators

红包扫雷苹果下载地址op amps are frequently used as comparators –i do this commonly. this is practical where high speed is not a requirement and where single supply operation is feasible. note also that op amps and comparators have incompatible pin-outs and cannot easily be substituted.

Comparators as op amps

very, very seldom are comparators used as op amps, but never say never. here is an application note that shows how to make it work. the addition of the output capacitor slows the device so that it can operate without oscillation in the linear output voltage range. the only time this might be practical is when a low performance op amp function is required, but the only device available is one section of an lm339 quad comparator. now, i have never done this, but it would make a great experiment.

LM339 as an Op Amp

Use the LP311 instead of the LM311

红包扫雷苹果下载地址while the lm311 will probably never go away, it is a power hog with a supply current of 5ma. the lp311 runs about 300ua –much better for battery and experimental applications. “lp” indicates “low power.”


For the future

applying a comparator as an op amp, an experiment

RS Flip-Flop Using OP-AMP

红包扫雷苹果下载地址this rs flip-flop is op-amp version of classic flip-flop which uses two inverting amplifier. the non-iverting input is floating, and we can assume that the voltage level of this floating pin is between vcc and ground, while the outputs will always be high or low. the high level of the output will be 1-2 volts below vcc, but this level is surely still above the level of floating non-inverting input. the low level of output will not exactly as low as the gound/zero level, but it surely below the floating non-inverting voltage level. with all of these conditions, the two inverting amplifier will lock each other into a stable state, both after reset and  set. to set the circuit,  just touch the “set” input to vcc while the “reset” input is floating. resetting the circuit is done by touching the “reset” input to vcc while the “set” input is floating. we might think what will happen if we set both input to vcc at the same time, is it dangerous© no, the circuit will just give two active output on both q and q’, and will be back to normal if we set back to floating (the state will be random or depend on which input is kept to vcc longer). here is the schematic diagram of the circuit:


R S Flip Flop