Operational Amplifier (Op-Amp) Basics Circuit

Circuit Diagram 

Inverting Amplifier:

 The 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 noninverting 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. If RA is 1K and RB is 10K and the input is +1 volt then there will be 1 mA of current flowing through RA and the output will have to move to -10 volts to supply the same current through RB and keep the voltage at the inverting input at zero. The voltage gain in this case would be RB/RA or 10K/1K = 10. Note that since the voltage at the inverting input is always zero, the input signal will see a input impedance equal to RA, or 1K in this case. For higher input impedances, both resistor values can be increased.

Noninverting Amplifier:

 The noninverting amplifier is connected so that the input signal goes directly to the noninverting 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).

Voltage Follower:
 The voltage follower, also called a buffer, provides a high input impedance, a low output impedance, and unity gain. As the input voltage changes, the output and inverting input will change by an equal amount.
Source-  http://www.bowdenshobbycircuits.info/

06:00 0 comments

Digital Remote Thermometer Circuit Diagram

Remote sensor sends data via mains supply
Temperature range: 00.0 to 99.9 °C
Transmitter Circuit Diagram:

R1,R3________100K  1/4W Resistors
R2___________47R   1/4W Resistor
R4____________5K   1/2W Trimmer Cermet
R5___________12K   1/4W Resistor
R6___________10K   1/4W Resistor
R7____________6K8  1/4W Resistor
R8,R9_________1K   1/4W Resistors

C1___________220nF  63V Polyester Capacitor
C2____________10nF  63V Polyester Capacitor
C3_____________1µF  63V Polyester Capacitor
C4,C6__________1nF  63V Polyester Capacitors
C5_____________2n2  63V Polyester Capacitor
C7,C8_________47nF 400V Polyester Capacitors
C9__________1000µF  25V Electrolytic Capacitor

D1__________1N4148  75V 150mA Diode
D2,D3_______1N4002 100V 1A Diodes
D4____________5mm. Red LED

IC1___________LM35  Linear temperature sensor IC
IC2__________LM331  Voltage-frequency converter IC
IC3__________78L06  6V 100mA Voltage regulator IC

Q1___________BC238  25V 100mA NPN Transistor
Q2___________BD139  80V 1.5A NPN Transistor

L1___________Primary (Connected to Q2 Collector): 100 turns
             Secondary: 10 turns
             Wire diameter: O.2mm. enameled
             Plastic former with ferrite core. Outer diameter: 4mm. 

T1___________220V Primary, 12+12V Secondary 3VA Mains transformer

PL1__________Male Mains plug & cable

Receiver Circuit Diagram:

Receiver Parts:

R1__________100K   1/4W Resistor
R2____________1K   1/4W Resistor
R3,R4,R6-R8__12K   1/4W Resistors
R5___________47K   1/4W Resistor
R9-R15______470R   1/4W Resistors
R16_________680R   1/4W Resistor

C1,C2_________47nF 400V Polyester Capacitors
C3,C7__________1nF  63V Polyester Capacitors
C4____________10nF  63V Polyester Capacitor
C5,C6,C10____220nF  63V Polyester Capacitors
C8__________1000µF  25V Electrolytic Capacitor
C9___________100pF  63V Ceramic Capacitor

D1,D2,D5____1N4148  75V 150mA Diodes
D4,D4_______1N4002 100V 1A Diodes
D6-D8_______Common-cathode 7-segment LED mini-displays

IC1__________4093   Quad 2 input Schmitt NAND Gate IC
IC2__________4518   Dual BCD Up-Counter IC
IC3__________78L12  12V 100mA Voltage regulator IC
IC4__________4017   Decade Counter with 10 decoded outputs IC
IC5__________4553   Three-digit BCD Counter IC
IC6__________4511   BCD-to-7-Segment Latch/Decoder/Driver IC

Q1___________BC239C 25V 100mA NPN Transistor
Q2-Q4________BC327  45V 800mA PNP Transistors

L1___________Primary (Connected to C1 & C2): 10 turns
             Secondary: 100 turns
             Wire diameter: O.2mm. enameled
             Plastic former with ferrite core. Outer diameter: 4mm. 

T1___________220V Primary, 12+12V Secondary 3VA Mains transformer

PL1__________Male Mains plug & cable

Device purpose: 

 This circuit is intended for precision centigrade temperature measurement, with a transmitter section converting to frequency the sensor's output voltage, which is proportional to the measured temperature. The output frequency bursts are conveyed into the mains supply cables.
The receiver section counts the bursts coming from mains supply and shows the counting on three 7-segment LED displays. The least significant digit displays tenths of degree and then a 00.0 to 99.9 °C range is obtained.
Transmitter-receiver distance can reach hundred meters, provided both units are connected to the mains supply within the control of the same light-meter

Transmitter circuit operation:

 IC1 is a precision centigrade temperature sensor with a linear output of 10mV/°C driving IC2, a voltage-frequency converter. At its output pin (3), an input of 10mV is converted to 100Hz frequency pulses. Thus, for example, a temperature of 20°C is converted by IC1 to 200mV and then by IC2 to 2KHz. Q1 is the driver of the power output transistor Q2, coupled to the mains supply by L1 and C7, C8.

Receiver circuit operation: 
 The frequency pulses coming from mains supply and safely insulated by C1, C2 & L1 are amplified by Q1; diodes D1 and D2 limiting peaks at its input. Pulses are filtered by C5, squared by IC1B, divided by 10 in IC2B and sent for the final count to the clock input of IC5.
IC4 is the time-base generator: it provides reset pulses for IC1B and IC5 and enables latches and gate-time of IC5 at 1Hz frequency. It is driven by a 5Hz square wave obtained from 50Hz mains frequency picked-up from T1 secondary, squared by IC1C and divided by 10 in IC2A.
IC5 drives the displays' cathodes via Q2, Q3 & Q4 at a multiplexing rate frequency fixed by C7. It drives also the 3 displays' paralleled anodes via the BCD-to-7 segment decoder IC6.
Summing up, input pulses from mains supply at, say, 2KHz frequency, are divided by 10 and displayed as 20.0°C.

Notes:

• D6 is the Most Significant Digit and D8 is the Least Significant Digit.
• R16 is connected to the Dot anode of D7 to illuminate permanently the decimal point.
• Set the ferrite cores of both inductors for maximum output (best measured with an oscilloscope, but not critical).
• Set trimmer R4 in the transmitter to obtain a frequency of 5KHz at pin 3 of IC2 with an input of 0.5Vcc at pin 7 (a digital frequency meter is required).
• More simple setup: place a thermometer close to IC1 sensor, then set R4 to obtain the same reading of the thermometer in the receiver's display.
• Keep the sensor (IC1) well away from heating sources (e.g. Mains Transformer T1).
• Linearity is very good.
• Warning! Both circuits are connected to 230Vac mains, then some parts in the circuit boards are subjected to lethal potential! Avoid touching the circuits when plugged and enclose them in plastic boxes.

Source -  http://redcircuits.com/Page11.htm

09:21 0 comments

Voltage follower with 1G ohm input resistance

Circuit diagram 

This circuit uses an LM11 to form a voltage follower with 1G ohm input resistance built using standard resistor values. With the input disconnected, the input offset voltage is multiplied by the same factor as R2; but the added error is small because the offset voltage of the LM11 is so low. When the input is connected to a source less than 1G ohm, this error is reduced. For an ac-coupled input a second 10M resistor could be connected in series with the inverting input to virtually eliminate bias current error; bypassing it would give minimal noise.

 

Author: National Semiconductor
Source http://www.electronics-lab.com/

10:13 0 comments

10,000x With One Transistor

Description 

For a collector follower with emitter resistor, you’ll often find that the gain per stage is no more than 10 to 50 times. The gain increases when the emitter resistor is omitted. Unfortunately, the distortion also increases. With a ubiquitous transistor such as the BC547B, the gain of the transistor is roughly equal to 40 times the collector current (Ic), provided the collector current is less than a few milliamps. This value is in theory equal to the expression q/KT, where q is the charge of the electron, K is Boltzmann’s constant and T is the temperature in Kelvin.

For simplicity, and assuming room temperature, we round this value to 40. For a single stage amplifier circuit with grounded emitter it holds that the gain Uout /Uin (for AC voltage) is in theory equal to SRc. As we observed before, the slope S is about 40Ic. From this follows that the gain is approximately equal to 40I cRc. What does this mean? In the first instance this leads to a very practical rule of thumb: that gain of a grounded emitter circuit amounts to 40·I c·Rc, which is equal to 40 times the voltage across the collector resistor.

If Ub is, for example, equal to 12 V and the collector is set to 5V, then we know, irrespective of the values of the resistors that the gain will be about 40R(12–5) = 280. Notable is the fact that in this way the gain can be very high in theory, by selecting a high power supply voltage. Such a voltage could be obtained from an isolating transformer from the mains. An isolating transformer can be made by connecting the secondaries of two transformers together, which results in a galvanically isolated mains voltage.

Circuit diagram: 

That means, that with a mains voltage of 240 Veff there will be about 340 V DC after rectification and filtering. If in the amplifier circuit the power supply voltage is now 340 V and the collector voltage is 2 V, then the gain is in theory equal to 40 x (340–2). This is more than 13,500 times! However, there are a few drawbacks in practice. This is related to the output characteristic of the transistor. In practice, it turns out that the transistor does actually have an output resistor between collector and emitter.

This output resistance exists as a transistor parameter and is called ‘hoe’. In normal designs this parameter is of no consequence because it has no noticeable effect if the collector resistor is not large. When powering the amplifier from 340 V and setting the collector current to 1 mA, the collector resistor will have a value of 338 k. Whether the ‘hoe’-parameter has any influence depends in the type of transistor. We also note that with such high gains, the base-collector capacitance in particular will start to play a role.

As a consequence the input frequency may not be too high. For a higher bandwidth we will have to use a transistor with small Cbc, such as a BF494 or perhaps even an SHF transistor such as a BFR91A. We will have to adjust the value of the base resistor to the new hfe. The author has carried out measurements with a BC547B at a power supply voltage of 30 V. A value of 2 V was chosen for the collector voltage. Measurements confirm the rule of thumb. The gain was more than 1,000 times and the effects of ‘hoe’ and the base-collector capacitance were not noticeable because of the now much smaller collector resistor.

Author: Gert Baars, Elektor Electronics
Source http://www.extremecircuits.net/2010/05/10000x-with-one-transistor.html

09:50 0 comments