Friday, April 11, 2014

Three Opamp Differential Instrumentation

This is the best Instrumentation OpAmp, Great CMRR, ensure supply has no ripple and keep analog and digital grounds separate. Ri can be replaced with a trimpot and resistor to alter gain. Connect a preset ends to pins 1 and 8 and preset wiper to VCC for Offset Null when high gains are configured.

Thermocouple and Pt-100 RTD

The Input zeners and diodes form a protective clamp for all voltages above VCC-VDD. If supply is changed to +12 -12 change zeners to 12V zeners. Use similar Zeners at output to protect Output from being zapped by overvoltages or high energy - voltage*frequency transients. Add plastic capacitors across Rf for damping AC operation or ripple. Also avoid floating inputs by providing a bias.

3 Op-Amp Differential Instrumentation Amp

Vout = (Vp - Vn) * (2Rf+Ri)/Ri

Related Reading

Wednesday, April 09, 2014

Buffer or Unity Gain Op-Amp

If output impedance of a point is a high value then connecting another circuit at that point will load it resulting in malfunction or error. Buffers are used as interface between circuits. Low impedance of an output means it can source sink lot of current, when you need 2 opamps use LF353 or TL072 which are dual opamps.

Buffer or Unity Gain Op-Amp

Vout = -(Vin) for inverting

Vout = Vin for non-inverting

A non-inv FET input is the best buffer, for inverting buffer use high R values Using very high R values like 2.2M or higher requires a glass epoxy PCB and guard rings around pin 2, 3 to prevent leakage currents on the PCB reaching the PINs. Also moisture and dust has to be prevented by using RTV coating or Varnish. Use 78L05 79L05 for the dual supply required by this circuit.

    Friday, April 04, 2014

    Differential Amplifier - Op-Amp Circuits

    This amplifies the difference between two inputs Vp and Vn the low impedance of this configuration is a drawback, but can be used in analog computing. Optimum VCC VDD can be +12/-12. AC signals common to Vp and Vn are canceled by this configuration.

    Use a capacitor like 10nF plastic from pin 2 to 3 or across R2 to make circuit stable. For AC applications use LF351 TLO71 as they have good slew rate and also are FET inputs. For AC applications use a capacitor (1uF) in series with Ri to block DC Components. The Inputs have asymmetrical input impedance this affects CMRR, also use 1% tolerance MFR resistors for Rf and Ri.

    Differential Amplifier - Op-Amp Circuits

    Vout = (Vp - Vn) * (Rf/Ri)

    Related Reading

    Circuits by Application

    Analog Circuits

    1. Battery Level Indicator
    2. Simple Sample and Hold
    3. Sample and Hold Standby
    4. Voltmeter Attenuator
    5. Precision Current Source
    6. Opamp Supply Virtual Ground

    SCR and Triac

    1. Solid State Relay
    2. Normally Closed AC SSR
    3. AC-AC-SSR
    4. DC-DC SSR
    5. 2N2646 based Pulser
    6. Drive SCR thyristor

    Mains Power

    1. Flashing Neon Lamp
    2. Dimmer power control
    3. Edison Bulb Life Extend
    4. Mains Current LED
    5. Mains Voltage LED

    Digital Circuits

    1. Simple Digital Counter
    2. Running Lights
    3. Frequency Divider
    4. Crystal Oscillator
    5. Simple High speed switch
    6. Differential TTL converter

    Measureall DMM

    1. Ohmmeter Measure Resistance
    2. Precision Digital Attenuator
    3. Precision Amplifier

    Mixed Circuits

    1. Monostable Multivibrator
    2. Digital to Analog
    3. LM311 Oscillator
    4. PLL using 4046
    5. VCO with LM331
    6. BCD Thumbwheel to Analog
    7. V to F Converter ICL8038
    555 Circuits
    1. OR gate with two 555
    2. fixed frequency duty cycle
    3. Pulse width modulation
    4. Astable Multivibrator
    5. uC Reset Generator
    6. LM555 Voltage Doubler
    7. 555 Power Oscillator
    Discrete Circuits
    1. Isolated dual supply
    2. Sound to light converter
    3. Water operated relay
    4. Telephone Indicator
    5. Passive volume control
    6. RS232 Opto-Isolation
    7. Voltage Level Indicator
    8. Relay Driver
    9. Constant Current LED
    10. Voltage Doubler
    11. FET Current Source
    Opamp Circuits
    1. Three Opamp Differential
    2. Two Opamp Differential
    3. Buffer Opamps
    4. Differential Op-Amp
    5. Inverting Opamp
    6. Non Inverting Opamp
    7. Digital gain control
    8. Square Triangle Oscillator
    9. Dual Polarity Output Amps
    10. Ammeter Precision Rectifier
    11. Voltage / Current 4-20 mA
    12. Current Source for RTD
    Power Electronics
    1. Dual Power Supply
    2. Single Power Supply
    3. Battery Backup Supply
    4. 5V 1A Supply LM2575
    5. 5V Power Supply L296
    6. Dual Power Supply
    7. Tubelight Electronic Choke
    8. Voltage Doublers Multipliers
    9. White LED Lamp on Ni-Cd

    uC and uP

    1. PC RS232 with MAX232A
    2. Battery Backup SRAM
    3. watchdog uC uP systems
    Instrumentation Circuits
    1. Mains monitor LM3914
    2. Simple Mains monitor
    3. single digit voltmeter
    4. High Resistance Meter
    5. Diode Thermometer
    6. Function Generator
    7. Diode Leakage Tester
    8. Analog LED Ohm Meter
    9. Millivolt Source Current Loop
    Process Control
    1. AD590 - temperature
    2. Thermocouple Amplifier
    3. Linearizing Thermocouple
    4. Thermocouple Amplifier
    5. 0-1V to 4-20 mA
    6. 1-5V to 4-20 mA
    7. InfraRed - Optical Switch
    8. InfraRed Detector

    Hobby DIY Electronics