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Download Voltage Follower Schematic
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VOLTAGE FOLLOWER The OP-AMP can be used as a VOLTAGE FOLLOWER. The output voltage follows the input. In this arrangement the OPerational AMPlifier is called a BUFFER and has unity gain. www.ustudy.in www.ustudy.in Definition 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. Vout = Vin www.ustudy.in Voltage Follower Schematic www.ustudy.in Cont.., This schematic shows an op-amp (the AD8515 from Analog Devices) wired up as a Voltage Follower. The Sensor is essentially a potentiometer with the outer leads connected to power and ground and the inner tap running into the positive input of the op-amp. You could easily substitute a voltage divider or many other sensors here. The op-amp’s output from pin 1 is connected directly back into the negative input to set it to voltage follower mode, as well as heading out to the Teabox through the center pin on J1 (either a cable or a three pin header). www.ustudy.in Cont.., Notice that pins 5 and 2 of the op-amp (somewhat disembodied at the far left of the circuit) are connected to power and ground and are bypassed with the 0.1µF Cap. This is very important as it smooths out fluctuations in the power supply. One final note is that the 5V and Ground indicators are not necessarily from a second power source. www.ustudy.in Cont.., Most likely this entire circuit will get its power from Pin 1 on J1 (the cable or header), and ground from Pin 3, which means you can ignore the 5V/Gnd connections. If you do need to power the device externally (for instance if you are using a few sensors that need a lot of power (like the Sharp IR sensors), you must be careful to have a very clean power supply. www.ustudy.in Cont.., The way sensor analog to digital convertors work is that they compare the sensor input to a reference voltage. If the power supply is fluctuating, it can’t compare accurately and you will end up with noisy data. We have a Power Injector and Powered Expander that can be used to add 500mA of power to an interface, although you can make one on your own using a wall wart and a decent voltage regulator: something like the LT1763 from Linear Technology. www.ustudy.in Voltage Follower Example Here a zener diode is providing a reference voltage such as 9 volts. The current available from this reference voltage circuit is minimal. The voltage follower outputs the same reference voltage but with enough current to supply the motor. If the motor load increases, the voltage follower maintains the same output voltage but allows more current to flow in the motor. Stabilised power supplies use this principle. www.ustudy.in Cont.., The zener diode needs to have at least 5mA breakdown flowing through it. This ensures that the zener voltage will be correctly established. www.ustudy.in