In the Article Linear Follower Amplifier we are going to discuss about current amplifier, its parameter, applications and comment. Current amplifiers are basically Class A Amplifier which usually have a voltage gain of 1 and effectively act as impedance transformers. Their main feature is their ability to develop a substantial output current. Sometimes they are called “linear followers,” similar to emitter follower transistor circuits. Current amplifiers are often used in series with an operational amplifier, inside the feedback loop, to provide additional output current.
Key parameters of linear follower amplifier
- Output current: Determines the application and useful range.
- Slew rate: Particularly important for servo systems and other motor-driving applications. Slew rates range up to hundreds of volts per microsecond.
- Bandwidth: Conventional frequency range.
- Full power bandwidth: The frequency ban over which the maximum output current is available.
- Output resistance: Usually below 50 ohms.
- Input resistance: Usually in the megaohm range.
Figure 1: Linear Follower Amplifier
Applications of Linear Follower Amplifier
Current amplifiers are used to drive coaxial cables, servo motor systems, precision data recorders, and set-up high-voltage transformers, and they are also useful as audio output amplifiers and in the regulator circuits of power supplies.
Representative Part Number: National Semiconductor LH0002.
Comments
Some manufacturer’s literature list current amplifiers as linear followers, and a wide range of slew rate, output current, and bandwidth is readily available.
Figure 2: High Output Current Amplifier
Description: This device is basically the same as a general-purpose op-amp, but its requirement for high-output current sometimes results in a special construction for more effective heat dissipation. Most op amps of the high-output-current type also have short-circuit protection at the output and feature wide bandwidth.
Key Parameters of High Output Current Amplifier
Essentially the same as for general purpose op amps except for the following
- Rated output current: From 100mA at
10 volts up to 2A at 30 volts.
- Bandwidth: Stated as the highest frequency for rated output current, with a typical value of 100 mA at 8 MHz.
- Slew rate: Ranges from 3 to 1,000 V/us depending on the type of unit and the total output current capability.
Applications
The combination of substantial output current and relatively high frequency response makes this type of op amp ideal for digital to analog current convertes, analog to digital input amplifiers, video pulse amplifiers, coaxial cable drivers, and CRT deflection amplifiers. When the frequency response is not as high, the op amp can be used successfully for audio output stage and servo motor drivers.
Representative Part Number: Analog Device AD380.