An AC Power Amplifier (amp) is an electronic device that increases the power of a signal. They adjust the output of a power supply by increasing the signal amplitude. Power can be calculated using the voltage (V, volts) and current (I, amperes):


The amplitude of the signal can be increased in terms of voltage, current, or both. There are four basic types of amplifiers: voltage, current, transconductance (voltage to current) and transresistance (current to voltage). Amplifiers can also be described as linear or nonlinear.

Classes of Power Amplifiers

The four basic types of AC power amplifiers previously described can be categorized further by class. Power amplifier circuits are classified as A, B, AB, C, D and E based on the proportion of the input cycle, or period of the AC waveform, that the circuit is passing current. The proportion can also be described as a conduction angle, which is derived from a sinusoidal input signal. If the circuit is always conducting, its conducting angle is 360°. Similarly, if the circuit is only conducting during half of the period, its conducting angle is 180°. Class A amps conduct the entire p, with a conducting angle of 360°. Class B amps conduct for half of a cycle. Class AB amps conduct for more than half the cycle, but not the full cycle. Class C amps conduct for less than half a cycle.  Class D amplifiers are described as “digital amplifiers” because they use pulse-width modulation to control its output and the circuit is either fully on or fully off. Class G and H amps have varying supply voltages following the input signal to minimize wasted power due to heating of the circuit components.  Class E and F amps are commonly used for radio-frequency (3K Hz – 300G Hz) applications and they are a subset of class C amps based on conduction angle characteristics. A common amplifier circuit is the push-pull circuit that uses a pair of active devices to alternatively supply or draw current to and from a load.

Applications of Power Amplifiers

The most common applications for power amplifiers are audio and radio frequency (RF) applications. Audio power amplifiers amplify low power audio signals to drive loudspeakers. An example of a RF amplifier application is amplifying a transmission signal to drive a transmission antenna. Common industrial and scientific applications include plasma excitation, induction heating, EMC and EMI testing, magnetic field generation and testing of various products including Helmholtz coils, Piezo elements, inductors, capacitors, Ferrite cores etc.

Amp-Line Corp.

Amp-Line Corp. manufactures linear class AB push pull power amplifiers for the industrial and scientific applications listed above. Amp-Line’s HF-A series power amplifiers operate in the entire audio frequency range (20 Hz – 20K Hz) as well as part of the ultrasonic and radio frequency ranges (up to 800K Hz). Typical output power rating ranges from 50 watts to 1400 watts and output voltage can be increased with output transformers. Amp-Line’s power amplifiers are perfect for a wide range of industrial and scientific applications.