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Ampere-Turn Amplification (Gain) in Magnetic Amplifiers

Ampere-turn amplification refers to the concept used in magnetic amplifiers, where the ratio of the ampere-turns produced by the load to the ampere-turns applied to the control winding is defined. This ratio is often referred to as the amplification or gain of the magnetic amplifier.

Key Concepts

Magnetic Amplifier

A magnetic amplifier is an electromagnetic device used to control high power with a small control signal. It operates on the principle of magnetic saturation and typically consists of a core, control winding, and load winding.


  • Control Ampere-Turns \((N_c I_c)\): The product of the number of turns in the control winding and the current flowing through it.
  • Load Ampere-Turns \((N_l I_l)\): The product of the number of turns in the load winding and the current flowing through it.

Amplification (Gain)


The ampere-turn amplification (or gain) is defined as the ratio of the load ampere-turns to the control ampere-turns:
\text{Gain} = \frac{N_l I_l}{N_c I_c}


  • \(N_l\) is the number of turns in the load winding.
  • \(I_l\) is the current through the load winding.
  • \(N_c\) is the number of turns in the control winding.
  • \(I_c\) is the current through the control winding.


  • Amplification Factor: The gain indicates how effectively the magnetic amplifier can amplify the control signal. A higher gain means that a small control current can control a much larger load current.
  • Efficiency: Magnetic amplifiers with higher gains are more efficient in controlling power, as they require less control current to achieve the desired load current.

Practical Application

  1. Control and Load Windings: In a magnetic amplifier, the core is wound with both control and load windings. The control winding carries the control current, while the load winding carries the load current.
  2. Core Saturation: The control current modulates the magnetic flux in the core, influencing the saturation level and, consequently, the impedance of the load winding.
  3. Current Control: By adjusting the control current, the magnetic amplifier can regulate the load current, achieving amplification.


Consider a magnetic amplifier with the following parameters:

  • Control winding: \(N_c = 50\) turns, \(I_c = 1 \text{ A}\)
  • Load winding: \(N_l = 200\) turns, \(I_l = 4 \text{ A}\)

The ampere-turns for the control and load windings are:

  • Control ampere-turns: \(N_c I_c = 50 \times 1 = 50 \text{ At}\)
  • Load ampere-turns: \(N_l I_l = 200 \times 4 = 800 \text{ At}\)

The gain is:
\text{Gain} = \frac{800 \text{ At}}{50 \text{ At}} = 16

This means that the load current is amplified 16 times compared to the control current, demonstrating the amplification capability of the magnetic amplifier.

Ampere-turn amplification (gain) is a crucial concept in magnetic amplifiers, representing the ratio of load ampere-turns to control ampere-turns. It highlights the efficiency of magnetic amplifiers in controlling large currents with small control signals. Understanding this ratio is essential for designing and optimizing magnetic amplifiers for various applications, including power regulation and signal processing.

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