Magnetic Amplifier


Magnetic Amplifier being an electromagnetic device is used in the amplification of electrical signals. The amplifier can be used as a better alternative to the vacuum tube amplifiers and transistor based amplifiers. The application of the amplifier is in the field of power control, nuclear applications and low frequency signal.

Principle of Operation

In visual, the magnetic amplifier resembles a transformer. But its principle is different. The basic project principle is that it makes use of the magnetic saturation of the core. Generally, a magnetic amplifier consists of two magnetic cores with the windings: Control Winding and AC winding. Here the AC winding is being connected in parallel or in series. A DC current is being given from a low impedance source, which is then given to the series winding or control winding. This small current will switch large currents on to the AC windings. Two magnetic cores are used because AC current will cause high voltage in to the control winding. By connecting them in an opposite phase, it cancels out each other, so that no current is being induced.


  • This amplifier is a static device with no moving parts.
  • It has no wear-out mechanism.
  • Higher tolerance to overloads than solid-state devices.
  • Magnetic Amplifiers has a good tolerance to mechanical shock and vibrations.
  • Multiple isolated signals is summed by control windings on the magnetic cores.
  • They do not require warm-up time.


  • Gain is low and minimum.
  • Frequency response is limited.
  • From single stage, gain available is less.
  • The gain available from a single stage is limited.


  • Used as voice modulator.
  • Used in the radio communication applications for high frequency alternators.
  • It helps to control the speed of high power alternators for telegraphy applications.
  • Control light circuits in order to control large currents.
  • Used in arc welders.
  • It helps in tuning radio indicators, controlling speed of fan and motors and further the control of battery charger.
  • Used as switch element in SMPS.
  • It helps in measuring of high DC-voltages.
  • Instrumentation based magnetic amplifiers are used in space crafts.
  • It is also used in computing applications.
  • Electric power generation purposes also make use of magnetic amplifiers.

Types of Magnetic Amplifiers

Full Wave Magnetic Amplifier Circuit

It uses both cycles of AC supply, so it is called as Full wave magnetic amplifier circuit. The wound of the output winding will cause the flux direction created by the center leg to be in the same direction of the control winding flux.

Even if no control voltage is given, flux will be present in the core. Due to which impedance of output winding will never reach maximum value and current through the load will never attain the minimum value.

Half wave Magnetic Amplifier Circuit

At first, a DC supply is given to the winding. Due to which a magnetic flux will be generated in the core. As the flux increases, impedance of the output winding will decrease. As a result, the current will be flowing through the winding. Since, current will flow through AC supply through winding, load will increase.

Since, it uses half cycle of AC supply; this magnetic amplifier is called as half wave circuit. When the current through the winding is zero, the impedance of the winding will be high. Due to this, no current will flow through the load.

Diode connection is given to the output winding so that it acts as a rectifier circuit. The direction and cancelation of the current through secondary is varied so that two flux gets reinforce each other produced by the output and control windings.