Understanding Impedance Transformers

Understanding Impedance Transformers

Impedance Transformers Defined

An Impedance Transformer is a special type of Transformer used to match impedance. The main difference between an Impedance Transformer and a typical power transformer is that with an impedance transformer the frequency response, primary/secondary impedance plus power capabilities are all taken into account and typically have a wide frequency response.

A typical transformer has a primary winding and a secondary winding. When an AC voltage is applied to the primary winding, the secondary winding will output an AC voltage but with a different amplitude depending on the ratio of the windings in the primary and secondary coils, which is known as the turns ratio.

Below in Figure 1, is a diagram of the relationship between the input voltage and current to the output voltage and current. Where “Vp” is the primary voltage, “Vs” is the secondary voltage, “Ip” is the primary current and “Is” is the secondary current. The ratio Np:Ns is the Turns Ratio, which is the number of windings in the primary over the number of the windings in the secondary. The relationship between the impedance and the turns ratio is shown in Figure 2, which shows us that the ratio of the primary impedance over the secondary impedance is equal to the square of the Turns Ratio.

 

 

 

 

Impedance transformers are used to match the load impedance to a source, which allows the maximum amount of power to be transferred to the load which can be explained by Jacobi’s law which states that “Maximum power is transferred when the internal resistance of the source equals the resistance of the load, when the external resistance can be varied, and the internal resistance is constant”.

Impedance Transformer Applications

Impedance transformers can be used in Audio applications, RF antenna’s and practically anywhere the load impedance needs to be matched to the source.

Constant Voltage Audio System

In a high voltage/low current system, the high voltage is provided by a step up transformer, which lowers power loss along the long lengths of cable. Each speaker has its own impedance transformer which matches the impedance of the high voltage line to the impedance of the speaker.

Another benefit of this is that designing a large scale audio system becomes much simpler as you do not need to wire the speakers in parallel or series to match the impedance of the amplifier.

Microphone Impedance Matching

Matching high impedance tube amplifiers to normal microphone output impedance or Matching low impedance low voltage ribbon microphones to normal output impedance.

Impedance Matching RF Antennas

With RF Antenna’s, impedance transformers are used to match an unbalanced impedance with a balanced impedance. They are commonly known as balun transformers.

Impedance Transformers offer a wider frequency response and a known primary/secondary impedance compared to a typical power transformer allowing impedance transformers to obtain high levels of signal integrity while maximizing power transfer.  They are not just limited to RF and Audio applications and can be utilized whenever there is a need to match the source impedance to the load impedance.


Resources
  • Basic Power Transformers, bristolwatch.com
  • Audio Transformer, electronics-tutorials.ws
  • Advantage of Direct, crownaudio.com
  • Special Transformers and Applications, allaboutcircuits.com

Impedance Transformers Defined

An Impedance Transformer is a special type of Transformer used to match impedance. The main difference between an Impedance Transformer and a typical power transformer is that with an impedance transformer the frequency response, primary/secondary impedance plus power capabilities are all taken into account and typically have a wide frequency response.

A typical transformer has a primary winding and a secondary winding. When an AC voltage is applied to the primary winding, the secondary winding will output an AC voltage but with a different amplitude depending on the ratio of the windings in the primary and secondary coils, which is known as the turns ratio.

Below in Figure 1, is a diagram of the relationship between the input voltage and current to the output voltage and current. Where “Vp” is the primary voltage, “Vs” is the secondary voltage, “Ip” is the primary current and “Is” is the secondary current. The ratio Np:Ns is the Turns Ratio, which is the number of windings in the primary over the number of the windings in the secondary. The relationship between the impedance and the turns ratio is shown in Figure 2, which shows us that the ratio of the primary impedance over the secondary impedance is equal to the square of the Turns Ratio.

 

 

 

 

Impedance transformers are used to match the load impedance to a source, which allows the maximum amount of power to be transferred to the load which can be explained by Jacobi’s law which states that “Maximum power is transferred when the internal resistance of the source equals the resistance of the load, when the external resistance can be varied, and the internal resistance is constant”.

Impedance Transformer Applications

Impedance transformers can be used in Audio applications, RF antenna’s and practically anywhere the load impedance needs to be matched to the source.

Constant Voltage Audio System

In a high voltage/low current system, the high voltage is provided by a step up transformer, which lowers power loss along the long lengths of cable. Each speaker has its own impedance transformer which matches the impedance of the high voltage line to the impedance of the speaker.

Another benefit of this is that designing a large scale audio system becomes much simpler as you do not need to wire the speakers in parallel or series to match the impedance of the amplifier.

Microphone Impedance Matching

Matching high impedance tube amplifiers to normal microphone output impedance or Matching low impedance low voltage ribbon microphones to normal output impedance.

Impedance Matching RF Antennas

With RF Antenna’s, impedance transformers are used to match an unbalanced impedance with a balanced impedance. They are commonly known as balun transformers.

Impedance Transformers offer a wider frequency response and a known primary/secondary impedance compared to a typical power transformer allowing impedance transformers to obtain high levels of signal integrity while maximizing power transfer.  They are not just limited to RF and Audio applications and can be utilized whenever there is a need to match the source impedance to the load impedance.


Resources
  • Basic Power Transformers, bristolwatch.com
  • Audio Transformer, electronics-tutorials.ws
  • Advantage of Direct, crownaudio.com
  • Special Transformers and Applications, allaboutcircuits.com