What is the difference between a high-frequency transformer and a low-frequency transformer?

Generally, a low-frequency transformer refers to a “mains frequency transformer”, which operates at (50Hz) and is used to change voltage. The iron core used in low-frequency transformers is typically made of high-permeability silicon steel sheets.

A high-frequency transformer refers to a transformer that operates at high frequencies and serves as a transducer. Due to the high frequency of the magnetic field, eddy currents are generated in silicon steel sheets (the small magnets within the sheets cannot switch fast enough), so high-frequency transformers generally use “high-frequency ferrite” as the magnetic core.

The difference between high-frequency transformers and low-frequency transformers lies in their operating frequencies, which leads to some differences in material selection. Both high-frequency and low-frequency transformers operate on the same principle: energy is transmitted through electromagnetic induction, regardless of the operating frequency.

Due to the different frequencies of high-frequency and low-frequency components, high-frequency components can only be used in circuits with high frequencies and where the excitation source frequency matches the transformer frequency. Conversely, low-frequency components cannot be used in such circuits. They cannot be mixed, and even high-frequency components cannot be used if their frequency does not match.

If a transformer transmits a certain amount of energy at a high operating frequency, and the number of energy transmissions within a certain period of time is high, the energy transmitted per transmission can be small, resulting in less material used for the transformer and a smaller structural size. Therefore, general high-frequency transformers have fewer coil turns and can be made very small in size, while low-frequency transformers have more coil turns.

For two transformers with the same power, the high-frequency transformer will be much smaller than the low-frequency transformer. In this case, the high-frequency transformer will only be about one-tenth the size of the low-frequency transformer. This is because the low-frequency transformer needs to be protected to reduce the u value, and it is made of silicon steel sheets, but the efficiency decreases, so a large volume of heat dissipation is required.

Why do power amplifiers use toroidal transformers?

Nowadays, many electronic enthusiasts opt for toroidal transformers when selecting audio power amplifier transformers. The use of toroidal transformers in audio power amplifiers is dictated by the characteristics of audio power amplification.

Unlike other devices, audio power amplifiers not only consume electricity rapidly but also exhibit significant variations in power consumption. This necessitates that transformers possess strong instantaneous overload capacity and rapid response speed, otherwise noise, lack of sound fullness, poor sound quality, and other issues may easily arise.

Due to its large capacity within the same volume, the toroidal transformer exhibits almost zero delay response in direct coupling, which meets the characteristics of audio power supply.

Advantages of using toroidal transformers in audio power amplifiers:

1. The electric high-speed railway core has no air gap and a high stacking factor.

2. With small external dimensions and light weight, the toroidal transformer can be half as heavy as the laminated transformer.

3. With minimal magnetic interference, the toroidal transformer core lacks an air gap, and the windings are evenly wound around the toroidal core. This structure results in minimal magnetic flux leakage and electromagnetic radiation.

4. The vibration noise is relatively low, and the absence of air gaps in the iron core reduces the noise induced by the iron core’s vibration. The winding is evenly and tightly wrapped around the toroidal iron core, effectively reducing the “buzzing” sound caused by magnetostriction.

5. Low operating temperature: Due to the small iron loss and low temperature rise of the iron core, the winding has good heat dissipation on the cooler iron core, resulting in a low temperature rise of the transformer.

6. Easy to install, the toroidal transformer only has one mounting screw at the center, making it particularly easy for quick installation and removal in electronic devices.

What is the use of an isolation transformer?

Definition of isolation transformer:

Transformers with two or more independently separated coils can all be called isolation transformers, because the primary and secondary are completely separated (isolated) and energy is transferred through the magnetic field.

To understand why an isolation transformer is used, we first need to know about China’s power supply system. When supplying power to low-voltage users, China’s power supply system generally adopts a three-phase four-wire system with the neutral line grounded. In layman’s terms, the wires that reach residents’ homes consist of one phase line (live wire) and another neutral line, which is connected to the ground. When a person touches a hot floor, it causes current to flow through the human body, forming a circuit with the ground, resulting in electric shock hazards.

If an isolation transformer is used, it will be safer because the primary and secondary sides exchange energy through a magnetic field without any physical hard connection. Even if a person touches a live object, the potential of the live part will be low due to the equal potential of the human body and the earth, thus avoiding electric shock hazards.

When using an isolation transformer, there are two points to note. Firstly, neither end of the secondary side of the transformer should be grounded. Secondly, the human body should not touch both ends of the secondary side simultaneously, otherwise there is still a risk of electric shock.

Description of isolation characteristics:

Assuming that transformer T1 in the circuit is a 1:1 transformer, that is, when it is fed with an input voltage of 220V AC, its output voltage will also be 220V. However, it should be noted that the 220V voltage output by the transformer refers to the voltage between the two ends of the secondary winding, specifically, the voltage between terminals 3 and 4.

The voltage between any terminal of the secondary winding (such as terminal 3) and the ground terminal is 0V. This is because the output voltage of the secondary winding does not use the ground as a reference terminal, but rather uses the other terminal of the secondary winding as the reference point. At the same time, there is high insulation between the primary and secondary windings.

In this way, when a person stands on the ground and only touches any one end of the secondary winding of transformer T1, there is no danger to life (it is absolutely forbidden to touch terminals 3 and 4 of the secondary winding simultaneously). However, if one touches the phase line terminal of the primary winding, they will get an electric shock. This is the isolation function of the transformer.

Isolation function of power transformer:

In many electronic appliances, AC 220V is used as the power source. To ensure the personal safety of users during equipment operation, it is necessary to isolate the 220V AC power supply, and a power transformer is used for this purpose.

Meanwhile, the power transformer reduces the 220V AC voltage to a suitable voltage, as shown in Figure 4 below. T1 in the circuit is a power transformer that serves both as a voltage regulator and an isolator.

In fault maintenance, it is often necessary to touch components or ground wires in the circuit when it is powered on. The addition of a power transformer can prevent the risk of electric shock.

Characteristics of isolation transformers at the AC power input end:

2. If the third harmonic and interference signals in the power grid are severe, employing an isolation transformer can eliminate the third harmonic and reduce the interference signals.

3. The use of an isolation transformer can generate a new neutral line, preventing equipment malfunctions caused by poor neutral lines in the power grid.

4. The current waveform distortion caused by nonlinear loads (such as third-order harmonics) can be isolated without polluting the power grid.

Characteristics of isolation transformers at the AC power output end:

Preventing current distortion from nonlinear loads from affecting the normal operation of AC power supplies and polluting the power grid, thereby playing a role in purifying the grid.

Sampling at the input terminal of the isolation transformer ensures that the distortion of nonlinear load current does not affect the accuracy of sampling, thereby obtaining a control signal that reflects the actual situation.

If the load is unbalanced, it will not affect the normal operation of the regulated power supply.

Eliminate high-frequency transient interference using a DC/DC converter.