Novice electricians experience certain difficulties when working with such a common element as a choke. Therefore, it is desirable to understand in more detail what this radioelement is and what function it performs in electrical circuits.
What is choke
From a practical and constructive point of view, an inductor is a coil of copper wire of a certain section wound on a magnetic or steel core.
Additional Information: There are varieties of this element that do not have a core at all.
When an alternating current is passed through the coil or when a constant current is suddenly switched, an electromagnetic field is formed around it. It is important to note that all the energy taken at the moment of connection is spent on its formation.
According to the law of induction discovered by M. Faraday (and then theoretically confirmed by D. Maxwell) the field formed at the initial moment will counteract the increase in the current in the coil. In other words, at this moment the flow of electrons through the choke will not keep up with the voltage changes (experts say "lagging behind it in phase").
Areas of use
If you imagine the impulsive nature of the change in the voltage applied to the inductor, you can find an interesting effect. Due to the "delay" of the current, it will completely absorb (as they say - "smooth") the impulse entering the line and will work as a filtering element. This feature is widely used in line filters, which are good at eliminating impulse noise and occasional "dips" in the line voltage. Below are diagrams of its change at the output of a circuit with a choke coil when a pulse is applied to the input from a DC source (it is turned on and off).
This property makes it possible to create step-down converters with adjustable output voltage based on choke coils. In their scheme, RF pulses are formed in the input circuits, which are fed to the choke element at a certain frequency. Due to the current delay, the latter outputs a rectified (smoothed voltage) at the output, the value of which can be controlled by changing the pulse repetition rate or their duration (photo below).
Specifications
To quantify the electromagnetic properties of a choke, a special characteristic called inductance L is used. In honor of the American scientist D. Henry, who studied the properties of electromagnets, the unit for measuring inductance was named after him (denoted as "H").
The following statements are true:
- the greater this indicator, the stronger the magnetic field generated by the coil at the same current value;
- with an increase in L, the amount of energy that is required to create an electromagnetic field increases;
- the more turns in the choke winding, the higher the inductance value it has.
Note: When a magnetic core is placed in it, the inductance increases many times.
At very high L values, the choke is able to block the flow of HF current components. This property is widely used for signal filtering and circuit separation purposes.