A transformer is a device that has no moving parts, which converts an alternating voltage given another AC voltage, increasing or decreasing its value, without changing the frequency. Unlike the auto-transformer , a transformer has a galvanic isolation between the input (primary) and output (secondary), ie no driver only electrically connects the two parts.
It is equipped with one or more windings (winding) primary and one or more secondary windings. The operating principle is based on the energy transfer by mutual inductance (electromagnetic induction): AC primary winding path which creates a magnetic field that is "captured" by the secondary winding which then transforms back into power. The transformation ratio is influenced by the number of turns of the primary winding with respect to the number of turns of the secondary winding. For example, if the secondary winding has 50 turns as the primary winding has 500, the transformation ratio will be about 10. By applying a voltage of 240V primary, secondary issue a voltage of about 24V. In practice, the energy transfer can not be total, a certain amount is lost. The transformer has a characteristic indicating this property, it is the coupling coefficient, which can be optimized by choosing materials and forms that go. Sometimes, elementary and secondary, there may be only one winding, but with one or several taps. It is important to remember that the transformer by its nature, can not transmit DC voltage and is limited to the transfer of AC voltages, including the range of amplitude and frequency depend on its type. There are several kinds of processors dedicated to various areas: audio sector, high voltage, HF, etc..
This type of transformer is commonly used in the production of power sector alone, mostly in amateur. Industrial side, this type of component is more often replaced by switching control systems, providing equal power, less heat, a smaller footprint, and often a range of input voltages greater.
Note: Sometimes, a transformer is used only for issues of isolation, the output voltage being equal to the input voltage.
The secondary of a power transformer can output a voltage higher than that specified. In general, the specified voltage (sold) that is obtained when the maximum demand to the transformer, ie that the secondary current is the maximum value for which it is sold. This involves mostly higher voltage when requesting less than the max. The maximum voltage is obtained vacuum is, when the secondary is connected to anything, and can reach a value of 10% to 30% greater than the nominal value. The difference between load voltage and load voltage is more important than the power transformer is low. Although this use is rare in practice (...), do not overlook this point. For this feature to be taken into consideration if you surdimmensionnez your transformer (fear of lack, or simple recovery).
It is customary to speak Watt power, but for the transformer, the unit adopted is the VA (Volt-Ampere), due to its use with AC and charges are not necessarily only resistive (when load is purely resistive, the VA is equivalent to W). The transformer has losses, more or less important depending on its type. Never choose a power transformer too limited, it too hot. If you need 24W (12V / 2A for example), choose a model of at least 30VA.
Association of secondary
When a transformer has two secondary identical, it is possible to combine to increase the voltage (series connection) or to increase the current (parallel). It should however be very careful with wiring, sense windings must be respected to allow such an association. For more information you can visit the Cables transformers , which gives some advice on cabling possible.
Types of transformers
There are several types of power transformers, transformers regular (rectangular as pictured above), caliper or solder directly onto a printed circuit board, toroidal transformers, transformers type "R". Both have the advantage of producing magnetic leakage (radiation) lower, which makes them particularly suitable for use in low level audio.
Examples of transformers PCB mount
Examples of processors caliper
Examples of toroidal transformers
Examples of type transformers "R"
Attention! Do not reverse the primary and secondary of a power transformer, the transformer may burn or explode!
3 phase transformer <=> 2 phases
It is a bit peculiar transformer specially designed for use with three-phase primary and secondary phases with two or vice versa. There are two types of cabling windings to ensure this function: "Connection Leblanc" and "Connection Scott."
Transformer for video
This type of transformer is able to pass all frequencies used for a video signal, ie several MHz.
The transformer shown on the picture above shows a bandwidth of 20 Hz to 11 MHz at -3 dB, while having an insertion loss of only 0.5 dB for a 75-ohm source and a load of 75 ohms .
Could perfectly classify this type of transformer audio transformers, since its role is to isolate equipment (telephone, answering machine) to an analog line public network phone, allowing only the transfer of voice. The main difference with the "real" audio transformers is the quality of the transmission bandwidth of such a component is in fact very limited (300Hz to about 4KHz) with a very poor linearity (+ /-3dB over said range frequency). Of course, these characteristics a little more than enough to limit the audio telephone. This type of transformer has an impedance of 600 ohms for both the primary and for the secondary (about 60 ohms continuous).
Transformer for strobe
This type of transformer, which has a high transformation ratio, is designed to produce pulses of high voltage (several thousand volts) for triggering a flash tube (tube supplied with DC voltage xenon under some about 300V) electrode via the boot. Its dimensions are reduced because little power is required (continuous). Some retailers sell electronic components flash tubes with their specific transformer, avoiding to look elsewhere which is well suited to the tube.
This type of transformer is mainly used in electronic circuits emission opening hours or HF: TV transmitters, radio transmitters, CB, son without some intercoms, radios, etc.. The photo above shows some examples of transformers used in RF circuits radio receivers legacy. There HF transformers whose size is very different from them, because exceeding a height of 2 meters (using short wave transmitters in high power for example). In the same vein, there are transformer IF (Intermediate Frequency) used eg in stages of change in frequency of the sending or receiving. The Theremax (one of many versions of Theremins) operates as such transformers for oscillators "OFF" (see Theremin 002 ).
Used in cars (to produce sparks candles that trigger the explosion of the fuel), in televisions (EHV transformers for very high voltage needed to operate the CRT) in certain consumer gadgets such as "balls plasma "or Tesla transformer (transformer high voltage and high frequency) that produce arcs very long (over a meter). Handling this kind of processors (when they are operating regime) can be dangerous, even deadly, so extreme caution is required.
Example of arcs produced by a Tesla transformer:
This is a component whose principle is also based on the transfer of electromagnetic energy between two windings, with the difference that the primary is arranged in series in the circuit which it is desired to know the consumption. Sometimes it is the power wire of the circuit to be measured is the primary of the transformer (in this case, there is no winding, a thread can just stay right), the secondary being added by the means of a clamp which can be closed around (clamp). The interest of this method is that it is not necessary to interrupt the power supply circuit for inserting a measuring instrument.
Source of images own clicked digital images
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