What are the common types of transformers available for use in electronic circuitry? |
| Power |
| These operate at 50 to 400 Hz at a nominal line voltage from 105 to 130 V. They are made with single and multiple secondaries with varying step-up and step-down turns ratios. |
| Secondary |
| Secondaries can have a single tap, multiple tap or no tap. Some units are made with a tapped primary. Output voltages can range from three to several thousand volts with output currents from .01 to 1500 A. |
| The Cores |
| The cores are iron or steel laminations. They are packaged in a hermetically sealed case for military or space use or with an open frame or plastic enclosure for commercial, industrial or consumer use. |
| Isolation |
| These types operate with a one-to-one turns ratio between primary and secondary, while still isolating the line from the secondary load. Usually, an isolation transformer also includes a Faraday shield, which is a screen of nonmagnetic metal wound between the primary and secondary and connected to the transformer core. |
| The Shield |
| The shield acts to prevent capacitive coupling of spurious signals and noise between windings, and it also reduces transformer efficiency by increasing leakage current. |
| Ferroresonant (Constant Voltage) |
| These types operate from a varying ac power line (95 to 130 volts) to maintain a constant ac output (typically from 6 to 118 volts ac ± 1%). Line voltage frequency variations of more than 1 Hz above or below the nominal frequency cannot be tolerated without going out of regulation. |
| Control |
| These are small power transformers used for control components such as relays and low voltage ac control devices. Common output voltages are 12 and 24 Vac at current capabilities of 4 to 16 A. |
| Autotransformer |
| These are single winding types with either fixed or variable step-up or step-down turns ratios. They are smaller and less expensive that the equivalent two-winding types. |
| Audio |
| These transformers differ from the power types in that they are used to provide matching of the electrical characteristics of an output amplifier to that of a load speaker. In high-fidelity audio systems, they operate from 20 Hz to 20 KHz. In audio systems involved with voice communications only, they operate from 200 to 500 Hz. |
| Radio Frequency |
| These transformers operate at a fixed high frequency with a capacitor across either primary, secondary or both, to create a tuned or resonant circuit. Most types use an air core, however some are made with a ferrite slug to permit adjustment of the inductance of the windings over a given range. They are usually assembled in an aluminum shielded can to reduce pickup or radiation of magnetic fields. |
| Pulse |
| These types are used for the generation and transmission of square wave pulses with emphasis on fast rise and fall times of the pulse and high-frequency response. These transformers are packaged in a miniature enclosure, 1/4 inch to 1/2 inch in diameter, and use an air core. |
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