What is a power transformer?
Products in the power transformers family include those designed for transformation of AC utility power at nominal frequencies of 400 Hz or less that contain galvanically isolated primary and secondary windings. They are not packaged or equipped with the common connectors used for AC utility powered products, making them unserviceable as an end-use product in an isolation transformer capacity.
Introduction to DigiKey’s Product Selection Guide
This page is one of many in DigiKey’s Product Selection Guide (PSG). This particular page is focused on power transformers. It provides a description of the individual parameters used to characterize the part. This information will allow you to better understand and navigate DigiKey’s parametric search engine. Click here for a case study showing how to use the search tools.
How are power transformers categorized?
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Type: Refers to the specific construction or design configuration of the transformer’s core and winding arrangement.
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Voltage - Primary: Indicates nominal AC input voltages with which a device is designed for use: multiple values indicate different connection options, allowing production of the listed secondary voltages from any of the listed primary voltages.
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Voltage - Secondary (Full Load): Nominal AC RMS output voltage appearing at the device output windings when the rated output current is being drawn and the nominal primary voltage is applied.
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Current - Output (Max): The maximum amount of current that can be output by the device.
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Primary Winding(s): Describes the configuration of the transformer’s primary winding(s), which are those typically connected to a power source.
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Secondary Winding(s): Indicates the number of separate windings present on the side of the transformer that is typically used to deliver power to a load.
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Center Tap: Indicates whether or not a user-accessible connection to the midpoint of the secondary winding is present.
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Power - Max: Typically this represents the maximum power rating to which a device will meet its given specifications. Exceeding this power rating may damage the device and other system components.
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Mounting Type: Indicates how the device is attached.
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Termination Style: Selection of termination style used to connect the device to a system, such as PC pin, solder pad, or wire leads.
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Size / Dimension: The physical dimensions of the device, typically listed in length and width or diameter.
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Height - Seated (Max): Indicates how far the device will extend above the surface to which it has been attached.
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Voltage - Isolation: Indicates the level of electrical isolation provided between the primary and secondary windings of the transformer.
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Weight: Indicates the overall weight of the transformer, typically listed in pounds or grams.
Examples of power transformers
- The Triad Magnetics brand VPM240-4170 is a 1000 VA toroidal transformer designed for the demanding requirements of medical electrical equipment. Datasheet
Schematic symbol
The schematic symbol for a transformer is shown below.
Schematic symbols courtesy of Scheme-it.
Related media links
Videos
DigiKey Tech Forum articles
- An Engineer’s Perspective on Power Transformers
- Power Transformer - inherently and non-inherently limited - Power / Transformers
- Transformers vs. Power Supplies
- Transformer Rated Power Capacity
- Triad Magnetics Transformers “B” Suffix
- Transformer Primary / Secondary Impedance
Follow up
If you have any general questions on the specifications for selecting power transformers, please reply using the button below. If you have questions on a specific transformer, please post your questions in the forum’s transformers category.
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