Glossary of Electro-Magnetics Terms

Capacitance:  (C)
A measure of the capability of storing electrical energy in an electric field.  Distributed Capacitance in a transformer has the (mostly) undesirable effect of storing electrical energy in the insulation layers within the transformer.  It is usually modeled as a capacitance in parallel with the ideal transformer primary winding.  Winding to winding capacitance can transmit unwanted high frequency signals.

Dielectric Withstanding Voltage (DWV or Hipot):
Dielectric withstanding voltage or Hipot/Isolation is the ability of the device to withstand a specific breakdown voltage between primary and secondary or a winding to another metallic / conductive surface.  The typical measurement is done with an RMS voltage at 60 Hz for a specified time period. 

Frequency Response:
Frequency response is the measured variation in output voltage and phase angle while varying the frequency of the input signal but keeping the input voltage constant.  This is usually described on a logarithmic scale in decibels.

Inductance: (L)
A measure of the capability of storing electrical energy in a magnetic field.  It is usually measured and modeled as series inductance across the transformer primary winding.

Inductor:
In our case, a custom-designed, wire-wound magnetic energy storage device, available in many different flavors.   Some of our favorites:

Buck-Boost Inductor:
A buck-boost switching circuit uses an inductor to compress a wide range of input voltages into a nominally smaller range of voltage.  These inductors typically operate in continuous mode where the current is always greater than zero. 

Common-Mode Inductor:
A typically two winding inductor meant to be connected in such a way as to cancel out the differential mode induced magnetic flux, but providing a high impedance to common mode noise.

Differential-Mode Inductor:
A typically two winding inductor meant to provide impedance to high frequency signals while allowing DC and low frequency current to pass with minimal interference. 

Insulation Resistance: (IR)
Insulation resistance is a measure of the relative losses of the insulating materials used in the construction of a transformer. 

Leakage Inductance:  (LL)
Leakage Inductance is that portion of the primary magnetic field that does not link with the turns of the secondary winding of a transformer.  Leakage is generally measured across the primary winding with the respective secondary winding(s) short-circuited.

Self Resonant Frequency: (SRF)

A frequency at which the inductive and capacitive reactance is equal and, therefore, cancels each other out.  The input current is at maximum and the phase angle of the impedance switches from positive to negative.

Soft Magnetic Material:
Shaped piece of ferromagnetic material that once having been magnetized is very easily demagnetized.  It requires only a slight coercive force to remove the resultant magnetism.

Switch Mode Power Supply:
A power conversion technique that involves breaking the input power into pulses at a high frequency (by switching it on and off) and recombining (filtering) these pulses at the output stage. This facilitates easy regulation because the amount of time (the amount of volt•seconds of energy) that the voltage is turned on can be controlled electronically. Generally the output power is monitored and the time of the switch is adjusted in response to the load. On switch mode power supplies with multiple outputs, control still is based on the activity of one of the outputs. Secondary regulation techniques (such as mag amps) can be used on unregulated outputs. Abbreviation is SMPS.

Some types of SMPS transformers that we design and build:

Flyback Transformer:
A device that functions as both an inductor and a transformer.  It stores energy as an inductor during the charge cycle and delivers that energy through the secondary winding to the load during the discharge cycle.  Discontinuous Mode Flyback circuits discharge the transformer completely during each cycle, while Continuous Mode Flyback circuits leave some energy continuously stored within the transformer.

Forward Transformer:
Similar to a flyback transformer in that the primary winding carries current only during the on cycle, but with the difference that the secondary conducts at the same time as the primary.

Full-Bridge Transformer:
A switching scheme where the application of voltage is alternated between the two primary ends of the winding, allowing full use of the power capability of the transformer.  These are among the most efficient power supplies, but can be the most expensive due to high parts count in implementing it. 

Half-Bridge Transformer:
A switching scheme that uses the full power capability of the transformer but has a slightly simpler circuit than the full-bridge.  It derives its name from the fact that, in the schematic, it looks like only half of the full H-bridge schematic having two input FETs instead of four.

Push-Pull Transformer:
A push-pull circuit uses a center-tapped primary winding and alternates the voltage between the high primary side to ground and the low primary side to ground, resulting in bi-directional AC power on the secondary side of the transformer.

Winding Resistance: (DCR)
DCR is the resistance of the windings when measured in DC (direct current) conditions.  It is a function of the wire size, number of turns and mean length turn of the core.

 

 

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