Home > Transformers/Inductors

Transformers and Inductors

Hill Technical Sales offers a large range of standard and custom designs from the best manufacturers in the world. Most custom designs can be processed in 1 to 2 weeks. Pricing on standard products can normally be quoted the following business day.

Theory and Application

Available Types



Auto-transformers are used strictly in a step-up or step-down application. They are very similar to isolation transformers with one important exception. In an auto-transformer the primary and secondary windings are electrically common to each other. The advantage of using an auto-transformer over an isolation transformer is its smaller size and lower cost. The major disadvantage is no isolation between the primary and secondary which allows noise on the power line to be directly coupled to the load. One last disadvantage is that auto-transformers provide no regulation. It is also important to note that the greater the change in voltage the less cost effective a auto-transformer is. Some common applications for auto transformers are motors, heaters, and other non sensitive loads.


Used primarily in a step-down environment to power low voltage accessories. Sizes: 5VA minimum rating.


Special type of ferroresonant transformer that has an additional winding which a variable DC control voltage is applied. When this winding is used in conjunction with a feed back circuit the transformer provides much tighter secondary regulation. This can also be used to add flexibility to the output voltage based on the designers requirements, for example regulation adjustment for different frequencies. .


This ballast offers a linear variation of output power from 40 to 100% as opposed to capacitor switching which changes lamp power as a step function. This is accomplished by varying the conduction time on an inductor which negates capacitance in the circuit allowing enhanced control of lamp current. Lamp current is sensed in a closed feedback loop circuit which can instantaneously respond to changes making the necessary adjustments. A PLC interface is available to communicate with the ballast in order to vary lamp output. In order to protect all of the control circuitry from power problems typically found on the primary the control circuits are all located on the secondary of the ballast.



Current transformers are designed for connection in series with the line in the same manner as that for ordinary ammeters- the secondary current bears a known relation with the primary current; consequently, any change in the primary current will be reflected in the meters or other devices connected in series with the secondary terminals of the transformer. Sizes vary from ID of 0.60" to 8" and up to 10" x 24" for bus bar designs.

Current Transformer Types


We can supply coils of most any size to be used with or in various OEM assemblies.


Edge winding is a technique in which a rectangular magnet wire is wound on its narrow edge. This allows a much greater surface area to dissipate more heat than conventional winding techniques. Edge winding is used mainly in isolation transformers and inductors that have high load currents at lower voltages.


Ferrite materials are used for high frequency magnetic applications which include transformers and inductors Ferrite materials are used because of their efficiency and responsiveness at these frequencies, enabling the power supply designer to reduce the size of magnetic designs dramatically. Cores come in over a dozen shapes and a multitude of sizes. The components in a power supply and the ferrite core transformer are closely intermingled electrically by design, and each has a great effect in the performance of the other. In this case it is important to fill out the general specification sheet and then for our engineers to work closely with you on these designs.


Used primarily in uninterruptible power supplies . The transformer is used to take a low voltage "pulsed square wave" generated by an inverter and battery and convert it to an AC sine wave where voltage is regulated 1 to 5% depending on your requirement. Sizes: The typical size range for this product would be 100VA through 25KVA 50Hz or 60Hz. However, we can produce inverter transformers with any VA rating


Used primarily in brute force DC power supplies. The ferroresonant transformer takes a sine wave input and creates a regulated square wave output which is ideally suited for rectification. The square wave will produce a lower ripple than a sign wave using the same filter capacitor. Sizes: 25 watts to 10 kilowatts 50Hz, 60Hz, or 50/60Hz.


This takes a sine wave input and produces a sine wave output with a choice of output voltage variations of 1, 3, or 5 % for an input voltage variation of +10/-20%. These are used in an integrated power protection systems, protecting the critical load from all power problems with the exception of a blackout. Multiple voltages are available so this transformer can replace a multi-tap input transformer. Sizes: This product is available in sizes from 30VA through 75KVA single phase or three phase 50hz or 60hz.


Similar to control transformers except they provide power to x-ray tube filament. Typically, one requirement is very high dielectric strength from the secondary to ground and from the primary to secondary. Sizes: over 50VA minimum rating.


These are used in high current applications. The coil is wound with either copper foil or aluminum foil. Used when low voltage high current is required.


Also known as chokes, DC link, AC line/load reactors, and buck/boost inductors. Inductors are found in most electrical power conversion applications. Smoothing chokes are used to filter the AC ripple in a low-frequency DC power supply. Inductors are used to filter out RFI (Radio Frequency Interference). In another application they are used as current-limiting reactors for overload and short-circuit protection or to limit high inrush currents that might occur on the start up of an electric motor.

Wide-band inductors are used at a multitude of frequency levels to filter out unwanted frequency noise leaving a clean fundamental signal. Inductors come in virtually all windings and constructions forms, dictated by the frequency and current they are to handle.

DC Filter Choke- Used primarily in filter applications or other tuned circuits. Can also be used in conjunction with capacitors to reduce ripple in DC circuits.

Swinging Choke- Similar to filter chokes except it has two inductance ratings at two currents.

AC Reactors - AC choke, line/ load reactors are used primarily to limit current. Both single phase and three phase versions are available. Also they can be designed for 50, 60 or 50/60Hz.


(See power transformers)


Used in medical equipment to protect the patient from electrical shock and potentially harmful leakage current. All transformers are double insulated and use a 5 mil copper safety shield to protect against a catastrophic failure on the primary or secondary side of the transformer in which case the current is shunted to ground. Also included are reset-able thermal fuses. Standard leakage current is less than 100uA. Transformers bear the following marks: UL2601, UL544, CSA22.2 no 601.1, IEC2601, and TUV.


Power transformers includes insulating or isolating transformers. These terms are used to describe the "electrical isolation" of the primary and secondary windings, or insulation between the two. Often a electro-static copper shield is placed between windings to reduce electrical noise from primary to secondary. A grounded electro-static shield provides a safety factor preventing accidental contact between windings under faulty conditions.

Sizes: These are available in single phase or three phase up to 250KVA.


Also known as Dial-A-Watt. Used primarily with mercury vapor ballasts to vary the output current (power) to the lamp.
This is done by introducing a DC current to the reactor. The reactor is connected across the capacitors on the ballast and "swings" current from the ballast. Primary current to the ballast remains constant regardless of power.


Used to either increase or decrease incoming voltage. Many are designed to do both (i.e. 120/208/240V in and 120/240V out) to handle worldwide voltages. Another very common application would he to step down voltage for DC rectification. Sizes: Single phase units from approximately 10VA to 100KVA and up to 250KVA for three phase units. Most voltages can be accommodated. Voltages are typically under 6KV for small units and 10KV for large units.


Toroidal transformers include power and auto-transformers, as well as inductors. Toroidal merely describes the geometric shape, similar to a donut. These transformer are typically more efficient because of the low core losses associated with a tape wound core, with no air gap. The shape also allows a larger portion of the copper windings to be exposed to the ambient air, enhancing cooling of the hotter copper windings versus the cooler iron core in a laminated transformer.

A toroid, when compared to a stacked laminated type transformer, would be about 50% lighter and 50% lower in volume simply because it is more efficient. Other advantages include low stray field, low mechanical hum, reduced no load losses, easy mounting and flexible dimensions.


The vibratory inductor is a unique application for a simple choke design, for use in Vibratory Feeding Systems and Sorting Lines or Bowls.

Vibrations are set up, between an I-armature assembly and an IE-armature assembly, through the changing magnetic field of the core. The E-armature is usually secured to the solid equipment base, while the I-armature is secured to the bowl or line to be vibrated. The two armatures are positioned only a fraction of an inch from each other so that the E's and I ' s are coupled through the magnetic field. This gap can be variable to change the strength of vibrations. Coils can be provided potted or unpotted and are available with heavy weldments for solid attachment to the vibratory unit. Terminations are provided through flying leads, STO line cords, solder lugs, or quick connect lugs.


Custom transformers or inductors are wound on any bobbin or core. Typical cores included but are not limited to: EP's, ETD's EE's, EC's, PQ's, RM's, UU's, drums, pots, rods and toroids. Common wire types, MW, Rubadue, Furukawa, Triple insulated, Nyleze, Polythermaleze, Litz, and Copper foil.

Typical operating parameters:

Typical applications: