Safety Standard Agency Approvals
We supply our custom designed transformers- including fast turn-around prototypes- certified to applicable safety standards issued by UL, CSA, EN, and/or IEC and with CE marking. We have family approvals which allow a wide variance of design modifications. Our standard and custom designed transformers are certified to the following standards.
General Purpose Transformers
UL506,CSA C22.2 No.66-1988, EN 61558-1, IEC61558-1
Medical Application Transformers
UL60601-1, CSA C22.2, No.601.1-M90, EN61558-2, EN601.1, IEC61558-2, IEC601.1
Our transformers are certified to EN/IEC610000-3-2 and EN/IEC61000-3-3 for Electromagnetic Compatibility.
Our transformers are also designed to the applicable sections of other standards, such as UL950, IEC950, UL813, UL1236, EN742, VDE0750, VDE0551, CSA C22.2#125, and many more.
Primary Windings
Choose from the inputs listed in the Standard Line Section, or specify your custom input – by line frequency and voltage.
Operating Frequency
Standard transformers are designed to operate at 50 or 60 Hz line frequency. Grain-oriented steel cores can be used at frequencies up to 1KHz. If the transformer will only be operating at 400Hz, we can use a core that is about 1/3 smaller than for normal line frequency. A 50Hz core is 20% larger than an 60Hz core. For higher frequencies, we substitute such materials as ferrite, powdered metal and other composites.
Power
We can quote on power requirements from 7VA to 20KVA (Single Phase) or 60KVA (Three-Phase)
Insulation
The standard insulation is Class B (130ºC). Other insulation classes may be specified as required, such as class F (155ºC).
Secondary Windings
You can specify the output loading in either of two ways:
1. AC (RMS) voltage and current or power (VA) and duty cycle for each secondary output.
2. DC load parameters.Bridgeport Magnetics can design the optimum transformer from your DC load data. This data should include: DC voltage, current, rectifier type (full wave, full wave bridge, etc.) and specification, capacitor type and value, regulator type and specifications, and special load characteristics, including duty cycle. Please supply a schematic, if possible. With this information, we will determine the optimum secondary DC specifications for each output.
Mounting
We supply the standard hardware, potted center or vertical bracket listed in the Standard Design Section. We also supply custom toroids with threaded inserts or studs pressed into a potted center. We offer special molded bases, complete molded enclosures, or custom sheet metal brackets and enclosures.
| Standard Sizes of Steel Washers |
| Dimensions in Inches |
| Size |
A |
B |
C |
T |
D |
| 1 |
2.00 |
.75 |
.188 |
.04 |
.18 |
| 2 |
2.38 |
.88 |
.188 |
.05 |
.22 |
| 3 |
2.75 |
1.13 |
.25 |
.06 |
.26 |
| 4 |
3.50 |
1.25 |
.25 |
.06 |
.28 |
| 5 |
4.38 |
1.38 |
.31 |
.08 |
.33 |
| 6 |
5.70 |
1.75 |
.31 |
.08 |
.50 |
|
Connections and Leads
Our factory standard is to provide our transformers with multi-stranded leads to simplify termination. Connector assembly is an available option. Just specify what type you would like to have.
Thermal Protection
Thermal protection by auto-resettable switch or fuse is optional. Unless otherwise requested we will use fuse that opens at 100ºC. All lighting transformers have 110ºC thermal auto-resettable cut-offs.
Static Shielding
The transformer may need static shielding to minimize capacitive coupling between primary and secondary windings when operating in an extremely noisy environment.
Ultra-Low Magnetic Stray Field Emission
Our standard design greatly reduces stray fields compared to a laminated transformer. For sensitive electronic applications, our optional Ultra-Low Stray Field Design, achieved through a special process, further reduces the emissions. In applications such as high-resolution CRT displays, a magnetic shield around the circumference of the transformer achieves even lower stray field levels.
Aspects of Size Reduction
Increasing the working flux density permits fewer turns and/or a smaller cross sectional core area. Experience has shown that working flux densities of 12 to 14 kilogauss are the practical limits for the conventional laminated cores with air gaps. Since toroidals can be designed with flux density of 16 kilogauss, the toroidal core geometry may directly reduce the core size and the number of turns. The former lowers the size and weight of the transformer and the latter reduces the copper losses.
You can significantly reduce transformer size and weight where the transformer is loaded intermittently. In such cases, the load is energized for a small time duration, which is much shorter than the overall thermal time constant of the transformer.
Physical Dimensions
Typical sizes and weights listed in the chart below serve as a basic guideline to determine size and weight based on power (VA) rating. Height and diameter can be varied, as long as the core cross section holds constant. Specify diameter and height or as maximum physical envelope available.
Quick Reference Guide
for Approximate Physical Sizes |
| Rating |
Dimensions-OD x HT |
Weight |
| VA |
inches |
mm |
lbs |
kg |
| 25 |
2.6 x 1.4 |
66 x 36 |
1.1 |
0.5 |
| 50 |
3.2 x 1.5 |
81 x 38 |
1.7 |
0.8 |
| 100 |
3.9 x 1.6 |
99 x 41 |
2.4 |
1.1 |
| 150 |
4.3 x 1.7 |
109 x 43 |
3.4 |
1.6 |
| 200 |
4.5 x 1.9 |
114 x 48 |
4.4 |
2.0 |
| 250 |
4.7 x 2.1 |
119 x 53 |
5.4 |
2.5 |
| 300 |
5.0 x 2.3 |
127 x 59 |
6.2 |
2.8 |
| 400 |
5.2 x 2.5 |
132 x 64 |
7.4 |
3.4 |
| 500 |
5.4 x 2.8 |
137 x 71 |
8.8 |
4.0 |
| 600 |
5.7 x 2.9 |
145 x 74 |
10.3 |
4.7 |
| 750 |
6.3 x 2.9 |
160 x 74 |
12.7 |
5.8 |
| 1000 |
6.6 x 3.0 |
168 x 76 |
15.4 |
7.0 |
| 1500 |
7.8 x 3.5 |
198 x 89 |
26.0 |
11.8 |
| 2000 |
8.4 x 3.9 |
213 x 99 |
34.0 |
15.5 |
| Power rating (VA) is determined by secondary RMS data. Physical size may vary from above data depending on number of primary and secondary windings and whether duty cycle is 100%.
|
Rectifier Circuits
When using a toroidal power transformer, some rectifier circuit designs are more efficient.
Power toroidal transformers find many applications in linear power supplies that generally incorporate rectifier circuits. Four typical circuits are illustrated here. Consult Bridgeport Magnetics
for further information and assistance.
Dual Center Tap Rectifier
This is a very efficient use of toroidal transformers, and the best choice for two balanced outputs with a common return. The output windings are wound for precisely matched series resistance, coupling and capacitance
Full Wave Bridge
Full wave bridge is the most efficient use of toroid technology and secondaries; best for high voltage outputs.
Full Wave Center Tap
The full wave does not make full use of secondaries. However, it is more efficient than the half wave. It is good for high current, low voltage applications.
Half Wave Rectifier
Avoid half wave rectifier circuits, as they are inefficient use of toroidal transformers. They cause the core to become polarized and saturate in one direction.
Voltage Regulation
Output voltage regulation varies with the size of the transformer. Regulation can be improved by selecting a transformer with a higher VA rating than actually required.
Shorted Turn Condition
A completed path by any conductor passing through the center hole of the toroid constitutes a shorted turn. A through-the-center screw making contact to the chassis at both ends can inadvertently establish a shorted turn. As with any short circuit, this condition will result in high circulating currents and high local heat.
Our standard mounting options include a single screw, two rubber washers and a steel washer (disk mount) with no outside metal structure to complete a shorted turn.
Inrush Current Precautions
Because toroidal power transformers have excellent magnetic properties and no air gaps, the inrush current when power is turned on is sometimes higher than with stacked transformers. Inrush current can be as high as 15 times the peak steady state rated current. However, the inrush transient rarely lasts over a half cycle. Choose a delayed action fuse or circuit breaker protection to avoid nuisance power loss.
| Transformer Rating | Suggested Protection |
| Up to 300VA | None |
| 300VA to 1000VA | Use slow-blow fuse in primary circuit |
| 1000VA to 2000VA | Add a small value resistor in series with primary circuit. |
| 2000VA and up | Add a by-pass relay that will momentarily short out the resistor after 100-200 milliseconds. An NTC thermistor may be sufficient for some applications. |
Aspects of Size Reduction
Increasing the working flux density permits fewer turns and/or a smaller cross sectional core area. Experience has shown that working flux densities of 12 to 14 kilogauss are the practical limits for the conventional laminated cores with air gaps. Since toroidals can be designed with flux density of 16 kilogauss, the toroidal core geometry may directly reduce the core size and the number of turns. The former lowers the size and weight of the transformer and the latter reduces the copper losses.
You can significantly reduce transformer size and weight where the transformer is loaded intermittently. In such
cases, the load is energized for a small time duration, which is much shorter than the overall thermal time constant of the transformer.
Efficiency
The graph illustrates the effect of increasing load on the toroid's efficiency for various nominal ratings.
Temperature Rise
May be specified as required, or tell us the operating ambient temperature. Our basic design guideline is not to exceed 50ºC to comply with ClassB(130C)
requirements for room temperature applications with a comfortable safety margin.
Operating temperature is an important safety factor. Our transformers, built for Class B (130C) operation, are normally calculated for a temperature rise of 40-50ºC. Actual increase will depend on how and where the transformer is mounted and how well it is cooled. When higher temperature ratings are needed, we offer transformers built to Class F (155C).
Using a larger core size will reduce the temperature rise. The toroidal's small core losses will cause the temperature rise to drop drastically when reducing the output power. At half the load, the temperature rise will only be about 25% of the rise at full load.
Temperature rise varies with the actual output power (P-out) in relation to nominal power (P-nom) for a given core size.
Total losses for the transformer, including winding loss and core loss per pound of silicon steel at a given flux level, may be calculated from design data and data furnished by steel suppliers. The graph illustrates the rise in transformer temperature as the actual power approaches the transformer's nominal power rating.
