70021 ACME ELECTRIC, 70021 Datasheet - Page 19

• Manufacturer Part Number: 70021
• Description: Toroidal Transformer
• Manufacturer: ACME ELECTRIC

Specifications of 70021

• Power Rating: 5VA
• Secondary Voltages: 2 X 9V
• Secondary Current Nom: 2mA
• Transformer Mounting: PC Board
• Weight: 144g
• Transformer Type: Toroidal
• Secondary Current Aac: 278mA
• Output Current, Secondary Series: 278mA
• Frequency: 60Hz
• Output Current: 278mA
• Rohs Compliant: Yes
• Primary Voltages: 2 X 115V
• Mounting Type: PC Board
• Features: Low Profile
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Substantial benefits may be derived from the use of toroids as long as
thought is given to their application. The following two considerations
are important.
A completed path by any conductor passing through the center hole of
the toroid around the outside constitutes a short circuited turn. As with
any short circuit, this condition will result in high circulating currents and,
more importantly, high heat.
Our standard mounting options utilize either a single bolt and large washer
(disk mount) with no outside structure to act as a conductor, completing
the circuit; or two metal flanges (flange mount) which clamp the toroidal
like a sandwich with four bolts at the outer periphery, but nothing
through the center. The L-Bracket and Clamping Bracket described
are both designed to avoid a shorted turn condition.
The excellent magnetic properties of the toroidal transformer and
the high remanence of the grain-oriented silicon steel, under certain
circumstances, occasionally leads to high inrush current at turn-on.
17
• 15 to 300VA
• 300VA to 1.0kVA
• 1.0 to 2.0kVA
• 2.0kVA and up
TRANSFORMER RATING
A) Shorted Turn Condition
B) Inrush Currents
CONSIDERATIONS WHEN USING TOROIDAL POWER TRANSFORMERS
SUGGESTED PROTECTION
None
Slow-blow fuse in primary circuit
Small value resistor in series with
primary circuit
Relay momentarily inserts resistor in
primary circuit at start-up, or NTC
Thermistors
[phone]
To prevent nuisance interruptions due to blown fuses or supply breakers,
some simple precautions should be considered. As the power rating of
the transformer increases, the potential effect of the inrush current
becomes greater. The following table suggests different types of circuit
protection according to the toroid’s power rating.
In addition, in those applications where an even lower in-rush current
is desired, AMVECO has developed several proprietary construction
techniques. Without added circuitry, both the peak value and the
duration of the in-rush current can be reduced. As a matter of fact,
AMVECO has manufactured toroidal transformers without any in-rush
current at all. In these cases, AMVECO works closely with the customer
to meet the specific requirements of the application. A slight increase in
the overall size of the transformer is sometimes necessary to facilitate the
lower in-rush current.
www.amveco.com
Applying Part of the Insulation System