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Current Carrying Capacity

It is clearly specified which contact partners (pin and jack) fit together in a connector. Generally, a contact system is selected so that the current carrying capacity corresponds to the attached tracks. Cable cross-sections and permissible currents are defined here; there are standards for this.

Power elements do not have any mating connector. The "mating connector" is in effect the circuit board with its own specific layout. Cable cross-sections (board width and copper thickness), number of layers, positioning of the high-current contact and heat management are only a few of the characteristics that influence current carrying capacity. There are also diverse conditions on the connection side of a power element. For example, a cable lug for cross-sections of 6 to 95 qmm can be applied to an M8 setscrew, a copper bus can rest on top, or a component e.g. mega-fuse can be attached.

With this background it becomes clear that the current carrying capacity of power elements must always be considered in the context of the overall system. Given the wide variety of influencing factors, it is thus not possible to define a specific amount of current carrying capacity for each individual power element. The information given for power elements from Würth Elektronik ICS is always related to a very specific test environment. We provide a statement about current carrying capacity and determine a derating curve based on these conditions.

This by no means is the maximum possible current carrying capacity. If done right, considerable more is possible.

What is a derating curve?

Derating means reduction in load. With electro-mechanical connections a derating curve thus describes how much current carrying capacity sinks as ambient temperature increases.

Derating curve for a PowerOne element

The figure shows derating curves of various PowerOne power elements. The connection on two wide 70µm circuit board layers allows 300A at 20°C ambient temperature with one element that has over 20 pins all around. Provided that sufficient cable cross-section is connected.

The curves end at 125°C, which is the so-called glass transition temperature of standard FR4 circuit board material. If a material is chosen with a higher value, e.g. TG170, the curves would end at 170°C. Currents considerably higher than 300A would be possible at room temperature.

What current carrying capacity limits do power elements have?

The PowerOne datasheet gives the value of 1000A. This indicates that the press-fit connection generally is not the limiting factor, and such a high current definitely could be achieved. An 8-layer circuit board at 105µm made of TG170 material with the appropriate layout design would definitely permit this value.

Diagramm showing the mechanic stress of a power element

Does the position in the conductor pattern impact conductivity?

If you want to feed high currents into the circuit board, the positioning of the power element in the layout plays an essential role. The schematic depiction shows that load capacity sinks considerably when the element is placed on the edge or even in the corner of a board surface. A copper surface should be added to a power element with an edge dimension of 13x13mm, e.g. with 6mm. The maximum amount of surface should be made of copper. It works like a cooling element.

What kind of switch-on or pulse current can power elements with solid pins handle?

Classic connectors have their limitations. If a connector is too overstressed, the contact surfaces between jack and pin can get welded together. The contact or contact surface is then destroyed. What's undesirable for this kind of connector is actually a basic characteristic of the press-fit contact. The press-fit procedure creates a cold weld. A short-term overload many times greater than the rated current has no impact on the characteristics of the press-fit zone.

Can the cold weld be damaged by excessive tightening torque?

Derating-Kurve für ein PowerOne-Element

The answer to this is no, it cannot. The depiction shows which areas absorb the force e.g. if a power element is tightened with a breakdown torque. Almost all of the energy is absorbed by the element, in particular in the area where the thread pin turns into the base element. No significant forces occur in the press-fit area.

Simply stated: before the cold weld is damaged, the pin or the thread pin itself will be damaged.

All of these properties make the Würth Elektronik ICS power elements in solid press-fit technology the element of choice if high currents need to be supplied and robustness and durability are required. We are happy to consult with our customers in designing their layout.