Roxburgh DC Feedthrough Capacitors
he Roxburgh EMC dc feedthrough capacitor range is uniquely positioned in the market as a cost effective, high capacitance design to be employed for EMI suppression of incoming 63V, 100V and 250V rated dc power lines into various electrical equipment.
The high capacitance values provide greater performance than is normally available and the feedthrough construction ensures excellent performance right up to GHz frequencies. The design utilises metallised plastic film dielectric material to provide self-healing properties in the event of unexpected transients beyond normal breakdown voltage of the dielectric material. A solderless capacitor assembly technique is incorporated to avoid heat damage to the dielectric, providing increased reliability. The technology used in this range of capacitors has been proven in service for more than 25 years and as an example of the extreme reliability, 81,000 units of one type of capacitor using this technology have been installed in high-end prestige computer servers without a single field return.
The compact capacitor construction and lightweight aluminium casing presents a practical product suitable for applications requiring high reliability coupled with good high frequency performance such as servers, base stations, telecommunications and medical equipment including MRI scanners. As well as protection against incident EMI, these capacitors are equally effective at preventing high frequency equipment generated noise from leaving the equipment, therefore providing an excellent solution to achieve EMC compliance of equipment, particularly where compliance at frequencies up to and above 1GHz is desired. The capacitors are particularly useful to achieve very high performance at very high frequencies where noise pollution due to mobile phones, Wi-Fi, microwave, radar and TV transmissions is becoming increasingly problematical. A more common two-terminal capacitor will resonate at frequencies of 1MHz due to the inductance of its leads and so at higher frequencies will progressively lose all performance as it becomes an inductor instead of a capacitor. Due to the internal construction of the Roxburgh EMC feedthrough capacitor there is virtually no internal inductance and hence no self-resonance. This means that the insertion loss performance of the capacitor continues to rise with frequency to a level more than 90dB and this performance is maintained to well beyond 1GHz. All products in the range are RoHS compliant and built in an ISO 9001 (2008) approved manufacturing facility where they are 100% tested.
The feedthrough capacitors are designed for through-bulkhead mounting to offer high frequency filtering in line to ground applications and should be mounted through a metal bulkhead or chassis. The bulkhead mounting surface should be clean and unpainted to offer a low impedance path from the filter to the equipment chassis. Conductive paint finishes should be avoided as they do not usually provide adequate conductivity. Poor earth bonding will limit the available performance of the product and could compromise safety.
The user should check materials compatibility between the aluminium case and the intended mounting surface to avoid any potential galvanic corrosion issues. EN60950 table J1 can be used for guidance on compatible materials.
All capacitors will store charge after power has been removed and must be treated with respect as this can be lethal when the voltage and charge are high enough. These capacitors do not contain internal discharge resistors consequently it should be ensured that capacitors are fully discharged before touching. Where necessary, terminals should be enclosed by the user to prevent any danger of electric shock or accidental shorting.
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