4145 FAIRCHILD | Alldatasheet
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ing this, the cutoff frequency (Fo) must not be below 600Hz. inductor will give a drop off of 12dB/octave or 40dB/decade. (above the minimum 600Hz limit). Table 1. Input Inductor Determination inductor can be created using equation 2. Table 2. Addition of a Second Inductor capacitor values can be computed. neutral lines), the result is divided by 2, giving 16mH. will be used to complete the filter.
4/6/04 0.0m 002 Stock#AN00004145
2004 Fairchild Semiconductor Corporation
FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS. LIFE SUPPORT POLICY FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPORATION. As used herein: Note: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, or (c) whose failure to per- form when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in significant injury to the user. Note: 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support de- vice or system, or to affect its safety or effectiveness. Note: www.fairchildsemi.com Safety Dealing with Medical Equipment Common mode noise is a problem for sensitive equipment such as those in the medical field. If a device touches a patient, the total system leakage is limited to 100µA. This means that most power supply designers want to restrict this leakage current 20 to 40µA. In order to meet this stringent requirement, common mode filters with capacitors to ground are not used. Using common mode chokes, feed through capacitors (high frequency noise is shunted to the chassis ground instead of signal ground) to ground and adding a transformer or isolating the power supply lines into the power supply reduces these common mode conducted emission pulses. Safety standard: IEC950/UL1950 class II is used in medical equipment. Conclusion EMC is an important stage of system design today and will become more stringent as time moves on. One must keep in mind that when switching occurs, so does noise whether it be conducted or radiated noise. This application note spoke about board level techniques to reduce noise, if more noise reduction is required, especially on the radiation side, conductive enclosures are an option. There is additional cost with all that is added so as a design engineer, standard compliance, safety compliance, and cost all play an important role in the final product. References: EMI Filter Design (1996) Richard Lee Ozenbaugh