Many electronic circuits are exposed to high pulse loads. In some applications these occur regularly, e.g. in pulse width modulated (PWM) devices. In others they are incidental, but also inevitable, e.g. electromagnetic interference signals (EMI). Due to increasing miniaturization or intrinsic limitations of electronic components, their pulse load capability is often insufficient to withstand these pulse loads, and hence they require protection. In both cases pulse-proof resistors are needed.
Here, MELF resistors are well suited due to their excellent pulse load capability, a prominent feature that is linked to their unique cylindrical design. Apart from the standard metal film technology, MELF resistors are also available with carbon film, which further enhances their pulse load capability. The largest case size (0207) carbon film MELF not only provides the highest pulse load capability of MELF resistors, but of all SMD film resistors, thus making it the optimum choice for high-pulse-load applications.
This application note is intended to guide designers in selecting the optimum resistor by identifying the pulse properties - power, duration, and shape - that need to be considered. For this, the effects of pulses on resistors, the factors determining their pulse load capability, and the resulting advantages of carbon film MELF resistors are illustrated.