Electrostatic discharge (ESD) can wreak havoc on sensitive electronic components and circuits. To protect electronic devices from ESD, system designers employ a number of protective measures, including surge resistors. This article examines the role of surge resistors in ESD management applications.
First of all, a definition, the term pulse generally refers to overload conditions with high power and long duration. Conversely, surges refer to high voltage overloads and short durations (e.g., ESD applications).
Surge resistors dissipate harmful energy surges and protect devices from ESD events. They are strategically placed in circuits to absorb and attenuate high-voltage transients.
In this article, we'll cover the basics of surge resistors, the types available, and the selection criteria.
Static magnetic fields pose a serious risk to personnel. In some applications, static fields are generated during the manufacturing process. Other production processes, including painting and food labeling, require a static field to function.
Shielding, grounding, proper safe wearing, and personnel training can address many risks. If these precautions are insufficient, a surge resistor will serve as an additional safety measure.
The design, manufacture, and installation of these devices are critical. It is important to follow the relevant industry norms.
Surge resistance values tend to be between 100 mohm and 500 mohm. Resistance tolerance is not an important consideration and can only be 5% at most, 10% to 20% is more common.
Resistors must dissipate the energy of the surge, so designers must carefully consider the nature of the ESD pulse. Based on this information, peak power specifications can be calculated.
The choice of surge resistance is often based on cost and performance calculations. Thin-film resistors are not suitable due to their power handling capabilities. Ceramic resistors are only used to protect against short surges because they have limited energy handling capacity. This leaves behind thick films, metal foils, and wirewound resistors.
Lower cost (than metal foils), smaller size (than wirewound resistors), and lower inductance (than wirewound resistors) mean that thick-film surge resistors tend to dominate the ESD suppression market. Foils and windings are used in a small number of specialized ESD management applications.
Many factors can contribute to an ESD event. Understanding the nature of ESD pulses is critical to selecting the right surge resistor. ESD pulses can have different durations (typically 10 s to 100 ms) and wide ranges.
To withstand an ESD surge event, a thick film resistor must be able to dissipate the surge energy. The design of surge conditions involves selecting the right size for the resistive element and selecting the best (performance vs. cost) resistive material. The choice of substrate (size and material) is critical to ensure that its quality is capable of dissipating pulse energy.
For extreme applications, surge resistor manufacturers may modify the resistor paste material or the resistor manufacturing process (or both). The sintering process used in the manufacturing of resistors is particularly important.
The degree of potential damage to the conductive mechanism of a resistive material depends on its composition. Therefore, the choice of thick film paste will directly affect the ESD performance of resistive devices. There are many resistive materials to choose from, each with its design trade-offs.
Thick film surge resistors have become a major choice in the ESD suppression market. However, it is important to recognize that surge resistor design is not a one-size-fits-all solution. For extreme applications, resistor customization may be required, including the selection of resistors and substrate materials.