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C h a p t e r 4 RESISTIVE SOLUTIONS FOR PRE/ DISCHARGING CIRCUITS The mystery of pre/ discharging resistors unveiled An essential component of many electrical circuits, pre/ discharging resistors are designed to regulate the flow of current to protect sensitive components from damage as well as provide safety against capacitive energy. Pre- charging resistors are used to limit inrush currents that occur during the charging process of large capacitors, while discharge resistors are used to safely discharge large capacitor banks that can hold onto charge for extended periods of time. The need for pre/ discharge resistors The primary reason for using pre/discharging resistors is safety. Without these resistors, circuits can conduct too much current, causing damage to sensitive components, cables, and traces on PCBs. Additionally, discharge resistors ensure that energy stored in capacitors is removed in a timely manner, typically within seconds. If energy remains stored for a long period of time, it can be hazardous to anyone working on the circuit, such as in the case of hybrids and electric vehicles. Discharge resistors are also important to ensure that DC-to-DC converters work effectively under no-load conditions, as a switched-mode power supply with no current draw on its output can behave unpredictably. Anton Dianov Senior Firmware Engineer, Samsung Electronics Discharge resistors are essential in high-energy circuits primarily for safety. When a device is turned off from the grid, its capacitors are still charged, placing maintenance personnel at risk of being harmed or electrocuted if they work on the device." 20 Passives and Their Emerging Applications