All drones are susceptible to many of the same fault and failure conditions, ranging from merely annoying to catastrophic, making robust electrical protection essential. The generic drone design in Figure 1 highlights some of the areas where circuit protection is critical.
Lithium polymer (LiPo) batteries are often used for drones because of their high energy density and for their small size. If not charged or used properly, they can begin to smoke or catch fire, commonly referred to as “thermal events”. A variety of circuit protection options are available to help guard drone batteries against over-current and over-temperature conditions which lead to those thermal events:
- Metal hybrid PPTC with thermal activation (MHP-TA) devices combine the advantages of low thermal cut-off temperatures, high hold-current ratings, and compact size. They are capable of handling voltages and battery charge rates common in high-capacity LiPo cells.
- Small-footprint surface mount resettable PPTCs are well-suited for protecting Lithium battery packs, providing fast over-current and over-temperature protection with ultra-low internal resistance, voltage drop, and power dissipation.
- PolySwitch setP digital temperature indicators help protect USB-C cables used for recharging drones and drone controllers. Cable-plugs are susceptible to damage caused by fault-causing debris. The risk of catastrophic failure is elevated due to the higher power levels likely used to quickly charge via the USB-C connection.
Electrostatic discharge (ESD) is a concern for multiple drone subsystems. To address this concern, a variety of protection options are available. Polymer ESD Suppressors (PGB or XGD) are well suited for antennae protection due to their very low capacitance which provides the least amount of signal disruption. Transient Voltage Suppressor (TVS) diodes can be used if higher surge levels are a concern.
ESD is also a concern for I/O ports on the flight controller and the electronic speed controllers (ESC) for the flight control motors. The primary factor to consider for protecting this signal port is the data rate of the signals. As data rates increase, it is crucial to consider the capacitance of the chosen suppressor so as not to introduce any signal integrity issues into the system. For example, circuits in this port running at low speeds can be protected with higher capacitance multilayer varistors (MLV) or TVS diode arrays.
For extremely high data rate protocols, suppressors with virtually no capacitance are essential so that the system can transmit and receive the data with no loss of signal quality. The latest TVS diode arrays and Polymer-based ESD suppressors are available with capacitance values far below 1.0 pF that can operate at these higher data transfer rates.
About the Authors
Todd Phillips, Global Strategic Marketing Manager for the Electronics Business Unit, Littelfuse
Todd Phillips is the Global Strategic Marketing Manager for the Electronics Business Unit. He joined Littelfuse as a sales engineer in 2006 for the industrial POWR-GARD business unit. Todd joined the electronics business unit in 2011 as a regional sales manager. His current responsibilities include development of marketing collateral material, management of marketing activities for new product launches and performing market studies and feasibility analyses for new product ideas. He received his BSEE from Milwaukee School of Engineering. Todd can be reached at email@example.com.
Henry Yu, Senior Technical Marketing Engineer in the Electronic Business Unit, Littelfuse
Henry Yu joined Littelfuse in 2011 and is currently Senior Technical Marketing Engineer in the Electronic Business Unit. He is responsible for developing business of target market segments including LED lighting and cloud computing. He received his BSME and MSME from National Taiwan University. He has served five years as a safety engineer in Underwriters Laboratories Inc. (UL). He can be reached at firstname.lastname@example.org.
For more information, see the EDN article Keep your Drone flying high with the right circuit protection design