App note: Designing reliable drones using proper circuit protection


Littelfuse’s application note on drone circuitry protection, offering guard against overcharging its batteries, I/O and ESD protection. Link here (PDF)

No doubt “pilot losing control” is behind many drone incidents and crashes. But what’s behind that “loss of control?” After all, even small recreational drones depend on a host of subsystems – GPS, receiver antennae, WiFi I/O ports and electronic speed controllers – to stay in the air. Lose one and that UAV becomes a UFO pretty quickly.

The number of consumer, professional, and commercial drones, sometimes called unmanned aircraft systems (UASs) or unmanned aerial vehicles (UAVs), sold annually has risen rapidly over the last few years. Future sales growth looks even more rapid, with the Federal Aviation Administration predicting that sales will grow from roughly 2.5 million this year to 7 million by 2020, with 4.3 million being sold to hobbyists and 2.7 million units being sold for professional and commercial applications. Non-military drones are available at a wide range of price points, anywhere from toys that cost less than $100 to sophisticated commercial drones for use in fields like aerial photography, public safety services, agriculture, and wildlife management that can cost thousands

Regardless of how a particular drone is used or how much it costs, all drones are susceptible to similar fault and failure conditions. These conditions can cause problems that range from the merely annoying (a drone that won’t start or take flight) to the catastrophic (a crash that causes major property damage or personal injury). A battery that catches fire during charging or a mid-flight failure due to any of a number of electrical issues are common examples that highlight why robust electrical protection is essential. Fortunately, a growing array of tools and techniques are available to implement passive battery safety systems, electrostatic discharge (ESD) protection, and stalled motor protection.

App note: Magnetic sensors’ and reed switches’ capacitive Loads

An application note from Littelfuse on peak current considerations when reed switches and magnetic sensors are handling capacitive loads. Link here (PDF)

When there is significant capacitance in a reed sensor, reed relay or reed switch circuit, the peak current and energy switched by the reed contacts should be considered. However, if the capacitance is less than 100 nF at 5 V or 0.1 nF at 150 V, and the cable length is less than 10 meters, the capacitance will not significantly effect switching life.

If a capacitor is placed in parallel across the reed contacts, the peak current will be determined by the load voltage, the contact resistance, the wiring resistance, the ESR of the capacitor, and the inductance of the circuitry. Because the resistance and inductance in the circuit path are likely small, the peak current can be amperes or tens of amperes, exceeding the maximum switching current of the reed switch, reed relay or reed sensor. Even if the maximum switching current is not exceeded, switching life may be reduced.

A capacitor not directly across the reed contacts may still generate a high current spike when the reed contact is closed. Depending on the circuit arrangement, the peak discharge current may occur when the capacitor is charged or discharged. Components other than capacitors can have significant capacitance, including long cables, MOVs (Metal Oxide Varistors), and MOSFET gates.

App note: Flow sensing in tankless water heaters


Contactless reed switches from Littelfuse provides flow and water presence monitoring. Link here (PDF)

Reed switches and sensors are highly effective solutions for flow sensing applications that can be used for detecting the presence of fluid flow in a system or even measure the rate of fluid flow.

Tankless water heaters are becoming a widely popular solution for water heating needs. The availability of hot water on demand and the perceived limitless supply of hot water make these types of water heaters much more attractive than traditional tank water heaters. These water heaters also provide long-term energy savings since energy is used only when there is a demand for hot water. In order to effectively heat the water when there is a demand, a sensor is needed to detect the flow of water.

App note: Enhancing workplace safety in hazardous locations with PICO® 259-UL913 intrinsically safe fuse


Application note from Littelfuse about their (IS) intrinsically safe fuse which doesn’t produce sufficient heat that could trigger sparks which are dangerous in an explosive environment. Link here (PDF)

Gases, petroleum products, and airborne dusts tend, by their very nature, to be explosive if sources of sparks or excess heat are present. Over the years, these hazards have led to some catastrophic losses of life and property. In response to this hazardous potential, regulatory bodies around the world, including Underwriters Laboratories, Inc., have worked to establish and refine a standard that will minimize the hazards associated with these working environments. UL 913, which was originally issued in 1971, establishes the standard for “Intrinsically Safe Apparatus and Associated Apparatus for Use in Class I, II, and III, Division 1, Hazardous (Classified) Locations.”

The purpose of this standard is to specify requirements for the construction and testing of electrical apparatus, or parts of such apparatus, having circuits that are not capable of causing ignition in Division 1 Hazardous (Classified) Locations as defined in Article 500 of the National Electrical Code, ANSI/NFPA 70. Limiting exposure to high surface temperatures and requirements for dust-tight enclosures are key aspects of the UL913 standard.

App note: Controlling LED lighting using triacs and quadracs

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Solid State device and circuits for controlling LEDs lighting, replacing conventional incandescent lamps, an App note from Littlefuse. Link here (PDF)

Light Emitting Diodes (LEDs) are fast becoming the most popular lighting option. Industry forecasts anticipate the market will continue to expand at an annual rate of 20% from 2011 to 2016, with the greatest growth coming in the commercial and industrial lighting sectors. As incandescent lamps have been made largely obsolete, given the U.S. government’s mandate to save energy, they have frequently been replaced by LEDs due to their long life (typically 25,000 hrs.) and the ease of adapting them to many different socket and shape requirements. However, LED lighting control presents a few problems not encountered with incandescent lamps. For example, with much less current from the LED load, normal types of triacs may be challenged in terms of latching and holding current characteristics.

Triacs make up the heart of AC light dimming controls. Triacs used in dimmers have normally been characterized and specified for incandescent lamp loads, which have high current ratings for both steady-state conditions and initial high in-rush currents, as well as very high end-of-life surge current when a filament ruptures.

Because they are diodes, LEDs have much lower steady-state current than incandescent lamps, and their initial turn-on current can be much higher for a few microseconds of each half-cycle of AC line voltage. Therefore, a spike of current can be seen at the beginning of each AC half-cycle. Typically, the current spike for an AC replacement lamp is 6–8 A peak; the steady-state follow current is less than 100 mA.

Designing an AC circuit for controlling LED light output is very simple when using the new Q6008LH1LED or Q6012LH1LED Series Triacs because only a few components are required. All that is needed is a firing/triggering capacitor, a potentiometer, and a voltage breakover triggering device.