Back in the spring, a rare break in the stormy weather gave me the opportunity to visit a home-improvement store for some home project supplies. With Father’s Day promotions everywhere, what should have been a quick errand turned into a leisurely stroll through the power and garden tool section of the home improvement store. My motivation was selfish as I anticipated my family’s annual last-minute questioning: “What do you want for Father’s Day?” If you’re like me, I have never met a power tool I didn’t like.
The battery-operated tools clearly outnumbered the traditional wall AC plug and gasoline-powered devices on display. The biggest displacement was the lawn tools that traditionally ran from small two-stroke gasoline engines in the past. These two-stroke engines have received increasing scrutiny from governments as a major source of noise and air pollution. A Washington Post article cited a 2011 test conducted by the car experts at Edmunds where “a consumer-grade leaf blower [emitted] more pollutants than a 6,200-pound 2011 Ford F-150 SVT Raptor.” The two-stroke engine emitted nearly 299 times the hydrocarbons of the pickup truck and 93 times the hydrocarbons of a sedan. The blower emitted many times more carbon monoxide and nitrogen oxide as well.
Manufacturers have tiered the products by battery voltage, with lower-end products falling below 20V; mid-tier products at 32-40V; and high-tier products at 56V, which can achieve runtimes approaching one hour. The batteries now are all “swappable” battery packs, so in case the battery capacity is not adequate, you can change it out for a fresh one to finish the job without having to wait for the charging cycle. Manufacturers are also smartly introducing tool families that share the same manufacturer-specific battery packs and chargers so the consumers doesn’t have to buy so many chargers, and manufacturers can enjoy multiple tool sales, leveraging the consumer investment in their specific charger and battery packs.
Figure 1: Battery tiers
This diversity of battery packs and chargers drives a range of product requirements, architectures and topologies. Chargers, for example, use many different power topologies, including flyback, forward, interleaved-flyback, LLC half bridge and phase-shifted full-bridge. Figure 1 shows a segmentation of these topologies by voltage level.
At TI, we support all of these topologies. You can quickly evaluate them by researching constant voltage-constant current TI Designs focused on power-tool charging applications. The 120V, AC-input 200W interleaved flyback design for ~21V battery charging applications, as shown in Figure 2, brings low-cost flyback topology to higher power levels through interleaving. It has interesting advantages for power-tool battery charging, delivering over 90% efficiency and spreading out heat generation by nature of the interleaved power stage. Smaller magnetic components are used allowing for a compact design with additional benefits that include reduced cooling efforts, reduced costs and electromagnetic emissions compliance.
Figure 2: Interleaved flyback design for 21V battery chargers
In addition to complete design files, bill of materials (BOM) and test reports, the reference design guide provides temperature data and a discussion on how to scale the design for higher voltages and currents.
Another popular topology not historically used in constant-voltage, constant-current regulated designs is the LLC half bridge. The half-bridge architecture supports higher power and current levels with the advantages of the zero voltage switching inherent in the LLC topology. Engineers can evaluate the 230V AC input 400W PFC + LLC battery charger for 36V power tools shown in Figure 3.
Figure 3: PFC+LLC battery charger for 36V power tools
The design achieves greater than 92% efficiency, has less than 0.5W of standby power consumption, can be used with or without secondary-side MCU control, is optimized for cost, and is fully tested for robustness and stability. It is also compliant with IEC61000-3-2 class A electromagnetic compatibility (EMC) limits.
Happy Father’s Day to all, and happy designing with battery and charging technologies, which make appreciating dad all the easier.