Companies Vie for Title of “World’s Smallest GaN Charger”
To meet the demand for faster chargers, many companies are investing in GaN-based power converters—the smaller, the better.
At this year's Applied Power Electronics Conference (APEC) in Houston, GaN Systems, together with Rompower Energy Systems, claimed to have developed the world's smallest 65 W and 100 W GaN chargers, featuring a power density of greater than 22 W per cubic inch. The 65 W charger measures 30.5 x 35.0 x 46.6 mm and specifies an efficiency of more than 94.5% at 115 Vac and more than 95% at 230 Vac.
In the same week, Silanna Semiconductor and Smarter Living also staked a claim for "the world's smallest in-wall 65 W fast charger"—theirs measuring 42 x 42 x 30 mm. Silanna's device features an efficiency of up to 95% across the voltage range from 90 Vac to 265 Vac.
It's not surprising that these two companies are concurrently vying for titles as the smallest in the industry; the trend of miniaturization continues as GaN becomes more widely adopted. There are a number of design considerations to be taken into account while implementing GaN-based power converters—especially at these sizes.
Design Considerations for GaN Converters
In GaN devices, the parasitic capacitances are very small, enabling faster switching. This feature introduces a high rate of change in current and voltage, which can falsely trigger a gate drive and cause a shoot-through. This causes a trade-off between size and reliability.
To get around the problem of false triggering, designers add series resistance to accurately detect shoot-through and provide a fast loop response for the protection circuit. This series resistor, however, increases the power dissipation and decreases efficiency.
Example of an isolated gate driver circuit for one GaN HEMT. Image used courtesy of GaN Systems
There are several other factors that can limit the size, efficiency, and reliability of GaN-based power converters. Silanna Semiconductor's 65 W GaN charger integrates an active clamp feedback (ACF) design that absorbs and recycles the back-EMF energy incurred by the turn-off and limits the primary FET drain voltage spike during the turn-off events.
In addition, this device embeds a digital control architecture to adjust the device's mode of operation on a cycle-by-cycle basis to maintain high efficiency, low EMI, fast dynamic load regulation, and other key power supply parameters in response to varying line voltage and load.
Miniature Chargers Specifications
GaN technology unlocks the full potential of power converter topologies as far as the efficiency limits allow. Though chargers are getting smaller and smaller, they continue to be highly reliable and faster.
As mentioned, GaN Systems' 100 W charger is 28.6 x 44.0 x 35.0 x 67.0 mm in size and provides an efficiency of more than 94.5% at 115 Vac and 230 Vac with a power density of more than 20 W per cubic inch.
The new 65 W and 100 W chargers. Image (modified) used courtesy of GaN Systems
In contrast, Silanna Semiconductor's new 65 W 3510PDFE charger is built around the SZ1131 ACF controller that enables high efficiency of 95% across universal (90 Vac to 265 Vac) input voltages and varying loads. Moreover, it specifies an ultra-low no-load power of less than 20 mW for smaller form factors and reduced overall energy consumption.
Silanna's in-wall 65 W GaN-based charger. Image courtesy of Silanna Semiconductors
Both of these products exemplify why GaN transistors are replacing silicon transistors for in-wall chargers: they are a faster, more efficient, and more compact solution. GaN HEMTS (high electron mobility transistors) switch efficiently and can operate at higher frequencies than silicon MOSFETs. These advantages allow designers to reduce the transformer size by operating at higher frequencies. Moreover, the high efficiency eliminates the need for heat sinks, further miniaturizing the converter.
The Race for Smaller GaN Power Converters
With different semiconductor technologies competing to reduce switching losses and improve efficiency, GaN-based technology seems to be a growing contender. By replacing silicon transistors with GaN, a compact charger can do more work than a larger one at a faster rate. This is why GaN is gaining traction in smartphone and laptop chargers. Now, the race is on among charger manufacturers to realize the smallest GaN chargers that provide high efficiency and faster charging.