Advanced: GaN Devices and why they make your chargers small

GaN Chargers High Speed
GaN Chargers High Speed

Notice how chargers for laptops and phones are shrinking in size while delivering higher wattage than ever before? One of the key techs behind that is Gallium Nitride(GaN) ICs. GaN has a wider band gap of 3.4 eV compared to Silicon substrates(1.1eV). What this means is that higher energy is needed to move an electron from the valence band to the conduction level for GaN. A wide bandgap allows these devices to work in higher breakdown Electrical fields, higher voltages, and temperatures. Another big difference is in electron Mobility, electrons can move 30% faster in GaN compared to their Silicon counterparts. Which means it can be used for very high-frequency switching applications. This enhanced conductivity also results in improved efficiency since it requires less energy to achieve the same output compared to silicon transistors.

GAN Charger Teardown

How does all this make your AC to DC charger smaller? The major element in any normal chargers is the transformers which are bulky. They are bulky since they use thicker wires around a core because of the low frequency of operation(50KHz-100KHz range). Now GaN ICs can work at 10x frequency which enables wires to be very thin and even them getting embedded on PCB traces, which enables the bulky transformers to be replaced by planar transformers(A big topic in itself). The higher freq of operation causes a linear scaling down of the size of inductors and capacitors in the design dropping them to tiny SMD ones. Another part you can get away with in GaN is dropping the input EMI filters altogether as the switching losses are minimal. All of these enable a drastic size reduction of the chargers.

How much reduction is the size? Oppo’s 50W GaN chargers launched 2yrs back is only 10mm thick. Let that sink in. AC to DC conversion at 50W at only a thickness slightly more than the thickness of your phones. There are even higher-powered ones at 300W on extremely small form factors. GaN is definitely the future for power electronics in the sub 500W range.

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Teardown of Akash Tablet

Found this old tablet lying around in our labs. It’s an old Akash tablet (2013 Model). It was designed and manufactured by the Indian company DataWind. It was a $50 tablet launched by the Indian Govt to provide low-cost tablets to students in order to increase access to educational resources and improve learning outcomes. IIT Bombay procured around 100k tablets for distribution across the country.

Coming to the internals and specs. It’s a capacitive 7-inch screen tablet with a front-facing VGA camera. The main processor is an Allwinner A13 SoC (ARM Cortex-A8 1GHz) which runs Android 4. It has a nifty Power Management IC in AXP209, which has 2 DC-DC converters and 5 adjustable LDOs and can support Lithium battery charging upto 1.8A. The I2C interface connects it to the main processor. The device supports WiFi connectivity with a prebuilt Realtek module, RTL8188CTV. It has a pair of 256MB RAM modules(256X8DDR3-WT, I think from HMD). This model seems to have a NAND Flash memory(MT29F32G08CBACA) of 32GB from Micron with a possibility of extending it to 64GB which remains unsoldered on PCB. SSD2532QN6 is the capacitive touch panel controller.

Well, the device is almost 10yrs old, I tried to turn it ON and it doesn’t turn ON without external power plugged in. Seems the battery is in deep discharge(2500mAh capacity) and the protection circuit is preventing charging it up even when I desoldered and tried to charge it separately. I have to remove the protection and bring it to a level then do the normal charge. There is no bulging or anything so I think the battery is fine but as always there is a risk with deeply discharged cells.

Overall the Akash project was an ambitious exercise but the hardware wasn’t upto the mark with a lot of complaints of overheating, boot crashes, software glitches, older specs etc. It never truly reached its potential of being a game-changer for students before the smartphone wave hit the country.

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