Creating a Better and Cheaper Power Delivery System for Amazon's Fire TV Stick
This DIY Fire TV Stick power circuit is a cheaper and improved alternative to the store bought version.
Problems with the Fire TV Stick
Streaming sticks are handy little devices that allow for anything with an HDMI port to display a wide variety of television and internet content. And on most televisions, the HDMI port is positioned right next to a USB port, which is what often gets used to power the stick. But there is a problem: this USB port typically only has a rating of 500mA current draw at max, and it can be exceeded when an update occurs or during boot. The solution is to add a buffering circuit in between the USB port and streaming stick that enables extra power to be given when needed while keeping the draw from the USB port to 500mA.
Measuring current draw
In order to get a better understanding of the problem, Scott, who runs the electrical engineering YouTube channel GreatScott!, got out a current measurement device and began plotting its values in real-time. He observed that the connected Fire TV Stick often exceeds the 500mA limit while booting up and scrolling through content libraries, although it settles at around 200mA while streaming videos.
Understanding the store bought solution
His store bought solution requires a quick charge before use, and that is due to its internal lithium ion battery cell, which provides extra boosts in power when required by the attached load. Looking back at the current draw plot revealed the Fire TV Stick now only drew a maximum of 500mA at all times, thereby proving the solution worked. One major downside was the inclusion of the lithium ion battery, as it can only withstand a couple thousand charging cycles before degrading and needs extra protection circuitry to prevent overloading/fires.
Building the DIY version
The obvious way to fix the issue was to change out the battery for a pair of high-capacity supercapacitors that can withstand current peaks while being rated for nearly 300,000 total charge/discharge cycles. Scott designed a circuit around these capacitors in order to limit their total current draw from the USB port to 500mA and letting the Fire TV Stick draw 500mA once they are charged.
As seen in his YouTube video, the entire system was able to achieve stable current delivery while having the added benefits of a longer lifespan and simpler circuit, all at half the price of the retail version. You can view this post to see the schematic and bill of materials.
