In my past series of videos I teach you how to create a battery-powered Raspberry Pi handheld This is still an interesting thing Even though I am still making the next generation The important thing is that he needs to be small and light That’s why I don’t want to use NiMH batteries And use lithium batteries as the main power source The only problem is the rated voltage of 3.7V Not suitable for this system So we need a circuit that can boost the voltage to at least 5V At least 1A current But it also makes sense to integrate a constant current/constant voltage charging circuit And a circuit with over-discharge and short-circuit protection I have tested a potential candidate in a previous video Unfortunately, he does not have sufficient current output capacity and protection functions Other chips with protection functions on Alibaba Global Express At least it seems to me that reusing a power supply circuit can save a lot of trouble So to solve this difficulty I created my own Boost circuit that meets all the above requirements let's start Maybe you know I used this one called EasyEDA Free online circuit production software for a long time And because it can also convert the schematic into a circuit I will use it in this project And to make things easier We can use their partner's component shop LCSC Provide ultra-low prices And the component package and library are in EasyEDA This means that there is not only a library of schematics And there are all PCB packaging libraries Save us a lot of time And from this there is a convenient trinity! We can send it directly to the PCB factory to make PCB Actually represented by JLC PCB They are not just sponsors of this video And provide a super low price And the overall PCB quality is very satisfactory But we still need to find the right chip You can see that there are so many choices here But as long as this TP4056 I have used it before without any problems So let's use this According to the manual he constant current and constant voltage single lithium battery charging chip Obviously this also applies to Li-Po batteries There is a typical application circuit diagram at the end of the data sheet This almost only requires the use of the originals in the library To rebuild on EasyEDA software So far, the only component we need to add by ourselves is the USB power input And two 1K resistors as USB identification to input 580mA current And we need to protect the chip The first item is DW01 Provides almost all the protection functions that I care about So I placed the order right away Another typical application There is nothing wrong with remaking in this software But these two necessary MOSs do not With a simple search, I quickly found the FS8205 protection chip with dual N MOS tubes.
Can withstand a current of 20V6A; the gate voltage is only 0.45V perfect So I combined this IC into the circuit diagram This means the circuit can be charged and boosted Then I added a small switch to control whether the boost is working Start looking for a suitable boost IC I am looking for SDB628 It supports low input voltage High efficiency boost up to 2A This also has a typical application circuit diagram But there is no specific parameter value of the component This makes me look up and down the data sheet First we use this formula to determine the voltage I used a 7.5K and a 1K feedback resistor Let the output voltage be 5.1V Then the data sheet says that the inductance is between 4.7-22uH I used the maximum Then add a 22uF capacitor to the input And a suitable Schottky diode All are according to the data sheet After adding input and output It's time to convert the schematic to PCB Then start designing the PCB trace It looks like this in the end Of course this is not the best design But it's pretty good Now I click the output production button Choose 10 boards Then give them only 2 dollars! ! ! You can also upload PCB files directly on the JLC website Even if you choose 48H, you still have this super low price! I received them after a week of payment anyway I checked it again and didn't see any problems So I got all the SMD components Then start soldering them on the PCB If you don’t know what to do, please make sure you watched my previous welding instructional video After finishing I connected a lithium polymer battery Provide 5V power at the input As you can see, the red LED is on! Battery charging current 300mA When the battery is about to be fully charged After a few minutes of charging The green light is on and the voltage is stable at about 4.209V Looks reasonable It’s time to toggle the switch to boost mode and measure The boost circuit works normally Finally, I used a 6.9 ohm resistor as the load According to Ohm's law, the output current should be 732mA However, the output voltage has dropped It means something is wrong This is why I soldered the boost chip Welded on MT3608 Have the same pins and datasheet And the previous Boost boost chip The only difference is that I have used this chip before.
But did not solve the falling voltage This shows that there is a problem with the design of the board So I enlarged the PCB diagram Rearranged several components to make the overall volume smaller Accurate 4.3*1.9 Another week I received the new PCB I immediately soldered all the components But this time a new chip was used in addition to MT6308 I used FS312F protection chip The data of the new chip is similar to the previous one the only difference Is the higher minimum input voltage of 2.9V Instead of the original 2.4V which is much lower than the lithium battery voltage In any case, at the end of the project welding is completed I connected the lithium battery to the circuit Then test the charging function Works as before without any problems The difference is that the output voltage will not decrease anymore There is no pressure drop! So I soldered the lithium battery Connected to my desktop test power supply Simulate the correct test for different voltages First I linked the output to my DIY detection device Link different loads And 3 different input voltages To calculate the overall boost efficiency As can be seen from the table The average efficiency is about 80% But low voltage input and high current output will pull down this value But the most important thing is the maximum output current is 1A There is a voltage drop only when the input voltage is lower than 3.4V Not perfect but still meets my expectations Then I reduced the input voltage to about 2.9V Let the boost chip stop working or even rise to the normal value It works without activating it Only after powering the TP4056 will there be a 5V output Explain that over-discharge protection is easy to use Finally I connected the 5V output to GND Boost chip stops immediately Shows that short-circuit protection is very effective My self-made lithium battery charging boost module passed all tests! Because the standby current is very low, only 4.7uA It can still be used safely for small lithium batteries If you need a similar circuit You can watch the video description You can find links to the website and EasyEDA projects You can use it on JLC PCB Who will make this project possible? I hope you enjoy this video anyway If so, don't forget to collect and pay attention to coin Insist on creating and see you next time!