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eap h C g U sinA sian nic o r t El e c d ul e s Mo im J y b 8 t r P a Row e Li-Ion and LiPo Charger Modules These modules are designed to charge Lithium-ion and Lithium-ion polymer cells. One is low-cost and has a simple design, while the other sports an inbuilt DC-DC boost converter to provide a regulated output voltage from the Li-ion/LiPo cell, since its voltage varies as it charges and discharges. A s noted in the feature article on page 88 of this issue, lithiumion (Li-ion) and lithium-ion polymer (LiPo) cells and batteries are rapidly overtaking all earlier kinds of rechargeable energy storage. They're now being used in just about all mobile and cordless phones, in the USB Power Bank devices used to recharge them, in laptop and tablet PCs and in many portable power tools. Not only that, but it now looks like Li-ion/LiPo batteries are the preferred power source in the most successful current generation electric cars, as well as providing some small scale grid storage. So it's not surprising that Li-ion/ LiPo charging modules have now become readily available on popular internet venues like eBay and AliExpress and we will be looking at three examples in this article. From here on, we’re assuming that you are already familiar with the operation of Li-ion/LiPo cells. If not please read the primer article on page 88. Basic charger modules Probably the most common charger modules you'll find on the web are those based on the TP4056 charge controller chip, like the one shown in the photo at lower right. These modules are quite tiny, measuring 44  Silicon Chip only 26 x 20mm and they're currently available for just a few dollars each, even in small quantities. There are a few minor variations but most are very similar to the one pictured; and they are all slight variations of the circuit shown in Fig.1. Some are fitted with a micro-USB type B socket on the input side, while others have the slightly larger and more rugged mini-USB type B socket. You might choose this type since microB sockets can be a bit fragile and can even part from the module PCB when you're removing the USB cable. Having said that, micro-B cables are very common and cheap as they are used to charge most modern smartphones so that’s a fairly strong reason to prefer the micro version, even if it’s a bit more fragile. As shown in Fig.1, there's little in one of these modules apart from the TP4056 controller chip itself. Made by Chinese firm Nanjing Top Power ASIC Corp, the TP4056 comes in a compact SOIC-8 package and provides all of the functions of a single-cell Li-ion/LiPo battery charger, powered from a 5V USB-compatible supply. It follows the standard CC-CV charging protocol, with a maximum current of 1000mA (1A) in CC (constant current) mode and a maximum voltage of 4.2V (±1.5%) in CV (constant volt- age) mode. Charging is automatically terminated when the charge current falls to 10% of the programmed value. The charging current in CC mode can be programmed by changing the value of the Rprog resistor connected between pin 2 of the IC and ground. As supplied, the module has a 1.2kW resistor fitted, corresponding to a charging current of 1000mA. If you want a lower charging current, you can select a higher value resistor – as shown by the table at lower right in the diagram. For example, if you replace the resistor with one of 2.0kW, the charging current in CC mode will drop to around 580mA. However, that should only be necessary if the cell you’re charging has a capacity of less than 1Ah which would make it quite small, and even some cells under 1Ah would be OK being charged at 1A; if in doubt, check the manufacturer’s ratings for that cell. As well as performing all of the charge control functions, the TP4056 also controls two indicator LEDs to signal the charger's current state. Red LED1 glows brightly during both charging modes (CC and CV) and ceases glowing when charging is terminated. Green LED2 only lights when charging is terminated. Both LEDs remain off if the USB input voltage is too low (<4.0V) or there is no cell or battery connected. siliconchip.com.au Note that if you want to power the charger from the USB port of your PC or laptop, it would be a good idea to change the value of Rprog to 2.4kW so that the charging current is reduced to around 500mA; this is the maximum that should be drawn from the USB port of a PC (even though many ports will allow you to draw 1A if you try, at least for a short period). But if you are powering the charger from one of the 5V/1A USB plug packs, Rprog can be left at its default value of 1.2kW. That's about it for the basic versions of the USB powered Li-ion/LiPo charger. They're cheap as chips but they actually do quite a good job of charging single cells and parallel-cell batteries. Do keep in mind though that the TP4056 is a linear device, utilising an internal P-channel Mosfet to reduce the incoming supply voltage of say 5.5V down to the charging voltage of the cell, which could be as low as 3V when fully discharged. At a 1A charge current, that’s a dissipation of (5.5V - 3V) × 1A = 2.5W which is quite substantial for an SOIC-8 package and it’s likely to get quite hot under this condition (even more so if you run the chip at its maximum input supply rating of 8V). This won’t cook the chip since it has thermal regulation, which essentially means that it reduces the charging current if it gets too hot. But it does mean that it will take longer to charge the cell if you run into thermal limiting and the charging process won’t be terribly efficient. Considering the size and cost of these modules, that really isn’t a problem. Fancier versions In addition to the basic charger modules, there are more elaborate versions available as well. One of the most popular of these is shown on the next page. It's made by the firm Elecrow, based in Shenzen, China, and is about four times the size of the basic modules, measuring 68 x 49mm. The circuit is shown in Fig.2. The actual Li-ion charger section is based around IC2 at the top. This is a Consonance CN3065 chip, which functions in much the same way as the TP4056 device used in the basic modules. As before, the CC mode current level is set via the resistor Rprog connected between pin 2 (Iset) and ground, and the default value of 2.0kW for this resistor gives a charging current of 900mA. The CN3065 again follows the siliconchip.com.au Fig.1: circuit diagram for the basic TP4056 module. Note that many modules of this type will differ slightly from this circuit diagram. standard CC-CV protocol, with mode switching at 4.2V±1% and charging terminated when the current in CV mode drops to 10% of the programmed CC level. An interesting extra feature is that the cell voltage level at which the device switches from CC mode to CV mode can be raised above 4.2V by adding an external resistor between pin 5 (BAT) and pin 8 (FB). This will result in it reaching full charge sooner. As with the TP4056, the CN3065 provides outputs to drive two LEDs. LED1 lights during charging, while LED2 lights when charging has terminated. Incidentally, the CN3065 is in a very tiny (3 x 3mm) DFN-8 leadless SMD package. Another nice feature of the Elecrow PSB01012B charger is that it provides a choice of two DC inputs. One is via CON2, the mini USB input socket, while the other is via CON1, a JST 2.0mm socket designated as the input from a solar photovoltaic panel. (A second JST 2.0 socket [CON3] is used for the Li-ion cell connection.) Schottky diodes D1 & D2 are used to feed the two inputs to IC2, so no input switching is required. Note that the D- and D+ USB data lines of CON2 are taken through to USB output socket CON4, a standard USB type A socket. That's because the PSB01012B is not just a charger but in effect a USB Li-ion power pack as well. It's also the reason for on-off switch S1, in series with battery connector CON3. But note that S1 will need to be in the ON position for charging to take place. The other half of the Elecrow PS- B01012B module provides a regulated +5V supply from the varying output of the Li-ion cell. This is the function of the circuitry around IC1, REG1 and IC3, in the lower half of Fig.2. IC1 is the actual output voltage regulator. This is an Intersil ISL97516 device, described as a high frequency, high efficiency step-up (boost) voltage regulator which operates in a constant frequency PWM mode. It's in a very small MSOP-8 package. The ISL97516 operates at a nominal frequency of 620kHz or 1250kHz, selected by connecting pin 7 (Fsel) to ground or pin 6 (Vdd). As you can see from Fig.2, in the Elecrow module it's programmed for 620kHz. The switching FET inside the device has a max- This TP4056 module shown uses a micro-USB[2] connector, but there are some that instead use mini-USB[1]. August 2017  45 Fig.2: circuit diagram for the Elecrow PSB01012B charger module which utilises a CN3065 instead of the TP4056 detailed earlier (the CN3065 is functionally identical to the TP4056). imum current limit of 2.0A and an on-resistance of 200mW. As a result, it's claimed to deliver over 90% conversion efficiency – quite impressive. The input voltage range of the ISL97516 is rated at 2.3-5.5V, which is well suited to its application here. The output voltage range is specified as 5-25V. The actual output voltage is determined by the proportion of the output voltage fed back to pin 2 (FB) of the device, via a resistive divider. In the Elecrow module, the divider formed from the 43kW and 15kW resistors programs it to give an output of 5V. Other attractive features of the ISL97516 include sensing of the current in the switching FET for thermal overload protection and a soft start feature which allows slowing down of the internal oscillator's startup by connecting a capacitor from pin 8 (SS) and ground. As you can see in the Elecrow module, a 27nF capacitor is used for this. The regulated 5V output from IC1 appears across the 47µF capacitor at the cathode of diode D3 and is then filtered before being fed to pin 1 of the USB output connector CON4. 46  Silicon Chip So that's the boost converter/regulator section. But what about the rest of the module's circuit, involving REG1 and two op amps in IC3? This additional circuitry is basically to monitor the Li-ion/LiPo cell voltage, and signal if it drops below a safe level. REG1 is a Micrel MIC5205-2.5 low noise LDO regulator, used to derive a 2.5V±1% reference from the cell voltage. This is fed to op amps IC3a and IC3b which are used as comparators. The second input of each “comparator” is fed with a proportion (0.6875) of the cell voltage, derived by the resistive divider formed by 150kW and 330kW resistors. This voltage is fed to the positive input of the IC3a comparator and the negative input of the IC3b comparator. As a result, when ever the divided-down cell voltage is above +2.5V, IC3a turns on LED3 to indicate that the cell voltage is OK. By contrast, if the divided-down cell voltage falls below +2.5V, IC3a turns off LED3 and IC3b turns on LED4 to indicate that the cell is nearing the limit of safe discharging. This occurs at 2.5V ÷ 0.6875 = 3.64V, a little above the minimum recommended discharge voltage to achieve the best cell lifespan. So the Elecrow charger module with its inbuilt +5V output regulator provides significantly more capabilities than the basic modules. It actually provides all of the functions needed for making your own USB Power Bank, using a Li-ion or LiPo cell/battery of your own choosing. Plus it has the ability to charge your Li-ion/LiPo cell from a solar panel. So although it will cost you significantly more than one of the basic modules, it's still good value for money. Trying them out I tried a couple of the basic TP4056based charger modules with both a single 18650 Li-ion cell and a battery of two parallel-connected 18650 cells. The chargers did everything that could be expected from them, charging the cells repeatedly with no problems – apart from the micro-B USB input socket breaking away from one of the modules when I tried to unplug the siliconchip.com.au track to pin 3 of IC1 and soldering it to output pin 1 of IC3a instead. However, note that this would cut off the output at the aforementioned cell voltage of 3.64V, which is a little high; ideally, alarm LED4 should light before the cell is discharged to the point where the output switches off. A second threshold in the range of 3.0-3.3V would do the trick, but that would require a number of extra components. Smaller Elecrow module The Elecrow charger module is a more advanced version of the smaller module, and provides a 5V regulated supply from the Li-ion cell.[3] cable from the USB plug pack. Hence my suggestion to prefer the mini-USB socket version. I also tried out one of the fancier Elecrow PSB01012B modules, although this did involve getting hold of some cables with the very small JST 2.0 connectors (for the Li-ion cell cables, to connect to CON3). As a charger, this one worked just as well as the basic modules. But where it really shone was on the output side, being able to provide a regulated +5V output (or reasonably close to it; about 4.85V) for the USB device connected to CON4's output, even for a load drawing 500mA and with a partly discharged Li-ion cell with a terminal voltage down to about 3.8V. In fact, it kept providing this regulated output voltage even when the Li-ion cell dropped down below 3.0V, after about 40 minutes. Quite impressive! (But not recommended if you want your cell to last a long time.) It might seem to be nit-picking, but I'd like to have seen the Elecrow module's regulated USB output closer to the nominal +5V under load than 4.85V. If you calculate the expected output voltage for IC1, you get 1.294V x (43kW ÷ 15kW + 1) = 5.0V, so this is likely a component tolerance issue, requiring trimming. This could be achieved by measuring the actual output voltage and then paralleling the 15kW resistor with a higher value SMD resistor, by soldering it on top. For example, in my case, the output needs to be raised by (5.0V siliconchip.com.au 4.85V) ÷ 4.85V = 3.1%, so a resistor of 15kW ÷ 0.031 = 483,870W or say 470kW should do the trick. I also think that ALARM LED4 should ideally be a red one, not another green one as it is at present. It's right next to green LED3, making it difficult to see when LED4 has lit up. You could fix this by de-soldering LED4 and fitting a red LED in its place. My only other complaint about the Elecrow module was that the very small slider switch used for power switch S1 was very flimsy. Perhaps it had been damaged in transit, but at one point the tiny actuator almost came out of the switch body – not a good sign. I also think that it would be a good idea if the unit could be set up to automatically switch off the output if the cell voltage drops too low, to prevent damage from over-discharge. Some Li-ion and LiPo cells have internal over-discharge protection circuitry but many do not. It would be possible to modify the module to provide this function, by cutting the It was only after I had checked out the Elecrow PSB01012B module that I learned about their other “mini” module. Luckily I was able to get a hold of one of these quickly, in order check it out as well. As you’d expect from the circuit (Fig.3), its performance as a Li-ion cell charger is very close to that of its bigger brother – it just takes a little longer to charge, because of the lower default charging current level. It functions in a very similar manner but is significantly smaller (46 x 32mm), costs less and they have made some tweaks to the design. It uses the same CN3065 chip for charging as the larger module. Unlike the larger module, it does not have a power switch, so the load is always powered. But I was particularly interested in measuring the performance of its DC-DC boost converter, because of its greater simplicity. And here I was pleasantly surprised, because the converter in the mini module was just as good as the one in its big brother. Even though its output voltage under 250mA of loading was slightly lower at 4.80V with a cell voltage of 3.84V, it only dropped to 4.78V when the cell voltage fell to the recommended minimum of 3.0V. So it might be a lot simpler, but it’s just as impressive in terms of conversion efficiency. There isn’t much going on underneath the Elecrow module, except for a few tracks and the eight through-hole pads provided for D+ and Dbiasing resistors.[3] August 2017  47 Fig.3: circuit diagram for the smaller Elecrow charger module. The DC-DC boost converter is much simpler than the larger Elecrow module and is based around an ETA1036-50 synchronous converter chip (IC2; SOT23-5). This allows for a drastic simplification of the boost converter to a 2.2µH inductor, four SMD capacitors plus the IC. Q1 allows the incoming 5V from USB or the solar cell to power IC2 directly, bypassing the cell. The other differences are as follows. Firstly, the input power socket is a micro type-B, rather than mini. Secondly, the output current capability is lower, at 500mA compared to 1A. They have also added a JST 2.0 2-pin output connector in parallel with the USB output, and added a pass-through function, which feeds the input voltage directly through to the output when it is present, to reduce the load on the cell. There are a couple of drawbacks to this module, though. Note that the USB and Solar inputs are wired in parallel so there’s a possibility of current being fed back into the USB source, which would be bad. Also, if the USB sup- The mini Elecrow module is a decent bit smaller (46 x 32mm) than the larger variant (68 x 49mm).[4] 48  Silicon Chip ply voltage is high enough, Q1’s body diode could allow current to pass into the cell, bypassing IC1 and possibly leading to over-charging. This is likely a design oversight and will probably be fixed in future revisions, but could be solved by placing a diode in series with Q1; a notable omission from the design. The bottom line Overall then, all of these modules seem to work quite well. The basic charger modules are fine if you just want to charge a Li-ion/LiPo cell (or two in parallel), although I would recommend the version with a mini-B USB input socket rather than a microB socket, for the greater robustness. With the enhanced Elecrow PSB01012B and mini variant, the main reason to go for the larger PSB01012B module is for its “through path” for the USB signal lines between input and output and for its use of the more reliable mini-B USB input connector. One final note: if you want to use either a basic charger module or one of the fancier modules to charge one of the flat pack LiPo cells, you’ll probably need to get a matching charging cradle to make reliable connections to the contacts on the end of the cell. These cradles are available at a quite low cost from sites like eBay or AliExpress, although some of them come with their own inbuilt chargers. Finding the charging modules You can purchase the modules featured in this article from the Silicon Chip online shop, at the following links. Postage within Australia is a flat rate of $10 per order. [1] TP4056 1A Li-ion/LiPo charger with mini USB socket – $2.50 each; www. siliconchip.com.au/Shop/7/4305 [2] TP4056 1A Li-ion/LiPo charger with micro USB socket – $2.50 each; www. siliconchip.com.au/Shop/7/4306 [3] Elecrow CN3065-based 1A Li-ion/ LiPo charger with 1A step-up circuit, USB pass-through and power switch; 68 x 49mm, mini type-B USB input, full-size type-A USB output, two JST cables included – $35.00 each; www. siliconchip.com.au/Shop/7/4307 [4] Elecrow CN3065-based 1A Liion/LiPo charger with 500mA stepup circuit; 46 x 32mm, micro typeB USB input, full-size type-A USB output, three JST cables included – $15.00 each; www.siliconchip.com. SC au/Shop/7/4308 siliconchip.com.au