LCD Display Inverter

“First of all, the author learned from the data that the voltage range of a lithium battery with a nominal name of 3.7V is generally 2.8V~4.2V. If you want to get a stable voltage of 5V, 3.8V and 3.3V, obviously you can’t get it directly. Need to use a specific power chip to achieve. So how to choose a power chip? First of all, if you want to get 5V voltage, there is no doubt that you must use a booster chip. So, can the two voltages of 3.8V and 3.3V be directly realized by the lithium battery through the LDO?No problem, it can be realized, but it seems to be a waste of lithium battery power, because no matter which LDO it is, the input voltage is always higher

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Recently, I have been working on a product powered by lithium batteries. The general requirements for the power supply are as follows:

1. Powered by a single-cell rechargeable lithium battery;

2. The board comes with a charging management module, which can be directly charged by an external 5V solar panel or an Android phone charger;

3. It needs to output 5V voltage stably to supply power to the 5V module;

4. It is necessary to stably output 3.8V voltage, with an instantaneous load capacity of more than 2A, to supply power to the 4G module power supply module;

5. It needs to output 3.3V voltage stably to supply power to MCU and other 3.3V Electronic modules;

First of all, the author learned from the data that the voltage range of a lithium battery with a nominal name of 3.7V is generally 2.8V~4.2V. If you want to get a stable voltage of 5V, 3.8V and 3.3V, obviously you can’t get it directly. Need to use a specific power chip to achieve. So how to choose a power chip? First of all, if you want to get 5V voltage, there is no doubt that you must use a booster chip. So, can the two voltages of 3.8V and 3.3V be directly realized by the lithium battery through the LDO? There is nothing wrong, and the implementation can indeed be achieved, but it seems to waste the power of the lithium battery, because no matter which LDO it is, the input voltage is always higher than the output voltage. In this way, take the 3.3V voltage as an example , the voltage of the lithium battery is a little more than 3.3V at most, and it cannot continue to get a stable 3.3V voltage, which is obviously not acceptable!

After thinking about it, the only way is to use the “boost first, then step down” solution, choose a suitable boost chip, first boost the voltage of the lithium battery to 5V, and then use the step-down chip to separate the voltages. Regulated to 3.8V and 3.3V, which seems to do what we want.

Of course, there are indeed many boost and buck chips on the market. I tried a solution before, but it didn’t feel very good, so I found another chip later. Under the guidance of the manufacturer’s technology, the previous circuit has been improved. So without further ado, let me share with you my plan.

First of all, it is the charging management part of the lithium battery. The author chooses the TC4056A chip as the charging management chip for the single-cell lithium battery:

This TC4056A is also a relatively common single-cell lithium battery charging management chip on the market. The charging voltage is fixed at 4.2V, and the maximum charging current can be up to 1A. At the same time, it comes with lithium battery temperature detection, undervoltage lockout, automatic recharging and two One LED status pin to indicate charging, end. Sharp-eyed experts may have discovered a problem in the author’s circuit, that is, the charging part of the lithium battery does not have a protection circuit, is there a safety hazard? In fact, it is not, because the battery I use is an aluminum-packed battery, not a lithium battery like 18650. This aluminum-packed battery itself already has a protective plate, so I don’t do it any more, which is a waste of materials.

Next, let’s take a look at the circuit of the boosting part. In the boosting part of the lithium battery, the author uses a synchronous boosting chip model KF2185. The synchronous boosting efficiency of this chip can reach up to 94%, and it can be continuously loaded. The capacity can reach more than 2A, the voltage output can be adjusted, and the peripheral circuit is also very simple.

Next, is the 3.8V voltage regulator chip. The author chose a chip KF7416 that can output voltage. The conversion efficiency of this chip can also reach up to 95%, and the peripheral circuit is also very simple. The package of SOT23-6 , which is also very space-saving.

Finally, it is the voltage regulator circuit of 3.3V voltage. There are actually two ways to obtain 3.3V voltage, one is from 5V, and the other is from 3.8V. Because the author’s 3.8V here is to supply power to the 4G module, and, for the sake of power saving, when the 4G module is not usually used, the power supply of the 4G module needs to be disconnected separately, while the MCU and other 3.3 The V module needs to be powered on all the time. Therefore, 3.8V cannot be directly used for voltage regulation here. There are too many voltage regulator chips for 3.3V, so I chose a ME6211 with a good price/performance ratio to use.

In addition, by the way, in some lithium battery applications, if you don’t need to use other voltages but only need to use 3.3V voltage, we can also choose a self-contained boost and buck chip to achieve, no need to first Boost and then step down. For example, the KF3448 chip I learned about can achieve our purpose:

Of course, when choosing these chips, factors such as load capacity, power consumption, volume, price, etc. must be considered in many cases. In the application, you still have to make a reasonable choice according to your actual situation. Perhaps the author’s this The plan is not optimal, but it can also be used as a reference, and I hope it can help you.