As portable products continue to grow, the demand for mobile power continues to increase. Lightweight, compact, fast charging, high conversion efficiency and high security have become the primary considerations for consumers when purchasing mobile power. To meet the needs of consumers, many companies We have launched mobile power solutions. Here we use the AIC6511 and AIC3420 developed by Peiheng Semiconductor as design examples for readers' reference.
A complete mobile power circuit consists of a battery charge management IC, boost converter IC and MCU, each of which affects the overall performance of the mobile power supply, so it is important to choose the appropriate IC. Figure 4 shows the mobile power circuit to be introduced in this paper. It is mainly composed of AIC6511 lithium-ion battery charge converter, AIC3420 boost converter and MCU. The proposed mobile power circuit will be described in detail below.
Lithium-ion battery charge converter
Lithium-ion battery is currently the most widely used rechargeable battery. It can be used for low-power products with single lithium batteries. It can also connect multiple lithium batteries in series to obtain higher voltage and capacity. For example, mobile power is more than one. Lithium batteries are connected in parallel to achieve high capacity. Lithium batteries have the advantages of high energy density, low self-discharge rate, no memory effect, long life and light weight, and are very suitable as power sources for portable products.
Lithium battery charging ICs are divided into linear and switching types. The cost of linear charging ICs is low, and the number of IC pins is small, requiring only a few passive components. However, the linear charging IC has a large power loss. If the design is not good, the IC temperature is too high, and most of the mobile power supplies generally use a poorly heat-dissipating plastic case, so that the linear charging IC cannot provide a large charging current. Linear charging ICs are generally suitable for low-capacity lithium-ion battery applications. If you want to fully charge the battery within a short period of time, you must increase the charging current. Consider using a switched charging IC. The switching charging IC utilizes high-frequency switching of the switch to achieve energy transfer, provides a large charging current, and has high conversion efficiency without overheating, and is suitable for charging applications of high-capacity batteries.
During the charging process, when the battery voltage rises to 4.2V, stop charging immediately to avoid danger caused by overcharging the battery. When the battery is discharged, if the battery voltage drops below 2.5V, stop discharging immediately to avoid the battery passing. Reduce the battery life. In addition, the lithium battery is also applied with a short-circuit protection circuit to prevent the lithium battery from being dangerous due to a short circuit.
Lithium batteries have high requirements for charging, and require precise charging circuits to ensure the safety of charging. In particular, it is required to terminate the charging voltage within ±0.5% of the rated value. At present, lithium battery charging is most commonly carried out by a three-stage charging method, namely, a precharge mode (TrickleChargeMode), a constant current charging mode (ConstantCurrentChargeMode), and a constant voltage charging mode (ConstantVoltageChargeMode). The charging IC will detect the state of the battery before charging. If the battery voltage is greater than 3V, it will be charged in the constant current charging mode; if the battery voltage is lower than 3V, it will be in the pre-charging mode (about 10% of the constant current charging mode charging current) Charging, when the voltage is close to the end voltage, it is changed to constant voltage mode charging. At this time, the battery voltage is almost unchanged, but the charging current will continue to decrease. When the charging current drops to a certain value (about 10% of the constant current charging mode charging current) ), the charging current will be turned off and the charging is completed. Figure 5 shows the charging characteristics of a lithium battery using a three-stage charging method.
There is a used laptop battery, intended to use waste, to make a mobile charging treasure. After disassembling the laptop battery, I measured it with a multimeter and found that the voltage of two batteries was 0V. It is estimated that the laptop battery could not be used for a long time. The reason is here, so the two batteries with the voltage of 0V are used. Throw it away. The schematic of the production is shown in the figure below. The battery pack can be charged by inputting 5V DC through the USB socket on the left side of the schematic. When it is full, it can be carried around, and it can output 5V DC through the 3.7V boost to 5V boost module to charge the mobile phone and other equipment.
Material: 3.7V boost to 5V DC-DC DC boost module, 1 switch, 1 USB socket female, several wires.
The production process is also relatively simple, according to the schematic diagram of the wire welding, and then use the hot melt adhesive to fix the battery pack, boost module, switch, USB female seat, fixed in the original laptop battery box can be completed.
Schematic
On the board that is bought online, it will be written that + (positive) - (negative) is connected to the two wires. As shown
The choice of battery; it is best to use a lithium battery, the voltage is preferably 3.7V, the voltage between the battery should be equal.
Just connect their positive and negative poles together, remember to be in parallel.
Analysis of a mobile phone charger power conversion circuit
Analyze a power supply, often starting with input. 220V AC input, one end through a 4007 half-wave rectification, the other end after a 10 ohm resistor, filtered by 10uF capacitor. This 10 ohm resistor is used for protection. If an overcurrent occurs due to a fault in the back, the resistor will be blown to avoid causing a larger fault. The right 4007, 4700pF capacitor and 82KΩ resistor form a high-voltage snubber circuit. When the switch tube 13003 is turned off, it is responsible for absorbing the induced voltage on the coil, thereby preventing high voltage from being applied to the switch tube 13003 and causing breakdown. 13003 is the switch tube (complete name should be MJE13003), withstand voltage 400V, collector maximum current 1.5A, maximum collector power consumption is 14W, used to control the on and off between the primary winding and the power supply. When the primary winding is continuously turned on and off, a varying magnetic field is formed in the switching transformer, thereby generating an induced voltage in the secondary winding. Since the same name end of the winding is not indicated in the figure, it cannot be seen whether it is a forward or a flyback.
However, from the structure of this circuit, it can be speculated that this power supply should be flyback. The 510KΩ at the left end is the starting resistor, which provides the base current for starting the switch. The 10Ω resistor below 13003 is the current sampling resistor. The current is sampled and becomes a voltage (the value is 10*I). This voltage is applied to the base of transistor C945 via diode 4148. When the sampling voltage is greater than 1.4V, that is, when the switching tube current is greater than 0.14A, the transistor C945 is turned on, thereby lowering the base voltage of the switching tube 13003 (clamping), thereby reducing the collector current, thus limiting the switch. The current prevents the current from being too large and burns out (in fact, this is a constant current structure, which limits the maximum current of the switch to about 140 mA).
The induced voltage of the winding (sampling winding) at the lower left of the transformer is rectified by a rectifying diode 4148, and the 22uF capacitor is filtered to form a sampling voltage. For the convenience of analysis, we take the end of the emitter of the transistor C945 to ground. Then the sampling voltage is negative (about -4V), and the higher the output voltage, the more negative the sampling voltage. After the sampling voltage passes through the 6.2V Zener diode, it is applied to the base of the switching transistor 13003. As mentioned earlier, when the output voltage is higher, the sampling voltage is more negative. When it is negative to a certain extent, the 6.2V Zener diode is broken down, which lowers the base potential of the switch 13003, which will result in the switch tube. Disconnect or delay the conduction of the switch, thereby controlling the energy input into the transformer, thus controlling the rise of the output voltage and realizing the function of the regulated output.
The lower 1KΩ resistor and the 2700pF capacitor in series are positive feedback branches. The induced voltage is taken from the sampling winding and applied to the base of the switching transistor to maintain oscillation. There is not much to say about the secondary winding on the right. It is rectified by diode RF93 and filtered by 220uF capacitor to output 6V. The diode RF93 data was not found. It is estimated to be a fast recovery tube, such as a Schottky diode. Because the switching power supply has a higher operating frequency, a diode with an operating frequency is required. Here, a common Schottky diode such as 1N5816 or 1N5817 can be used instead.
Self-made charging treasure minimalist circuit design (5)When USB_IN has power input, PA6 goes from low to high, and the external interrupt is used to wake up the MCU to enter charging operation.
Input/output voltage detection
The charging mode can detect the external voltage through the detection circuit. When the external voltage is higher than 5.5V, the PWM output is forcibly turned off by the hardware, and an interrupt is generated for processing. In addition, since the input voltage source may be a USB port on a general computer or a 5V output port of a wall transformer, the maximum current supply capability of the two sources is different, and it can be known by detecting the decrease of the input voltage during charging. Enter the limit of the source current supply capability, and then fix the charging current, no longer increase.
When the mobile power source discharges to the external load, the detection circuit monitors the discharge voltage. As shown above, the OVP is connected to the ADC inside the mcu, and the PWM voltage can be controlled by sampling the voltage value. When the output is overloaded (for example, output 5V / 1.5A), if the load is suddenly removed, the output voltage will suddenly rise. This rising speed will be slower by software adjustment PWM, so it can pass. The OVP mechanism forces the PWM output to be turned off by hardware and generates an interrupt for processing.
Since the mobile phone will detect that the output voltage of the mobile power source is higher than 5V, the mobile phone charging mode will be activated, so the output voltage can be set at 5.15V, which can prevent the startup charging mode from failing due to excessive loss of the charging line of the mobile phone.
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