The simplest circuit scheme of five self-made chargers

As the development of portable products, mobile power supply demand continues to increase. The requirements of thin and small, fast charging, high conversion efficiency and high security have also become the priority when consumers buy mobile power supply. In order to meet the needs of the consumers, many companies have launched mobile power solutions. Here we to Peiheng Semiconductor development AIC6511 and AIC3420 as a design example, provide a reference for readers.

Contains a complete mobile power supply circuit the battery Charging management IC, boost converter IC and MCU, each part will affect the overall effectiveness of mobile power supply, so it is very important to choose suitable IC.As shown in figure 4 for the mobile power supply circuit are introduced in this paper, mainly from AIC6511Lithium ion batteries charging converter, AIC3420 step-up converter and MCU. Under the proposed mobile power circuit is against doing detailed instructions.

Lithium ion battery converter

Lithium-ion battery is currently the most widely used repeatable rechargeable battery, can be single the lithium battery used for low power products, can also be more lithium battery series-parallel get higher voltage and capacity, such as mobile power supply is more than lithium batteries in parallel to obtain high capacity. Lithium-ion batteries with high energy density, low self-discharge rate, no memory effect, long service life, the advantages of light weight, very suitable for as a portable power source of the product.

Lithium battery charging IC divided into linear type and switch type two kinds, the low cost of linear type charging IC, IC pin number is less, only need a few passive components. However, linear type charging IC has large power loss, if the design is not good often leads to IC temperature is too high, and mobile power supply most commonly used cooling poor plastic shell, the linear type charging IC cannot provide larger charging current, so the linear type charging IC is usually suitable for low capacity lithium ion battery applications. If hope within a short period of time the battery is full, you must to improve the charging current, can consider to switch type charging IC application at this time. Switch type charging IC to use of high frequency switch to achieve energy transmission, can provide a large charging current, and there will be no overheating with high conversion efficiency, suitable for high capacity battery charging applications.

Charging process, when the battery voltage rises to 4.2 V, to immediately stop charging, in order to avoid the battery overcharge and dangerous, and when the battery discharge, if the battery voltage drop below 2.5 V, to immediately stop discharging, in order to avoid the battery discharge and reduce the service life of batteries. In addition, lithium battery in the application, also with short circuit protection circuit, to prevent the danger caused by short circuit lithium-ion batteries.

High demand for lithium battery to charge, the precision of the charging circuit are needed to ensure the safety of charging especially demanded an end to charging voltage accuracy within the plus or minus 0.5% of rating. The current lithium battery charging the most commonly used three method, namely the precharge mode (Trickle charge mode), constant current charging mode (Constant current charge mode), constant voltage charging mode (Constant voltage charge mode).Charging IC will detect the battery before charging status, if the battery voltage is greater than 3 v, charging with constant current charging mode; If the battery voltage is lower than 3 v, the charging mode with a warning (about 10% of the rated current charging current charging mode), to about the termination voltage, instead of constant voltage charging mode, the battery voltage is almost the same, but the charging current will continue to fall, when the charging current reaches a certain value (about 10% of the rated current charging current charging mode), the charging current will be closed, complete the charge. As shown in figure 5 for the three sections of the charging method of lithium battery charging characteristic curve.

Homemade charging treasure the minimalist circuit design (2)

There is a old laptop batteries, going to waste utilization, making a mobile charging treasure. After the battery apart, measured with a multi-meter and found that there are two batteries voltage of 0 v, estimated that after the battery not take long before, the reason right here, so get rid of the two batteries voltage of 0 v. The principle of making the figure is as below. Through the schematic diagram on the left side of the USB socket, the input 5 v dc, recharge the batteries group. After full, can carry through the 3.7 V booster to the 5 V output 5 V dc booster module, used to recharge the mobile devices such as.

Booster materials: 3.7 V to 5 V DC - DC booster module 1 piece, switch 1, only the USB socket mother 1 only, wire number.

Production process is simple, according to the principle diagram of the attachment welding, and then with hot melt adhesive for batteries group, the booster module, switch, USB female fixed, fixed in the original laptop battery box can be home and dry.

Homemade charging treasure the minimalist circuit design (3)

Schematic diagram

Buy on the net on the circuit board will set forth the + (positive) - (cathode) pick out two wires. As shown in figure.

The choice of battery; Had better use lithium battery, it is best to voltage of 3.7 V, the batteries in the battery voltage between should be equal.

Across the electrodes of them up in parallel line, remember is parallel.

Homemade charging treasure the minimalist circuit design (4)

A mobile phone charger power conversion circuit analysis

Analysis of a power supply is often from the input to start. After a 220 v ac input, end 4007 half-wave rectifier, on the other side after a 10 resistance by 10 uf capacitor filter. The 10 resistance for protection, if the malfunction causes such as over-current, the resistance will be burn out, then, to avoid causing greater failure. The right of the 4007, 4700, 82 k Ω pf capacitor, resistor, constitute a high pressure absorbing circuit, when 13003 shut off switch tube, responsible for the absorption of the induction voltage on the coil, thus preventing high pressure to the switch tube in 13003 and the breakdown.13003 for switch tube should be MJE13003) (full name, withstand voltage 400 v, collector current is 1.5 A, biggest collector of 14 w, power consumption is used to control the original edge between the winding and the power supply and broken. When the original winding kept on and off, will form a changing magnetic field in the switch of the transformer, thus the output voltage is induced in the secondary winding. Because the picture shows no winding end of the same name, so I can't see is a normal shock type or the flyback type.

However, from the point of the circuit structure, presumably, the power supply should be the flyback type.510 k Ω at left to start the resistance, to start with the base current switch tube.13003 below 10 Ω resistance for a current sampling resistor, electricity flows through after sampling (with a value of 10 * I) into voltage, the voltage diode after 4148, add to the transistor C945's base. When sampling the voltage is greater than about 1.4 V, that is, when the switch tube current is greater than 0.14 A, triode C945 conduction, thus will switch tube voltage lower base of 13003 (clamp), thus collector current decreases, and thus limit the current switch, prevent excessive current and burned (actually it is A constant flow structure, limit the maximum current switch tube to about 140 ma).

Winding transformer windings of the lower left (sampling) induces voltage of the rectifier diode rectifier, 4148 22 uf capacitor filter after sampling the voltage. In order to analyze conveniently, we take a triode C945 emitter for ground at one end. Then the sampling voltage is negative (around 4 v), and the output voltage is higher, the sampling voltage is negative. After 6.2 V Zener diode voltage sampling, and the switch tube 13003 base. Said earlier, when the output voltage is higher, so the sampling voltage negative, when negative to a certain extent, 6.2 V Zener diode is punctured, thus will switch base of 13003 potential down, this will lead to disconnection switch tube or conduction delay switch, to control the energy input to the transformer, and controls the output voltage increases, realized the function of the voltage output.

And below 1 k Ω resistance with 2700 pf series capacitance, is positive feedback branch, from sampling in the winding induction voltage, added to the base of the switch tube, to sustain oscillations. The right of the secondary windings is not too much to say, the diode RF93 rectifier, 220 uf capacitor filter after the output voltage of 6 v. Didn't find the material of the diode RF93, estimation is a fast recovery, Schottky diodes, such as, for example, because the work frequency of the switch power is higher, so you need to work frequency diode. Here can use a common n5816 1 and 1 n5817 Schottky diode instead.

Homemade charging treasure the minimalist circuit design (5)

When power supply access in USB_IN, PA6 from low to high, use external interrupt wake MCU into the charging work.

Input/output voltage detection

Charging mode can be through the detection circuit, external voltage detection, when the external voltage higher than 5.5 V, forced closure by the hardware PWM output, and interrupt processing. In addition, due to the input voltage source may be generally USB port on your computer or transformer 5 v output port on the wall, two sources of maximum current supply ability is different, when charging can be learned by detecting the input voltage to reduce input source current supply capacity limit, then the charging current is fixed, no longer.

When the mobile power supply to the external load discharge, monitor the quality of discharge voltage detection circuit, as shown above, OVP in MCU internal connection to ADC, by sampling the voltage value, to control the PWM voltage regulation. When output comprised overloading (such as the output 5 v / 1.5 A), if the load is suddenly pull out, the output voltage will rise suddenly, the rising speed will drop by software to adjust PWM is slow, so can through the OVP mechanism when closed by the hardware PWM output, and interrupt processing.

Because the general mobile phone can detect mobile power supply output voltage is over 5 V and will start mobile phone charging model, the output voltage can be set at 5.15 V, which can prevent start charging mode failure due to the phone line loss.

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