The working mechanism of the
Lithium Ion Battery is: when the battery is charged, the lithium in the positive electrode material is dissolved out and embedded in the modified graphite layer of the negative electrode; when the battery is discharged, the lithium ions are deintercalated from the graphite layer and pass through the separator to be backfilled to the positive electrode. In the layered structure of cobalt lithium oxide. As the charge and discharge progress, lithium ions are continuously inserted and extracted from the positive and negative electrodes, so some people call it a rocking chair battery. The rated voltage of the
Lithium Ion Battery Cell is 3.6V, the charging limit voltage is 4.2V, and the discharge limit voltage is 2.5V. .
The charging process of lithium-ion batteries is divided into two steps: first, constant current charging, the current is constant, and the voltage continues to rise. When the voltage is charged to 4.2V, it is automatically converted to constant voltage charging. During constant voltage charging, the voltage is constant and the current is constant. It is getting smaller and smaller until the charging current is less than the preset value, so when someone uses direct charging to charge the battery of the mobile phone, it is clear that the battery display is full, but it still shows that it is charging. In fact, the voltage at this time has reached 4.2V, so the battery is displayed as full. At that time, the constant voltage charging process is in progress. Then someone may ask why constant voltage charging is required. Isn`t it enough to charge straight to 4.2V with constant current? It`s actually very easy. Explain, because every battery has a certain internal resistance, when charging to 4.2V with constant current, this 4.2V is actually not the actual voltage of the battery, but the voltage of the battery plus the voltage consumed by the internal resistance of the battery The sum, if the current is large, the voltage consumed on the internal resistance is also large, so the actual battery voltage may be much smaller than 4.2V, so use a constant voltage charging process to slowly reduce the charging current , So the actual voltage of the battery is very close to 4.2V.
Working principle diagram of a switch-type switch-type mobile phone charger
This charger uses RCC type switching power supply, that is, oscillation suppression converter, which is different from pWM type switching power supply. The pWM type switching power supply is composed of an independent sampling error amplifier and a DC amplifier to form a pulse width modulation system; while the RCC type switching power supply is just a level switch composed of a voltage stabilizer, and the control process is an oscillation state and a suppression state. Since the switching tube in the pWM switching power supply is always on and off periodically, the system control only changes the pulse width of each cycle, and the control process of the RCC switching power supply does not continue to change non-linearly. It has only two states: When the output voltage exceeds the rated value, the pulse controller outputs a low level and the switch tube is turned off; when the output voltage of the switching power supply is lower than the rated value, the pulse controller outputs a high level and the switch tube is turned on. When the load current decreases, the discharge time of the filter capacitor is prolonged, the output voltage will not decrease quickly, and the switch tube is in the cut-off state. The switch tube will not be turned on again until the output voltage drops below the rated value. The cut-off time of the switch tube depends on the size of the load current. The on/off of the switch tube is controlled by the level switch by sampling the output voltage. So this kind of power supply is also called non-periodic switching power supply.
The 220V city power is bridge rectified by VD1~VD4 to form a DC voltage of about 300V on the collector of V2. The intermittent oscillator is composed of V2 and a switching transformer. After starting up, 300V DC voltage is applied to the collector of V2 through the primary of the transformer, and this voltage also supplies a bias voltage to the base of V2 through the starting resistor R2. Due to the use of positive feedback, V2Ic rises rapidly and saturates. During the cut-off period of V2, the induced voltage in the secondary winding of the switching transformer turns on VD7 and outputs a DC voltage of about 9V to the load. The induction pulse appearing in the feedback winding of the switching transformer is rectified by VD5 and filtered by C1, and a DC voltage proportional to the number of oscillating pulses appears. If this voltage exceeds the voltage regulation value of the voltage regulator tube VD17, VD17 will be turned on, and this negative rectified voltage will be added to the base of V2 to make it cut off quickly. The cut-off time of V2 is inversely proportional to its output voltage. The on/off of VD17 is directly affected by the grid voltage and load. The lower the grid voltage or the greater the load current, the shorter the conduction time of VD17 and the longer the conduction time of V2. On the contrary, the higher the grid voltage or the smaller the load current, the higher the rectified voltage of VD5 and the conduction time of VD17. The longer, the shorter the on-time of V2. V1 is the overcurrent protection tube, and R5 is the sampling resistor of V2Ie. When V2Ie is too large, the voltage drop on R5 causes V1 to turn on and V2 to cut off, which can effectively eliminate the inrush current at the moment of startup, and it is also a compensation for the control function of VD17. VD17 uses voltage sampling to control the oscillation time of V2, while V1 uses current sampling to control the V2 oscillation time.
If you are charging nickel-cadmium or nickel-metal hydride batteries, due to the memory effect of these batteries, you need to discharge them on time. SW1 is a charge switch for nickel-cadmium, nickel-metal hydride, and lithium-ion batteries. SW1 and the precision reference power supply SL431 supply two different precision reference sources for the operational amplifier LM324⑨, which are switched by SW1. When charging nickel-cadmium and nickel-metal hydride batteries, the reference voltage of LM324⑨ pin is about 0.09V (no load); when charging lithium-ion batteries, the reference voltage of LM324⑨ pin is about 0.08V (no load). The design is determined by the unique chemical characteristics of these two types of batteries. Press SW2, the V5 base will be turned on at a low level instantly, the residual voltage on the rechargeable battery will be discharged on R17 through the ec pole of V5, and the discharge indicator VD14 will light up at the same time. After SW2 is pressed, it will be released immediately. At this time, the residual voltage on the rechargeable battery is divided by R16 and R13. After C9 is filtered, it supplies a high level to the base of V4, and V4 is turned on, which is equivalent to shorting SW2. With the extension of the discharge time, the residual voltage on the rechargeable battery is getting lower and lower. When the voltage on the base of V4 can't maintain its continuous conduction, V4 is cut off, the discharge is terminated, and the charger turns into the charging state.
Since the lithium battery does not have a memory effect, when the battery is lower than 3V, it cannot be turned on. The residual voltage is divided by the resistors R40 and R41 to get 2.53V and sent to the non-inverting terminals ③, ⑤, and ⑩ pins of the operational amplifier. Because of the voltage of the LM324 ⑨ pin It is always 2.66V under load, so pin ⑧ outputs low level, V3 is turned on, and +9V voltage charges the rechargeable battery through the V3ec pole and VD8. When IC1d is used as capacitor C6, pin {14} outputs a pulse signal. Because pin IC1⑧ is low, VD12 is in a blinking state to indicate that the battery is charging, and the corresponding capacity is 20%. As the charging time increases, the voltage on the rechargeable battery gradually rises. When the voltage division value of R40 and R41 is approximately equal to 2.58V, that is, when IC1③ is equal to 2.58V, IC1② pin is divided by resistance to get 2.57V, and its ① pin outputs high level (because IC1⑨ The pin voltage is always 2.66V, and V6 is on; on the contrary, when there is no load, IC1⑨ pin is 0. 08V, V6 is off), VD10 and VD11 are lit, and the corresponding indicating capacity is 40% and 60%. When the voltage division value of R40 and R41 rises to 2.63V, that is, IC1 ⑤ pin is equal to 2.63V, and its ⑥ pin is divided by resistance to get 2.63V, ⑦ pin outputs high level, VD9 lights up, corresponding to the charging capacity Is 80%. Only when IC1⑩ pin voltage ≥ 2.66V, ⑧ pin outputs high level, VD13 lights up, and the corresponding charging capacity is 100%. Even when VD13 is lit, VD12 is still flashing, which means that the battery has not reached full saturation. Only when IC1⑧ pin voltage is 6.5V, VD12 gradually goes out, indicating that the battery is fully charged to saturation.
VD16 is used for overcharge and overcurrent protection in the circuit, and VD8 is used for reverse protection. After the charger is powered off, the battery will discharge in the reverse direction.
