Given market Shang nickel CD battery and lithium battery coexistence of situation, this design of charger can on this two species battery for charging, on nickel CD battery pack used pulse charging way, on lithium battery pack used constant flow charging way, this is pursuant to battery of different mechanism and design of, Nikon D5000 Battery Charger real do has a machine dual-use, this for the charging device of innovation points, is design of difficulties. Widescreen LCD display 4 sets of charger charger charging status, can also show the parameters of a set of batteries on the charger, real time monitoring of the process of charging the battery.

Overall design of the system

System design goals are:

1. 4 group at 8.4V or 9.2V for lithium-ion batteries NI-CD battery for charge and discharge.

2. Communicate with the chip in the battery pack, judging the battery chemistry.

3. Batteries for different chemical properties, use the appropriate charge.

4. Communicate with the chip in the battery pack, get the battery voltage, charge current, capacity, and other parameters.

5. Charger with LCD, displays battery information.

Functional block diagram for the charger as shown in Figure 1.

System hardware design

Design and realization of the control unit

Master control unit is made up of ZLG7289A PIC16F873 micro-controller and the keyboard controller. Main task is responsible for communicating with the individual charging unit, LCD display and user input and processing information. Keyboard control chip is responsible for 6 and 12 LED control button. ZLG7289A two-way communication through the SPI bus with the micro-controller. Main control unit of queries per second charging unit, gets the information of the current charging unit, if there is no battery, battery, battery voltage, and so on. From LCD after module is displayed to the user.

Charging unit design and implementation

LTC4002 lithium-ion battery charging control chip

LTC4002 is a high performance lithium-ion battery charger controller independent switching mode. The controller has two versions and 4.2V. LTC4002-8.4 with 500kHz switching frequency, is the high performance current mode PWM controllers. By driving an external p-Channel MOSFET, it can provide a charge current of 4 a, which can be as high as 90%. Output voltage is set to 8.4V, the ultimate precision of the float voltage and 1% and charging accuracy of 5%. In addition, the device can be in the range 9V~22V range of wall run on the adapter. Compared with hysteresis topology charger, fast operating frequency of LTC4002-8.4 and current model so that it can use small inductors and capacitors.

Dual-use lithium-ion/NI-CD battery charging unit design

Analysis of LTC4002, the chip is for lithium-ion battery charging controller, to achieve the nickel-cadmium battery charging needs to address the following issues: first, LTC4002 to monitor the voltage of the battery, ensure that the battery voltage is not more than 8.4V. But for nickel-cadmium batteries, charge cutoff voltage can reach 9.2V. Second, the nickel-cadmium battery charging toward the end, needs and 30% in the normal current to battery trickle charging. So, the second problem is how to control the size of constant-current charging current. In addition, charge the nickel-cadmium battery pulse charging method should be used. That 1s as cycles, 95% time of charging, 1% time to discharge, the remaining time is neither charging nor discharging. Last, how to Panasonic Lumix DMC-LX3 Battery Charger tell if a battery is a lithium-ion battery is a nickel-cadmium battery, because if the misjudgment of the nickel-cadmium battery lithium-ion battery makes the charging voltage is higher than 8.4V, this is very dangerous for lithium-ion batteries and misjudgment of nickel-cadmium battery for lithium-ion batteries, may cause insufficient battery charge. Therefore, must ensure that the extremely low rate of misjudgment.

This section under LTC4002 works, design can be either constant current-constant voltage charging lithium-ion battery and charge the nickel-cadmium batteries for pulse circuit. Charging units for overall functional block diagram shown in Figure 2. Signal conditioning circuit allows the charger to charge the 8.4V lithium-ion battery, and 9.2V of nickel-cadmium batteries can be charged, while also controlling the charging current.

State control LTC4002 using micro-controllers, with the discharge circuit allows the charger to charge the nickel cadmium batteries for pulse mode.

Certain micro-controller communication protocol (HDQ16) and smart cell communications, determines its capacity, key parameters such as chemical properties.

Design of signal conditioning circuit

In order for LTC4002 to higher than the 8.4V constant-current charging the battery, and charging current adjustable, and sampled at the BAT and SENSE of LTC4002 end level of resistance between signal conditioning circuit. The sampling resistor at each end of the circuit's main function is to signal operations, batteries for different chemical properties, the corresponding signal to the LTC4002. The signal conditioning circuit as shown in Figure 3.

Sampling resistor at each end of the voltage value is defined here and VBAT Vsense, the charging current in the sampling resistor voltage drop on VRS: VRS=Vsense-VBAT, the output of the signal for subtraction. Set multiplier coefficient is k, then the output of the multiplier KVRS. Lithium battery, to choose a strobe VBAT battery voltage switch; for nickel-cadmium batteries, to choose a strobe 7V constant voltage switching. Set up alternative output of analog switches for V1, Adder's output Vs: Vs=KVRS+V1, then, sent to LTC4002 should be greater than the ends of the BAT and SENSE as KVRS. As long as the k value of proper control, you can make the charge current to normal charging current of 1/K. Therefore, you can choose a switching control currents as a constant-current charging or 10%.

LTC4002 BAT side of the input value, when the switch is selected through lithium-ion batteries, BAT's input that is battery voltage. In this case, LTC4002 can control the entire process of lithium-ion rechargeable. Without any outside intervention.

Strobe 7V constant voltage when the switch, BAT end of input constant 7V, at this point, the LTC4002 has no way of knowing the true voltage of the battery, just think the battery voltage to 7V. So, although the battery voltage is higher than the 8.4V, will remain at a constant current to charge the battery. In this case, you need micro-controller's intervention, otherwise will cause the overcharging of the battery. Because of the micro-controller with ADC, you can monitor the battery voltage changes. When the battery voltage reaches a specified value, reducing the charging current, until the battery is fully charged. This 9.2V of nickel-cadmium batteries can be charged.

Because of LTC4002 is constant-current charging control chip, therefore, you must use the microcontroller controls the charging pin COMP. When you need to LTC4002 when the charging pulse is output, make the control COMP pin port high resistance State, when COMP pin itself rose above 360mV, a charging current output. When discharging, COMP pins must be pulled down, making the LTC4002 off the charging current. , Then open the discharge circuit. Selection PIC16F873 micro-controller, it is a Flash-based 8-bit micro-controller. Internal timer, watchdog circuit, 10-bit ADC and other modules.

Charging charging process of micro-controller unit is primarily responsible for control and communication with the master control board, program flow as shown in Figure 4. First of all determine whether battery charging unit, if there is a battery in, you judge the State of charge and discharge, the default is the charging status, the status can be changed by the master control unit. If charging unit in charging status, continue to judge the battery's chemical properties, charge the battery using a variety of different ways. If in a State of discharge, discharge the battery until the battery voltage falls below the threshold voltage, to charge status.

In addition to the main program, a master control unit communicates with the charging unit is implemented in the interrupt service routine. After receiving the master control unit instructions when charging unit, enter the interrupt. Queries data JVC BN-V408U Battery Charger  if instructions are directives, data that is sent to the master control unit required. If charging status setting instructions, pursuant to instructions charging unit charge status.

With the method of electric energy measurement chip in the battery pack communication to determine the nature of the battery. This system can communicate with the intelligent battery pack and follow the HDQ16 interface protocol, in addition to chemical properties of battery pack, battery capacity, voltage, charge current, number of data read in conjunction, charger for display purposes.

Smart battery charging unit via HDQ bus for read operations. HDQ16 interface protocol is based on the instructions of the Protocol. A processor to send 8-bit instruction code for smart battery, this 8-bit instruction code is composed of two parts, 7-bit HDQ16 instruction code (0~6) and the 1-bit read/write instructions. Read/write command indicates that the intelligent battery store next to the 16-bit data to a specified register, or from a specified output 16-bit data registers. HDQ16, bytes of data (instructions) or Word (data) least significant bit would give priority to transport.

A block of transfer consists of three different parts. Part I by the host or the intelligent battery logic low HDQ16 PIN reset status after a tSTRH:B time to start sending. Next part is really a data transfer, data in tDSU:B time interval is valid, negative boundary to begin communication. Data is maintained a tDH V interval, to allow a host or smart battery data sampling.

Boundary once communication is started, the last part of a logic high State by returning to the HDQ16 pin, at least tSSU:B to stop transmission time interval. Finally a logic high State must keep a tCYCH:B time interval, so that there is time for block transmission full stop.

If a communication error occurs (e.g.,tCYCB>250 μ s), the host sends a BREAK signal intelligent battery, allow it to control the serial interface. When the HDQ16 pin in a time interval, or for a longer time to logic low State, smart battery will detect the BREAK. And then, HDQ16 pin back to its normal preset high-logic state of a tBR time interval. Then, smart battery is ready to receive instructions from the host.

HDQ16 PIN is open drain, requires an external pull-up resistor.

Figure 5 is displayed with the logic analyzer HDQ communication on the bus waveform.

Charging system proposed in this article is technically very good solution to these problems, through the LCD screen is clear and easy to read out the remaining capacity, number of charge and discharge, power, battery voltage, charge and discharge current capacity statistics, and cell properties and other important content, and by setting, you can determine if the power supply to the scrap standards, timely remind the operator updates the power. Provide clear reference data for power maintenance work, reduced requirements for professional skills in operations, ensure the safety of train rear power use.

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