uc3842 data sheet

This design uses a current control mode pulse width modulation. The whole working process is the exchange of input by the filter, rectified into a DC high voltage, then switch chopper, after high-frequency step-down transformers are high frequency rectangular voltage, and finally through the output rectifier obtain the required DC voltage. System requirements on the switching power supply is the AC input voltage range of 90 ~ 270 V, it can output +5 V (power supply as the control part) and 12 ~ 60 V (main circuit) voltage. Output current of 1 ~ 3 A. 2.2 Microcontroller Circuit Design

MCU control circuit is composed of MCU AT89S52, ADC (TLC0832), multi-selector switch (CD4051), digital potentiometers (X9C102), digital temperature sensor DSl8820, sampling resistor Rs and Rw, 2 × 4 keyboard, LCD (CONl6), etc. composition. This part of the design should be the first under the battery model parameters corresponding to the keyboard design of the charge current, charge voltage and charge time, when the circuit connected to the battery, the charging process begins, then by the MCU by detecting the battery voltage sampling resistor RM If the detected battery voltage is lower than normal because of the scope of the transitional discharge Er Shi. So, in order to avoid excessive charge current damage caused by batteries, should first implement a stable low current battery charge (in this design process set l / 5 of the set charging current), while SCM start time, after the microcontroller will continue to test battery voltage and charge current and displayed on the LCD screen, with the charge to the battery voltage rise, when up to normal range, the microcontroller can control the digital potentiometer to adjust output voltage, high current constant current to turn charge (that is, setting current) way, then, has remained constant SCM test the battery voltage, when the voltage reaches the set value, the SCM to issue an order to increase the digital potentiometer's resistance, and reduced by pulse-width modulation output voltage. Thereby reducing the charge current when the charge current is reduced to 1 / 5 to set the current time, and then to trickle charge, charge time to finally turn off the power, thus avoiding excessive temperature rise due to the battery or serious charge polarization affect quality, improve battery life. When the detected battery voltage, charge current and temperature exceeds a set value of 1 / 10 times (set by the program), microcontroller output alarm signal alarm immediately. At the same time to relay and cut off the mains, to improve the safety and reliability of charge.

Display can be used to display real-time sampling to the single chip battery voltage, charge current, charge time and battery have been the temperature, the keyboard is used to set the charging voltage (charging limit voltage), constant charge current (charge current limit) and the charging time. Circuit in the microcontroller through the serial port RS232 and PC connected to the virtual display is used to store data and charging parameters settings. When the detected charge current is zero, the microcontroller into sleep mode. When the detected charge current is not zero, the microcontroller is activated. 2.3 PWM Controller

PW M Controller UC3842 is the core part. UC3842 chip with 5.0 V reference voltage regulator, high gain error amplifier and pulse width of the comparator, it can control the drive chip. The drive can provide 25 mA of output current. Can directly drive NOSFET adjustment control to adjust the charger output voltage and current. Since the drive also features over-current, over-voltage protection, supply voltage can be 8 ~ 40 V, while the starting current is less than 1 mA, operating temperature for the O ~ 70 ℃, which is the ideal new pulse-width modulator. The PWM controller at startup, by R1, Rw. To provide for the UC3842AD start voltage, let it work, its auxiliary winding terminal voltage of 3,4 rectified by D1, C4, C5 filter, DW1 after regulators received 16 V DC voltage, all the way to 7 feet for added power UC38427 another pass digital potentiometers R3 and after the partial pressure of added UC3842 X9C102 2 feet. As a PWM input signal. Generally in the design of such power, the output voltage sampling of the supply voltage can be connected with the UC3842. In order to reflect changes in output voltage, this design does not increase regulator, but this will work UC3842 voltage instability, the output harmonic components increased, in order to overcome this shortage, the design of the power supply voltage used by the UC3842 winding 3,4 side pressure single rectifier, filter, regulator, he has provided to the stability of UC3842 voltage 16 V-chip. Regulation of charging voltage is the battery voltage by the outer voltage sampling circuit R12, RM sampling, multi-electronic switch via options, MD transform, single chip processing, into the digital potentiometer, digital potentiometers to control the effective resistance. Indirectly control the UC3842 voltage of 2 feet, then control the pulse duty cycle to change the charging voltage. When the charger output voltage is high, the feedback back to 2 feet UC3842 voltage higher (than the reference voltage of 2.5 V), the drive signal of the pulse duty cycle decreases, the output voltage drops, so as to achieve the purpose of regulation. Charge current is regulated by a first charge current sampling resistor Rs by the outer current sampling and LM358 amplified (R1 adjust magnification available), multi-electronic switch to select, MD transform, sending single chip processing, and then adjust the resistance of digital potentiometer . The adjustment process and the voltage regulator similar, in fact, current regulation is achieved through the voltage regulator.