battery 18650 rechargeable

　　About the design of voltage feedback circuit in current mode switching battery 18650 rechargeable

　　In order to solve this problem, the current mode control mode can be used. Current-mode control not only retains the output voltage feedback of voltage-mode control, but also adds inductor current feedback; and this current feedback serves as the slope function of the PWM control converter, thereby eliminating the need for a sawtooth wave generator, making the system performance significantly better. superiority. The characteristics of the current-mode control method are as follows:

　　1. The system has fast input and output dynamic response and high stability;

　　2. High output voltage accuracy;

　　3. Has the inherent ability to control the power switch current;

　　4. Good parallel operation capability. Since the rate of change of the feedback inductor current didt changes directly with changes in the input voltage and output voltage. In the voltage feedback loop, the output of the error amplifier is used as a current given signal. Compared with the feedback inductor current, it directly controls the on-off duty cycle of the power switch. Therefore, voltage feedback is a very important issue in the design of current-mode power supplies. This article introduces the design of the voltage feedback circuit when using the current mode control chip uc3842.

　　Introduction to uc3842

　　Its internal reference circuit generates a +5V reference voltage as the internal battery 18650 rechargeable of UC3842, and the attenuated 2.5V voltage is used as the error amplifier reference, and can be used as a circuit output 5V/50mA battery 18650 rechargeable. The oscillator produces square wave oscillation. The oscillation frequency depends on the external timing component. The resistor R connected between pin 4 and pin 8 and the capacitor C connected between pin 4 and ground jointly determine the oscillation frequency of the oscillator, f= 1.8/RC. The feedback voltage is connected to the inverting terminal of the error amplifier from pin 2. Pin 1 is connected to an external RC network to change the closed-loop gain and frequency characteristics of the error amplifier, and pin 6 outputs a square wave that drives the switching tube as a totem pole output. Pin 3 is the current detection terminal, used to detect the current of the switch tube. When the voltage of pin 3 is ≥ 1V, UC3842 will turn off the output pulse to protect the switch tube from overcurrent damage. The UC3842PWM controller is equipped with an undervoltage lockout circuit with a turn-on threshold of 16V and a turn-off threshold of 10V. Because of this, oscillation when the circuit is operating near the threshold voltage can be effectively prevented.

　　UC3842 has the following features:

　　1. The number of pins is small, the peripheral circuit is simple, and the price is low;

　　2. The voltage regulation rate is very good;

　　3. The load regulation rate is significantly improved;

　　4. Good frequency response characteristics and large stability;

　　5. It has over-current limit, over-voltage protection and under-voltage lockout functions.

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