①Electronic product dismantling analysis-hand warmer

1. Function introduction

• ① Press the button for three gears to warm your hands;
• ② Long press to enter the ambient breathing light;
• ③Android interface charging and support USB output;

2. Disassembly circuit analysis and device function

1. The overall circuit of the hand warmer

Overall interface analysis: ❤️ ❤️ ❤️

1. USB output discharge interface
2. Macio USB Android input charging interface
3. Key shift interface
4. Lithium battery power supply interface
5. PTC heating pad

2. Lithium battery charging boost circuit

Brief analysis: ❤️ ❤️

1. Lithium battery master control is TP4333 data sheet
   TP4333 is a single-chip synchronous boost solution specially designed for mobile power
   , which integrates linear charge management module, synchronous discharge management module,
   power detection and LED indication module, protection module
2. TP4333 typical application circuit
   
   pin description:
   

Draw the schematic diagram according to the data sheet and the actual circuit

TP4333 can discharge and output 5V/1A, and the lithium battery can be discharged to 2.85V to stop the discharge to prevent excessive discharge and loss of the battery. It integrates overvoltage, short circuit, and overload protection functions; when charging: LED1 flashes at a frequency of 1Hz, and LED1 will always be on when
fully charged ;
During discharge : LED2 will always be on, when the battery is lower than 3.0V, LED1 will flash at a frequency of 1Hz;

3. Control PTC heating pad shift circuit

Brief analysis: ❤️ ❤️

1. 2300 is an N-channel MOS transistor, which controls the switch of the PTC heating pad;
   PT2300 reference manual
2. The G gate of the 2300 is directly connected to the button and the PWM output IO of the microcontroller, and the temperature rise is controlled by adjusting the duty cycle of the PWM;
3. The PWM is connected to the IO of the single-chip microcomputer. No button is pressed to detect the state of the SW1 button, and the gear is adjusted and the LED display is controlled according to the number of times SW1 is pressed . The output PWM can be analyzed by a logic analyzer to be 100Hz;
4. The heating sheet can generate heat directly from the positive and negative electrodes of the lithium battery, and R1 is the current limiting resistor;

According to the principle of physical painting

4. Main control MUC circuit

Brief analysis: ❤️ ❤️ ❤️

1. According to the physical circuit, reverse the function of each pin of the single-chip microcomputer, LED1, 2 set the push-pull output high and low level to control the LED display status
2. LED3 outputs RGB data to control the breathing and color change of RGB lights;
3. Pins 2 and 3 are mainly connected to a thermistor to detect the internal temperature of the hand warmer and adjust the switch of the heating pad to prevent high temperature from damaging the device;
   

3. Schematic diagram corresponding to each module

The circuit of the hand warmer mainly has two chips , one is TP4333 lithium battery management chip, and the other is an 8-pin single-chip microcomputer, which controls the MOS tube to control the heating of the heating pad and the display of the shift status, as well as the breathing status light. Control; lithium battery charging and 5V power output through Macio USB interface and Type-A interface~~~
❤️ ❤️ ❤️ ❤️ ❤️ ❤️