01

Design requirements for flashlights

1、 Battery: 4 18650s in parallel, with a voltage of 2.6-4.2V.
2、 Lamp beads: 3 3A lamp beads in parallel, shared by VF3.3V/VF10V.
3、 Circuit architecture: Built in charging detection
Chip TP4056, microcontroller dimming, LTC3785 chip boost/expand current, microcontroller output PWM signal controls MOS transistor duty cycle dimming.
4、 Function
1. Battery level display, using dual color LED lights. When charging, the red light is on, and when fully charged at 4.2V, the green light is on. When discharging, the red light flashes slowly (about 800MS) when the battery voltage is 3.6V, and the red light flashes rapidly (100ms) when the battery voltage is 3V.
2. Dimming: Use a single key to select high brightness 100/medium brightness 50/low brightness 30/SOS/flash/off/long press infinite dimming downwards, and another key to define infinite dimming upwards.
3. SOS definition: As shown in the figure below, I drew it based on the waveform of the oscilloscope. To understand, connect the two lines, flash three times, stop 2500mS, flash three times, stop 800mS, and then flash slowly three times. Repeat this process. Flash time: on 300mS/off 300mS, slow flash time: off 800ms/on 800ms.

02

Circuit characteristics

Flashlight source file screenshot

03

Introduction to Charging Chip TP4056

Introduction to Charging Chip TP4056 TP4056 is a complete single cell lithium-ion battery that uses a constant current/constant voltage linear charger. The SOP8 package with heat sinks at the bottom and fewer external components make the TP4056 an ideal choice for portable applications. TP4056 is suitable for working with USB power supplies and adapter power supplies. Due to the use of internal PMOSFET architecture and anti reverse charging circuit, there is no need for external isolation diodes. Thermal feedback can automatically adjust the charging current to limit the chip temperature under high-power operation or high ambient temperature conditions
Chip features
·4.2V preset charging voltage with an accuracy of ± 1.5%
·Charging current monitor output for battery level detection
·Automatic Recharge
·Charging status dual output, no battery, and fault status display
·C/7 C/10 charging terminated
·The power supply current in standby mode is 55uA
·2.9V trickle charger version
·Soft start limits surge current
·Battery temperature monitoring function
·Adopting 8-pin SOP packaging

Foot position definition diagram

Design considerations
It is best to maintain the charging current of TP4056 at 0.37C of the battery capacity, which is 0.37 times the capacity. For example, for a 1000mAh battery, a charging current of 400mA is sufficient. Excessive charging speed will result in poor charging performance, causing the battery voltage to drop significantly after being fully charged.
If the input voltage of TP4056 is too high, such as 5.2 or even 5.5V, it will cause the charging current to be less than 1000mAh, which is normal. When the voltage is high, the chip will generate heat and automatically reduce the charging current, so as not to burn out the chip.
In addition, it is normal for the chip to generate heat at around 60 degrees Celsius during operation, as its charging current is high. (PS: If you have the conditions, you can use 8 * 8mm aluminum heat sinks+3M thermal conductive tape to increase chip heat dissipation.).
Remember!! If TP4056 is charging a lithium battery, remember to disconnect the battery load, that is, during charging, the battery cannot supply power to other components anymore, otherwise TP4056 will be burned.