Hot melt glue gun driver board

Since personal DIY often requires the use of hot melt glue guns, the original hot melt glue guns purchased on Taobao use ceramic heating elements. The power changes greatly with temperature and the heating speed is extremely slow. So I want to modify it.

The first step in modification is to replace the ceramic heating element. Here, an aluminum substrate PCB of the same size as the ceramic heating plate is drawn for heating. When making prototypes of the heating element, the aluminum substrate must be printed!

     Then there is the design of the driver circuit according to the housing size. There are some actual deviations, but it can be used normally.

         In this drive circuit, CH224K is used to decoy 9V voltage for circuit power supply. The resistance of the heating element at room temperature is 2.35Ω (actually due to process problems, the resistance of the heating element fluctuates in the range of 2.1Ω to 2.5Ω, with 2.3Ω being the majority). . However, due to wire loss, tube loss, etc., the peak heating power is 28W under 9V power supply. After reaching the set temperature, the resistance of the heating piece becomes larger and the heating power is 20W. Therefore, you need to use a 9V3A or above charging head that supports QC or PD protocol for power supply! ! !

One channel of LM358 forms a hysteresis comparator, which is used to drive the mos tube, and the other channel drives the heating. The indicator light comes on when heating. When the temperature is reached, heating stops and the indicator light goes out. Please refer to the schematic diagram for specific component parameters.

It is recommended to use solder above 183℃ and 20AWG silicone wire to weld the heating plate .

When installing the heating plate, it is recommended to use silicone to fix the heating plate and ntc thermistor. After the installation is completed, press tightly and wait for solidification. After solidification, seal with silicone glue

Wait for the silicone to solidify before installing other parts. For specific driver board dimensions, please refer to the picture below with slight modifications.

Finally, test it in practice. After the modification, the glue can be released in about one and a half minutes , and because the temperature control temperature is relatively stable using an operational amplifier and an NTC thermistor, the glue leakage phenomenon has been greatly improved. According to the actual measurement, there is no glue leakage in one hour of normal use . The specific heating situation is shown in the figure below: heating to 100°C in one minute and twenty-two seconds. One minute and 40 seconds to heat to 110°C. The set operating temperature of 120°C can be reached in two minutes (the operating temperature can be modified by modifying the op amp input voltage dividing resistor value) and stabilized here. Considering the differences between different charging heads and the presence or absence of line compensation function, the actual time will have a slight deviation .

Let’s play with the original heating data again, and you can see that the speed is much faster.