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Power supply solutions for vape pod electronic cigarette kits

by Martin Smith

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This article provides a power supply solution for vape pod electronic cigarette kits, which mainly includes a lithium battery, a boost circuit (TPS61022) and the resistance of a coil (2 Ω). This solution supports up to 12.5W (5V/2.5A) output, and the power is continuously adjustable. By adding a booster circuit to the vape pod kit, it can obtain a higher and more stable output voltage, which can improve the flavor. At the same time, this solution has the function of continuously adjustable output power, which makes the design of the pod vape kit more flexible.

The main function of electronic cigarettes is to replace the original method of burning tobacco by heating tobacco or e-liquid and to bring vapers the same experience as traditional tobacco. Because electronic cigarettes are non-burning, there is almost no smoke, and there is no pollution from second-hand smoke. Compared with traditional cigarettes, electronic cigarettes are less harmful to health and can help users quit smoking.

The basic structure of a vape pod kit is shown in Figure 1. It mainly includes lithium batteries, related charging circuits and ports; vape pod cartridge (with pre-filled e-juice inside), heating resistor wires; microcontroller Unit (MCU), and sensors for airflow detection. The pod vape E-cigarettes use coils heated and e-liquid to simulate the same taste like real cigarettes. In general, the resistance value of the coils is generally about 0.4 Ω~2.8 Ω. The traditional method is to use the battery to directly heat the coils or a switch tube can be connected in series between the battery and the coils to adjust the output power. However, the maximum output power of this method will be limited by the battery voltage. At the same time, because the battery voltage is unstable, the output power is unstable, which affects the flavor of smoking.

Figure 1

TPS61022 introduction

TPS61022 is a boost chip that supports input from lithium battery and output 15W (5V/3A). It has a minimum switching current of 6.5A in the valley of the full temperature range. TPS61022 has a small on-resistance, the on-resistance of the lower switch tube is 12mΩ, and the on-resistance of the upper switch tube is 18mΩ. So it has relatively high efficiency. For example, when Vin=3.6V, Vout=5V, Iout=2.5A, the overall efficiency is about 95%. Meanwhile, the typical start-up load capacity of TPS61022 is 1Ω, so it can support most coils to start. The operating switching frequency of TPS61022 is 1MHz, and the package is 2mm*2mm VQFN, which can help customers obtain a smaller design area.

System introduction

The power supply circuit of the vape pod kit is shown in Figure 2. The output power can be dynamically adjusted by PWM modulating the EN pin. By connecting the MODE pin to GND (low level), the TPS61022 can work in a light-load and high-efficiency mode, which can achieve higher efficiency under light-load conditions. According to the application manual of TPS61022 [3], the inductor of 1μH is selected, and the output uses 3 ceramic capacitors of 22μF. You can connect the GPIO of the MCU to the EN pin, and adjust the output power by adjusting the duty cycle of the output PWM. The advantage of the entire system is that the output power is stable and not affected by changes in the input voltage.

Figure 2

Test Results

Fig. 3 is a steady-state waveform diagram when Vin=3.6V and a duty cycle of 50%. TPS61022 can adjust the output power by modulating the EN pin. When the EN pin is high, the TPS61022 will soft-start and start working; when the EN pin is low, the TPS61022 will shut down. The TPS61022 is constantly turned on and off to achieve the purpose of controlling the average output power. The recommended frequency of PWM is 100Hz.


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