TPS61022 Constant Adjustable Heating Unit Power Supply Solution

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TPS61022 Constant Adjustable Heating Unit Power Supply Solution [Copy link]

A power supply solution for a heating unit, mainly including a lithium battery, a boost circuit (TPS61022) and a heating resistor (2 Ω). This solution supports a maximum output of 12.5W (5V/2.5A), and the power is continuously adjustable. By adding a boost circuit to the heating unit, the heating unit can obtain a higher and more stable output voltage. At the same time, this solution has the function of continuously adjustable output power, making the design of the heating unit more flexible.

1 Introduction of heating unit

The basic structure of the heating unit is shown in Figure 1, which mainly includes a lithium battery, related charging circuits and interfaces; a heating resistor; a central controller (MCU) and a sensor for airflow detection. In general, the resistance of the resistor is about 0.4 Ω~2.8 Ω. The traditional method is to use the battery to directly heat the resistor, or to connect a switch tube in series between the battery and the resistor to adjust the output power. However, the maximum output power of this method will be limited by the battery voltage, and the unstable battery voltage will cause the unstable output power.

Figure 1 Basic structure of the heating unit

2 TPS61022 Introduction

TPS61022 is a boost chip that supports input from lithium battery and output of 15W (5V/3A). Its minimum valley value of switching current is 6.5A in 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 a relatively high efficiency. For example, when Vin=3.6V, Vout=5V, and Iout=2.5A, the overall efficiency is about 95%. At the same time, the typical startup load capacity of TPS61022 is 1Ω, so it can support the start-up of the mouthpiece resistance of most heating units. The operating switching frequency of TPS61022 is 1MHz, and the package is 2mm*2mm VQFN, which can help customers obtain a smaller design area.

3 System Introduction

The power supply circuit of the heating unit 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 works in a light-load high-efficiency mode, which can achieve higher efficiency under light load. According to the application manual of TPS61022 [1], a 1μH inductor is selected and three 22μF ceramic capacitors are used for the output. The GPIO of the MCU can be connected to the EN pin, and the output power can be adjusted by adjusting the duty cycle of the output PWM. The advantage of the entire system is that the output power is stable and is not affected by changes in the input voltage.

Figure 2 Power supply circuit diagram of heating unit realized by TPS61022

4 Test Results

Figure 3 is a steady-state waveform diagram working at 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, TPS61022 will first soft-start and start working; when the EN pin is low, TPS61022 will shut down. By continuously turning TPS61022 on and off, the purpose of controlling the average output power is achieved. The recommended PWM frequency is 100Hz.

Figure 3 TPS61022 steady-state waveform

Figure 4 shows the output power curve as the PWM duty cycle changes. It can be seen from the curve that the relationship between output power and duty cycle is not linear. This is because TPS61022 has a soft start process. When the duty cycle is 100%, the output power is 12.5W, working at full load. When the duty cycle is 50%, the output power is 5.6W. Users can adjust the output power by adjusting the PWM duty cycle, and then adjust the taste of the heating unit.

Figure 4 Relationship between output power and duty cycle

Figure 5 shows the curves of efficiency and PWM duty cycle. The input voltage for the test is 3.6V. From the curve, it can be seen that the overall efficiency of the system is 95% at full load output power (5V/12.5W).

Figure 5 Efficiency and duty cycle relationship curve

Figures 6 and 7 show the temperature rise under different duty cycles. Figure 6 shows that the temperature rise of the chip is 19.6℃, and the output power is 12.5W (full load power) at Vin=3.6V. Figure 7 shows that the temperature rise of the chip is 13.6℃, and the output power is 3W (50% PWM duty cycle) at Vin=3.6V. The temperature rise is within the acceptable range.

Figure 6 Thermal imaging at a duty cycle of 100%

Figure 7 Thermal imaging at a duty cycle of 50%

toothache

What is this heating unit used for? It seems to have very little power.

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toothache posted on 2020-6-19 09:11 What kind of application is this heating unit? It seems to have very little power

The heating unit has a wide range of uses, such as industrial pipeline heating, insulation monitoring, etc.

The heating unit mentioned here is mainly for heating electronic cigarettes.

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Figure 2 is a typical electronic cigarette power supply circuit, which controls the average output power by continuously turning the TPS61022 on and off.