We know that diodes, transistors and MOS tubes are all basic switching devices in electronic circuits, but they have some differences in their applications.
First of all, diodes and triodes are current control components, while MOS tubes are voltage control components. Under the same conditions, the power consumption of MOS tubes is lower.
Secondly, when the MOS tube is turned on, the conduction voltage drop is close to 0V, and the minimum conduction voltage drop of the triode and the diode is greater than 0.3V. It can be seen that it is more suitable to use MOS tube as the switching circuit of electronic cigarette.
It can be seen from the circuit prototype that the switching circuit of the power supply direction of the cigarette rod is actually a rectifier full-bridge circuit. We built a rectifier full-bridge circuit with MOS tubes. In order to reduce the number of MCU control ports, we use P-MOS tubes as the upper bridge arm and N-MOS tubes as the lower bridge arm, which is also conducive to simplifying the drive circuit. Use the P03 and P04 ports of the RJM8L003 to drive the two bridge arms directly. As shown in Figure 1.
Figure 1 Two-wire encrypted pod circuit built by MOS tube
Because the RSD pin of RJGT101D6 is both a power input pin and a data communication pin, when it is used as a data communication pin, an external pull-up resistor is required to output a high level, so we add a common 2.2KΩ on the two upper bridge arms After the pull-up resistor to the power supply VCC.
The heating wire needs a current of more than 1A when it is working. It cannot be driven by an H-bridge with a pull-up resistor, because the pull-up resistor will limit the output current, and two upper bridge arms need to be designed, that is, MOS5 and MOS6 in the figure.
When the heating wire needs to work, MOS5 or MOS6 is turned on, the battery current directly drives the heating wire, and finally flows into GND through the lower bridge arm MOS2 or MOS4.
As mentioned in the previous chapter, we connected the heating wire inside the cartridge and the encryption chip RJGT101D6 in series. Because only the RJGT101D6 is polarized, we consider designing a one-way bypass circuit in parallel with the RJGT101D6 to achieve the effect of the RJGT101D6 forward work and reverse bypass.
After verification, we chose P-MOS tube to design one-way bypass circuit, of course, N-MOS tube can also be used. But you can’t use a diode, because the forward voltage drop of the diode is greater than 0.3V, which is equivalent to providing a negative 0.3V working voltage to the RJGT101D6, which will cause its damage.
In fact, the operating voltage of many logic chips cannot be less than negative 0.3V. The reason why the heating wire and RJGT101D6 can not be connected in parallel is also because the excessive negative voltage will damage the RJGT101D6, because the instantaneous voltage drop of the heating wire will reach more than 3V.
The switch circuit is built, and the next step is to consider how to design the drive circuit.
The electronic cigarette is usually powered by a 3.6V single-cell lithium battery, and the GPIO output voltage of the MCU is up to 3.6V. Whether the switch can be directly driven by 3.6V depends on the MOS switch parameters we choose, as long as the VGS(th) threshold voltage is lower than 3V is fine.
Also pay attention to the on-resistance RDS(ON) of the MOS tube, because the lower the RDS(ON), the lower the on-voltage drop, but the higher the cost. The MOS tube used as the working path of the heating wire should be selected with RDS(ON) lower than 100mΩ, and the MOS tube used as the working path of the RJGT101D6 can be appropriately relaxed.
In the test, the N-MOS we selected is Si2302, and the P-MOS is CJ3401A. The performance indicators are shown in Table 1, and these two general models are produced by many brand manufacturers, which are cheap and easy to purchase.
After the MOS tube switch circuit is built, how the main control MCU sends high and low level signals to the RJGT101D6 of the pod, we still analyze from the situation when the pod is plugged in, as shown in Figure 2.
P00 is always kept as an input port, P01, P02, P04 are set to output high level 1, at this time MOS3 is disconnected and MOS4 is closed, MOS5 and MOS6 are both disconnected, MCU sends data to RJGT101D6 through P03, when P03 outputs low level 0 , MOS1 is closed and MOS2 is disconnected, which can send a high level bit to RJGT101D6. When P03 outputs high level 1, MOS1 disconnects MOS2 and closes, then a low level bit can be sent to RJGT101D6. When the pod is plugged back, the MCU sends data to the RJGT101D6 through P04, and the specific analysis will not be repeated.
Figure 2 The principle of the main control MCU sending data
The main control MCU reads the return data of RJGT101D6 through the P00 port, as shown in Figure 3. When the pod is plugged in, P00 is set as the input port, P01, P02, and P04 are set to output high level 1, and P03 is set to output low level 0. At this time, MOS3 is disconnected and MOS4 is closed, MOS5 and MOS6 are both disconnected, and MOS1 Close MOS2 to open. At this time, the high and low levels output by the RSD pin can be input to the P00 pin through MOS1. When the pod is inserted backwards, the high and low levels output by the RSD pin are input to the P00 pin through MOS3.
Figure 3 The principle of the main control MCU reading data
This is the two-wire encrypted pod solution based on the RJGT101D6 encryption chip of Renage Semiconductor. The solution achieves the design goals of simplicity, low cost and easy implementation without changing the appearance of traditional pods, and can be applied to traditional electronic pods. The transformation and upgrading of cigarettes can also be used for encryption and anti-counterfeiting of medical consumables and office consumables.
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