Tips on designing gas stove pulse ignition controller based on PICl6C711

At present, there are about 1,000 gas stove manufacturers in my country. The annual output is about 30 million units. Among them, there are only about 100 companies with large scale, good product quality and management level, and most of the others are simple assembly companies. Because the product quality and technology of these assembly companies are generally low. With the implementation of the national gas stove product production license renewal (issuance) system, more than 600 companies will be forced to eliminate. How to reduce costs, produce stable performance, and save energy is the key to the success of gas stove manufacturers, and the pulse ignition controller is the core part of the gas stove. This paper introduces a cost-effective gas pulse ignition controller design, using the PICl6C7ll microcontroller produced by Microchip as the main controller, realizing the intelligent ignition and sensorless design of flame detection, while minimizing energy consumption.

2 Pulse ignition control system
The main functions of the pulse ignition controller system are: safety self-check; ignition control; flameout protection; fault alarm.
Figure 1 is the working process of the pulse ignition controller. The whole system is controlled by the ignition switch. When the user presses the ignition switch, the ignition needle generates a high-voltage spark. In order to ensure safety, the ignition controller controls the gas valve to open after a delay of 0.1 seconds, and determines whether the ignition is successful through flame detection. If there is a flame signal, the ignition is stopped and the feedback detection function is started at the same time. The whole process can effectively avoid the situation where the gas valve is opened but not burned, greatly improving the safety and reliability of the product.

Compared with ordinary gas stoves, the pulse ignition controller system has added pulse ignition control circuit, solenoid valve control, flame detection needle and other devices. The system block diagram is shown in Figure 2. That is, when working, the single-chip microcomputer PICl6C7ll first outputs a control signal to trigger the ignition control circuit and the flame detection feedback circuit, detects the flame through the flame detection feedback circuit, and feeds back the detection result to the single-chip microcomputer. The single-chip microcomputer can control the opening and closing of the solenoid valve according to the input flame detection signal, thereby ensuring that when the gas stove is accidentally turned off or backfired, the control system can close the solenoid valve in time and cut off the gas path, avoiding safety accidents caused by flameout.

3 System Design Hardware
3.1 Introduction to PICl6C71l
PICl6C71ll is an 8-bit MCU with CMOS technology launched by Microchip. It has a high-performance RISC structure CPU, 8-level hardware stack, 13 bidirectional I/0 ports, and 4 8-bit A/Ds. The I/0 drive absorption current can reach 25 mA. It also has a watchdog circuit. Because its instructions are simple (only 35) and easy to operate, it can be widely used in instrumentation and control fields.
In the design of the pulse igniter, PICl6C71ll is the main controller responsible for the user's key query, flame detection, solenoid valve clearance, ignition control and other functions. The following focuses on the pulse ignition control circuit and flame detection circuit.
3.2 Pulse ignition control circuit The
pulse ignition control circuit is shown in Figure 3. Its working principle: transistor Q2 controls the TT transformer oscillation voltage, Q1 maintains the transformer oscillation, and Q1 and Q2 are controlled by the I/O port of the MCU. Among them, D1 is a 10 V voltage regulator. When an I/O port sends an ignition signal, the transformer starts to oscillate, and the secondary generates a high-voltage signal of about 180 V. The high-voltage signal is rectified by a diode to charge C1, so that the high-voltage signal can be applied to the thyristor. At the same time, the secondary of TT also generates a high voltage to the voltage regulator. If the high voltage reaches the breakdown voltage of the voltage regulator, the voltage regulator is broken down. At this time, the diode is turned on, triggering the thyristor D3 and D4 to turn on, thereby generating a high voltage in the primary of the single ignition high-voltage package, and the secondary also generates a high voltage of 12 kV to 18 kV. The ignition pin is connected to the secondary of Tl and T2, so after the ignition signal is sent from the single-chip microcomputer, an electric spark will be generated at the ignition pin, thereby achieving the purpose of ignition. The principle of the ignition circuit is relatively complicated, and generally, it is considered to use multiple I/O ports for control. However, this system only uses one I/O port for the dual stove design, saving the I/O port resources of the single-chip microcomputer, thereby simplifying the ignition control, reducing product costs, and making it easy for the program to control ignition. The ignition control circuit is not only used for stove ignition, but also can be used for household appliances such as water heaters.

3.3 Flame detection circuit
The flame detection circuit is shown in Figure 4. This circuit integrates the ignition circuit and the flame detection circuit, abandons the traditional sensor detection idea, adopts physical principles and simple circuits to realize flame detection design, simplifies circuit design, reduces product cost, and is easy to implement software programming. Its working principle: the oscillation circuit of the transformer in Figure 4 can be shared with the ignition circuit. The function of transistor Ql is exactly the same as Q2 in the oscillation circuit, both of which maintain the transformer oscillation. Because the transformer outputs an AC signal, gas combustion produces ions, and the flame produces positive and negative ions. When the AC signal reaches the flame detection signal probe, the AC signal can form a path on the flame, so that the flame plays a diode rectification role, charging the capacitor on the left side of the flame probe, generating a negative voltage, which becomes a low level after passing through the comparator and is detected by the I/O port of the microcontroller, thereby completing the detection of the flame signal.

4 System software design
In order to enable the gas stove ignition controller to realize the separate and simultaneous opening of the two stoves, in addition to the common system safety self-check, the program can run in three ignition modes: stove 1 ignition; stove 2 ignition; stove 1 and stove 2 ignition at the same time. The program flow of single stove ignition is shown in Figure 5. The ignition process detects the flame at the same time. If it fails to ignite, it can be repeated several times and the time can be set. If it fails to ignite successfully within the limited time, an alarm will be issued.

5 Conclusion
The system design uses PIC16C7ll as the main control device to realize the design of gas stove pulse ignition controller, update the existing gas stove and improve product quality. By adding pulse ignition circuit and flame detection circuit in hardware and optimizing the ignition control sequence in software, the stability and safety of the entire gas system are guaranteed.