3.2 Introduction of Chip Characteristics

Analysis of power supply system of SPMC65P2408A3.3

There are three voltages on the whole main control board: AC220V, DC 12V and DC5V. AC220V directly supplies power to compressor, outdoor fan, indoor fan and negative ion generator; AC220V is converted into DC 12V and DC5V after step-down, which is used for power supply of relays and micro-control systems. The power supply system is shown in Figure 4-3. AC220V is first stepped down by transformer, then input from socket J 1, rectified by rectifier bridge, filtered by capacitor C2 to obtain DC 12V, and stabilized by voltage regulator 7805 to obtain DC5V. In the figure, the sampling point ZDS is used to detect zero crossing, and the diode D 1 prevents the filter capacitor C2 from affecting the sampling point ZDS. Figure 4-3 Power System 4.4 Zero Crossing Detection Circuit

The zero-crossing detection circuit is shown in Figure 4-4, which is used to detect the zero-crossing of AC 220 V. The full-wave rectified signal is sampled in the rectifier bridge, and then it is shaped into a pulse wave through a triode and a resistor and capacitor, which can trigger an external interrupt for zero-crossing detection. The sampling points and shaped signals are shown in Figure 4-5. The function of zero-crossing detection is to control the trigger angle of optocoupler SCR, thus controlling the wind speed of indoor fan. Figure 4-4 Zero Crossing Detection Circuit Diagram 4_5 Sampling Point and Shaping Signal 3.5 Indoor Fan Control

Figure 4-6 shows the control circuit of the internal fan, and U 1 is the optocoupler silicon controlled rectifier, which is used to control the conduction time of AC220V, so as to realize the adjustment of the wind speed of the internal fan. Pin 3 of U3 is a trigger pin, which is driven by a triode. AC220V is input from 1 1 pin and output from 13 pin. The specific turn-on time is controlled by the trigger angle. The specific control methods of indoor fan wind speed: first, the zero-crossing detection circuit detects the zero-crossing of AC220V, resulting in zero-crossing interruption; Then in the interrupt handling subroutine, start the timer function, such as the timer timing is 4 ms. After 4 ms, the CPU generates a trigger pulse, which is driven by a triode and input from pin 3 of U3 to trigger the internal circuit of U3, so that pins 1 1 and 13 of U3 are turned on, and AC220V supplies power to the indoor fan. In this way, the turn-on time of AC220V can be controlled by changing the timing length of the timer, so as to control the power and speed of the indoor fan. Figure 4? 6? 26 Indoor Fan Control Circuit 3.6 Indoor Fan Wind Speed Detection

When the indoor fan is working, the speed sensor feeds back the rotating speed of the indoor fan in the form of sine wave, and the frequency of the sine wave has a specific corresponding relationship with the rotating speed of the fan, as shown in the following table. Sine wave is shaped into square wave through triode, and CPU uses external interrupt to detect frequency, thus realizing wind speed measurement. wind speed

high

middle

low

Fan frequency (Hz)

70

50

30

Figure 4-7 Indoor Fan Wind Speed Detection Circuit 3.7 Overcurrent Detection Circuit

The current transformer L 1 is used to detect the change of current on the live wire. L 1 in the figure is a current transformer, which outputs 0 ~ 5 mA alternating current. When the current suddenly increases, the output current of the current transformer also increases. The DC voltage signal is output from the COD terminal after full-bridge rectification, current-voltage conversion and low-pass filtering. The CPU senses the change of AC220V current by collecting the terminal voltage of COD through AD. When the terminal voltage of COD is too high, CPU can take protective measures for the circuit. Figure 4-8 Overcurrent Detection Circuit 3.8 Low Voltage Detection Circuit

Based on the principle of resistance voltage division, CPU uses AD acquisition to detect the 12V voltage at the front end of 7805. When the power grid fails, the AD terminal will collect the voltage drop of 7805 front end 12V. Because of the capacitance at the output of 7805, even if the voltage of 12V drops to 6V, 7805 can still provide 5V to make the CPU work normally. At this time, the CPU will immediately save the current operating parameters of the air conditioner in AT24C0 1. Figure 4-9 Low voltage detection circuit 3.9 Control of compressor, four-way valve, external fan and negative ion generator (healthy operation)

The compressor, outdoor fan, four-way valve and negative ion generator are all powered by AC220V, so the operation of each part can be controlled by controlling the on-off of AC220V through relay. R 1 is a varistor for overvoltage protection. SI 1 is the safety tube. Socket J2 is the output terminal of AC220V, which is connected with an external transformer. After step-down, DC 12V and DC5V are respectively obtained by accessing the power module. Figure 4- 10 compressor, four-way valve and healthy operation control circuit 3. 10 drive circuit

The relay, buzzer and stepping motor are all controlled by 12V DC voltage, and U4 is the driving chip. Neg-lonC controls the relay of negative ion generator; ValveC controls the relay of four-way valve; ComprC controls compressor relay; The buzzer controls the buzzer; A, B, C and D are four phases of stepping motor. Figure 4- 1 1 driving circuit 3. 1 1 power-off memory

U5(AT24C0 1) is used as a serial memory chip to store the operating parameters of the air conditioner before power failure. The chip only needs two lines to control: clock line SCL and data line SDA/Ion, and the memory size is128× 8 bytes.