Automobile HID lamp control system based on HR6P62 single chip microcomputer

Single chip microcomputer control technology has been widely used in automotive electronics, which significantly improves the intelligent control level and safety performance of automobiles. This article will systematically introduce a cost-effective Haier HR6P62 single chip microcomputer and its application in HID lamp controller. 

1. The development history of automobile headlights 

It is said that the first automobile headlight was a household portable lamp. When the car was first invented, there was no headlight. When a driver got lost in the dark wilderness, a farmer led him home with a portable lamp. In 1898, the Columbia electric car used electricity for headlights and taillights, so the headlights were produced. The original headlights could not be dimmed, so they were a bit dazzling when meeting other cars. The 

first generation of automobile headlights were acetylene gas headlights. 

The brightness of the acetylene gas flame was twice as high as the brightness that the electric light source could achieve at that time. Therefore, almost all automobile headlights used before 1925 were acetylene headlights. 

The second generation of automobile headlights are electric light source headlights. 

In 1913, the inflatable incandescent bulb with spiral filament was introduced. Because of its high brightness, it opened up a broad prospect for electric light source headlights. 

The third generation of automobile headlights are dual-beam wick headlights. 

In order to solve the problem of traffic accidents caused by the strong light of the headlights when crossing vehicles, dual-beam wick headlights came into being. Although the dual-beam wick improves the dazzling phenomenon of lights when crossing vehicles, it does not completely solve the problem of light distribution of automobile lights. 

The fourth generation of automobile headlights are asymmetric low-beam headlights. 

The dual-beam wick headlight system belongs to a symmetrical low-beam system. In order to solve the problem that the headlights do not produce dazzling strong light during the process of crossing vehicles, and can ensure good lighting of the road, the asymmetric headlight was invented in the United States in 1932. It is centered on the reference axis and divides the light beam into two. The landing distance on the side close to the oncoming vehicle is short (that is, the light beam is depressed to prevent glare), while the landing distance on the other side is long (that is, the light beam is raised to enhance the lighting effect). The 

fifth generation of car headlights is halogen tungsten headlights 

. In 1964, the French company Spey produced the first batch of car headlights equipped with halogen tungsten bulbs. The filament of this lamp allows a higher operating temperature than ordinary incandescent bulbs, the light efficiency is increased by about 50%, and the life is doubled. Since then, the headlights of cars have also adopted the principle of halogen tungsten bulbs. The 

sixth generation of car headlights is xenon-filled bulbs  .

BEST xenon lamps are one of them. The bulb is filled with high-quality inert gas xenon, and high-quality tungsten filaments and high-quality quartz glass tubes are selected. The service life and brightness of the bulb are maximized, with a brightness of more than 3200 lumens. This type of bulb does not change the outer dimensions of the original car bulb, so there will be no problem of inaccurate focusing. Such bulbs have very good focusing effect, and the K value is above 4300K, with soft color and bright white light. 

The seventh generation of car headlights are xenon bulbs (recommended) 

. HID xenon lamps are also called high-intensity discharge gas lamps, and the English name is HID Higt-Intensity Discharge Lamp (HID for short). This lamp uses high-voltage discharge technology to inject xenon gas (×enoN) into the quartz inner tube, and then uses a precision ballast to instantly increase the 12 volt electricity to more than 23,000 volts through three voltage transformations, which stimulates the xenon electrons in the tube to be ionized, forming a beam of super-strong arc light between the two electrodes, making the light color brighter and the light emitted close to sunlight. 

It has been almost 120 years since the early acetylene gas headlights developed to today's free-surface reflector gas discharge headlights. 

HID xenon lamps increase the brightness of original halogen lamps by three times, with better color and stronger color temperature penetration. The lighting range can be expanded to 400 meters, the field of view is very wide, the performance is more stable, and the safety of night driving is greatly improved. Therefore, it has been favored by more and more car users around the world. At present, more than 60% of new mid- and high-end cars in Europe, the United States, Japan and other countries are equipped with xenon lamps. Among domestic cars, Audi A6, Passat Lingyu, Sonata and other mid- and high-end cars are currently equipped with H1D xenon lamps. It is expected that in the next two or three years, the number of domestic cars equipped with HID xenon lamps will increase greatly. It is an inevitable trend for HID xenon lamps to replace halogen lamps. 

2. The luminous principle of HID xenon lamps 

Automobile HID xenon lamps are different from traditional halogen lamps. It is a high-pressure discharge lamp. Its luminous principle is to use positive and negative electricity to stimulate the chemical reaction of xenon gas and rare metals to emit light. Therefore, there is a small glass ball in the lamp tube, which is filled with xenon gas and a small amount of rare metals. As long as they are stimulated by electric current to react chemically, both will emit light with a color temperature of up to 4000K to 12000K. It uses a special trigger to generate a trigger voltage of more than 23000V using the 12V voltage of the car battery to start the lamp. The brightness at 0.8 seconds after starting is 20% of the rated brightness, reaching the brightness of the halogen lamp. At the same time, the headlight will reach more than 80% of the rated brightness within 4 seconds. After the lamp is stable, the ballast provides about 80V power supply voltage to the lamp to keep the lamp running at a constant power. 

The working process of xenon metal halide lamps is very complicated and requires high voltage. According to the automotive application, there are many strict requirements for the light output characteristics of xenon metal halide lamps during the starting process and stable operation, and ballasts are required for control and ballast. Therefore, in recent years, high-end cars have begun to use ballasts to drive high-intensity gas discharge lamps as the light source of car headlights. 

Xenon metal halide lamps require a high voltage pulse of nearly 23kV or more when starting. After starting, in order to keep the lamp glowing stably, an appropriate voltage must be supplied to the lamp at the moment of ignition. In order to meet the different requirements of the lamp at startup and steady state, the basic circuit structure of the current general car lamp ballast includes four parts, as shown in Figure 1. 



(1) DC boost circuit: Since the power supply used in current cars is generally a 12V lead-acid battery. The steady-state voltage of the lamp is about 85V, so the battery voltage must be increased through a first-stage boost circuit. Fly-bake converters are usually used as boost circuits to provide the voltage required for steady-state operation of the lamp and the high voltage required by the starting circuit.

(2) High-voltage starting circuit: Since a high-voltage pulse is required to break down the lamp and start discharging, a high-voltage starting circuit is required. The starting circuit can use a one-stage or two-stage boost method to generate a high-voltage pulse of at least 23kV. 

(3) DC/AC conversion circuit: Since the output of the DC boost circuit is DC, an inverter circuit must be used to convert the DC into the AC square wave current required after the lamp is lit. The inverter circuit generally uses a full-bridge inverter. The full-bridge inverter circuit provides a low-frequency AC square wave current to the lamp to avoid resonance. 

(4) Drive and protection circuit: When the lamp starts, the start-up circuit is controlled. After the lamp is lit, detect whether there is overvoltage or short circuit. By detecting the signals of lamp voltage and lamp current, the drive circuit and protection circuit are controlled to ensure that the lamp can work stably. 

3. Characteristics of Haier HR6P62 MCU 

Shanghai Haier Integrated Circuit Co., Ltd. is currently the first high-tech enterprise in China that specializes in MCU design and development. The general-purpose and special-purpose 8-bit microcontroller chips developed have the characteristics of high anti-interference and high reliability, which can help customers improve system performance, reduce product development risks, reduce total system costs and shorten product time to market. The company's HR6P series MCU adopts a 48-line reduced instruction set high-performance architecture design, has rich peripheral interface circuits and good code protection mechanism, and has been widely used in home appliances, electric meters, automotive electronics, and industrial control systems. In HID ballast applications, Haier recommends customers to use HR6P62 MCU for design and development. [page]

HR6P62 MCU has the following features: 

◆High-performance RISC CPU structure, high-speed OTP CMOS process, only 48 simplified instructions
◆Except for some program jump instructions which require two instruction cycles, the rest only require one instruction cycle
◆Working speed: DC-20MHzInstruction cycle: minimum 200ns, one instruction has 4 clock cycles
◆Support 8-level hardware stack structure
◆Direct, indirect and relative addressing methods
◆Program memory is 2k×16-bit OTP; data memory is 224 bytes
◆Embedded power-on reset circuit, power-off reset circuit, support hardware watchdog
◆Support programming code protection
◆Operating voltage range: 2.7V～5.5V;Operable temperature range: -40℃～85℃
◆16 groups of I/O pins, using SOP20/SOP18/PDIP18/PDIP14 package
◆TIMER0: 8-bit timer/counter with 8-bit prescaler
◆TIMER1: 16-bit timer/counter with prescaler
◆TIMER2: 8-bit timer with period register, prescaler and postscaler
◆One CCP: Capture/Comparator module/Pulse Width Modulator module
◆High-speed synchronous/asynchronous transmitter/receiver HUSARTHR6P62 chip has rich internal resources, which provides a good foundation for the design of HID ballast system. 

4. Design of HID control system based on HR6P62 microcontroller 

The ignition of HID lamp is mainly divided into four processes: 1. High voltage generation, according to the aging state and hot and cold state of the lamp, a high voltage of about 20,000 volts is generated; 2. High voltage breakdown, the high voltage breaks down the gas in the HID lamp in the insulating state, and the impedance of the lamp drops rapidly; 3. The high voltage stops working, and the HID lamp enters the constant power adjustment state; 4. After the HID reaches steady state, it enters the stable management state. From the above four processes, it can be seen that the control process of HID lamps is relatively complex, and the characteristics of HID lamps from different manufacturers are often different. How to achieve the best match between the ballast and HID lamps with different characteristic curves is a problem that all HID ballast manufacturers must focus on studying and solving. The quality of the ballast design has a very important impact on the life and reliability of the HID lamp. 

The HR6P62H chip core adopts a two-stage pipeline, a Harvard RISC structure, and integrates many peripheral devices such as analog comparator circuits, reference voltage modules, hardware watchdogs, a 16-bit calibration timing/external counter, an 8-bit calibration timing/external counter, an 8-bit calibration timer with a cycle register, a CCP (capture/compare/pulse width modulation) module, a HUASRT (high-speed synchronous/asynchronous receiver transmitter) module, and an 8-bit 4-channel ADC module. It supports low-power sleep mode, external interrupts, PB port high 4-bit change interrupts, etc. It has powerful interrupt processing capabilities and can handle 8-level interrupts. The data memory storage depth is 224×8 bits. The program memory storage depth is 2k×16 bits. There are three addressing modes: direct addressing, indirect addressing and relative addressing. There are power-on reset and power-off reset circuits and 16 bidirectional ports on the chip. The entire HID ballast control circuit will become very simple by using the HR6P62 chip design. The flexibility of control is retained by using the internal software design. Through the software, the microcontroller can detect and send signals to realize the functions of cold and hot start, power closed-loop regulation, and abnormal lamp protection of the HID lamp. The circuit structure diagram of the HID ballast based on the HR6P62 microcontroller is shown in Figure 2. The 



on-board DC power supply provides energy to the high-voltage ignition circuit through the DC/DC converter, and provides energy for the normal operation of the HID lamp after successful ignition. The full-bridge inverter controller inverts the DC voltage into a high-frequency square wave voltage. The HR6P62 microcontroller controls the charging and discharging of the capacitor at the beginning, the empowerment after ignition, the inverter control during normal operation, and the detection of the working status of each system. The operation of the HID lamp includes the following four stages: 

1. Capacitor charging ignition stage 

HR6P62 single-chip microcomputer control program performs a 400V constant voltage closed loop through the bus capacitor of the DC/DC converter, and the double voltage rectifier output voltage is charged through the over-discharge capacitor, gradually charging the discharge capacitor to 600V. After the discharge capacitor on the primary side of the high-voltage package reaches 600V, it will break down and discharge the discharge tube, and instantly generate a 23kV~30kV high-voltage pulse on the secondary side of the high-voltage package.

2. Arc stabilization and empowerment stage 

Once the high-voltage pulse breaks through the xenon lamp, the lamp impedance will immediately drop to tens of ohms. 

At this time, a current of 3A~12A is required to maintain the stability of the arc. After the arc is stable, the characteristics of the HID lamp will depend entirely on its initial temperature. The voltage of the hot-started HID lamp will remain at around 85V, while the voltage of the cold-started HID lamp will remain at around 20V. Therefore, a certain empowerment time is required during cold start to provide sufficient energy to ensure that the HID lamp can work normally. 

3. Power reduction stage 

After the HID lamp is started, if the power drops slowly, it will affect the life of the lamp. If it drops too quickly, it will easily cause the lamp to go out. Therefore, for cold start, the lamp power must be reduced to the normal allowable range within 10s to stabilize the HID lamp voltage to about 85V. In the case of hot start, there is generally no danger of extinguishing the lamp, so the lamp power can be reduced faster. 

4. Stable operation stage 

After the power reduction stage, the HID lamp enters the stable operation stage. The voltage of the HID lamp at this stage depends on the initial state and life of the lamp, which is generally 80V to 100V, so that the power of the HID lamp is kept within the rated range, thereby ensuring the service life of the HID. 

5. Development of HID lamp control system 

The development of HID ballast has gone through three main stages: analog, analog plus digital and full digital control. It is currently in a period of comprehensive transition to digital control. 

Analog control has been widely used in the early development of HID lamps due to its fast response speed and easy use. However, analog controllers also have obvious disadvantages, such as difficulty in achieving standardization and integration. At the same time, the analog circuit design is complex and various parameters need to be adjusted, which is not conducive to large-scale assembly line production. 

Analog plus digital hybrid control is currently a more commonly used control method. The so-called digital-analog hybrid control means that the closed-loop control of the system has both digital control and analog control. The entire HID lamp control system is a dual-loop system, the outer loop is a power loop, current loop or voltage loop, and the inner loop is a current loop. Since the inner loop implements PWM control, it requires a very fast response speed. The most typical digital-analog hybrid control is a hybrid control scheme that uses a fast internal analog current loop and a cheap external digital control loop with a small bandwidth. 

With the continuous development of electronic technology, the functions of digital chips are becoming increasingly powerful and the cost is continuously reduced, making the full digital HID lamp control system a hot topic in current research. Since the system uses MCU for AD sampling control, the quality stability of mass-produced HID lamp ballasts has been greatly improved. The output power control accuracy of the original analog solution is about ±2W, while after adopting digital control, the output power control accuracy can be controlled within ±0.5W. At the same time, the single-chip microcomputer controls the entire system loop, which can achieve a perfect HID control curve. The rich resources of the single-chip microcomputer greatly simplify the system structure of the HID lamp ballast, and can realize the miniaturization and flattening of the HID ballast. The single-chip microcomputer can quickly detect and determine the system status, which can effectively improve the safety performance of the HID lamp. Therefore, the fully digital HID lamp ballast has the following advantages: 

(1) Before starting, the full-bridge switch is controlled to charge the discharge capacitor. After starting, the full-bridge is controlled to work in DC mode first, and then enter AC working mode. 

(2) According to the hot and cold conditions of the lamp, the DC working time and current of the lamp are controlled. 

(3) The power of the lamp during the starting process is accurately controlled so that the lamp starting characteristics conform to the Vedilis curve. 

(4) Keep the lamp in a constant power state within the normal operating range of the lamp voltage. 

(5) Protect the battery voltage from overvoltage and undervoltage. 

(6) Protect the lamp from overvoltage and undervoltage, and overcurrent. 

Therefore, the full digital HID lamp control system will be more and more widely used in the ballast market in the future. The use of full digital control implementation methods is undoubtedly the future development direction of HID lamp ballasts.