Adjust The Light For The Car LED Light Accurately And Easily

- Dec 21, 2017 -

 20171212071236405.jpgWhen driving at night, you may not think of the headlights and taillights of the car, but I am fascinated by many of the design elements in these lighting systems:

The body stylist designed an amazing headlight and taillight outline and shape, to stimulate consumers' desire to buy

Government regulators focus on the shape and brightness of the beam

The system architect determines the light source and function

Optical engineers have developed reflectors and glass properties

The mechanical engineer selects the material and designs the physical structure of the light source

Electrical engineers design circuits for light sources and communicate with on-board electronic devices.

Given the many disciplines involved in lighting design, the final product development process will naturally have many design choices. Today, I want to talk about LED lights.

LED lights

As with household lighting, incandescent bulbs are used more often than outside lighting. As light-emitting diode (LED) lights become more common in homes, it has become increasingly popular in the car market. LED car taillights and brake lights are examples. Designers often use a Shared set of LED strings as a light source for both lights. When the driver brakes, the brake lights turn on and the rear lights dim. This function is achieved by the designer through the dimming function of the electronic device that drives the LED light source.

Figure 1 shows the block diagram of the electronic components that drive LED headlights and rear lights.LED.jpg

Figure 1: a block diagram of a typical architecture that drives a car's lighting LED.

Some key considerations in the lighting of LED headlights and taillights are:

LED drive with PWM: as shown in figure 1, LED drive, the electronic circuit that provides current to the LED, receives pulse width modulation (PWM) signals from the timer circuit. The PWM signal has an air ratio that controls the average current driven by LED drives, while the average current controls the brightness of the LED light source. Thus, when the driver brakes, the light from the LED lights up, while the light is dimmed only when the surrounding vehicles and pedestrians are prompted. Electronic design engineers usually use TI's 555 timer integrated circuit (IC) to generate PWM signals, and the timer integrated circuit (IC) is widely used in automobiles, industry and many other industries.

The ratio accuracy: the shortcoming of PWM signal based on 555 timer is the lack of accuracy. The 555 timer IC parameters which affect the space ratio are different in different IC. This means that even if each component of the design is the same, a 555 IC timer produces a void ratio that can be different from that of another 555 IC. In the car, that means the lights on the left and right sides may be different. One way to solve this problem is to replace the 555 IC with a microcontroller for the crystal as the clock source, thus generating an accurate PWM signal. However, this solution requires more expensive components and more complex software programming. Another method is to calibrate the brightness of the taillight in the manufacturing process. However, this method requires electronic equipment to support calibration, so the production time required is longer and the overall product cost can be raised.

Feedback: the third possibility is to use feedback. Figure 2 depicts this approach. The principle is simple: compare PWM with the exact reference value, then adjust the circuit output of the timer accordingly. This method is simple and cost-effective.LED2.jpg

Figure 2: feedback is added to improve the accuracy of PWM signal generated by TI 555 timer circuit.

I am sure you will ask: is this effective? The answer is yes! The precise PWM dimming LED drive reference design for automotive lighting includes relevant design details and test results.

Hopefully, I've provided a useful tip for car lighting designers. I believe that adopting feedback to improve the accuracy of the space ratio is simpler and more expensive than the other methods. Now, try it and don't forget to give me feedback!

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