The car lamp flash control ASIC 7208 is an essential component in the controller of a vehicle's turn signal system. When the car is turning, this integrated circuit ensures that the front and rear lights, along with the monitor light, flash simultaneously at a frequency of 80 beats per minute. In the event of a bulb failure, the flashing frequency of the monitor light doubles, serving as an early warning to the driver. By utilizing the 7208-based flash controller, driving safety can be significantly improved.
The 7208 IC is housed in an eight-pin dual-in-line plastic package, offering advantages such as compact size, minimal external components, low power consumption, high precision, and a wide operating voltage range. This makes it an ideal replacement for traditional car turn signal controllers.
As shown in the internal block diagram and application wiring diagram above, the 7208 features a voltage comparator that detects the presence or absence of a power supply input, ensuring the circuit operates correctly. The voltage detection section includes a high-precision current sensor that measures the voltage drop across the sampling resistor Rs. This helps determine the amplitude of the RC oscillator’s charge and discharge cycle, which in turn controls the flashing frequency. The oscillator is composed of a comparator and an external RC network. A feedback resistor, Rl, stabilizes the circuit, while the output stage is capable of driving relays with an operating current of less than 180mA.
The value of Rs is critical for the proper operation of the 7208. When selecting the resistance, it is important to consider the lamp current and allow for sufficient margin. To ensure reliable operation within the 9–15V power supply range, Rs should be determined using the following method: short the relay contacts so that the lamp is on but not flashing, then measure the voltage drop across Rs under a 15V power supply. Calculate VRS = Ig × Rs, where Ig is the lamp current. Adjust Rs so that VRS falls between 1.15–1.20 VTHmax, approximately 160–180mV. Once set, this value of Rs will ensure stable performance.
The outline drawing of the 7208-based flash controller is displayed above. The controller has a frame size of 30 x 30 x 40 mm and uses an AT3S molded case. The three lead legs extend 15mm, with E representing the negative power supply terminal, B as the positive power supply terminal, and L as the flash control terminal. The design should be adjusted according to the lamp current (typically 3.0A). The wiring diagram below illustrates the specific electronic flash controller, where the relay contacts control the lamp's flashing or switching. These controllers are also suitable for use in applications such as holiday lights, beacon lights, and warning systems. For a 12V power supply, Rs is typically selected as 10Ω, and R is chosen as 680Ω.
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