Integrated circuits used for flashing come in various types, but most are limited to three-way or five-way flash configurations. In many cases, the number of available channels is insufficient, and the flash patterns tend to be repetitive and unexciting. The eight-way flash integrated circuit addresses these limitations by offering more flexibility and a wider range of lighting effects.
Figure 1 shows the pin layout of the Y978 eight-way flash IC, which uses a standard 16-pin dual in-line plastic package. Pins 1, 8, VDD, and VSS serve as the power supply and ground connections. Pins 4, 5, and 6 handle the oscillator inputs and outputs. The oscillator uses an RC (resistor-capacitor) configuration, with the oscillation frequency determined by the formula f = 1/(K × Rx × Cx), where K is typically between 2.2 and 2.5. This means that larger values of Rx and Cx result in slower flash rates. By selecting appropriate resistor and capacitor values—usually between 47kΩ and 1.5MΩ for Rx, and 1nF to 10μF for Cx—you can achieve the desired flashing speed.
Pin 6 (BI) is the all-zero input. When a logic low (VSS) is applied, all eight output pins go low. The output becomes active only when a logic high (VDD) is applied. Pin 7 (L1) is the full-light control input, allowing the circuit to produce maximum brightness. These features, BI and L1, are especially useful in real-world applications, enabling a variety of flashing patterns and dynamic lighting effects.
The output pins (01 to 08) correspond to pins 9 through 16 on the IC. Figure 2 illustrates the internal logic block diagram of the Y978. The output stage uses Bi-CMOS technology, combining the advantages of both bipolar and CMOS circuits. This design offers low power consumption and strong driving capability, making the Y978 ideal for applications requiring high current output.
As shown in the diagram, the output structure includes an inverting driver made up of MOS transistors P1, N1, N2, and a bipolar transistor T. When the input is high, N1 and N2 turn on while P1 and T turn off, resulting in a low output. Conversely, when the input is low, P1 and T turn on, and N1 and N2 turn off, producing a high output. Due to the bipolar transistor's ability to deliver up to 35mA of current, it can effectively drive typical loads such as LEDs.
The voltage at the output points can exceed the VDD and VSS ranges, sometimes reaching up to twice the VDD or below twice the VSS. Such transient voltages may potentially damage the 5th pin of the CMOS input if not properly protected. To prevent this, a protective R/C network (ranging from 100kΩ to 1MΩ) is added, though it does not affect the oscillator timing.
Switch K1 acts as a full-light control terminal; when closed, it turns all outputs on. Switch K2 resets the entire circuit, turning all outputs off. The internal pull-up resistor ensures stable operation when the switches are open. Each output includes a current-limiting resistor R, which is calculated based on the required operating current. This allows each channel to drive multiple LEDs as needed.
In normal operation, the LED sequence follows a specific pattern: 01-01, 02-01 02, 03-02 03, 04-03 04, 05-04 05, 06-05 06, 07-06 07, 08-All-off-01-01 02, and so on.
The Y978 flash circuit is widely used in vehicle taillights and various electronic decorations. LEDs can be arranged in different shapes, creating effects such as center-to-side flashing, one-sided flashing, or a flowing circular pattern. The soft, smooth flashing of the Y978 provides a visually pleasing experience without any abrupt or jarring transitions.
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