74HCT123DB,118

Logic multivibrators are one of the most important and widely used building blocks in digital electronics. Built around simple logic gates like NAND, NOR, and Flip-Flops, these time-based pulses generators can be configured for a variety of applications such as oscillators, square wave generators, and timing circuits. Among the many kinds of logic multivibrators available on the market, 74HCT123DB and118 are two of the more widely used varieties. This article will look into the application field and working principle of the two devices.

74HCT123DB is an 8-pin dual-monostable multi-vibrator that is perfect for applications such as motor speed control, time-delay generation, or frequency divider. It is also useful as a wide range noise generator when programmed using the appropriate trigger levels. This device contains two independent monostable multivibrators with each having a fixed pulse width that can be extended through retriggering. 74HCT123DB has a trigger level of 75% of the supply voltage, and the output pulse width can be extended up to the maximum which is the range of 10 µs to 10 s.

118 is a 14-pin dual-monostable multi-vibrator that is capable of providing a wider range of pulse widths than the 74HCT123DB. It is designed for applications such as short time delay, frequency generators, and can also be used as a wide-range noise generator. 118 features two independent monostable multi-vibrator circuits with each having adjustable pulse widths between 5 µs and 10 s. It also has a wider supply range between 2.5 to 6.5V.

Their operation can be classified as two-state or flip-flop. In two-state mode, one of the two monostable multivibrator circuits is always in the triggered state while the other is in the rest state. As a result, one output is always present, and when either of the two inputs is triggered, the output switches to its inactive state, thus changing the state of the output. In flip-flop mode, the two monostable multivibrator circuits are triggered simultaneously, thus achieving bi-directional signaling. This operation is useful for applications such as frequency dividing, frequency multiplication, and waveform generation.

Both 74HCT123DB and 118 have internal circuitry that allows for pulse width adjustment. The pulse width adjustment is done via the  pulse width adjust line, which is a single pin that is connected to a voltage-controlled oscillator (VCO). By changing the voltage of the VCO, the pulse width can be adjusted to provide a greater range of pulse widths depending on the application. In addition, both devices feature anti-lockup circuitry, which eliminates any possibility of pulse widths exceeding their predetermined limits when reset during an active state, thus allowing reliable and accurate operation.

Finally, both devices include a latch line which can be used to trigger the output without triggering the circuitry. This feature is useful when it is necessary to output a pulse that has the same width regardless of the reset action. This helps in eliminating synchronization errors in applications that require high accuracy such as frequency dividers or frequency multipliers.

74HCT123DB and 118 are two of the most versatile and widely used logic multivibrators for various applications such as time-delay generation, frequency dividers, waveform generators, and short time delays. Their internal pulse width adjustment circuitry, anti-lockup circuitry, and reliable operation ensure that they are a great choice for any design requiring a high level of accuracy and reliability.