Discrete 8-Bit PWM Generator Circuit Design

Description

Pulse-width modulation (PWM) signals are frequently utilized to regulate the rotation speed of DC motors. The duty cycle of the digital waveform can be determined either through the application of a variable analog voltage level (as in a NE555-based PWM generator) or digitally, utilizing binary values. Digitally derived PWM waveforms are predominantly created by timer/counter modules within microcontrollers, though it is also relatively straightforward to generate these signals employing discrete logic components if a microcontroller is not desired.

Circuit diagram:

An expansion of the illustrated circuit can yield two PWM waveforms stemming from an 8-bit digital input word. Each signal possesses 15 distinct values. The 8-bit word can originate, for example, from an expansion board integrated into a PC, or from an 8-bit port of a processor lacking built-in PWM capabilities, or from a laptop’s printer port. The mark/space ratio is only configurable up to 15/16, rather than 16/16; a binary input of 0000 generates a continuous low output on both outputs, disabling both motors.

Similar circuits often incorporate a dedicated ‘enable’ input to deactivate the motors, although this is not required within this design. The diagram outlines the circuitry needed to produce a single waveform. For the complete two-channel circuit, an additional 74HC193 is necessary. The clock signal produced by the HCF4060 generator can drive both channels, and the free flip-flop within the 74HC74 package can be utilized for the second channel (corresponding pin numbers are indicated in parentheses). Consequently, the entire two-channel circuit can be constructed utilizing only four ICs.

More about components

Integrated circuits (ICs) are complex electronic circuits fabricated on a single silicon chip. They represent a fundamental building block in modern electronics, offering significant advantages over discrete components in terms of size, performance, and reliability. The use of ICs simplifies circuit design and construction, reduces component count, and enhances circuit stability. Many circuits rely on specific ICs for precise control and signal manipulation.

The NE555 is a versatile analog IC commonly used in timer, oscillator, and voltage regulator applications. It operates from a wide range of supply voltages and provides precise timing control through its internal circuitry. The 74HC193 is a versatile Octal Shift Register commonly used for data manipulation and conversion. It shifts data between different levels, enabling the creation of complex waveforms and data processing functions. The 74HC74 is a versatile Flip-Flop commonly used for data storage and switching operations. The HCF4060 is a high-speed decade counter, providing a precise clock signal for timing and control applications. Its ability to generate a clock signal at various frequencies makes it a valuable component in many timing and counting circuits. These ICs are essential for the proper functioning and performance of the described circuits.