PWM Signal
What is a PWM Signal?
A PWM (Pulse Width Modulation) signal is used to control devices such as heaters and motors by adjusting the pulse width to regulate the duration of current flow through components like FETs.
A pulse is a general term for a signal that changes rapidly over a short period, including digital signals. Each pulse consists of an H (High) pulse width and L (Low) pulse width, with their sum defining the pulse period. The most critical parameter of a PWM signal is the duty cycle, which represents the proportion of the H pulse width relative to the pulse period.
Circuit Configuration of a PWM Signal Generation Circuit
A PWM signal generation circuit consists of data registers, comparators, and a counter, similar to a timer. The data registers include a period register that determines the PWM signal's period and a duty register, which sets the pulse width (duty cycle). The circuit also integrates two comparators for the period and duty registers linked to a flip-flop, designated as Comparator 1 and Comparator 2, respectively. Comparator 1 sets the flip-flop output to 1 at the start of the cycle, and Comparator 2 resets the flip-flop output to 0 when the counter value reaches the duty register value.
The period register sets the width of the PWM signal's cycle, while the duty register defines the pulse width. The flip-flop output is set to 1 when the counter matches the period register at the start of a new cycle. As the counter increments, the flip-flop resets when it matches the duty register, inverting the output signal. When the counter matches the period register, it resets to 0, restarting the cycle and inverting the output again. This process continuously repeats, generating a PWM signal with a defined period and duty cycle.
Features of PWM Signals
PWM is an optimal control method for regulating heaters using components like FETs. A FET controls current flow to the heater. When the FET is OFF current flow stops, preventing heat generation, but when ON current flows to the heater, producing heat.
The FET turns ON when the PWM signal is H and OFF when the signal is L. When the FET is ON, current flows through the heater. Since heat generation increases with current flow, a longer H pulse width leads to more heat. Therefore, adjusting the H pulse duration allows for precise regulation of heat output. In other words, the biggest advantage of PWM signals is the ability to fine-tune power output by adjusting the duty cycle, which is directly proportional to the amount of heat generated.
PWM is not only used for heaters, but also for energy-related applications such as motors, LEDs, and speakers.
