How To Use Relays For PWM Control
Using relays for pulse width modulation (PWM) control is not recommended and almost always underperforms for most real-world scenarios. These devices function as mechanical contactors designed to turn circuits on and off by mechanically actuating terminals, and they are not engineered for millisecond-level transitions. Inherent physical components imposes fundamental constraints that make them inappropriate for PWM. Typical electromechanical relays can operate at frequencies below 10 Hz, while PWM requires switching frequencies of up to thousands or even over 10,000 times per second to effectively regulate power to inductive loads such as LED arrays and DC motors.
If you attempt PWM via relay switching will rapidly expose a host of operational flaws. Primarily, the mechanical contacts fail prematurely under frequent switching, causing premature failure. Second, response time is far too slow to produce a smooth average power output. Instead of a steady control signal is repetitive mechanical bangs and jittery energy fluctuations that may induce shaking, audible buzz, or erratic behavior in lighting systems. Finally, voltage transient generated when motors or solenoids power is cut can damage the relay contacts and corrupt or destroy any driving circuitry.
When precise power regulation is required, you should utilize semiconductor switching devices such as power transistors or insulated-gate bipolar transistors. Modern semiconductor switches can operate at frequencies exceeding 20 kHz over billions of cycles and while dissipating little heat. are compatible with programmable logic circuits to deliver accurate modulation over the RMS value supplied to a load. A high-current MOSFET combined with a dedicated MOSFET driver IC and a heat sink can handle high currents and ensure consistent modulation reliably.
Should your project that demands pulse width modulation and you are limited to electromechanical switches, you should rethink your architecture. Limit the relay to high-level power activation, and apply solid-state switching for a solid state component. As an illustration: you might activate a furnace via relay during a full duty period and a transistor to dim an LED array during the same time window.
In summary, using relays for PWM is unfeasible for PWM control. Their mechanical nature makes them too slow, too noisy, and too unreliable for the high-frequency switching that PWM demands. Always choose solid state switching elements like IGBTs and MOSFETs when you need PWM. Semiconductor switches respond quicker, operate silently, consume less power, and last orders of magnitude longer for this type of application.