Pulse Width Modulation (PWM) is the fundamental control technique used in switch-mode power supplies (SMPS). By varying the duty cycle of a switching signal, PWM regulates output voltage or current efficiently. This article explores PWM principles, topologies, and design considerations for modern power supplies.
PWM controls power delivery by switching between ON and OFF states at high frequency. The ratio of ON time to switching period is the duty cycle (D = Ton / T). Output voltage is proportional to duty cycle: Vout = Vin × D (buck) or Vout = Vin / (1-D) (boost).
Simplest method: compares output voltage to reference, generating error signal that controls duty cycle. Good noise immunity but slower response to input changes.
Uses both voltage error and inductor current feedback. Faster transient response, inherent overcurrent protection. More common in modern designs.
Switches when output exceeds thresholds. No compensation needed. Fast transient response but variable switching frequency.
Step-down: Vout = Vin × D. Common for voltage regulators, point-of-load supplies.
Step-up: Vout = Vin / (1-D). Used for LED drivers, battery boost circuits.
Isolated topology using coupled inductor. Common in AC-DC adapters.
PWM is a versatile and efficient power control technique essential for modern electronics. Understanding the trade-offs enables optimized power supply design. FANYE Technology offers comprehensive power supply design services for your next-generation products.