How does an SMPS work?
1 Answer
An SMPS (Switched-Mode Power Supply) is a type of power supply that efficiently converts electrical power from one form to another, usually from mains AC (alternating current) to DC (direct current) with a regulated output voltage. It is widely used in various electronic devices, from computers and smartphones to industrial equipment, due to its higher efficiency, smaller size, and reduced heat generation compared to traditional linear power supplies.
Here's a simplified explanation of how an SMPS works:
Rectification: The first stage involves converting the AC input voltage (typically from the mains) to an unregulated DC voltage. This is done by passing the AC voltage through a diode bridge, which rectifies the AC waveform into a pulsating DC waveform.
Filtering: The pulsating DC from the rectification process contains significant ripples. To smoothen the output, a capacitor is used as a filter to reduce the voltage fluctuations, resulting in a more stable DC voltage.
Switching Circuit: The main component that distinguishes an SMPS from a linear power supply is the switching circuit. This circuit includes a power semiconductor switch, typically a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), which rapidly switches the DC voltage on and off. The switching is controlled by a pulse-width modulation (PWM) controller.
Transformers and Inductors: The switching action drives an isolation transformer and/or inductors. In high-frequency SMPS designs, transformers and inductors can be much smaller and lighter than those used in linear power supplies, thanks to the higher operating frequency.
Isolation and Voltage Regulation: The transformer provides isolation between the input and output, protecting the user from electrical shocks and noise. It can also step up or step down the voltage as needed. After the transformer, additional filtering and regulation circuits are used to maintain a stable and precise output voltage.
Output Rectification and Filtering: Once the voltage is regulated and isolated, it is rectified to DC again and passed through another filtering stage to further reduce any remaining ripples.
Feedback Control: To achieve proper regulation, the SMPS utilizes a feedback loop. A portion of the output voltage is fed back to the PWM controller, which continuously compares it to a reference voltage. If the output voltage deviates from the desired value, the controller adjusts the duty cycle of the switching circuit to bring the output back to the correct level.
Load and Overcurrent Protection: SMPS often includes protection mechanisms to safeguard against overloading and overcurrent situations. These protections can prevent damage to the power supply and the connected devices.
Overall, the switching action of the MOSFET allows the SMPS to be highly efficient compared to linear power supplies, which dissipate excess energy as heat. The high efficiency, smaller size, and reduced heat generation have made SMPS the preferred choice in modern electronic devices.
Here's a simplified explanation of how an SMPS works:
Rectification: The first stage involves converting the AC input voltage (typically from the mains) to an unregulated DC voltage. This is done by passing the AC voltage through a diode bridge, which rectifies the AC waveform into a pulsating DC waveform.
Filtering: The pulsating DC from the rectification process contains significant ripples. To smoothen the output, a capacitor is used as a filter to reduce the voltage fluctuations, resulting in a more stable DC voltage.
Switching Circuit: The main component that distinguishes an SMPS from a linear power supply is the switching circuit. This circuit includes a power semiconductor switch, typically a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), which rapidly switches the DC voltage on and off. The switching is controlled by a pulse-width modulation (PWM) controller.
Transformers and Inductors: The switching action drives an isolation transformer and/or inductors. In high-frequency SMPS designs, transformers and inductors can be much smaller and lighter than those used in linear power supplies, thanks to the higher operating frequency.
Isolation and Voltage Regulation: The transformer provides isolation between the input and output, protecting the user from electrical shocks and noise. It can also step up or step down the voltage as needed. After the transformer, additional filtering and regulation circuits are used to maintain a stable and precise output voltage.
Output Rectification and Filtering: Once the voltage is regulated and isolated, it is rectified to DC again and passed through another filtering stage to further reduce any remaining ripples.
Feedback Control: To achieve proper regulation, the SMPS utilizes a feedback loop. A portion of the output voltage is fed back to the PWM controller, which continuously compares it to a reference voltage. If the output voltage deviates from the desired value, the controller adjusts the duty cycle of the switching circuit to bring the output back to the correct level.
Load and Overcurrent Protection: SMPS often includes protection mechanisms to safeguard against overloading and overcurrent situations. These protections can prevent damage to the power supply and the connected devices.
Overall, the switching action of the MOSFET allows the SMPS to be highly efficient compared to linear power supplies, which dissipate excess energy as heat. The high efficiency, smaller size, and reduced heat generation have made SMPS the preferred choice in modern electronic devices.