Switching power supply; Challenges of selecting the right one
A linear power supply takes an AC input, steps the voltage down to what is needed with a transformer and then rectifies and filters it to create a clean direct current signal. A switching power supply takes an alternating current input and uses a rectifier along with some filters to create direct current. Next this is converted back to alternating current at a high switching frequency, the voltage reduced with a transformer and rectified and filtered again into direct current again.
Power supply solutions will use this process to create the correct power output. The difference between linear and switching processes is that physically different components impact the form factor of devices. In addition, while you may expect that the switching power supply may be less efficient than the linear one that has less to do, it is actually the switching power supply that is more efficient as a higher switching frequency can be used enabling the device to produce less losses. In addition, less costly and smaller transformers can make a switching power supply much smaller. Also, as these are more efficient with less cooling, either passive or active is needed.
Regulated versus unregulated wall adapters
In addition to the efficiency and form-factor of the device another decision is whether to use a regulated or unregulated wall power adapter. A regulated wall adapter keeps the necessary output close to the rating of the device using it by changing the duty cycle to compensate for load variation from the grid. These are typically 50% more expensive than an unregulated wall adapter however will likely keep the switching power supply in operation for much longer due to less component wear experienced.
Applications of a switching power supply
There are a whole host of applications a switching power supply regulator can use including home and business devices that need better energy efficiencies. This could be based on regulatory compliance to energy standards providing an energy efficiency requirement or based on a user’s requirements.
In some small electrical device applications, a low dropout regulator (LDO) could be used inside a device as a low noise alternative to a switching power supply regulator however these are linear and again not as efficient but can be sourced as single integrated components. Additionally, only voltage control is provided for these while a switching power supply regulator allows a manufacturer to control both voltage and current. LDO’s are only efficient when the input is higher than the dropout voltage while a switching power supply will always have a circa 95% power efficiency or even higher for more modern devices. Some have even reported circa 98% to 99% efficiencies with newer technology being used. Interestingly these power devices can be made almost half the size of an older model.
A switching power supply is highly robust to input variation, making them ideal for non-regulated inputs from a mains supply. This can be especially important for use in recreational vehicle systems as campground hookups have been known to have exceptionally bad regulation. This means also that a relatively lower cost product could be produced through allowing product designers to use an unregulated wall adapter.
No matter the application a switching power supply can improve the energy specification of a product allowing for it to become part of the marketing strategy along with offering a device that will last longer in service due to better regulation and reduced component fatigue in service. For most mid-sized or larger electrical devices, a switching power supply provides a much more efficient solution than a linear power supply.