Switching Power Supplies

Power supplies can be regulated or unregulated. Regulation refers to how the output is maintained. A constant current power supplies output current will be maintained at a specific level. A constant voltage power supply will have the output voltage monitored and controlled any constant level. The vast majority of power supplies are voltage controlled/regulated power supplies. In a regulated power supply the output is sampled in a feedback circuit which will control the necessary components to keep the output at a constant predetermined voltage.


There are three basic regulation technics, Pere feroresonant, linear, and switcher. Each offers inherent advantages and disadvantages. Equally important with the regulation technique is the specific circuit configuration. For this discussion we are focused on the constant voltage regulated power supplies. The vast majority of modern equipment today is the use of the switching power supply. Switching regulated power supplies are much more complex than either the linear's or ferros. Out of this complexity comes a power supply with high efficiency, high power density, and good line and load regulation. Regulation in switching supplies generally takes place on the primary side of the main power transformer. In off line switchers ( the most common type), the input rectifier filter section is situated directly across the AC input line. This section performs payment four primary functions: (1) voltage rectification and doubling, (2) energy storage, (3) inrush current limiting at turn on, and (4) suppression of electromagnetic interference.

The AC, alternating current, input is first rectified and, in the case of 115 V AC units, doubled to 300 V. The power conversion occurs in the chopper section at the 300 V DC and a corresponding low current depending on the output load. The 300 full DC is used to charge a bank of large capacitors actually feed the chopper section these capacitors provide energy for the holdup time the power supply. In most modern day switching power supplies the input section is power factor corrected. This allows for higher powered designs in power supplies than those without power factor correction. This adds more complex city at the backend which translates into higher failure rates. With today's technology has made switching power supply very reliable.

Switching regulation can be achieved using flyback, forward, half bridge, or full bridge converters in either constant voltage or constant current. Each converter technique offers unique price/performance trade-offs. Pulse width modulator (PWM) regulation can be of the flyback converter, forward converters, push/pull or bridge converters. The type and selection of these tech geeks is done at the design stage and is beyond the scope of this text. The control of this switching regulating circuit is done by sampling the output creating a feedback into the control circuitry. The input section, especially with power factor correction, the chopper section and the output section must all be coordinated electronically.

In summary, the AC line voltage is converted to a DC voltage via input rectification or power factor correction. The chopper section is controlled by a pulse width modulator circuit that provides power to the output. The output is monitored and feedback is provided should chopper section to maintain a constant regulated output voltage or current.

Siress Enterprises as it's been in business since 1989, and is equipped to service all types of power supply topologies, be it linear, or switching power supplies. Older power supplies can be repaired to the original specifications, or refurbished to increase its longevity. Oftentimes power supplies are designed specifically for their applications and are thus, difficult to replace with more recent technologies.