How ac/dc power supplies save you money

Choosing a high-quality, high-efficiency power supply that costs $50-$100, will probably pay for itself in the course of a year. Today’s trend is for power supplies to do more, have more, but cost less. Engineers that use power supplies are seeking less expensive supplies with additional features, while maintaining the same amount of energy needed for their devices. Power supply units (PSU) are the devices that powers computers, servers and data center devices. They convert ac power from electric utilities into dc power used in most electronics. One important factor in power supplies is the efficiency. Power supply efficiency is defined as the amount of power actually provided to the internal components, divided by the amount of power drawn at the wall. The amount of money you save from upgrading to a high-efficiency PSU is minimal if you don’t actually draw much power to start with. The 80 PLUS performance specification requires power supplies in computers and servers to be 80% or greater energy efficient at 10, 20, 50 and 100% of rated load with a true power factor of 0.9 or greater. This makes an 80 PLUS certified power supply substantially more efficient than typical power supplies. In a recent post, TDK-Lambda 2500 Watt Server Power Supply Achieves 80 PLUS® Platinum Efficiency, you may read some of the specs offered in this power supply.

80 PLUS Certification	115V Internal Non-Redundant				230V Internal Redundant
% of Rated Load	10%	20%	50%	100%	10%	20%	50%	100%
80 PLUS	—	80%	80%	80%	N/A
80 PLUS Bronze	—	82%	85%	82%	—	81%	85%	81%
80 PLUS Silver	—	85%	88%	85%	—	85%	89%	85%
80 PLUS Gold	—	87%	90%	87%	—	88%	92%	88%
80 PLUS Platinum	—	90%	92%	89%	—	90%	94%	91%
80 PLUS Titanium	—	—	—	—	90%	94%	96%	91%

In the past, power supplies were bulky, had costly components, and high-energy losses with low efficiency, resulting in high-energy costs. The basic construction of a power supply (See schematics below), is to design a rectifier circuit. If passive components, such as a filter capacitor were added after the rectifier diode (half-bridge), the voltage output would improve considerably getting a continuous voltage. If a center-tapped transformer with two rectifier diodes (full-bridge), or perhaps a simple transformer and four rectifier diodes (full-bridge) were designed, you would get continuous voltage starting from an alternating voltage. The capacitor would supply the load current. Consequently, the diodes increases ripple. With zero load current, the dc output voltage is equal to the peak value of the rectified ac voltage. When a low ripple voltage is needed, an LC filter network may be used. The ripple in the output voltage can be reduced; however, the inductor was costly and bulky.

The current trend is to design stabilized supplies with passive components, such as resisters, capacitors, and diodes that are smaller in size. For example, OEMs are using boost inductors built with a low-cost powder core material and a single layer coil. Inductors are being reoriented to allow more room on the breadboard. This arrangement has been shown as a suitable layout for applications when constraints such as power density, leakage capacitances, irradiated noise and costs are taking into account. Switching frequency and input current ripple, during design procedure, can bring magnetic volume reduction when compared with the commonly adopted power supply designs.

Active components such as MOSFETs and ICs, have become smaller as well. Simplified dramatically by the introduction of voltage regulators, ICs provide a stable output and includes current limiters and thermal protection functions. International Rectifier (IR) is making ac/dc ICs meet power supply demands for higher power density, smaller size, more portability and more flexible systems. Its ICs provides low switching and conduction losses to increase efficiency, reduce thermal problems and improve power density.

 

In the power supply market, multi-channel units with high output accuracy are available at increasingly lower prices. In the past, multi-channel power supplies didn’t offer remote sensing capabilities, but the newest designs feature remote sense terminals on each channel to compensate for voltage drops in the power supply leads to ensure that the correct voltage is delivered to the load terminals of the DUT. This helps enhance overall system accuracy. Another important feature is the addition of isolated outputs for added testing flexibility: when each channel of a multi-channel supply is isolated, it can power multiple isolated circuits with different reference points, eliminating the need for a second supply. The newest models also allow each channel to be turned on or off independently, so they can be used to power up a circuit that requires turning on multiple voltage levels in a specified time sequence.

Smaller components result in smaller board space. Smaller board space results in more compact power supplies. High quality, more features, and energy efficiency is part of the product development financial equation costs.

Special thanks to ASI Partners, Ecova and P. Antoniazzi.