Silent Power Supply
or Powerful Power Supply?

 Important Factors for Successful Power Supplies 

A power supply is arguably the most important component in every electrical device. It must supply a steady, reliable source of power to every other component in the system, and it must do so without making too much heat or noise. If the power supply is incapable of providing the power needed, data corruption and possibly physical component damage could result. That's why when purchasing a switching power supply, those items are necessary to be checked: the wattage, capacity of electrolytic, fan or fan-less, certifications, test results and temperature tolerances, etc. A switch power supply of good quality and with enough capacity can increase the durability of your equipment and reduce your electricity bill. On the other hand, a low-quality power supply can cause several intermittent problems, which are mostly difficult to be solved. Consideration of the ambient environment is also important since it will dictate the general temperatures of your power supply thus directly influencing the power output of your supply. Power supplies should not be bought under the impression "more is better" because in some cases more is actually worse and much more costly.

Capacity of Electrolytic Equals the Lifetime of Power Supply

Aluminum electrolytic capacitors are made with two layers of metal physically separated by a dielectric layer of material that is bathed in a liquid electrolyte. The surface area of the two metal layers is so great that the thickness of the metal is microscopically thin.

A very high quality electrolyte used in military application may last about 20 years. Lower grade capacitors may last only a year or two, and failure of low grade (or over stressed) capacitors at three years does not seem unusual. Many industrial systems that use electrolytic capacitors have them replaced every three years as preventative maintenance. Sometimes a defective electrolytic filter capacitor can have lower capacity and cause a lower dc output voltage from the power supply.

Electrolytic is easy to measure since they have relatively high equivalent series resistances. But it is important to vary the temperature of the capacitor to see its effect on the characteristics. Electrolytic will also vary substantially with aging, especially at elevated temperature. This is another involved topic which is beyond the scope of this article, but you must check the lifetime and temperature of operation in your power supply to ensure that the electrolytic are not going to fail.

Electrolytic capacitors also fail for another reason. When placed in a design, they have a voltage safety margin, and the capacitors can take a voltage surge and not fail. However, over time, the capacitors reform to the voltage they are being used at and any voltage surge may destroy them. For this reason, electrolytic capacitors are often periodical reformed as part of maintenance by applying the voltage they operate at and then slowly (over many hours) increase the voltage, while monitoring leakage current, until their surge rating is restored. Failures can also be accelerated by cleaning with halogenated solvents, mounting method, and mounting orientation.

Fan or Fan-less - The Silent Goal of Switching Power Supply

Which do you sacrifice? Silence or power? New silent cooling products are constantly being released, allowing us to keep our hardware specs high, while maintaining nice, silent operation. Lots of power supply users prefer fanless switching power supply because of its noise and size. That is why some PSU manufacturers are starting to come out with FANLESS power supplies.

Running a "silent" power supply is all good if you have adequate airflow to keep case temperatures down. Of course, if you're going for a 100% fanless system, you won't have that luxury. Most silent PSU's operate in "silent" mode up to a certain level (usually around 60 degrees). Once the temperature goes past that point, the fans spin up to incredible levels, rendering them ANYTHING but silent.

Power Supply Signal Integrity

The power supplies have been assumed to have an impedance low enough at the frequencies of interest to permit return currents to flow as desired. In fact, the connection from an integrated circuit to the power system has substantial inductance, which blocks all but the lowest frequency return currents from flowing through the power sources. Proper bypassing and decoupling techniques improve overall power supply signal integrity, which is important for reliable design operation. These techniques become more significant with increased power supply current requirements as well as increased distance from the power supply to the point-of-load (generally the FPGA or CPLD device).

Power connector decoupling provides three benefits to a design: 1. improves power supply integrity, 2. improves signal integrity, and 3. helps control EMI. Generally, designs with good power supply and signal integrity has the fewest EMI problems, and designs with good power supply integrity provide the best electrical environment for signal transmission. Proper decoupling, the placement of capacitance between power the return can make the difference between a design working marginally and one that is reliable.

Power Supply Thermal Management

Power supply voltage and temperature variations play an increasing role in signal integrity loss, which lead to performance degradation, reliability problems and functional errors. To improve synchronous circuits' tolerance to switching power-supply voltage and temperature oscillations, without degrading its performance. The underlying principle of the proposed methodology is to introduce additional tolerance to the clock edge trigger in specific memory cells, by dynamically controlling the instant of occurrence of the clock edge trigger. The clock duty-cycle (CDC) is locally modulated, according to the signal propagation delay through the logic whose power supply voltage or temperature is being disturbed. The methodology is based on a clock stretching logic (CSL) block, used to dynamically modify the CDC, while maintaining at-speed clock rate.

The temperature test chamber is a room for power supply to be tested for their temperature tolerances. Temperature test chamber supplied from extensive range of standard equipment, and include performance ranges of -40°C to +180°C or -70°C to +180°C or -10°C to +100°C. Temperature test chamber is fitted with a microprocessor controlled fully programmable PID control system, which can be used either as single set point controller for long term stability tests or as Fully programmable controller for cyclic type testing.

Power Supply Design Team - R&D technology

To design a power supply that has very low ripple, tight regulation, high stability, compact, fan-less, noiseless, high temperature tolerance, longer life cycle, design team's design capability could be critical for achieving the goals. For instance, a medical power supply would need a current share design to avoid the failure during operation and great performance of power supply comes from a great design team.

The switching power supply engineer needs to either sit elbow-to-elbow with the person doing the layout or spent time with him every few hours. Failure to do so can either ruin an otherwise good design or result in a schedule slip or cost over-run if the layout needs to be redone to avoid ruin. The reason is that there are innumerable ways a circuit can be layout and all of them have some compromises between performance, EMI, and thermal. Only the circuit designer who did the design and spent time in the lab getting to know their circuit has the detailed knowledge needed to make these tradeoffs and compromises.

Factors Leading to Reduction in AC/DC Power Supply Sizes in Recent Years

Power-Supply Voltage and Temperature Oscillations

A new methodology is proposed to increase the robustness of pipeline-based circuits. The goal is to improve signal integrity in the presence of power-supply voltage (VDD) and/or temperature (T) variations, without degrading circuit performance. In the proposed methodology, we dynamically control the instant of data capture (the clock edge trigger) in key memory cells, according to local VDD and/or T variations. This way, data integrity loss is avoided, and circuit tolerance to power supply and/or temperature variations is enhanced. The methodology is based on a Dynamic Delay Buffer (DDB) block, used to sense VDD/T variations and to induce dynamic clock skews driving a limited subset of memory elements. Experimental results based on SPICE simulations for 2 sequential circuits are used to demonstrate that careful design may lead to improvements on circuit tolerance to VDD and/or T variations.

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