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Watts News is an informative newsletter from PSUI providing technical details regarding power.  Sign up to receive your free copy in your email, or browse our latest articles below.

07/17/2017
power-factor-basicsGood power quality is necessary for providing stable, sustainable power for the world's increasing and varying load demands. Power quality  management  is an essential way to maximize the efficiency of the power grid, lessen the burden for resources and reduce operating costs. Power Factor (PF) is a measure of power quality.  Power Factor Correction (PFC) is the implementation of methods to increase power factor, thereby increasing power quality.  This article is a quick review of Power Factor (PF) and Power Factor Correction (PFC). PFC circuits are beyond the scope of the article. Power Factor Definition Power Factor in it's simplest terms is...
05/04/2017
dc-dc-converters-isolated-and-non-isolatedDC-DC converters are used in applications where voltage levels need to shift or where an isolation barrier is necessary. Voltage conversion can be achieved locally or at the point of load (POL).   All converters fall into two types, isolated and non-isolated. Let's look at the differences.   Isolated Converters   As the name implies, isolated converters have an isolation barrier. The isolation barrier is typically provided by a transformer which separates the input and output terminals. It can withstand hundreds to thousands of volts. Most isolation voltages are in 1500 to 4000V range, depending on the application. Isolation falls into three...
04/24/2017
status-signals-power-good-and-power-failA power supply's main job is to deliver power, but sometimes delivery of that power is delayed, interrupted or otherwise compromised. These situations can be deleterious to sensitive systems like computers and other applications that rely upon a stable, reliable source of power. In these applications, it's incumbent on the user to monitor the status of the power supply at all times. To that end, some power supplies are equipped with status signal lines to alert the user to changes that threaten the stability of the power source. The careful monitoring and manipulation of status signals affords the user a method to identify and avoid adverse...
03/03/2017
the-difference-between-ul-listed-and-ul-recognizedThe two most common types of UL marks are recognized and listed. The differences are discussed in this review.UL ListedUL listing means that UL has tested representative samples of a product and has determined that it meet's UL requirements. These requirements are based primarily on UL's published and nationally recognized standards for safety. Standards for safety include both construction and performance requirements. Products bearing this mark are typically complete systems of equipment or materials. When installed according to the manufacturer's instructions, they must be compliant to model codes such as the national electrical code (NEC)...
03/01/2017
load-sharing-for-parallel-redundancyToday's electronics must power  many of our most vital systems. Service interruptions are not easily tolerated in the financial, transportation, telecom, military or healthcare sectors, just to name a few. Redundant or Fault-Tolerant designs provide assurance that power is always available to these critical systems.   When applied properly, power supplies can be very reliable components. However, as with any physical component, there's a limited and somewhat calculable  lifetime of service. Mean between failures or MBTF helps us measure the reliability of the power supply. Regardless of the reliability and careful design considerations, a failure...
02/09/2017
ruggedized-dc-dc-converters-in-railway-and-other-industrial-applications DC/DC converters for railway and other ruggedized applications must withstand greater disruptive forces then most stationery applications and are subject to greater demands for operational safety, durability and thermal shock. There are 3 important standards to consider for these applications. EN 50155 is the governing standard for Electronic Equipment used in Rolling Stock. EN 50121 is a referenced standard that specifies limits for electromagnetic emissions and immunity for railways and equipment used within those railways. The sub category EN 50121-3-2 specifically defines the requirements for conducted emissions and immunity for rolling...
11/30/2016
thermal-management-of-power-suppliesPower applications require proper thermal management. Without it even the most efficient systems can fail at operating temperature or exhibit reduced reliability and lifetime.  The scope of this paper is to outline 3 basic principles for thermal management. While the focus here is on power supplies, these principles are applicable to all power systems.  In future Watts News, we'll discuss specific cooling methods for thermal management in more detail.Thermal Circuits Thermal circuits model heat flow from the power supply to the outside world (see figure 1). Every power supply, no matter how efficient will generate some heat from the power it...
11/01/2016
evolution-of-power-supply-densityPower density is defined as the ratio of output power per volume. It's typically represented as Watts/cm3 or Watts/In3. Power densities have increased greatly since the 1960s. Their evolution is synonymous with the evolution of the power supply industry as a whole. To understand the evolution of power supply density it's important to understand the types of power supplies, their relative power densities and ability to meet the needs of today's applications. The two basic types of supplies: 1. Linear regulated: These supplies employ a bulky transformer to increase or decrease voltage followed by a rectification  and regulator circuit.  They have...
10/03/2016
iec-62368-1-a-new-approach-to-safetyGlobal users of Audio Visual (A/V) and Information Technology Equipment (ITE) products number in the billions. The safety of these users, whether lay person or professional, is a growing concern. Since these two markets share many technologies, the IEC (International Electrotechnical Committee) has established a hazard-based standard to combine both IEC 60065 (A/V) and IEC 60950-1 (ITE).   The standard also includes Communication Technology Equipment (CTE). The principal methodology used in the development of this standard is a new approach called Hazard-Based Safety Engineering. What is Hazard-Based Safety Engineering? Hazard-Based Safety...
08/01/2016
ac-dc-power-supply-inrush-currentCause: When an electrical device like a power supply is turned on, an inrush current will momentarily flow in that device. In the case of an AC/DC switching power supply, the inrush current is primarily due to the charging current of the large electrolytic storage capacitor(s) employed in the rectification stage. See the simplified schematic Figure 1 . These currents can easily exceed 50 amps. The reason for this is that there is very little impedance present at turn-on, typically just a few ohms. Consider the Ohm's law equation, V/R = I . Ex. If turn on is at the peak of the AC cycle, 120VAC and we assume an input impedance of 3 ohms, then (120...
06/01/2016
high-peak-load-power-suppliesBy John BenattiPower supplies are employed in various applications. Many have standard load requirements that fall within the rated output current of the supply. In these cases, Vout x Iout  will  yield  a sufficient power rating for the power supply selection.  However, some applications will require a high peak load or Ipeak to initialize their operation. Examples of these are electric motors, pumps, fans, disk drives and other devices that need a start-up or peak current.  Peak currents can be several orders of magnitude higher than the static (steady state) load. Even though an Ipeak duration tends to be relatively short, typically  a few...
05/02/2016
choosing-a-power-supplyBy John BenattiThere are several factors to consider when choosing a power supply. An important first step is to categorize the major attributes of the supply. These can be generally be summarized as Fit, Form and Function:    Fit is the ability to interconnect, interface or become an integral component of another item.    Form is the size, mass, weight, shape and any and all dimensions that uniquely identify a power supply.    Function defines the performance of a power supply under a quantified criteria (environment, electrical stress, physicality etc.). Four Important Guidelines Priority Every power supply has a data sheet which identifies...