How Power Over Ethernet (PoE) Works

Knowing how annoying it can be to watch long videos when all you want is a quick explanation, I put up a How PoE Works video, in which basic principles of PoE operation are explained in less than two minutes. Learn how power can be superimposed onto data pairs in ethernet cables.

Intel ATX 3.0 PC Power Supply Specification

19 years after publishing ATX2 power supply standard (a.k.a ATX12V2), Intel has released new ATX 3.0 Multi Rail Desktop Platform Power Supply specification. The main innovation in ATX 3.0 is new auxiliary 12VHPWR connector intended for next generation hardware, such as PCIe 5.0 desktop graphics cards. This connector can provide up to 600W on 12V bus directly to a graphic card. In addition, auxiliary "sideband" pins can communicate to the card the available power of PSU, and can also provide some communication back from the card to the PSU. 

For the details of the new spec, pinout of 12VHPWR connector and designation of the sideband control signals, see our review of ATX 3.0 Connectors and Pinout.

12VHPWR connector

HP Recalls Notebook AC Power Cords Due to Fire and Burn Hazards

According to CPSC.gov, HP recalls more than 5 million power cords for HP and Compaq notebooks due to fire and burn hazards. I can understand how a sloppy designed power supply can overheat. But a power cord? Could not HP genius figure our proper wire rating?

One Million Dollar Prize for Next Generation of Power Inverters

Google recently announced their so-called Little Box Challenge, a $1 million prize to develop the next generation of power inverters. If you want to know what power inverter is, here is the basics. Unfortunately, they did not provide any technical details on what exactly they are looking for. The referred website http://www.littleboxchallenge.com/ as of today provides zero useful info either. Hopefully, they will clarify the competition shortly.

Power Supply Seminar 2012/13 Textbooks Online

Those who missed Texas Instruments latest 2012-2013 power supply design seminar can now download all the materials here. This time they archived online both the manuals and the presentations, which are quite handy. Unfortunately, TI is doing a pretty good job making it very hard to find these files in their website. If you want to read past TI (formerly Unitrode) seminar manuals beginning 1983, I listed them all here. I kept maintaining and updating these links for over a decade now. Originally I got the list of their topics (which at that time was much shorter) from one of TI application engineers who interviewed me for a job. I did not get the job back then, but I got a list of the links. It was a good deal. (-:

Higher Distribution Voltage for Server Efficiency Increase

Several years ago Google suggested an open standard for desktop PC power supplies with a single 12V rail instead of multiple rails. The point was the higher buss voltage the higher overall PC PSU efficiency.

This year Google power designers are going to present at DesignCon 2013 their strategies for reducing energy losses in servers, including DC-DC regulator architectures as well as higher voltage distribution. Google apparently is going to make a case that higher distribution voltage levels improve overall conversion efficiency. Obviously, raising the buss voltage will lower conduction losses. On the other hand, switching losses in downstream DC-DC regulators will increase. In addition to this, you will need to use higher voltage MOSFETs whose characteristics generally degrade with their rated voltage. That's why it will be interesting to see their experimental results and  conclusions on optimal distribution level.

China Safety Standard- Higher Clearance for Power Supplies

We used to think that if our power supply design meets IEC or corresponding UL requirements for a given application, we would automatically meet most national standards of other countries. Now, the main ITE Standard in China GB 4943.1-2011 appears to set more stringent requirements to ITE equipment. Although in general, GB 4943.1-2011 is based on IEC 60950-1 2nd addition, it includes certain deviations. Particularly, par.1.1.2 states that unless specified by manufacturer, the equipment is to be used up to 5000m altitude above sea level. Therefore, in the absence of the marking of par.1.7.2.1 specifying the altitude below 2,000 m, the equipment shall comply with the requirements for 5000m altitude. For such equipment, the minimum electrical clearance has to be multiplied by the factor of 1.48.
In many offline SMPS the minimum UL required creepage between primary and secondary circuits is 6.4mm. If both primary and secondary circuits are located on the same side of PCB, this number also determines the spacing (clearance) between the circuits. With the new China standard that goes into effect December 1, 2012, this spacing will now have to be greater than 9 mm. Note that GB 4943.1-2011 will apply to not only the devices for use in the China, but to all those produced there too. So, if you manufacture power supplies in China, in my understanding, you either need to redesign the PCB and replace certain surface mount optocouplers (if any), or add a warning label showing that your PSU is not for use above 2000m.

New Proposed Efficiency Standards for Battery Chargers and External Power Supplies

U.S. Department of Energy recently issued Battery Chargers and External Power Supply (BCEPS) Notice of Proposed Rule. DOE proposes amended efficiency standards for Class A external power supplies (EPSs) and new standards for non-Class A EPSs and battery chargers. The proposed standards set the minimum average efficiency in active mode and the maximum power consumption in no-load mode as a function of the nameplate output power. The greatest challenge for SMPS power supply designers in my view will be the proposed limit of maximum power in no-load mode. For EPS below 50 watt it will be <0.1 watt. Since a power supply has to be able to “wake up” when connected to a load, it needs to keep active certain control circuit. Keeping a consumption of an off-line bias supply below 0.1 W will be a real challenge.

The U.S. Department of Energy (DOE) will hold a public meeting on May 2, 2012 to discuss the analyses presented and issues identified in the Notice of Proposed Rulemaking and Technical Support Document. These proposed standards, if adopted, would apply to all applicable external power supplies manufactured in, or imported into, the United States on or after July 1, 2013.

At abote the same time, U.S. Customs and Border Protection (CBP) issued a notice of proposed rulemaking about Consumer Products and Industrial Equipment Non compliant with applicable Energy Conservation or Labeling Standards. CBP will refuse admission into the customs territory of the United States to consumer products and industrial equipment deemed non compliant with the Energy Policy and Conservation Act of 1975 (EPCA).

I feel our government is just one step short of stopping anyone at the border for carrying a cell phone with non-efficiency-compliant charger.

Recall of Sanus Surge Protectors Due to Shock Hazard

Milestone AV Technologies LLC voluntary recalled all low-profile power conditioners (surge protectors) Sanus Elements model ELM205, which used to be sold by home theater dealers. It was reported that improper grounding of the case and inadequate insulation poses an electrical shock hazard to consumers. More info is available from U.S. Consumer Product Safety Commission.

Power Supply Efficiency and Power Factor: Regulations Update

The U.S. Environmental Protection Agency (EPA) has recently announced that effective December 31, 2010, external adapters will no longer be eligible for the Energy Star label. The main reason for this move is in 2008 a mandatory federal minimum efficiency standard went into effect for adapters, mandating basically the same Energy Star performance level.

Last month the ENERGY STAR also published its Draft 3 revision to the proposed criteria for LED lamps, which can be screw into standard lamp sockets to replace incandescent bulbs. To earn the ENERGY STAR logo the LED lamp should have power factor ≥ 0.70. Of course, Energy Star is a voluntary program. However, chances are their requirements will be eventually incorporated in a federal standard. Also, Europe already requires lighting PF>0.9. These developments will certainly cause LED lamps manufacturers to use active power factor correction (PFC) circuits for LED drive. Given the efficiency and size requirements, it's likely that the SMPS designers would also have to use other techniques such as bridgeless PFC rectifiers and synchronous rectification.

"True" Bridgeless PFC Claims Power Supply Efficiency Increase

I am going to discuss Dr.Slobodan Cuk article entitled “The True Bridgeless PFC Converter Achieves Over 98% Efficiency, 0.999 Power Factor”. It was featured in the July issue of Power Electronics Technology Magazine. The article describes the latest invention of Dr.Cuk aimed at eliminating input bridge rectifier from the offline PFC power supplies and thus increasing their efficiency and power factor.
The bridgeless PFC circuits were known before. The diagram below compares Dr.Cuk’s circuit with a different circuit described in ST’s App Note 1606.

The Dr.Cuk approach is certainly novel and very interesting, just like probably all of his converter circuits. However, I believe the above article contains some exaggerations more suitable for advertising than for a technical paper.

For example, the author says: “This method also leads to a rather unusual converter topology consisting of three switches only: one controllable switch S and two passive current rectifier switches CR1 and CR2”. He also claims: “…The odd number of switches, three, is a distinctive characteristic of this converter with respect to all conventional switching converters…” However, later he admits: “…At present, a single MOSFET implementation is not possible due to built-in body-diode, so that switch S must be implemented by use of the two MOSFET devices connected in series at their sources and driven by a common floating gate drive circuit…” So, in reality, the switch S must consist of two real switches and overall there are still four switches, not three. When the power switch S in ON, the current flows through three switches: S1, S2 and CR1, which is a drawback of this converter. With respect to the conduction losses during the ON time interval, I see no improvement relative to the known circuit of a “bridgeless PFC”, in which ON-state current flows through only two switches, S1 and S2. For the same reason I would say, it is not more "true" bridgeless than the original circuit. I understand, the reduction of conduction losses in Cuk's circuit comes during OFF state of the switch when the current flows through a single switch CR2 while in the known circuit it flows though two switches, such as CR1 and S2. Therefore the main advantage of this circuit would probably be realized when ON time is low and OFF time is high. Since at low input line the duty cycle and ON-time tend to be high, while at high line they tend to be low, the advantage of the Cuk’s proposed converter would be at high input lines where PFC has higher efficiency anyway. The article claims 98% efficiency, but unfortunately it does not state under what input and output conditions it was achieved. I tend to doubt very much it is achieved at low line.

For more information see my review of schematics of various bridgeless PFC.

Meeting Energy Efficiency Standards for External Power Supplies

I previously wrote about the Energy Independence and Security Act of 2007 (EISA 2007). Its Section 301 establishes efficiency standards for external power supplies (EPS), such as power adapters. The U.S. Department of Energy (DOE) has recently published a Final Rule on "Energy Conservation Program: Certification, Compliance, and Enforcement Requirements for Certain Consumer Products and Commercial and Industrial Equipment." In this document under section 430.24 (bb), is the requirement for determining the number of EPS units to be tested to claim compliance with EISA 2007. In short, the DOE document requires 97.5% confidence level to reflect variations in materials, the manufacturing process, and testing tolerances.

The Section 24(bb) of Title 10 of the Code of Federal Regulations (10 CFR) Part 430 states:
For each basic model of external power supply selected for testing, a sample of sufficient size shall be selected at random and tested to ensure that—

(1) Any represented value of the estimated energy consumption of a basic model for which consumers would favor lower values shall be no less than the higher of: (i) The mean of the sample, or (ii) The upper 97.5 percent confidence limit of the true mean divided by 1.05;

and

(2) Any represented value of the estimated energy consumption of a basic model for which consumers would favor higher values shall be no greater than the lower of: (i) The mean of the sample, or (ii) The lower 97.5 percent confidence limit of the true mean divided by 0.95.

To demonstrate compliance with EISA 2007 standards for Class A EPSs (in effect since July 1, 2008), manufacturers must test representative sample of units according to the DOE test procedure, and certify their compliance by submitting a compliance statement and the first certification report to DOE by July 6, 2010.

To translate their language to plain English, when they say the "represented value of energy consumption for which consumers would favor higher values" they refer to the efficiency. Conversely, the "represented value for which consumers would favor lower values" is input watts. (Our lawmakers of course presume they know what we, the consumers would favor. Would you favor a charger with 51% efficiency over a charger with 49% if the latter one costs twice less?)

To determine the number of the samples to be tested to confirm the compliance with 97.5% confidence level, the manufacturers would have to revisit the statistical analysis theory. To be able to sell the affected external power supplies in US, they have to do the testing, the math, and to submit the required docs to DOE by 07/06/10.

Medical Power Supplies: New Efficiency Standards are Ahead

This week the U.S. Department of Energy (DOE) has published a notice of proposed rule on its "Energy Conservation Program for Consumer Products: Determination Concerning the Potential for Energy Conservation Standards for Non-Class A External Power Supplies." In this document, DOE proposes to determine that energy conservation standards for so-called non-Class A external power supplies (EPS). Class A in DOE terminology refers to single output EPS with nameplate power under 250 watts.

For reference, currently there are three domestic programs that mandate certain minimum efficiency levels of external power supplies: the Federal mandatory standard for Class A EPSs, the EPA’s voluntary ENERGY STAR standard, and California’s mandatory standard for so-called ‘‘State Regulated EPSs.’’ They all apply to low-power single-output units and particularly exclude medical supplies. Did you think the government would let anything to be unregulated? Nah! The DOE is now is trying to regulate efficiency of four more types of external power supplies that do not fall under class A: (1) Multiple output EPS (2) EPS above 250 W, (3) EPS for medical use, and (4) EPS for battery charging. The new proposed rule can affect power supplies for a wide variety of applications such as amateur radio equipment, Xbox 360, nebulizers for home use and other medical equipment, cordless power tools, etc. Note that this rule does not set any specific standards yet; it only positively determines that future standards may be warranted and should be explored in an energy conservation standards rulemaking. DOE will be accepting comments by December 18, 2009, after which it will make an actual determination.

Power Supply Efficiency Compliance Calculator

I previously wrote about various US and international regulations related to an external power supply efficiency. Power Integrations came up with a nice free online tool that let you quickly check whether your charger or an adapter complies with the energy-efficiency regulations. You just enter your power supply's nameplate wattage, no-load power consumption and the efficiency in the active mode at various load levels. The calculator then tells you whether you meet various worldwide standards and actually displays the required no-load input wattage and required efficiency you need for the compliance.
The calculator currently checks for compliance to the following standards for PSU below 250W:
• ENERGY STAR (version 2.0), a voluntary standard sponsored by the U.S. Department of Energy and the EPA;
• EISA 2007 section 301, a mandatory U.S. efficiency standard, based on the California Energy Commission’s Appliance Efficiency Regulations;
• European Commission Code of Conduct (version 4) issued in April 2009;
• European Eco-design Directive: The Commission’s Eco-design Directive for external power supplies, which aligns with the EISA 2007 standard for Tier 1 and ENERGY STAR (version 2) for Tier 2;
• China USB Charger Specification (YD/T 1591-2006) for mobile telecommunication terminal equipment power supplies;
• EC Integrated Product Policy (IPP) for mobile phone adapters/chargers.

Hopefully, PI will be promptly updating their calculator when the applicable standards change.

How to Measure Efficiency of a Multiple-Output Power Supply

On March 27, 2009, the US Department of Energy (DOE) published an amendment to its test procedures for battery chargers and external power supplies (EPS). The amendment includes provisions for measuring standby mode and off mode energy consumption and adds a test procedure for testing switch-selectable external power supplies. Since the document basically clarifies existing test procedures, which DOE originally could not formulate clearly, it is mainly clerical and would not be worth noting if not for one funny thing. The amendment still does not include a test procedure for multi-output power supplies because of "the number of stakeholder comments and the limited timeframe for this rulemaking." OK, here is a little background. The Energy Independence and Security Act of 2007 (EISA 2007) set Federal efficiency standards for certain types of adapters and single-output EPS for consumer electronics. DOE has a test procedure to verify this efficiency. However, this procedure [which is basically: multiply output volts times amps and divide by the input power under various loading conditions] was written for single-output power supplies. It has therefore left out a significant group of products, powering applications such as radio transceivers, video game consoles, and printers. On August 15, 2008, DOE proposed a procedure for the testing of multiple-voltage external power supplies. On page 6 of the Proposed Rule we read: "DOE is not aware of any existing test procedure developed specifically to measure the efficiency or energy consumption of multiple-voltage external power supplies." Huh? Millions of multi-output power supplies both external and internal including PC PSUs are being built around the world and tested for Energy Star® and 80 PLUS® efficiency compliance. Folks, how about this: take a 5th grader, ask him/her to add up volt-amps of all outputs, divide by the input power, and you are done! Seriously, the main obstacle for DOE seems to be the loading profile. The PSU's nameplate power is often smaller than the sum of the nameplate power of each individual output. So what's the big deal? Derate (scale down) the loads of all the outputs proportionally, so that their sum does not exceed the limit for the entire power supply. Of course, it would not be the worst case efficiency (which you would probably encounter if you shift the bulk of the load onto the lowest voltage outputs), but it would be kind of typical efficiency. Back in 2006, at the APEC conference, EPRI Solutions and Ecos Consulting presented their Enhanced Proportional Allocation Method for Loading Power Supply. Their method is incorporated by Intel in its PC power supply guides. DOE did propose to adapt the ‘‘proportional allocation’’ method. Nevertheless, the DOE 2009 final rule still reads: "Due to the limited time provided by EISA 2007 and limited resources available prior to the publication of this final rule, DOE was unable to address the large number of stakeholder comments received and decided to defer action on multiple-voltage EPSs to a 2009 rulemaking." In a private sector usually a new power supply will be designed, built and tested in this timeframe or in a shorter one. It's entertaining to watch how long will it finally take for US DOE to make up their mind on how to test the efficiency and to move to something else.

First Generic Power Supply Standard

Despite the fact that practically every electronic device needs a power supply unit (PSU), its requirements have not yet been standardized. Although some industries do have power supply standards (such as PICMG spec 2.11 for CompactPCI Power Interface and Power Supply Design Guide for Desktop PCs), these standards are for specific applications and do not have general usage.

IPC standard IPC-9592 is the electronic industry's first attempt to come up with a generic power conversion standard. The draft was initially developed by the IPC Power Conversion Subcommittee that included Dell, IBM, Lenovo, Hewlett Packard, Cisco Systems, Alcatel Lucent and Apple. This document standardizes the performance parameters for power conversion devices for various applications such as computers and telecommunications. It sets the requirements for design, qualification and conformance testing, manufacturing quality processes, and regulatory requirements. The document particularly lists applicable EMI standards and provides components derating guidelines. Although this standard is not mandatory (just like all IPC standards), due to the participation and support of major power supply users, one can expect its widespread acceptance.

In preparation for the standard release, IPC is planning a conference on November 6, in Irving, Texas, to discuss the details of the specification and outline the ideas that went into developing this standard.

Note that unlike Intel's Computer PSU Guides, IPC-9592 does not include any functional requirements such as voltages, currents, timing, connectors, etc. This is actually good for us, power supply designers. If our fellow digital engineers and system integrators would come up with a scalable power supply standard and would design their systems around standard PSU "bricks", OEM power supplies would become a commodity and would be primarily designed and built in the Far East. As a result, many of us designers, would have to become salespersons. But for as long as our fellow engineers choose to design their systems the way they please and then look for a custom PSU because their electrical and mechanical requirements can't be satisfied by off-the-shelf models, we, designers are in business. (-:

Efficiency Standards for Power Adapters

In a previous post I wrote about various programs and regulations aimed at increasing PSU efficiency.

Here is a brief update. On December 19th, 2007, the Energy Independence and Security Act of 2007 (EISA 2007) that is intended to reduce US Oil Dependence, became law. Although the act is aimed mainly at improving vehicles fuel economy and increasing the production of clean renewable fuels, it contain sections that affect power supplies.
Particularly, Section 301 External Power Supply Efficiency Standards establishes energy conservation standards that take effect on July 1, 2008 for so called “Class A External Power Supplies,” and establishes the processes to review and possibly amend those standards.
The term "class A external power supply' means basically a single output low-voltage AC-AC or AC-DC converter under 250W that is intended to be used with a separate end-use product.
According to this law, a class A external power supply manufactured on or after July 1, 2008 should meet specific efficiency standards depending on its nameplate power Po. For example, in the power range from 1 to 51 W [which is typical for most adapters] if you convert EISA requirement into percentage, the minimum efficiency in active mode should be 50% + 9*Ln(Po), where Ln(Po) is natural logarithm of the nameplate output power.

EISA 2007 requires US Depratment of Energy to issue a final rule prescribing energy conservation standards for battery chargers, if technologically feasible and economically justified, by July 1, 2011. DOE will also have to complete the determination on non-Class A external power supplies by a new deadline of December 19, 2009.

Note that unlike voluntary Energy Star® and 80 PlUS® programs, the above requirements are mandatory.

Power Supply Efficiency Increase: Requirements and Trends

The industry drive towards smaller and lighter electronics as well as raising energy cost stimulate continuous efforts on more efficient power conversion. However, specific levels of PSU efficiency used to be virtually unregulated worldwide and were left up to the manufacturers and their customers.

Although U.S. Environmental Protection Agency (EPA) along with the U.S. Department of Energy (DOE) since 90's promoted the voluntary labeling program called Energy Star®, this program focused primarily on sleep mode requirements of appliances. To qualify for the label a personal computer needed a capability to enter a low-power sleep mode after a period of inactivity. As a stimulus for high computer power supply's efficiency this program was mainly useless since it did not address active mode and allowed to consume as much as 10% of the PSU's power rating in sleep mode. Furthermore, in practice the sleep mode is disabled on most office computers: the studies found that this mode is actually enabled on only about 5% commercially used PCs.
To stimulate efforts on reduction of PC power consumption in operational mode, Ecos Consulting in partnership with a group of electric utilities has recently created another voluntary program called 80 PLUS®. To qualify for 80 PLUS, a power supply must demonstrate efficiency ≥80% at 20, 50 and 100% of rated load, and power factor >0.9 at rated load. They test power supplies and offer manufacturers of desktop computers and desktop-derived servers $5 and $10 rebates respectively for every unit with a certified power supply sold in participating utilities territories. EPA incorporated 80 PLUS requirements in their new revised Energy Star® Computer Specification (version 4.0) effective July 20, 2007. Under this revision PCs, notebooks, workstations, and game consoles will all have to meet both active mode efficiency and "idle power" consumption requirements to qualify for the label.
EPA also revised ENERGY STAR® specification for single output external power supplies (casually called adapters) for laptops, mobile phones, printers, scanners, digital cameras and others appliances. Under rev.1.1 the minimum active mode efficiency of an adapter with nameplate output power Po is ranging from 0.49*Po for Po below 1W to 0.84 for Po above 49W. Slightly higher Tier 2 requirements may become effective January 1, 2008. Similar programs harmonized with Energy Star exist in other countries including EU, Japan, and China.

Although both 80 PLUS® and ENERGY STAR® programs remain voluntary, mandatory standards for power supply efficiency are currently under consideration in US and various counties. Particularly, The Energy Policy and Conservation Act (EPCA) directed the Department of Energy to determine by August 8, 2008 whether energy conservation standards shall be developed for battery chargers and external power supplies.

California Energy Commission has already adopted mandatory Appliance Efficiency Regulations, that among other things include new ENERGY STAR® requirements for external power supplies.

Further energy loss reduction needs joint efforts of manufacturers of PC PSU and computer components- obviously you can't address all energy issues with power supplies alone.
For example, in a white paper presented at the 2006 Intel Developer Forum, Google suggested to switch from multi-voltage PC power supplies to a single output 12-volt open standard and generate all other voltages required by motherboard components via VRMs. They argued that most of the voltages produced by multiple output PC power supplies are no longer used directly in today’s PCs. Although additional voltage conversion would still take place on the PC motherboard, the single-output 12V PSU would make it easier to achieve higher overall efficiencies. Google servers already use this approach.

What else can be done to further reduce energy losses in computers? One of the computer PSU requirements that affects its efficiency is 16 ms hold-up time. To meet this requirement, turns ratio of the power transformer is normally reduced to provide secondary voltages overhead. This in turn requires higher voltage rating of output rectifiers, higher peak currents of primary FETs and results in lower efficiency. If we set the turns ratio higher (closer to what is needed to regulate 12V at nominal PFC boost voltage) the power supply will be 1-3% more efficient, but during one-cycle AC line interruption the 12V bus may drop to about 8-9 V with typical values of storage capacitance. This voltage is still high enough to allow VRM's and POL's maintain regulation of any voltages 5V and below. The only problem would be with the computer components that use 12V directly. If they were designed to briefly operate at reduced voltage levels or at least to not latch up or loose data, the computer system could be made more efficient and could still ride through the one-cycle line interruptions. In my humble opinion, if computer industry eventually accepts single 12V bus standard, it should also require wider operating range of components that use 12V and respectively modify PSU holdup requirement by allowing 12V drop by some 25-30%.

Power Electronics Search Engine

I have previously written about Google Custom Search Engine (CSE) program. In a nutshell, this program allows you to use your expertise to help improve web search for specific subjects. Originally CSE could be only hosted on Google's website. Now Google lets you host a search box and the search results for your CSE on your own website which lets you add various enhancements (such as radio buttons) by modifying the script.
You can access my power electronics search engine at http://www.smps.us/smps-search.html . The HTML script for radio buttons is courtesy of Ed Schmidt http://www.lures.info/ .

I encourage you to give my custom search engine a try and compare your results with the results you are getting with a standard Google search. If you like this search engine you can add it to your Google homepage or to your website.

Power electronics resources

Hi, there. To divert a portion of the traffic from my main website I've opened a supplementary site with Power supply/ Power electronics calculators, news and career resources: http://www.smpspowersupply.com/ .
Although it is still under development, feel free to stop by and check it out.