Computer Power Supplies

COMPUTER POWER SUPPLIES AND SYSTEM PROTECTION What is a power supply and what does it do? • • • • • • The power supply unit (PSU) in a PC regulates and delivers the power to the components in the case. Standard power supplies turn the incoming 110V or 220V AC (Alternating Current) into various DC (Direct Current) voltages suitable for powering the computer's components. Power supplies are quoted as having a certain power output specified in Watts, a standard power supply would typically be able to deliver around 350 Watts. The more components (hard drives, CD/DVD drives, tape drives, ventilation fans, etc) you have in your PC the greater the power required from the power supply. By using a PSU that delivers more power than required means it won't be running at full capacity, which can prolong life by reducing heat damage to the PSU's internal components during long periods of use. Always replace a power supply with an equivalent or superior power output (Wattage). Page 14 of 52 There are 3 types of power supply in common use: • • • AT Power Supply - used in very old PCs. ATX Power Supply - still used in some PCs. ATX-2 Power Supply - commonly in use today. The voltages produced by AT/ATX/ATX-2 power supplies are: • • • • • • +3.3 Volts DC (ATX/ATX-2) +5 Volts DC (AT/ATX/ATX-2) -5 Volts DC (AT/ATX/ATX-2) +5 Volts DC Standby (ATX/ATX-2) +12 Volts DC (AT/ATX/ATX-2) -12 Volts DC (AT/ATX/ATX-2) Page 15 of 52 What is the Difference between AT and ATX power supply. • The main power connector on AT and ATX power supplies are very different, and require different motherboards because of this. The main power connector on an AT power supply is actually two separate six-pin connectors that plug into the motherboard side by side in a single row. The ATX main power connector is a single 20 or 24-pin connector that places the pins on two rows. • The power switch of AT style power supplies is integrated directly into the power supply itself. This is a physical switch that turns the power supply on and off. ATX style power supplies use a "soft switch" that is controlled by the motherboard. This enables a computer with an ATX power supply to power off via software. • Older power supplies provide a lower wattage rating than newer ones. Newer ATX style power supplies typically provide 300 or more watts, whereas AT style power supplies typically provide wattage of less than 250. • Though AT and ATX power supplies share many connectors, ATX power supplies may have connectors, such as SATA and 4-pin ATX12V, that never appeared on AT power supplies due to the technology post-dating the AT power supply. Additionally, an AT power supply has more mini-Molex connectors for devices such as floppy drives. • • • AT is an old standard that has been totally replaced by ATX AT boards are wider compared to ATX by almost 4 inches ATX allows board makers to customize the ports in the back with back plates which is not possible with AT AT computers had their power switches connected directly to the power supply while in ATX systems, the switch is connected to the motherboard • Page 16 of 52 Common PSU Connectors Type Description Illustration P1 A 20-pin or 24-pin connector that provides power to the motherboard. On some PSUs, the P1 is split into one 20-pin connector and one 4pin connector which can be combined if required (see illustration) to form a 24-pin connector. ATX12V (or P4) A 4-pin power connector that goes to the motherboard in addition to a 20-pin P1 to supply power to the processor. Molex A 4-pin peripheral power connector that supplies power to IDE disk drives and CDROM/DVD drives. Berg (or MiniMolex) A 4-pin power connector that supplies power to the floppy disk drive (it can also be used as an auxiliary connector for AGP video cards). Page 17 of 52 Serial ATA This is a 15-pin power connector mainly used for SATA hard drives. A 6-pin or (more recently) 8-pin power connector used for PCI Express graphics cards. Some 8-pin connections allow for either a 6-pin PCI Express or an 8-pin card to be connected by using two separate connectors on the same cable (one with 6 pins and another with 2 pins). P1 (PC Main / ATX connector) The primary task of the Power Supply Unit (PSU) is to provide your motherboard with power. This is done via the 20-pins or 24-pins connector. A 24-pins cable is backwards compatible with a 20-pins motherboard, often this cable can be split into 20- and 4-pins (like in the image above). Page 18 of 52 P4 (EPS Connector) At some point in time the motherboard’s pins were no longer sufficient to provide the processor (cpu) with power. With overclocked cpu’s drawing as much as 200W a need to provide power directly to the CPU was created. Nowadays it is the P4, or EPS connector, to provide the cpu with power. Cheap motherboards are equipped with a 4-pins connector. More expensive “overclocking” motherboards have 8-pin connectors. The extra 4 pins ensure that enough power can be provided to the cpu when overclocking. For regular usage there is absolutely no need for the additional pins. Most PSU’s provide two cables; one with 4-pins and one with 8-pins. Obviously you only need to use one of these cables. It is also possible that your 8-pin cable can be split into two segments to provide backwards compatibility with cheaper motherboards. Page 19 of 52 PCI-E Connector (6-pin en 6+2 pin) The motherboard can provide a maximum of 75W through its PCI-E interface slot. Faster dedicated graphics cards require much more power. To solve that issue the PCI-E connector was introduced. The left 2 pins of the 6+2 pin connector on the right is detached to provide backwards compatibility with 6-pin graphic cards. The PCI-E 6-pin connector can supply an additional 75W per cable. So if your Graphic card contains a single 6-pin connectors it can draw up to 150W (75W from the motherboard + 75W from the cable). More expensive graphic cards require the 6+2 pin PCI-E connector. With it’s 8 pins this connector can provide up to 150W per cable. A graphics card with a single 6+2-pin connector can draw up to 225W (75W from the motherboard + 150W from the cable). Molex (4 Pin Peripheral Connector) Molex connectors have been around for a very long time and can deliver 5V (red) or 12V (Yellow) to hardware peripherals. In the past these guys were often used to connect Hard drives, CD-ROM players, etc. Even some graphics cards like the Geforce 7800 GS were equipped with Molex. However their power draw is limited so nowadays most of their purpose has been replaced by PCI-E cables and SATA cables. All that is left is powering case fans. Page 20 of 52 Thanks to its angular side you cannot go wrong when connecting a Molex cable. Keep in mind that they can be extremely difficult to detach. SATA Connector The SATA connector is the guy that made the Molex obsolete. All modern DVD-players, hard disk drives and SSD’s are powered by SATA power. Thanks to their L-shape the SATA power connector can only connected the right way. Mini-Molex / Floppy connector Completely obsolete, but some PSU’s still come with a mini-molex connector. These guys were used to power floppy disk drives. For those of you who do not remember; these were square magnetic disks that could contain up to 1.44 MB of data. Basically they were superseded by the USB stick. Page 21 of 52 Adapter: Molex to SATA Power cable Old power supply unit or simply lacking the required number of SATA power connectors? Use a Molex to SATA connector to power your latest hard disk drive. Adapter: Molex to PCI-E 6-pins Need another PCI-6 pin cable to power your graphics card? Use the “2x Molex to 1x PCI-E 6pin” adapter. Please make sure you connect both molex to different cable strains. This reduces the risk of overloading your power supply. If you don’t 75W will flow through your Molex cable. Page 22 of 52 Adapter: ATX adapter With the introduction of ATX12 V2.0 are change was made to a system with a 24-pins connector. The older ATX12V (1.0, 1.2, 1.2 and 1.3) used a 20-pins connector. In total there are ober 12 versions of the ATX standard, but they are so similar that you do not need to worry about compatibility To create backwards compatibility most modern power supplies allow you to disconnect the last 4 pins of the main connector. It is also possible to create forward compatibility by using an adapter. Page 23 of 52 An ATX 20pins to ATX v2 24pins adapter. This cable also demonstrates the ability to detach the last 4 pins. Page 24 of 52 The main PSU connectors and their pin outputs are illustrated in the diagram below. Common PSU connectors and their pin outputs Page 25 of 52 For an ATX power supply, state the voltage levels for the following color codes • • • • • Red Blue Yellow Orange Black Page 26 of 52 Identify the color codes for the ATX power supply cables Complete the table below which shows the color codes of ATX power supply. PIN 1 2 3 4 5 6 7 8 9 10 Signal voltage 3.3v 3.3v Color Black Red GND 5V GND POWER GOOD 5V/SB(standby) Yellow Identify the color codes for the ATX power supply cables shown below PIN 1 2 3 4 5 6 7 8 9 10 SIGNAL 3.3V 3.3V GROUND 5V GROUND 5V GROUND POWER OK 5V 12V Page 27 of 52 COLOUR 24-pin ATX 12V 2.x Power Supply Connector Color Pin Pin Signal Signal Color +3.3 V Orange +3.3 V sense Brown Orange +3.3 V 1 13 Orange +3.3 V 14 −12 V Blue Black Ground 15 Ground Black 16 Power on Green 17 Ground Black 18 Ground Black 19 Ground Black 20 Reserved None 21 +5 V Red 22 +5 V Red Red Purple +5 V standby Yellow +12 V 2 3 4 5 6 7 8 9 10 Yellow +12 V 11 23 +5 V Orange +3.3 V 12 24 Ground Red Black Red +5 V Ground +5 V Black Ground Grey Power good Black Identify the voltage levels for the following ATX power supply color cables PIN 1 2 3 4 5 6 7 8 9 10 SIGNAL Page 28 of 52 COLOR Orange Orange Black Red Black Red Black Green Purple yellow With reference to power supplies explain the following • • Power good signal Power good delay Power good signal The Power Good signal (power-good) prevents a computer from attempting to operate on improper voltages and damaging itself by alerting it to improper power supply. • • • • • • When we first turn on the power supply, voltages are not immediately available on the power supply outputs: they increase until reaching their correct values. This increase happens is a fraction of a second (maximum of 20 ms or 0.02 s to be more exact). In order to prevent these lower-than-normal voltages to be provided to the computer, the power supply has a signal called “power good” (also called “PWR_OK” or simply “PG”), which tells to the computer that the +12 V, +5 V and +3.3 V outputs are in their correct value and thus can be used, and the power supply is ready to work in a continuous fashion. This signal is available through pin eight (gray wire) from the main power supply connector. There is also another reason for this signal to exist: the under voltage protection (UVP) When the power supply first starts up, it takes some time for the components to get "up to speed" and start generating the proper DC voltages that the computer needs to operate. Before this time, if the computer were allowed to try to boot up, strange results could occur since the power might not be at the right voltage. It can take a half-second or longer for the power to stabilize, and this is an eternity to a processor that can run half a billion instructions per second! To prevent the computer from starting up prematurely, the power supply puts out a signal to the motherboard called "Power Good" (or "PowerGood", or "Power OK", or "PWR OK" and so on) after it completes its internal tests and determines that the power is ready for use. Until this signal is sent, the motherboard will refuse to start up the computer. In addition, the power supply will turn off the Power Good signal if a power surge or glitch causes it to malfunction. It will then turn the signal back on when the power is OK again, which will reset the computer. If you've ever had a brownout where the lights flicker off for a splitsecond and the computer seems to keep running but resets itself, that's probably what happened. Sometimes a power supply may shut down and seem "blown" after a power problem but will reset itself if the power is turned off for 15 seconds and then turned back on. The nominal voltage of the Power Good signal is +5 V, but in practice the allowable range is usually up to a full volt above or below that value. All power supplies will generate the Power Good signal, and most will specify the typical time until it is asserted. Some extremely el-cheapo power supplies may "fake" the Power Good signal by just tying it to another +5 V line. Such a system essentially has no Power Good functionality and will cause the motherboard to try to start the system before the power has fully stabilized. Needless to say, this type of power supply is to be avoided. Unfortunately, you cannot tell if your power supply is "faking" things unless you have test equipment. Fortunately, if you buy anything but the lowest-quality supplies you don't really need to worry about this. Page 29 of 52 Power good delay • • • Power Good Delay (PG Delay) is the amount of time it takes a power supply to start up completely and begin delivering the proper voltages to the connected devices. According to the Power Supply Design Guide for Desktop Platform Form Factors, Power Good Delay, should be 100 ms to 500 ms. Power Good Delay is also sometimes called PG Delay or PWR_OK Delay. Page 30 of 52 State all DC levels required in PC systems in terms of voltages and currents. VOLTAGE -12V PURPOSE Used on some older types of serial port amplifier circuits. Generally unused on newer systems. Current is usually limited to 1A. -5V Used on some early personal computers for floppy disk controllers and some ISA add-on cards. Generally unused on newer systems. Current is usually limited to 1A. 0V The zero volt ground (also called common or earth) and reference point for other system voltages. +3.3V Used to supply power for the processor, some types of memory, some AGP video cards, and other digital circuits (most of these components required a +5V supply in older systems). +5V Still used to supply the motherboard and some of the components on the motherboard. Note that there is also a 5V standby voltage present when the system is powered down which can be grounded (e.g. by the user pressing the power switch on the front of the case) to restore power to the system. +12V Primarily used for devices such as disk drives and cooling fans which have motors of one sort or another. These devices have their own power connectors that come directly from the power supply unit. Voltage +12V -12V +3.3V +5V 0V Use Disk drive, fans, cooling devices Serial ports Newer CPUs, video cards Motherboard, Motherboard components Ground, used to complete circuits with other voltages Page 31 of 52 With aid of clearly labelled diagrams, describe the operation of an • • On-line Uninterruptable Power Supply (UPS). Off -line Uninterruptable Power Supply (UPS). On line UPS Page 32 of 52 PRINCIPLE OPERATION • • • • • • • • During normal or even abnormal line conditions, the inverter supplies energy from the mains through the rectifier, which charges the batteries continuously. In addition to that it can also provide power factor correction. When the line fails, the inverter still supplies energy to the loads from the batteries. As a consequence, no transfer time exists during the transition from normal to stored energy modes. Online UPS system is the most reliable UPS configuration due to its simplicity (only three elements), and the continuous charge of the batteries, which means that they are always ready for the next power outage. This kind of UPS provides total independence between input and output voltage amplitude and frequency. When an overload occurs, the bypass switch connects the load directly to the utility mains, in order to guarantee the continuous supply of the load, thereby avoiding the damage to the UPS module (bypass operation). In this situation, the output voltage must be synchronized with the utility phase, otherwise the bypass operation will not be allowed. Typical efficiency of the online ups systems are up to 94%, which is limited due to the double conversion effect. Off line UPS Page 33 of 52 PRINCIPLE OPERATION • • • • • The inverter is off when the mains power is on and the output voltage is derived directly from the mains. The inverter turns on only when the mains supply fails. Its switching time is less than 5 ms. These UPS are generally used with PCs or computers or other appliances where a small duration (5 ms or less) interrup-tion in power supply can be tolerated. Usually, sealed batteries or lead-acid batteries are used. The running time of these supplies is also low (about 10 to 30 minutes). Offline UPS has high efficiencies, since charger is not continuously on. The power handling capacity of charger is reduced. Offline UPS are not very costly. Internal control is simpler in offline Uninterruptible Power Supply. Page 34 of 52 The Main Power Problems Something as simple as a power surge may not seem detrimental—in fact it may go unnoticed until equipment fails. At the other end of the spectrum, blackouts can cause entire systems to immediately go dark. While power anomalies are inevitable, their effects should not affect your systems, if the proper steps are taken to protect them. With aid of diagrams, define the following terms: • • • • • Surge Spike Noise Black out Brown out a) Surge • Dramatic increase in voltage above the normal flow of electrical current. • A power surge lasts for a few nanoseconds, or one-billionth of a second. • • Surge is an unexpected increase in voltage in an electrical current that causes damage to electrical equipment. A power surge takes place when the voltage is 110% or more above normal. Surges/Spikes (voltage increase from lightning, etc.) can damage equipment incrementally or catastrophically Surges and spikes are short-term voltage increases. They are typically caused by lightning strikes, power outages, short circuits or malfunctions caused by power utility companies. They cause data corruption, catastrophic and costly equipment damage and incremental damage that degrades equipment performance and shortens its useful lifespan. Common causes of surges/spikes: • Utility company load shifting • Miswired electrical systems • Lightning strikes Page 35 of 52 Problems caused by surges/spikes: • System lockups • Incremental or catastrophic equipment damage • Lost productivity b) Spike • • • Sudden increase in voltage that lasts for a short period and exceeds 100 percent of the normal voltage on a line. Spikes can be caused by lightning strikes, but can also occur when the electrical system comes back on after a blackout. High-voltage spikes occur when there is a sudden voltage peak of up to 6,000 volts. These spikes are usually the result of nearby lightning strikes, c) Black out (power outage) • • • • Complete loss of AC power. A blown fuse, damaged transformer, or downed power line can cause a blackout. A power failure or blackout is a zero-voltage condition that lasts for more than two cycles. It may be caused by tripping a circuit breaker, power distribution failure or utility power failure. A blackout can cause data loss or corruption and equipment damage. Blackout refers to the total loss of power to an area and is the most severe form of power outage that can occur A blackout, or power outage, is a complete loss of utility power, whether short- or long-term. Blackouts cause reduced productivity, lost revenue, system crashes and data loss. Unplanned outages may occur as aging electrical grids and building circuits are overwhelmed by high demand. Blackouts are particularly dangerous at sites where safety or life support rely on power, such as hospitals, treatment centers and power plants. Blackouts, a complete loss of power, result in lost productivity, time and money. Common causes of blackouts/power outages: • • • • Utility company failure Accidental AC line disconnection Tripped circuit breakers Severe weather Page 36 of 52 Problems caused by blackouts/power outages: • • • • Data loss System downtime Lost productivity Lost revenue d) Brown out • • Brownout / under voltage / Sag A brownout is a voltage deficiency that occurs when the need for power exceeds power availability. Brownouts typically last for a few minutes, but can last up to several hours, as opposed to short-term fluctuations like surges or spikes. They are caused by the disruption of an electrical grid and may be imposed by utility companies when there is an overwhelming demand for power. Brownouts, more common than blackouts, cause equipment failures, incremental damage, decreased equipment stability and data loss. Reduced voltage level of AC power that lasts for a period of time. Brownouts occur when the power line voltage drops below 80 percent of the normal voltage level. • Overloading electrical circuits can cause a brownout • A brownout is a steady lower voltage state. An example of a brownout is what happens during peak electrical demand in the summer, when utilities can’t always meet the requirements and must lower the voltage to limit maximum power. When this happens, systems can experience glitches, data loss and equipment failure. • A brownout is a drop in voltage in an electrical power supply. • The term brownout comes from the dimming experienced by lighting when the voltage sags. • Brownouts can cause poor performance of equipment or even incorrect operation • • 87% of power problems are caused by brownouts, not blackouts Page 37 of 52 Common causes of brownouts/under voltages/sags: • • • Inadequate utility service Heavy power draw in area/facility Poor electrical circuit design Problems caused by brownouts/under voltages/sags: • • • • Active data loss System lockups Lost productivity Slow electronic degradation e) Swell / Overvoltage Swells are basically the opposite of a brownout: instead of a voltage deficiency, or sag, a swell is a voltage increase for a long duration (seconds to a minute), as opposed to a brief increase, like a surge/spike. A swell is caused when the power being provided outweighs the power accepted by connected equipment, resulting in an increase in voltage. Much like sags, deterioration may not be apparent until it's too late, resulting in lost data and damaged equipment. A swell is the opposite of a sag; an increase in voltage instead of a deficiency. Common causes of swells/overvoltage’s: • • • Sudden/large load reductions Oversupply of power from utility source Fault on a 3-phase system Problems caused by swells/overvoltage: • • • Slow electronic degradation Flickering lights Overheating and stress on equipment Page 38 of 52 f) Line Noise Line noise refers to distortion on AC, telephone/DSL, network or coaxial lines caused by Electromagnetic Interference (EMI) and Radio Frequency Interference (RFI). Line noise is unavoidable and will appear on every signal at some point, though it is not always detrimental, or even noticeable. It causes incremental electronic circuit damage, data corruption, audio/video quality problems and confusion between system components. Line noise generated by electronic devices varies greatly and can be produced by energy disturbances from a variety of sources, both natural and man-made. Electrical noise can confuse system logic and damage electronic components, resulting in random server lockups and premature board failure. Common causes of line noise: • • • • Radio transmissions High voltage power lines Severe weather Fluorescent lights Problems caused by line noise: • • • • System lockups Audio static Video "snow" Slow electronic degradation Page 39 of 52 g) Surge protector • • • • • A surge protector is an appliance or device designed to protect electrical devices from voltage spikes. A surge protector attempts to limit the voltage supplied to an electric device by either blocking or shorting to ground any unwanted voltages above a safe threshold. A surge protector is an electrical device that is used to protect equipment against power surges and voltage spikes while blocking voltage over a safe threshold (approximately 120 V). When a threshold is over 120V, a surge protector shorts to ground voltage or blocks the voltage. Without a surge protector, anything higher than 120V can create component issues, such as permanent damage, reduced lifespan of internal devices, burned wires and data loss. A surge protector is usually installed in communications structures, process control systems, power distribution panels or other substantial industrialized systems. Smaller versions are typically installed in electrical service entrances located office buildings and residences The Solution Affordable solutions protect equipment, data and productivity against the hazards of power problems. Solutions are available for any size application, from home to enterprise business, and offer varying levels of protection, ranging from protection against common hazards like surges and line noise, to the most complete protection available against all hazards. The chart below illustrates which solutions fit certain needs: Surge/Spike Line Noise Brownout Swell Blackout Surge Protector Good Good — — — Standby UPS Good Good Good Good Good Line-Interactive UPS Good Good Better Better Good On-Line UPS Best Best Best Best Best Page 40 of 52 Surge Protectors Protect all computers and electronics Surge protectors provide heavy-duty surge/spike protection and line noise filtration. Premium surge protectors incorporate more and substantially stronger protective components, as well as isolated filter banks that eliminate interference between devices plugged into the same surge protector. Select models include data line protection (telephone/DSL, coaxial and/or Ethernet). Standby UPS Systems Protect PCs and workstations Standby UPS systems provide surge/spike/line noise protection like surge protectors, and they add battery backup to keep connected equipment operating without interruption during blackouts. They also provide limited brownout protection by switching to battery power to correct undervoltages. Select models include data line protection and communication ports that enable automatic shutdown of connected computers during extended blackouts. Page 41 of 52 Line-Interactive UPS Systems Protect workstations, servers, data centers and network equipment In addition to the protection features offered by standby UPS systems, line-interactive UPS systems add automatic voltage regulation (AVR). AVR allows the UPS system to adjust voltage to safe levels during brownouts without switching to battery power, reducing battery wear and preserving charge levels for blackout protection. On-Line UPS Systems Protect servers, VoIP systems and other mission-critical equipment On-Line UPS systems offer the best protection available against all power problems. True online operation with continuous AC-to-DC-to-AC double conversion completely isolates electronics from power problems. Precision-regulated output power with pure sine waveform guarantees maximum stability for connected equipment. Page 42 of 52 Differentiate • Surge protector and a surge suppressor A suppressor regulates the voltage and makes the power constant in a case of a spike or surge. A protector simply detects the surge and turns the unit off. Suppressor is good for things like computers you don't want to keep turning on and off. Suppressor suppress surge but protector get its fuse blown on surge. • • • • Surge Protector Surge Suppressor • Surge protectors, are a device used to protect against electrical surges. • Surge suppressors are devices used to provide a constant voltage to any connected electrical devices. • When a surge is detected, a surge protector diverts the surge to the ground, preventing it from reaching the connected device. • If the voltage given to an electrical device is too high or too low, it could cause damage. Surge suppressors help prevent this, adjusting the provided voltage up or down to keep it at the correct levels. • Surge protectors are normally used with expensive electronic devices, such as computers or televisions. Since electric surges can happen almost anywhere under the right conditions, surge protectors are usually considered an easy and cheap investment. • Surge suppressors are not used as often as surge protectors, but can be useful in certain situations. Some households or business may receive so called "dirty power," where the power fluctuates frequently. Surge suppressors can be used in such situations to even out the power supply and help protect electrical devices. • A protector simply detects the surge and turns the unit off. • A suppressor regulates the voltage and makes the power constant in a case of a spike or surge Page 43 of 52 Differentiate • Power conditioner and a Surge protector/suppressor The difference between a power conditioner and a surge protector mostly lies in their intended function. A power conditioner takes in power and modifies it based on the requirements of the machinery to which it is connected. A surge protector doesn't alter the power flowing through it at all, unless that power is over a certain amount. When the power exceeds the set amount, it blocks it from passing through. It is not uncommon for the two devices to be in the same unit. Both power conditioners and surge suppressors are important parts of modern electronics. They protect the inner workings of devices, often without users even realizing it. Many people go the extra step of placing additional protective devices between the wall outlets and the electronic products. A power conditioner modifies voltage as it passes through. Some systems require very tight or nonstandard power tolerances, and they use power conditioners to alter the power to meet their requirements. They are also a common method of prolonging the lifespan of electric devices, as the properly formed electricity creates less wear on the internal parts of the device. Most electric systems have power conditioners built into them, usually as very small devices that are integrated right into an internal circuit board. They monitor the voltage moving across the board and keep it within a specific tolerance. There are larger power conditioners available, ranging from small ones in high-end surge protectors all the way to car-sized industrial units connected to factory machines. Surge protectors prevent power overloads. When power exceeds a certain amount, they stop it from passing through. Different surge protectors do this in different ways, but the most common method is creating a shunt to a ground wire. This connection to the ground only happens when the power is prevented from passing through the unit; otherwise, the unit would constantly waste electricity. If a surge protector is improperly plugged in, such as through a two- or three-pronged adapter, it cannot send power to the ground. In this case, the surge protector may overload and catch on fire or even send the surge through to the connected device. It isn't unusual for a power conditioner and a surge protector to be placed in the same unit. Since these systems both work on passing voltage, it makes sense to put them together. Some systems have a very advanced power conditioner that works as a surge protector when needed; this is common in battery backup systems. Page 44 of 52 Describe the operation of the following and give advantages and disadvantages of each • • Switched mode power supply (SMPS) Linear Mode Power Supply (LMPS) Switched Mode Power Supply (SMPS) • • • • • • • • • A switched-mode power supply (switching-mode power supply, SMPS, or switcher) is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently. The pass transistor of a switching-mode supply continually switches between low-dissipation, full-on and full-off states, and spends very little time in the high dissipation transitions, which minimizes wasted energy. Voltage regulation is achieved by varying the ratio of on-to-off time. Switched-mode power supply regulates either output voltage or current by switching ideal storage elements, like inductors and capacitors, into and out of different electrical configurations. Ideal switching elements Switched Mode Power Supply uses a switching regulator to convert electric power efficiently. SMPS transfers electric power from a source (AC mains) to the load by converting the characteristics of current and voltage. SMPS always provide a well regulated power to the load irrespective of the input variations. SMPS incorporates a Pass transistor that switches very fast typically at 50Hz and 1 MHz between the on and off states to minimize the energy waste. SMPS regulates the output power by varying the on to off time using minimum voltage so that efficiency is very high compared to the linear power supply. • Page 45 of 52 Input Rectifier and Filter Stage • The process of converting AC to DC is called Rectification. SMPS converts AC to DC • The rectifier produces an unregulated DC voltage which is then sent to a large filter capacitor. Inverter Chopper Stage • The inverter “Chopper” stage converts DC (whether directly from the input or from the rectifier and filter stage described above) to AC by running it through a power oscillator. • Power oscillator has a very small output transformer with few windings of kilohertz (kHz). Output transformer • The transformer converts the voltage up or down to the required output level.. Output Rectifier and Filter • The AC output from the transformer is rectified and converted to DC Chopper Controller • A feedback circuit monitors the output voltage and compares it with a reference voltage. • If there is an error in the output voltage the feedback circuit compensates. • This part of power supply is called switching regulator. • Chopper Controller performs the function of switching regulator 1. 2. 3. 4. 5. 6. ADVANTAGES The switch mode power supply has a smaller in size. The SMPS has light weight. It has a better power efficiency typically 60 to 70 percent. It has a strong anti-interference. SMPS has wide output range. Low heat generation in SMPS. 1. Greater efficiency because the switching transistor dissipates little power when acting as a switch 2. Smaller size and lighter weight from the elimination of heavy line-frequency transformers 3. High efficiency: The switching action means the series regulator element is either on or off and therefore little energy is dissipated as heat and very high efficiency levels can be achieved. 4. Compact: As a result of the high efficiency and low levels of heat dissipation, the switch mode power supplies can be made more compact. 5. Flexible technology: Switch mode power supply technology can be sued to provide high efficiency voltage conversions in voltage step up or "Boost" applications or step down "Buck" applications Page 46 of 52 DISADVANTAGES 1. 2. 3. 4. 5. 6. The switch mode power supply (SMPS) is more complex. The SMPS has higher output ripple and its regulation is worse. It can be used only as a step down regulator. It has only one output voltage. It has high frequency electrical noise. SMPS also cause harmonic distortion. 1. Greater complexity, due to the generation of high-amplitude, high-frequency energy that the lowpass filter must block to avoid EMI 2. Noise: The transient spikes that occur from the switching action on switch mode power supplies are one of the largest problems. spikes or transients can cause electromagnetic or RF interference which can affect other nearby items of electronic equipment, 3. External components: These components all require space, and add to the cost. 4. Expert design required: It is often possible to put together a switch mode power supply that works. To ensure that it performs to the required specification can be more difficult. Ensuring the ripple and interference levels are maintained can be particularly tricky. Linear Mode Power Supply • • • • (LMPS) A linear regulator provides the desired output voltage by dissipating excess power in ohmic losses A linear regulator regulates either output voltage or current by dissipating the excess electric power in the form of heat, and hence its maximum power efficiency is voltage-out/voltage-in since the volt difference is wasted. Uses a transformer to convert the voltage from the wall outlet (mains) to a different, usually a lower voltage. The voltage produced by an unregulated power supply will vary depending on the load and on variations in the AC supply voltage Page 47 of 52 ADVANTAGES 1. Simplicity-One can purchase an entire linear regulator in a package and simply add two filter capacitors for storage and stability. Even if a Design Engineer plans to design a linear regulator from scratch, with the help of design books and some little effort, he can achieve it. 2. Quiet Operation & Load-handling Capability: The linear regulator generates a negligible amount of electrical noise on its output. It’s dynamic load response time (The time power supply takes to respond to changes in the load current) is very short. 3. Low Cost: For output power of less than 10W, linear power supply’s component costs and manufacturing costs are less than the comparable switching power supply’s cost. 4. Low noise: The use of the linear technology without any switching element means that noise is kept to a minimum and the annoying spikes found in switching power supplies are now found. 5. Established technology: Linear power supplies have been in widespread use for many years and their technology is well established and understood. DISADVANTAGES 1. Range of application: It can be used only as a step down regulator. In case of AC-DC power supplies, a transformer with rectification and filtering must be placed before the linear power supply. 2. Number of Outputs: It has only one output voltage. To get additional output voltage, an entire separate linear regulator must be added. 3. Average Efficiency: Normally linear regulators have 30% to 60% efficiency. It means for every watt delivered to the load, more than one watt is lost within the supply. This loss is called headroom loss. It occurs in the pass-transistor. Heat sink is required over the transistor for the heat dissipation. 4. Efficiency: In view of the fact that a linear power supply uses linear technology, it is not particularly efficient. Efficiencies of around 50% are not uncommon, and under some conditions they may offer much lower levels. Page 48 of 52 5. Size: The use of linear technology means that the size of a linear power supply tends to be larger than other forms of power supply. 6. Heat dissipation: The use of a series or parallel (less common) regulating element means that significant amounts of heat are dissipated and this needs to be removed. Compare and contrast Switched Mode Power Supply (SMPS) & Linear Mode Power Supply (LMPS) • • • • • • The traditional linear power supplies are typically heavy, durable, and have low noise across low and high frequencies. For this reason they are mostly suitable for lower power applications where the weight does not pose a problem. The switching power supplies are much lighter, more efficient, durable, and have limited high frequency noise due to the design. For this reason, the switching power supplies are not suitable for high frequency audio applications but are great for high power applications. Other than that, these two types are pretty much swappable for various applications, and they cost about the same to make. Switching power supplies are used more broadly nowadays than linear power supplies, BASIS SWITCHED MODE POWER SUPPLY Circuit Design • SMPS's are more complicated and difficult to design. • Simple to moderately complex Applications • Higher power applications, can handle a large output current • Lower power applications, handles a lower output current Cost factor • More expensive for lower powers than linear regulators • Linear supplies are less expensive for lower currents/powers. Part Count • Has a lot of parts • Has few parts Output voltage • Any voltages available, limited only by • transistor breakdown voltages in many circuits. Voltage varies little with load. Page 49 of 52 LINEAR MODE POWER SUPPLY With transformer used, any voltages available; if transformerless, limited to what can be achieved with a voltage doubler. If unregulated, voltage varies significantly with load Noise • Noisier due to the switching frequency • of the SMPS. An unfiltered output may cause glitches in digital circuits or noise in audio circuits. Low noise Reliability • Less reliable Highly reliable Efficiency • High efficiency. Efficiencies in the • region of 80% are common. The transistors are switched fully on or fully off, so very little resistive losses between input and the load. Low efficiency. Output voltage is regulated by dissipating excess power as heat resulting in a typical efficiency of 30–40%. EMI (electromagnetic interference) • Mild high-frequency interference may be generated by AC rectifier diodes under heavy current loading • Very low, EMI filters reduce the disruptive interference. Leakage • high • low Risk of equipment damage • Failure of a component in the SMPS • itself can cause further damage to other PSU components; can be difficult to troubleshoot. Very low, unless a short occurs between the primary and secondary windings or the regulator fails by shorting internally. Size (power density) • small size (high power density) • large size (low power density) Weight (Power to Weight Ratio) • light (high) • heaviest (low) Heat • Dissipates very little power (Low heat loss) • Dissipates a lot of power (High heat loss) Frequency & capacitor size • Due to the higher frequency, SMPS's also need much smaller smoothing capacitors on the final output. • The low frequency AC needs quite large capacitors to smooth the rectified output. • Page 50 of 52 ? MSMPS vs Linear Power Supply SMPS directly rectifies the mains AC without Linear power supply reduces the voltage to reducing the voltage. Then the converted DC is the desired value at the beginning by a switched in high-frequency for a smaller bigger transformer. After that, the AC is transformer to reduce it to the desired voltage rectified and filtered to make the output level. Finally, the high-frequency AC signal is DC voltage. rectified to the DC output voltage. Voltage Regulation Voltage regulation is done by controlling the The rectified and filtered DC voltage is switching frequency. The output voltage is subjected to an output resistance of a monitored by the feedback circuit and the voltage divider to make the output variation of voltage is used for the frequency voltage. This resistance is controllable by a control. feedback circuit that monitors the output voltage variation. Efficiency The heat generation in SMPS is comparatively low The excess power is dissipated as heat to since the switching transistor operates in the cutmake the voltage constant in a linear off and starvation regions. The small size of the power supply. Moreover, the input output transformer also makes the heat loss transformer is much bulkier; thus, small. Therefore, the efficiency is higher (85transformer losses are higher. Therefore, 90%). the efficiency of a linear power supply is as low as 60%. Build Transformer size of an SMPS does not need to be Linear power supplies are much bulkier large as it operates in high-frequency. Therefore, since the input transformer has to be large the weight of the transformer will also be less. As due to the low frequency it operates on. As a result, the size, as well as the weight of an more heat is generated in a voltage SMPS is much lower than a linear power supply. regulator, heat sinks should be used as well. Noise and Voltage Distortions SMPS generates a high-frequency noise due to Linear power supplies do not produce switching. This passes into the output voltage, as noise in the output voltage. Harmonic well as to input mains sometimes. Harmonic distortion is much less than that of SMPSs. distortion in mains power could be also possible in SMPSs. Applications SMPS can be used as portable devices due to the Linear power supplies are much larger and small build. But as it generates a high-frequency cannot be used for portable devices. Since noise, SMPSs cannot be used for noise-sensitive they do not generate noise and the output applications such as RF and audio applications. voltage is also clean, they are used for most of the electrical and electronic tests in laboratories. Page 51 of 52 COMPARISON Size and weight SMPS Smaller due to higher operating frequency (typically 50 kHz - 1 MHz) Efficiency, heat, and power dissipation Regulated using duty cycle control, which draws only the power required by the load. In all SMPS topologies, the transistors are always switched fully on or fully off. Consists of a controller IC, one or several power transistors and diodes as well as a power transformer, inductors, and filter capacitors. Complexity Radio frequency interference Power factor EMI/RFI produced due to the current being switched on and off sharply. Therefore, EMI filters and RF shielding are needed to reduce the disruptive interference Ranging from low to medium since a simple SMPS without PFC draws current spikes at the peaks of the AC sinusoid. Page 52 of 52 LMPS If a transformer is used, large due to low operating frequency (mains power frequency is at 50 or 60 Hz). Small if transformer less. If regulated, output voltage is regulated by dissipating excess power as heat resulting in typical Output efficiency of 30-40%; if is unregulated, transformer iron and copper losses significant. Unregulated may be diode and capacitor; regulated has a voltage regulating IC or discrete circuit and a noise filtering capacitor. Mild high-frequency interference may be generated by AC rectifier diodes under heavy current loading, while most other supply types produce no high-frequency interference. Some mains hum induction into unshielded cables, problematical for low-signal audio. Low for a regulated supply because current is drawn from the mains at the peaks of the voltage sinusoid.