Psu how does it work

If you have ever removed the case from your personal computer to add an adapter card or memory , you can change a power supply. Make sure you remove the power cord first , since voltages are present even though your computer is off.

Recent motherboard and chipset improvements permit the user to monitor the revolutions per minute RPM of the power supply fan via BIOS and a Windows application supplied by the motherboard manufacturer. New designs offer fan control so that the fan only runs the speed needed, depending on cooling needs. Recent designs in Web servers include power supplies that offer a spare supply that can be exchanged while the other power supply is in use.

Some new computers, particularly those designed for use as servers, provide redundant power supplies. This means that there are two or more power supplies in the system, with one providing power and the other acting as a backup. The backup supply immediately takes over in the event of a failure by the primary supply. Then, the primary supply can be exchanged while the other power supply is in use. Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots.

Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe. Computer Hardware. Power Supplies. The power supply in your PC provides all of the different voltages your computer needs to operate properly. See more computer hardware pictures. Switcher Technology " ". In this photo you can see three small transformers yellow in the center. To the left are two cylindrical capacitors.

The large finned pieces of aluminum are heat sinks. The left heat sink has transistors attached to it. These are the transistors in charge of doing the switching -- they provide high-frequency power to the transformers.

Attached to the right heat sink are diodes that rectify AC signals and turn them into DC signals. Personal computer power supply label. VSB is the standby voltage provided to the power switch. Power Supply Standardization " ". A PC power supply removed from its PC case. Cables and connectors at right supply DC voltages. Power Supply Wattage A watt switching power supply will not necessarily use more power than a watt supply. Power Supply Problems The PC power supply is probably the most failure-prone item in a personal computer.

The two most common frequencies are 50 Hz and 60 Hz. The equipment designed to use AC tends to require large amounts of voltage, so the voltage is not stepped down as frequently as equipment using DC. DC allows for a constant flow of current to a device. Most smaller electronic devices such as computers require direct current to operate with an AC-to-DC converter from wall power. Alternating current is used for equipment that have motors refrigerators are an example.

Which type of current to use depends on the load being powered. Because unregulated power supplies do not have voltage regulators built into them, they typically are designed to produce a specific voltage at a specific maximum output load current. These are typically the block wall chargers that turn AC into a small trickle of DC and are often used to power devices such as household electronics. The DC voltage output is dependent on an internal voltage reduction transformer and should be matched as closely as possible to the current required by the load.

Typically the output voltage will decrease as the current output to the load increases. With an unregulated DC power supply, the voltage output varies with the size of the load. It typically consists of a rectifier and capacitor smoothing, but no regulation to steady the voltage. It may have safety circuits and would be best for applications that do not require precision.

The advantages of unregulated power supplies are that they are durable and can be inexpensive. They are best used, however, when precision is not a requirement. They have a residual ripple similar to that shown in Figure 3. A regulated DC power supply is essentially an unregulated power supply with the addition of a voltage regulator. This allows the voltage to stay stable regardless of the amount of current consumed by the load, provided the predefined limits are not exceeded.

In regulated power supplies, a circuit continually samples a portion of the output voltage and adjusts the system to keep the output voltage at the required value. In many cases, additional circuitry is included to provide current or voltage limits, noise filtering, and output adjustments. There are three subsets of regulated power supplies: linear, switched, and battery-based.

Of the three basic regulated power supply designs, linear is the least complicated system, but switched and battery power have their advantages. Linear Power Supply Linear power supplies are used when precise regulation and the removal of noise is most important.

While they are not the most efficient power source, they provide the best performance. The name is derived from the fact that they do not use a switch to regulate the voltage output. Linear power supplies have been available for years and their use is widespread and reliable. They are also relatively noise-free and commercially available. The disadvantage to linear power supplies is that they require larger components, hence are larger and dissipate more heat than switched power supplies.

Although they have more components, they are smaller and less expensive than linear power supplies. One of the advantages of switched mode is that there is a smaller loss across the switch. Because SMPS operate at higher frequencies, they can radiate noise and interfere with other circuits.

Interference suppression measures, such as shielding and following layout protocols, must be taken. The advantages of a switched power supply is that they are typically small and lightweight, have a wide input voltage range and a higher output range, and are much more efficient than a linear supply.

However, a SMPS has complex circuitry, can pollute the AC mains, is noisier, and operates at high frequencies requiring interference mitigation. Battery-based Battery-based power is a third type of power supply and is essentially a mobile energy storage unit. Battery-based power produces negligible noise to interfere with electronics, but loses capacity and does not provide constant voltage as the batteries drain.

In most applications using laser diodes, batteries are the least efficient method of powering the equipment.

Most batteries are difficult to match the correct voltage to the load. Using a battery that can exceed the internal power dissipation of the driver or controller can damage your device. Along with the above considerations, the power supply must operate below its maximum rated output current.

Loads drawing more current than the adapter is rated for can cause inconsistent results or device malfunction. Overloading the converter can lead to overheating and ultimately failure, potentially causing a fire hazard or damaging the load itself.

While all power supply specifications are valuable, some are more critical than others. A few specifications of note are: Output Current: The maximum current that can be supplied to the load. Load Regulation: The load regulation is how well the regulator can maintain its output with a load current change, and usually is measured in millivolts mV or as a maximum output voltage.

These are typically combined into one measurement. In switching power supplies, the measurement is given in peak-to-peak, showing the extent of the noise spikes that arise from the switching.

Overvoltage Protection: Sometimes output voltages can exceed their nominal values and can damage the load. Overvoltage protection is a circuit that shuts down the power supply should the voltage limits be exceeded. Overload Protection : Overload protection is a safety measure used to prevent damage in the event of a short circuit or overcurrent event.

Much like the circuit breaker in a house, the overload protection shuts off the power supply so the load will not be damaged. Efficiency : Efficiency is the ratio of power being pulled from the power grid that is effectively being converted to DC power. If a voltage is applied across a conducting material e. These are one of the building blocks of atoms, that make up the material, and metals have lots of electrons free to move about. This flow of electrons is called a current and gets measured in amps.

One good analogy for the techno-speak is that electricity can be thought to be like water in a hose: voltage is akin to the pressure you're using, the flow rate of the water is the current, and any restrictions in the pipe acts the same as electrical resistance. We can see that mains electricity varies over time and this is known as an alternating current voltage supply - or just AC, for short. In the US, the mains voltage alternates 60 times per second, reaching a peak of V or V, depending on the location and supply.

The UK hits a slightly lower peak, and varies a little slower, too. Almost all countries around the world have mains outlet voltages like this, with just a few having lower or higher peak voltages. The need for a PSU lies in the fact that computers don't work with AC: they need a constant voltage, one that never changes, and it also needs to be of much lower level.

Using the same graph scales, it looks something like this:. And because these values are constant, they're called direct current or DC, for short. Time to open the unit and have a look at how it does this! At this stage, we should warn you to not try this if you don't know what you're doing. Messing about with the insides of a PSU can be potentially very dangerous. There are components inside every unit that store electrical energy, and some store a lot. The layout of this PSU is similar to many others, and although the make and model of the various parts used inside will be different, they fundamentally do the same thing.

The mains outlet connection to the PSU is at the top-left hand corner of the picture and the supply essentially runs clockwise around the picture, until reaching the output of the PSU big cluster of colored wires, bottom left-hand corner. If we flip the circuit board over, we can see that compared to connections on a motherboard , these are broad and deep -- they're designed to have lots of current flowing through them.

Something else that's immediately obvious is the big gap running down the middle, like a river cutting a path in a field. This highlights the fact that all PSUs have two clearly defined sections to them: primary and secondary.

The former is all about setting up the input voltage so that it can be efficiently changed from the mains supply level; the latter is everything about that change and the processes afterwards. The very first thing the PSU does to the mains electricity isn't about changing it from AC to DC, or dropping voltage -- instead, it's all about smoothing out the input voltage. Because we have lots of electrical devices in our homes, offices, and business that switch on and off, as well as emit electromagnetic signals, the varying AC is often lumpy and with the occasional spikes the length of the variations isn't constant either.

Not only do these make it harder for the PSU to adjust the mains, it can also damage some of the components inside it. This PSU has two stages of so-called transient filters , the first of which is directly applied to input socket, using 3 components called capacitors to do the job.

Think of these as being like a speed bump for sudden changes in the input voltage. The yellow blocks are more capacitors, whereas the green rings wrapped in copper wire are inductors although they're usually called chokes when used this way. Inductors store electrical energy in a magnetic field but this field also 'pushes back' on the voltage supplying the energy -- so a sudden spike in the voltage results in a sudden kick back from the magnetic field to suppress it.

The two little blue discs are yet more capacitors and just below them hidden under a black plastic cover is a metal oxide varistor MOV. These are also used to help counter jumps and spikes in the input voltage; you can read more about different types of transient filter circuits here. This section of a PSU is often the first sign of where costs have been cut to ensure the model hits a specific budget. Cheaper ones will have less filtering, and the cheapest of all will have none at all which is not what you want!

Now that we're all smooth and chilled, let's get on with the day job of a PSU: changing the voltage. Remember that the PSU needs to change an AC voltage that might be averaging volts technically, it's root mean squaring volts, but that doesn't exactly roll off the tongue and hack that down into DC voltages of 12, 5, and 3. In the picture below, this is the flat black object glued to the chunk of metal which acts as a heatsink.

Once again, this is another area where a PSU manufacturer can cut costs, with cheaper components doing a worse job of the AC-to-DC conversion e. Now, if the input voltage peaks at volts which is the case for V mains , then the bridge rectifier will output volts DC. This gets passed on to the next stage of the PSU and in the one we're looking at, it's called an active power factor correction converter APFC. This circuit adjusts the current flow in the unit to take into account that it is full of components that store and release energy in a complex way; this can result in the actual power output of the unit being less that what you're supposed to be getting.

Other supply units use passive converters, that essentially do the same job. They're less effective but fine for low power units -- they're also cheaper, so you can guess what kinds of PSUs have these, when they really shouldn't!

The APFC can be seen in the image above - those big cylinders on the left are capacitors and they store the adjusted current, before sending them on to the next step in the PSU's chain of processes. Its job is to take the DC voltage and use several field effect transistors to switch the voltage on and off at a very high rate -- it essentially converts the DC voltage back into an AC one.

It does this because the part of the PSU that turns the mains voltage right down into 12 volts is a transformer. These devices use electromagnetic induction and a set of two coils of wire one having more loops in the coil than the other to step down the voltage; however, transformers only work with an alternating voltage. The more efficient a transformer is, the smaller it can be. This super fast switching of the DC voltage is the source of the name for this type of device: a switched mode power supply SMPS.

You can see 3 transformers in the picture below - the largest generates just the 12 volt output; in other PSUs, the big transformer might make all of the voltages. The next larger one creates a single 5 volt output that we'll talk about in a bit, and the smallest one acts as an isolator for the PWM circuit, keeping it safe from harm and also stopping it from causing interference with other voltages in the PSU.

It'll all depend on budget constraints and how much power the unit needs to offer.