Category Archives: Switching power supply

Switching power supply

The two major types of power supplies, linear and switch mode SMPSoperate according to entirely different principles and have distinguishing characteristics.

switching power supply

Design work and maintenance on each one requires totally different mindsets. The SMPS is now widely used because of its greater efficiency, lower cost and better weight and thermal qualities. There are some disadvantages, which however can be mitigated by careful planning in the design stage.

It was a familiar part of analog CRT TVs, contributing to the considerable weight because of the heavy power transformer. This was a plus, however, because multiple secondary taps made available any number of voltages, as needed for bias, filaments, picture tube deflection, etc.

In linear power supplies, the active devices operate in the linear portion of their response curves. This is in contrast to the SMPS, where first the input power is converted to square waves of varying duty cycle. The active components operate in non-linear modes.

When components operate in linear portions of their response curves, they effectively act like variable resistors that dissipate power because of I 2 R.

switching power supply

This is why a considerable amount of the input power is dissipated in the form of heat, and this is the situation in a linear power supply. The linear power supply consists of a series of stages. The ac line, often starting with a plug to pick up V, single-phase utility power, passes through a grommeted opening in the cabinet where, at the point of entry, there is always a fuse and switch with optional power light.

It feeds the primary of the power transformer, which may have any number of secondary windings. Besides the capability of providing a number of voltages, this type of transformer has no electrical connection between primary and secondary windings, so it is known as an isolation transformer.

Grounding does not pass through a transformer unless it is an autotransformer, where primary and secondary are a single winding, tapped at different points. It goes to the rectifier, consisting of one or more diodes, to electrolytic filtering capacitors, parallel-connected to remove ac ripple, and occasionally to more expensive series-connected inductors to further purify the dc. Then comes a linear regulator and final dc output.

It is all easy to design and diagnose. The most common troublemakers are the electrolytic capacitors, which can be visually inspected and checked with a multimeter. As mentioned before, the semiconductors in a linear supply can effectively form a large resistance that dissipates heat, and linear supplies incorporate bulky components such as the transformer that make the supply physically large.

For small consumer appliances, the heat may not be an issue but the larger component sizes and weight might be. Cell phones and laptops as we know them would not be possible with linear power supplies.

In contrast, an SMPS incorporates a transistor that operates as a digital switch. The switch is either off, conducting virtually no current, or fully on, with little resistance. The extremely fast rise and fall times of the square wave make these transitions vanishingly brief. This factor accounts for the great efficiency of the SMPS. Furthermore, as we shall see, the isolation transformer operates at the switching frequency, so it can be smaller compared to the Hz power line transformer that is an essential part of the linear power supply.

Small component size, greater efficiency and lower cost have resulted in widespread use of the SMPS in nearly all electronic equipment.

Recent innovations have permitted its use in high-power applications. But SMPS implementation has not been totally free of problems. One of these is the generation of electronic noise, which if not mitigated can appear at both the input and output of the SMPS. In addition, electronic noise generated by the switching process can propagate as radiation from the device.

This is because the square wave, with its near instantaneous rise and fall times, resembles a high-frequency energy source rich in damaging harmonics. When powered on, the SMPS exhibits inrush current, which can affect nearby sensitive equipment through the power distribution system. Another potential problem caused by harmonics is the heating of the neutral conductor in the power supply.

The solution is to oversize this wire. Generally speaking, even where refinements are required, the overall benefits in SMPS are significant regardless of scaling.A switched-mode power supply SMPS is an electronic circuit that converts power using switching devices that are turned on and off at high frequencies, and storage components such as inductors or capacitors to supply power when the switching device is in its non-conduction state.

Switching power supplies have high efficiency and are widely used in a variety of electronic equipment, including computers and other sensitive equipment requiring stable and efficient power supply.

A switched-mode power supply is also known as a switch-mode power supply or switching-mode power supply. Switched-mode power supplies are classified according to the type of input and output voltages.

Anatomy of Switching Power Supplies

The four major categories are:. The high-frequency voltage pulses from the inverter are fed to the transformer primary winding, and the secondary AC output is rectified and smoothed to produce the required DC voltages. A feedback circuit monitors the output voltage and instructs the control circuit to adjust the duty cycle to maintain the output at the desired level. There are different circuit configurations known as topologies, each having unique characteristics, advantages and modes of operation, which determines how the input power is transferred to the output.

Most of the commonly used topologies such as flyback, push-pull, half bridge and full bridge, consist of a transformer to provide isolation, voltage scaling, and multiple output voltages. The non-isolated configurations do not have a transformer and the power conversion is provided by the inductive energy transfer. Switched-mode power supplies are used to power a wide variety of equipment such as computers, sensitive electronics, battery-operated devices and other equipment requiring high efficiency.

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switching power supply

Jul 13 Article core. Switching Power Supply. Development History of Switching Power Supply. Circuit Composition of the Switching Power Supply. Principle of Input Circuit and Common Circuit. Power Conversion Circuit. Output Rectifier and Filter Circuit. Principle of Voltage Regulation Loop.

Short Circuit Protection Circuit. Output Current Limiting Protection. Principle of Output Overvoltage Protection Circuit. Battery Management. Intelligent Fan Cooling. Current Sharing Technology. The switching power supply has replaced the transistor linear power supply for more than 30 years. The first to appear is the series switching power supply.

The main circuit topology is similar to that of the linear power supply. However, after the power transistor is in the switching state, the pulse width modulation PWM control technology has developed.DC power supplies are quite important for our devices that require high and stable power to operate.

There are hundreds of manufactures like www. As compared to this, switching power supply is much lighter with a higher rate of efficiency which are really great for the applications that require higher power intensities. These two types of power supplies are swappable for various applications as per the requirement because they cost around the same to get manufactured. Despite of the fact that linear power supplies are more durable, the switching power supplies are used broadly nowadays in most of our applications.

You might have come through different blogs, articles and even online sellers who claim that switching power supplies are not suitable and reliable. We would like to confirm you that this is just a false allegation over its efficiency and against the popularity. Following are the typical application for which switching power supply are being used Sign in. Log into your account. Password recovery. Recover your password. Forgot your password? Get help. Manufacturing industry things. What is Glass Window Equipment?

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12V 10A switching power supply (with schematic and explanation)

You can see what is the difference between a power supply with active PFC and one without this circuit by comparing Figures 3 and 4. This is a very basic diagram. If you want detailed schematics, see Figure 5. This figure is just here for the readers that want to go deeper. Figure 5: Schematics for a typical low-end ATX power supply. You may be asking yourself where is the voltage regulation stage on the Figures above.

The PWM circuit does the voltage regulation. The input voltage is rectified before passing the switching transistors, and what they send to the transformer is square wave. So what we have on the transformer output is a square waveform, not a sine waveform. Since the waveform is already square, it is very simply to transform it into a DC voltage. So after the rectification after the transformer, the voltage is already DC.

That is why some times switching power supplies are also referred as DC-DC converters. The loopback used to feed the PWM control circuit is in charge of making all the necessary regulation. If the output voltage is wrong, the PWM control circuit changes the duty cycle of the signal applied to the transistors in order to correct the output. This happens when the PC power consumption increases, situation where the output voltage tends to drop, or when the PC power consumption decreases, situation where the output voltage tends to increase.

All you need to know before moving to the next page and that you can learn from paying attention to Figures 3 and 4 :. Several different configurations can be used and we will talk more about this later. The waveform applied to the transformer is square. Thus the waveform found on the transformer output is square, not sine. The PWM control circuit — which is usually an integrated circuit — is isolated from the primary through a small transformer. Sometimes instead of a transformer an optocoupler a small integrated circuit containing a LED and a phototransistor packed together is used.

As we mentioned, the PWM control circuit uses the power supply outputs to control how it will drive the switching transistors. If the output voltage is wrong, the PWM control circuit changes the waveform applied on the switching transistors in order to correct the output.

On the next pages we are going to explore each one of these stages with pictures showing where you can find them inside a power supply. Saturday, April 18, Hardware Secrets.It includes topics from backing up computer files to small engine repair to 3D graphics software to basic information on diabetes.

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Switch Mode Power Supply

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The actual charging system voltage is generally between This is simply not enough for many uses. For car audio, amplifiers and high output preamplifiers need more voltage. To boost the voltage, a switching power supply is typically used. The most common type of switching power supply uses a transformer to boost the voltage.

A less common method uses diodes and capacitors in what's commonly referred to as a 'voltage doubler'. This creates an alternating magnetic field around the primary winding and the core of the transformer. Since the secondary winding is also wrapped around the core and is in close proximity to the primary windings, a voltage is induced in the secondary windings. The secondary winding may or may not be electrically connected to any point of the source of the DC power.

switching power supply

The output of the secondary is an AC voltage. In most power supplies, the AC output of the transformer is rectified by using diodes. This rectified 'DC' output voltage is commonly referred to as 'rail voltage' in amplifiers.

The rail voltage is what supplies power to the output transistors in an amplifier.If you are reading this message, Please click this link to reload this page. Do not use your browser's "Refresh" button. Please email us if you're running the latest version of your browser and you still see this message.

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Picking The Right Power Supply: What You Should Know

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