As a result, the input current of such basic switched mode power supplies has high harmonic content and relatively low power factor. This creates extra load on utility lines, increases heating of building wiring, the utility transformers, and standard AC electric motors, and may cause stability problems in some applications such as in emergency generator systems or aircraft generators. Harmonics can be removed by filtering, but the filters are expensive. Unlike displacement power factor created by linear inductive or capacitive loads, this distortion cannot be corrected by addition of a single linear component. Additional circuits are required to counteract the effect of the brief current pulses. Putting a current regulated boost chopper stage after the off-line rectifier (to charge the storage capacitor) can correct the power factor, but increases the complexity and cost. All isolated topologies include a transformer, and thus can produce an output of higher or lower voltage than the input by adjusting the turns ratio. [41] [42] For some topologies, multiple windings can be placed on the transformer to produce multiple output voltages. [43] Some converters use the transformer for energy storage, while others use a separate inductor. Smaller than linear power supply. Compared to linear, a SMPS that is 20KHz is 1/4, 100-200KHz is 1/8, and 200KHz-1MHz types can be even smaller. [27] :5–8 With high quality extension leads and plenty of related products from top manufacturers such as Eveready and Energizer, you can feel confident that each of our items will be safe, durable and ideal for the job at hand. The high-frequency transformer is very important in this circuit. Because it has 3 main functions that we need, which are:

To keep your devices on full power all day, why not browse our selection of budget friendly Phone Chargers? Recycle your old Electricals with us!If the SMPS has an AC input, then the first stage is to convert the input to DC. This is called ' rectification'. An SMPS with a DC input does not require this stage. In some power supplies (mostly computer ATX power supplies), the rectifier circuit can be configured as a voltage doubler by the addition of a switch operated either manually or automatically. This feature permits operation from power sources that are normally at 115VAC or at 230VAC. The rectifier produces an unregulated DC voltage which is then sent to a large filter capacitor. The current drawn from the mains supply by this rectifier circuit occurs in short pulses around the AC voltage peaks. These pulses have significant high frequency energy which reduces the power factor. To correct for this, many newer SMPS will use a special power factor correction (PFC) circuit to make the input current follow the sinusoidal shape of the AC input voltage, correcting the power factor. Power supplies that use active PFC usually are auto-ranging, supporting input voltages from ~100 VAC – 250 VAC, with no input voltage selector switch. An SMPS can usually cope with wider variation of input before the output voltage changes. Universal or "wide input" power supplies, which work with mains voltages from 90 to 250 V, are common. More specialized designs could accept even wider input voltage range.

Kilbane, Doris (2009-12-07). "Robert Boschert: A Man Of Many Hats Changes The World Of Power Supplies". Electronic Design . Retrieved 2019-09-12.

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The main advantage of the switching power supply is greater efficiency ( up to 96%) and lower heat generation than linear regulators because the switching transistor dissipates little power when acting as a switch. Pressman, Abraham I. (1998), Switching Power Supply Design (2nded.), McGraw-Hill, ISBN 0-07-052236-7 The (A) signal graph shows the filter effect of the capacitor. When the waveform reaches its highest point, the capacitor will charge up. Then, the waveform will start to drop. At the same time, the capacitor will discharge, filling the gap between each highest point of the waveform. Simple off-line switched mode power supplies incorporate a simple full-wave rectifier connected to a large energy-storing capacitor. Such SMPSs draw current from the AC line in short pulses when the mains instantaneous voltage exceeds the voltage across this capacitor. During the remaining portion of the AC cycle the capacitor provides energy to the power supply. Quasi-resonant zero-current/zero-voltage switch [ edit ] Quasi-resonant switching switches when the voltage is at a minimum and a valley is detected.