Circuits Essay

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Introduction Digital devices are used by almost everyone in the U.K. on a daily basis and these devices require a DC voltage. Such devices include computers, radios and televisions. However the electricity transmitted into homes is AC, which is fine for some appliances but not for digital devices. Therefore to power these devices the AC mains must be converted to DC and the voltage must be stepped down as the rated 230V of the mains will damage most digital circuitry. DCPS To achieve this DC Power Supply (DCPS) is used. It works by taking an AC input into the primary side of a transformer and steeping it down to produce an AC output of lower voltage. The number of turns of the transformer will depend on how low the output voltage should be. Then this voltage is passed through what is called a Rectifier Circuit. This will manipulate the AC voltage and convert it into a DC voltage. Then it can be used to power digital devices. “In many DCPS circuits, a regulator is generally employed to maintain the output voltage at a fixed level regardless of input signal and load variations” [1] A diagram of this process is shown below A linear DC Power Supply [1] SMPS Most modern systems however use Switched-Mode Power Supplies (SMPS) as they are smaller and much more efficient than DCPS systems. [1] An AC/DC SMPS consists of a rectifier and filter circuit which will produce a rough dc output. Then what’s called a Chopper Circuit (Switching Circuit) will ‘chop’ the DC at a high frequency (usually greater than 20khz) to produce a square wave. [1] Next a power transformer is placed and the output of it passed through a rectifier to produce a smooth unregulated DC output. [1] Transformers can be made to be smaller when they are operating at high frequencies, therefore the higher the frequency of the chopper, the smaller the transformer that is required and so the

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