Switch Mode Power Supplies (SMPS) is now widely used in modern electronic equipment due to its compact design and high efficiency of about 80% or more. The switch-mode regulator circuit presented here has an efficiency of around 85%.
Power supply is probably the most computer components are often overlooked by PCs buyers. However, this component is very important : such as when the power is insufficient or if the voltage is too unstable, the power supply can cause crashes or reboots the machine. Even worse, if power is working too hard and / or in poor quality, maybe just by turning on the computer may cause damage to most of the components: motherboard, CPU, hard drive and a DVD player! Note that branded manufacturers are also found in the market often overlook the power supply in order to reduce the selling price of the computer. Most buyers assume the power supply is not important, some unscrupulous manufacturers introduce large-sized power and poor quality for their machines.
The IC8211 (Programmable Voltage Detectors) provides the voltage reference and regulator amplifier, while Q1 is the series pass transistor. R1 defines the output current of the IC8211, while Cl and C2 provide loop stability and also act to suppress feedthrough of input transients to the output supply. R2 and R3 determine the output voltage as follows :
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The regulator circuit uses an LM117K three-terminal adjustable output positive voltage regulator in a TO-3 can. The variable voltage regulator lets you adjust the output voltage of a fixed DC power supply between 1.2 and 37 VDC, and will supply the output current in excess of 1.5 A.
This circuit acts like a zener diode with a wide range of voltages. The current passing via the voltage divider R1-R2 is substantially greater compared to the transistor base current and is in the region of 8 ma.
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