transformerless low cost power supply


Posted on Feb 7, 2014

In Capacitor Power Supplies we use a Voltage Dropping Capacitor in series with the phase line. An ordinary capacitor should not be used in these applications because Mains Spikes may create holes in dielectric of ordinary capacitors and the capacitor will fail to work. This may destroy the device by rushing current from the mains. Thus we use X Rated Capacitor with required


transformerless low cost power supply
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voltage is used for this task. X Rated Capacitors rated for 250, 400, 600 V AC and higher are available. Reactance of the voltage dropping capacitor should be greater than the load resistance to keep constant current through the load. Where f is the frequency and C is the Capacitance. Thus a 0. 22G F capacitor has reactance of 14. 4KG © on mains frequency (50Hz). The approximate value of maximum current can be find out by dividing mains voltage byG‚reactanceG‚of the capacitor (since load resistance is small). As shown 1A fuse may be used to avoid damages due to short circuit and a MOV ( Metal Oxide Varistor ) also may be connected as shown above to avoid problems due to voltage transients. The resistor R1 is used to limit the high current that may occur during power on. Capacitor C1 225K (2. 2G F) is used as the Voltage Dropping Capacitor. A Bleeder resistor is connected parallel to it for discharging the capacitor when the supply is switched off. G‚Diodes D1 D4 is wired as Bridge Rectifier and the capacitor C2 is used to filter the pulsating DC. Zener Diode is used to regulate the filtered DC or you can use IC Voltage Regulator for better results. Resistor R3 is used to limit the current through the Zener Diode. Resistive Transformer Less Power Supply is similar to Capacitor Power Supply except that instead of Reactance it uses resistance to limit current. Thus here excess energy is dissipated as heat across the Voltage...




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