Chordry Posted November 11, 2015 Report Share Posted November 11, 2015 Hello. I want to make a transformerless power supply and have surf the web on it but the major problem here is that when driving a load is it not necessary to include the output voltage of the supply as a parameter? Is the supply going to come down to the voltage of the load? e.g a transformerless power supply with 334j x rated capacitor having a current of 23mA connected to 10led in series having characteristic drop of 1.5v at 15mA. Now, how can I calculate the value of the current limiting resistor? Thanks Quote Link to comment Share on other sites More sharing options...
audioguru Posted November 12, 2015 Report Share Posted November 12, 2015 A transformerless circuit powered from the mains electricity is Extremely dangerous. All wired parts must be completely covered so they cannot be touched. A fuse should be used to prevent a fire if a voltage spike shorts the capacitor.The reactance of the capacitor limits the operating current but its charging current is extremely high when the circuit is turned on at the peak voltage of the electricity sinewave so a current-limiting resistor is needed. The spec's of your LEDs will show a range of forward voltage not simply 1.5V and might show the maximum peak current for a short duration while the capacitor charges. Do you have the LEDs back-to-back or do you have a rectifier? Quote Link to comment Share on other sites More sharing options...
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