Ultra Bright LED Lamp


Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
CIRCUIT IDEAS ELECTRONICS FOR YOU FEBRUARY 2003 whereas no power is dissipated in a ca- pacitor. The value of capacitor is calcu- lated by using the following relationships: X C = 1/(2 π fC) ohms —————(a) X C = V RMS /I ohms ———— (b) where X C is capacitive reactance in ohms, C is capacitance in farads, I is the current through the LED in amperes, f is the mains frequency in Hz, and Vrms is the input mains voltage. The 100-ohm, 2W series resistor avoids heavy ‘inrush’ current during transients. MOV at the input prevents surges or spikes, protecting the circuit. The 390-kilo-ohm, ½-watt resistor acts as a bleeder to pro- vide discharge path for capacitor Cx when mains supply is disconnected. The zener diode at the output section prevents ex- cess reverse voltage levels appearing across the LEDs during negative half cycles. Dur- ing positive half cycle, the voltage across LEDs is limited to zener voltage. Use AC capacitors for Cx. Filter capaci-
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.
Ask a homework question - tutors are online