I read: Have 350mA LED(s) in series with 1000mF cap from +ve to -ve within full > bridge rectifier. So far so good. -ve of bridge to mains N. +ve of > bridge goes through a 4.7mF "motor start" rated capacitor to main L. > > Is this legal? > Will it run foul of CE regs. > How do I measure the power efficiency?
As described the circuit has some problems. Is this LED mounted on the PCB or brought out to a panel? If it is on the power supply PCB, and is kept in the line section, it has a chance. The two motor start capacitors would be connected in series to form a 2.35 uF cap. The LED is in series. To limit charging current (when the unit is plugged in at the peak of the AC cycle) a 120 ohm resistor could be placed in this series string. During normal operation the resistor will dissipate 1.4 watts. The peak charging current is 1.5 amps for few hundred microseconds. Can the LED survive this? Then there is the surge testing. If this circuit is placed directly across the bridge rectifier inputs you have built-in surge protection. Other issues: Does a single-fault test need to be planned for one of the caps shorting? If so, the resistor dissipation will increase to 5.6 watts , requiring a larger wattage resistor. It could be cheaper to use a lower current LED with simply a series resistor across the output of the bridge. Or, to lower the power, place the circuit across the input to the bridge along with a rectifier diode and an antiparallel diode across the LED. Or, use a bridge and drive the LED and resistor from the unfiltered output. Dave Cuthbert Micron Technology This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
