MC34063A Boost LED string

First Start Clock by closing bottom middle switch. Then turn on Feed Back by opening lower right switch (yes there is no voltage feedback, it is always in current mode). 7V to drive ten LED string with current pulse. Peak Forward Current is 150mA, D is about .25, Avg current during on time is 75mA. Avg current per LED cycle is D*75mA = 18.75mA. Boost diode (and load) is the LED string. LEDs are a little less efficient at high forward current, and the other loss is a sense resistor. Which is 75mA*75mA*2=11.25mW. Power input is 75mA*6.5V =.4875W. Almost 97% of the input power is applied to LEDs. An old Cree LED, C503B-RCN-CW0Z0AA1 makes 16.8 lum/W. But they are reporting 300+ Lumens per watt for some new LEDs, which is unbelievable. The max Lumens per watt is 683 if it is an intense neon green :-/ http://www.carbonlighthouse.com/2014/02/13/683-lumens-per-watt/

published 11 years ago